Download Invited speakers

Invited speakers:
Pawel Artymowicz, Stockholm Obs., Sweden
Mailing Address: Stockholm Observatory, SCFAB, SE-106 91 Stockholm,
Sweden
E-Mail: [email protected]
Alan Boss, CIW, DTM, USA
Mailing Address: 5241 Broad Branch Road, NW, Washington, DC 200151305 U.S.A.
E-Mail: [email protected]
Adam Burrows, U. Arizona, USA
Mailing Address: Department of Astronomy, University of Arizona, Tucson,
AZ 85721 USA
E-Mail: [email protected]
Mark Harrison, RSES, ANU, Australia
Mailing Address: RSES, Building 61, The Australian National University,
Canberra ACT 0200 Australia
E-Mail: [email protected]
Ray Jayawardhana, U. Michigan, USA
Mailing Address: University of Michigan Astronomy Department, 953
Dennison Building, Ann Arbor, MI 48109-1090 USA
E-Mail: [email protected]
Laurie Leshin, Arizona State U., USA
Mailing Address: Arizona State University Department of Geological
Sciences, Box 871404, Tempe, AZ 85287-1404 USA
E-Mail: [email protected]
Doug Lin, UC Lick Observatory, USA
Mailing Address: UCO/Lick Observatory, University of California, Santa
Cruz, CA 95064 USA
E-Mail: [email protected]
Jonathan Lunine, LPL, AZ, USA
Mailing Address: LPL, 1629 E. University Blvd., Tucson, AZ 85721-0092
USA, Office location: Space Sciences 522
E-Mail: [email protected]
Kevin McKeegan, UCLA, USA
Mailing Address: Dept. of Earth & Space Sciences, UCLA, 595 Young
Drive, Los Angeles, CA. 90095-1567 USA
E-mail: [email protected]
Frank H. Shu, National Tsing Hua U., Taiwan
Mailing Address: National Tsing Hua University 101, Sec. 2, Kuang Fu Road,
Hsichu 30013, Taiwan, R.O.C.
E-Mail: [email protected]
Chris Tinney, Anglo-Australian Obs., Australia
Mailing Address: PO Box 296, Epping 1710 Australia
E-mail: [email protected]
Contributed talks:
Francis Albarede, Ecole Normale Sup. de Lyon, France
Mailing Address: Ecole Normale Supérieure de Lyon 46, Allee d'Italie 69364
Lyon Cedex 7, France
E-Mail: [email protected]
Yuri Amelin, Geological Survey of Canada
Mailing Address: Geological Survey of Canada, 601 Booth St., Ottawa, ON,
Canada, K1A 0E8
E-Mail: [email protected]
Jeremy Bailey, AAO, Australia
Mailing Address: Anglo-Australian Observatory, PO Box 296, Epping,
NSW 1710
E-mail: [email protected]
Victoria C. Bennett, RSES, ANU, Australia
Mailing Address: RSES, Building 61, The Australian National University,
Canberra ACT 0200 Australia
E-Mail: [email protected]
Mike Bessell, RSAA, ANU, Australia
Mailing Address: Mount Stromlo Observatory, Cotter Road, Weston, ACT
2611, Australia
E-Mail: [email protected]
Brad Carter, U. of Southern Queensland, Australia
Mailing Address: Centre for Astronomy, Solar Radiation and Climate,
Department of Biological and Physical Sciences, Faculty of Sciences, University
of Southern Queensland, Toowoomba Queensland 4350, Australia
E-Mail: [email protected]
Geoff Davies, RSES, ANU, Australia
Mailing Address: RSES, Building 61, The Australian National University,
Canberra ACT 0200 Australia
E-Mail: [email protected]
Ulyana Dyudina, RSAA, ANU, Australia
Mailing Address: Mount Stromlo Observatory, Cotter Road, Weston, ACT
2611, Australia
E-mail: [email protected]
Justin Freeman, RSES, ANU, Australia
Mailing Address: RSES, Building 61, The Australian National University,
Canberra ACT 0200 Australia
E-Mail: [email protected]
Andrew Glikson,RSES, ANU, Australia
Mailing Address: RSES, Building 61, The Australian National University,
Canberra ACT 0200 Australia
E-Mail: [email protected]
Karl E. Haisch Jr., U. Michigan, USA
Mailing address: Dept. of Astronomy, Univ. of Michigan, 830 Dennison
Bldg., Ann Arbor, Michigan 48109-1090 USA
E-mail: [email protected]
Masahiko Honda, RSES, ANU, Australia
Mailing Address: RSES, Building 61, The Australian National University,
Canberra ACT 0200 Australia
E-Mail: [email protected]
Trevor Ireland, RSES, ANU, Australia
Mailing Address: RSES, Building 61, The Australian National University,
Canberra ACT 0200 Australia
E-Mail: [email protected]
Ing-Guey Jiang, Astronomy, National Central U., Taiwan
Mailing Address: Institute of Astronomy, National Central University, No.
300, Jungda Rd, Jungli City, Taoyuan, Taiwan 320, R.O.C.
E-Mail: [email protected]
Warrick Lawson , UNSW@ADFA, Australia
Mailing address: School of PEMS/Physics, UNSW@ADFA, Canberra ACT
2600
E-mail: [email protected]
Kurt Liffman, CSIRO and Monash U., Australia
Mailing Address: Energy & Thermofluids Engineering, CSIRO/MIT P.O. Box
56, Graham Rd, Highett VIC 3190 AUSTRALIA
E-mail: [email protected]
Charley Lineweaver, UNSW, Australia
Mailing Address: School of Physics, University of New South Wales,
Sydney, NSW 2052
Email: [email protected]
Sarah Maddison, Swinburne U., Australia
Mailing Address: Centre for Astrophysics and Supercomputing, School of BSEE,
Swinburne University of Technology, PO Box 218, Hawthorn, 3122 Victoria, Australia
E-Mail: [email protected]
Rosemary Mardling, CSPA, Monash U., Australia
Mailing Address: School of Mathematical Sciences, Monash University, 3800
E-mail: [email protected]
Franklin Mills, RSPhysSE, ANU, Australia
The Research School of Physical Sciences and Engineering, Building 60,
ANU Campus, Canberra ACT 0200
E-Mail: [email protected]
Louis Moresi, Monash U., Australia
Mailing address: School of Mathematical Sciences Building 28, Monash
University, Clayton 3800, Victoria, Australia
E-mail: [email protected]
James Murray, Swinburne U., Australia
Mailing Address: Centre for Astrophysics and Supercomputing, Swinburne
University of Technology, PO Box 218, Hawthorn Victoria 3122, Australia
E-Mail: [email protected]
Marc Norman, RSES, ANU, Australia
Mailing Address: RSES, Building 61, The Australian National University,
Canberra ACT 0200 Australia
E-Mail: [email protected]
Allen Nutman, RSES, ANU, Australia
Mailing address: Research School of Earth Sciences, Australian National
University, Canberra, ACT 0200, Australia
E-mail: [email protected]
Andrew Prentice, Monash U., Australia
Mailing Address: Room 329, Building 28, School of Mathematical Sciences,
Monash University Vic 3800, Australia
E-Mail: [email protected]
Penny D. Sackett, RSAA, ANU, Australia
Mailing Address: Mount Stromlo Observatory, Cotter Road, Weston, ACT
2611, Australia
E-Mail: [email protected]
Thomas Sharp, Arizona State U., USA
Mailing Address: Arizona State University Department of Geological
Sciences, Box 871404, Tempe, AZ 85287-1404 USA
E-Mail: [email protected]
Therese Schneck, Consulting Civil Engineer, France
Mailing Address: 11/13 Rue Lobineau 75006 Paris
E-Mail: [email protected]
Robert G. Smith, UNSW@ADFA, Australia
Mailing Address: School of Physical, Environmental & Mathematical
Sciences, University of New South Wales at The Australian Defence Force
Academy, Canberra, ACT 2600
E-mail: [email protected]
Dave Stegman. Mathematical Sci., Monash U., Australia
Mailing Address: School of Mathematical Sciences, Monash University
Building 28 Victoria 3800 Australia
E-Mail: [email protected]
Ross Taylor, Geology, ANU, Australia
Mailing Address: Geology Department, The Australian National University,
Canberra 0200 ACT Australia
E-Mail: [email protected]
Mark Wardle, Macquarie U, Australia
Mailing Address: Department of Physics, Macquarie University, Sydney NSW
2109
E-mail: [email protected]
David Wark, Monash U., Australia
Mailing Address: School of Geosciences, Building 28 Monash University
Victoria 3800, Australia
E-Mail: [email protected]
Peter Wood, RSAA, ANU, Australia
Mailing Address: Mount Stromlo Observatory, Cotter Road, Weston, ACT
2611, Australia
E-Mail: [email protected]
Chris Wright, ADFA@UNSW, Australia
Mailing Address: School of Physical, Environmental & Mathematical
Sciences, University of New South Wales at The Australian Defence Force
Academy, Canberra, ACT 2600
E-Mail: [email protected]
Li-Chin Yeh, National Hsinchu Teachers College, Taiwan
Mailing Address: Department of Mathematics, National Hsinchu Teachers
College, Hsin-Chu, Taiwan
E-mail: [email protected]
Williaml Zealey, U. of Wollongong, Australia
Mailing Address: Faculty of Engineering, University of Wollongong,
Wollongong, NSW2500
E-mail: [email protected]
Students:
Daniel Bayliss, MSO, ANU, Australia
Mailing Address: Mount Stromlo Observatory, Cotter Road, Weston, ACT
2611, Australia
E-mail: [email protected]
Adrian Brown, Macquarie U, Australia
Mailing address: Dept of Earth and Planetary Sciences, Macquarie Uni, NSW
2109
E-mail: [email protected]
Andres Carmona, ESO Garching., Heidelberg U., Germany
Mailing Address: European Southern Observatory, Karl-SchwarzschildStrasse 2, 85748 Garching bei Muenchen, Germany
E-mail: [email protected]
Marie Gibbon, Monash U., Australia
Mailing Address: 42 Park Street, Seaford Vic 3198
E-mail: [email protected]
Antti Kallio, RSES, ANU, Australia
Mailing Address: RSES, Building 61, The Australian National University,
Canberra ACT 0200 Australia
E-Mail: [email protected]
Gareth Kennedy, Monash U., Australia
Mailing Address: 2/33 Golf Links Ave, Oakleigh, Vic, 3166
E-mail: [email protected]
A-Ran Lyo, UNSW@ADFA, Australia
Mailing address: School of PEMS/Physics, UNSW@ADFA, Canberra ACT
2600
E-Mail: [email protected]
Marco M. Maldoni, UNSW@ADFA, Australia
Mailing address: School of PEMS/Physics, UNSW@ADFA, Canberra ACT
2600
E-Mail: [email protected].
Charles Morgan, Monash U., Australia
Mailing Address: School of Mathematical Sciences, Monash University,
Clayton, Vic. 3800
E-mail: [email protected]
Craig O'Neill, U. Sydney, Australia
Mailing Address: The School of Geosciences, Department of Geology and
Geophysics Edgeworth David Building F05, The University of Sydney, NSW
2006
Dr. John Patten, Unaffiliated Student, Australia
Kala Perkins, SRES, ANU, Australia
Postal Address: School of Resources, Environment and Society, Australian
National University, Canberra 0200 Australia
E-Mail: [email protected]
Tamara Rogers, U. Santa Cruz, USA
Mailing Address: 5350 S. Morning Sky Ln, Tucson, AZ. 85747
E-mail: [email protected]
Raquel Salmeron, U. Sydney, Australia
Mailing Address: School of Physics A28, University of Sydney, NSW 2006,
Australia
E-Mail: [email protected]
Patrick Scott, MSO, ANU, Australia
Mailing Address: Mount Stromlo Observatory, Cotter Road, Weston, ACT
2611, Australia
E-Mail: [email protected]
Christine Thurl, MSO, ANU, Australia
Mailing Address: Mount Stromlo Observatory, Cotter Road, Weston, ACT
2611, Australia
E-Mail: [email protected]
Miguel de Val Borro, Stockholm U., Sweden
Mailing Address: Stockholm University, AlbaNova Center, Department of
Astronomy, 10691 Stockholm
E-mail: [email protected]
David Weldrake, RSAA, ANU, Australia
Mailing Address: Mount Stromlo Observatory, Cotter Road, Weston, ACT
2611, Australia
E-Mail: [email protected]
Abstracts
Yuri Amelin (1), Alexander Krot (2) and Eric Twelker (3)
1)
2)
3)
Geological Survey of Canada
Hawaiian Institute of Geophysics and Planetology, SOEST, University of Hawaii at Manoa,
Juneau
Duration of the chondrule formation interval: a Pb isotope study
Chondrules are among the earliest solid objects that formed in the solar system.
We have determined the ages of chondrules from several carbonaceous chondrites
using the Pb-Pb isochron method. High precision Pb isotope dates are obtained for
three silicate clasts (large chondrules) from the CBa (Bencubbin-like) chondrite
Gujba. Additional analyses of chondrules from the CV3 chondrite Allende allowed to
improve precision of the age. The summary of precise Pb-Pb ages of chondrules from
primitive chondrites is shown below:
Meteorite
Allende (CV3)
Acfer 059 (CR2)
Gujba (CBa)
Pb-Pb isochron age, Ma
4566.7±1.0
4564.7±0.7
4562.7±0.5
Comment
this study
Amelin et al. (2002)
this study
From these data, we deduce that the period of chondrule formation started
simultaneously with, or shortly after the CAI formation [4567.2±0.6 Ma (Amelin et
al., 2002)], and continued for at least 4.0±1.5 m.y. If the dates of the chondrules
reflect their timing of formation, then there were probably a variety of processes
occurring over at least 4-5 m.y. that we now combine under the umbrella name of
"chondrule formation". More high-precision Pb-Pb and extinct nuclide dating, as well
as geochemical and petrologic studies of chondrules from primitive meteorites, will
be required to understand individual processes of chondrule formation.
Pawel Artymowicz
Stockholm Univ
Migration of bodies in disks: Timescales and unsolved problems
Solid bodies with size ranging from dust to planets are present in protoplanetary
disks, with which they couple via processes involving gas drag, radiation pressure,
and gravitational torques of several types (due to Lindblad and corotational
resonances). As a result, several size-dependent migration modes exist, operating on
timescales shorter than the lifetime of the disks. Theory of migration studies the role
of mobility in accumulation of solids, origin of the orbital distance distribution of
extrasolar planets, and the ring-like appearence of some circumstellar dust disks. This
talk presents an overview of the underlying physics, timescales, and the outcomes of
migration in the scenarios of planetary system formation. We discuss in some detail a
newly discovered, fast migration mode of protoplanets (timescale ~1000 yr),
dependent on corotational torques (tentatively named type III).
Jeremy Bailey
AAO
Evolution of Terrestrial Planet Atmospheres
Time when the process started in the solar system: -4.5 byr
Time when it ended: still continuing
The planets Venus, Earth and Mars have developed very different atmospheres over
4.5 billion years of evolution, although we suspect that their early atmospheres may
have been quite similar. Mars has a very thin (7 mbar) and dry atmosphere of mostly
CO2. The Earth's 1 bar atmosphere is predominantly nitrogen and oxygen with very
low CO2 content, and Venus has a 90 bar atmosphere of mostly CO2 in which a
runaway greenhouse effect has heated the planets surface to 720K. I will review some
of the processes which have operated on the three planets to control the evolution of
their atmospheres, and discuss issues including the "early faint Sun" problem,
"snowball Earth" events and the rise of oxygen in the Earth's atmosphere.
Jeremy Bailey (1,2), Sarah Chamberlain (2), Malcolm Walter (2) and David
Crisp (3)
(1)
(2)
(3)
AAO
Australian Centre for Astrobiology, Macquarie University
Jet Propulsion Laboratory, Caltech
Poster: IR Observations of Mars during the August 2003 opposition
We present some preliminary results of observations obtained during the very
favourable opposition of Mars in August 2003 using the UIST instrument on the
United Kingdom Infrared Telescope (UKIRT) at Mauna Kea, Hawaii. We obtained
narrow band images which we believe are probably the sharpest ever obtained with a
ground-based telescope, as well as spectral scans of the disk at a range of near-IR
wavelengths and resolving powers. The observations include absorption features due
to atmospheric gases, CO2 ice at the south pole, and water ice clouds in the north. We
can use the CO2 band strength to image the distribution of surface atmospheric
pressure and hence topography.
The data may be used to search for absorption features due to hydrated clay minerals,
carbonates and sulphates which might provide evidence for the past presence of
surface water.
Jeremy Bailey (1), Phil Lucas (2), Jim Hough (2) and Motohide Tamura (3)
(1)
(2)
(3)
AAO & Australian Centre for Astrobiology, Macquarie U.
University of Hertfordshire
National Astronomical Observatory, Japan
Poster: Direct Detection of Extrasolar Planets by Polarimetry
Despite the detection of more than 100 extrasolar planets by the radial velocity
method, no extrasolar planet has yet been seen directly by its emitted or reflected
light. Detections by spectroscopic techniques have so far been unsuccessful while
photometric detection requires accuracies which are beyond current ground-based
photometry.
However, we believe that planets orbiting close to their stars (Hot Jupiters) might be
detected by means of the polarization of the light scattered from their atmospheres.
While the resulting polarization of the combined light of the planet and star is small,
polarization measurements can in principle be made with very high sensitivity since
polarimetry is a differential measurement and is not limited by the stability of the
Earth's atmosphere as photometry is.
We have designed and built a stellar polarimeter which should be capable of
achieving the required sensitivity. The instrument is now being tested, and on a 4m or
larger telescope should be capable of detecting the polarization signature of bright hot
Jupiter systems such as Tau Boo, Upsilon And or 51 Peg.
Daniel Bayliss, Ulyana Dyudina and Penny Sackett
RSAA, ANU, Australia
Modeling of Reflected Light from Extra Solar Planets with Eccentric Orbits
An extra solar planet will shine by reflecting light from its parent star. As the planet
orbits the star the amount of light reflected will vary as the phase of the planet
changes with respect to the observer, resulting in a light curve with a periodicity equal
to the orbital period of the planet. We model the reflected light from extra solar
planets at different phases based the reflective properties of Jupiter and Saturn
obtained by the Pioneer space probes. Since a large proportion of the known extra
solar planets display highly elliptical orbits, our models include changes in angular
velocity and orbital distance resulting from such elliptical orbits. Current Earth based
photometry is limited to a precision of about 100ppm of the parent's stars luminosity
due to atmospheric extinction. However, new space photometers such as MOST and
Kepler, are expected to have precisions down to less than 10ppm. At these new
sensitivities the light curves from many known extra solar planets should be
detectable. These light curves should give us information not only on the size and
orbital properties of the planet, but also on atmospheric particle size, cloud cover, and
the presence of rings. We discuss the likelihood of these properties being extracted
from the light curves with the data from space and earth based instruments in the next
5-10 years.
Alan Boss
Carnegie Institution
The Formation of Giant Planets
[All times relative to formation
Time core accretion started: 0 Myr
Time core accretion finished: 5 Myr
Time disk instability started: 0 Myr
Time disk instability finished: 0.1 Myr
of
the
protosun and solar
Error bar: 0 Myr
Error bar: 2 Myr
Error bar: 0.1 Myr
Error bar: 0.1 Myr
nebula]
Two very different mechanisms have been proposed for the formation of the gas and
ice giant planets. The conventional explanation for the formation of gas giant planets,
core accretion, presumes that a gaseous envelope collapses upon a roughly 10 Earthmass, solid core that was formed by the collisional accumulation of planetary
embryos orbiting in the solar nebula. The more radical explanation, disk instability,
hypothesizes that the gaseous portion of the nebula underwent a gravitational
instability, leading to the formation of self-gravitating clumps, within which dust
grains coagulated and settled to form cores. Core accretion appears to require several
million years or more to form a gas giant planet, implying that only long-lived disks
would form gas giants. Disk instability, on the other hand, is so rapid (forming clumps
in thousands of years), that gas giants could form in even the shortest-lived disks.
Core accretion has severe difficulty in explaining the formation of the ice giant
planets, unless two extra protoplanets are formed in the gas giant planet region and
thereafter migrate outward.
Recently, an alternative mechanism for ice giant planet formation has been proposed,
based on observations of protoplanetary disks in the Orion: disk instability leading to
the formation of four gas giant protoplanets with cores, followed by photoevaporation
of the disk and gaseous envelopes of the protoplanets outside about 10 AU by a
nearby OB star, producing ice giants. In this scenario, Jupiter survives unscathed,
while Saturn is a transitional planet.
Adrian Brown
Dept of Earth and Planetary Sciences, Macquarie University
Evidence for the earliest Hydrothermal System on Earth in the East Pilbara
Granite-Greenstone Terrane
Time when the process you describe started in the solar system: 3.45 Gy
The error bar on the start time: 100 My
Time when this process ended: 3.46
The error bar on the end time: 100 My
The East Pilbara Granite Greenstone Terrane is a well preserved Archaean succession
of domical granite batholiths surrounded by thick greenstone synclinoria. The North
Pole Dome region in postulated to be a granite dome predominantly covered by
greenstones of the Warrawoona Group. Following intrusion of the granite and
eruption of the felsic Panorama Formation around 3.45 Gya, it is hypothesized that a
hydrothermal event took place, utilising the felsic magma conduits to propel water to
the palaeosurface, thereby creating an epithermal hydrothermal deposit at Miragla
Creek. The alteration caused by this event is in the process of being mapped using
airborne hyperspectral sensing as part of a three year PhD project. It provides an
opportunity to examine one of the earliest hydrothermal events in the history of the
Earth.
The 600 sq. km hyperspectral dataset was captured in October 2002 and covers the
wavelengths from 400 to 2400 nm at 5m resolution. Mapped litholgies so far include
sericite, chlorite and pyrophyllite alteration zones, along with a serpentine-rich
komatiite flow at the base of the Apex Basalt. These will be discussed and
implications of the event, including its possible links with putative stromatolite
structures within the 3.42 Gyr Strelley Pool Chert, which overlies the Panorama
Formation.
Adam Burrows
U. Arizona
Direct Detection of Extrasolar Giant Planets
Over the past eight years we have seen the number of known extrasolar giant planets
(EGPs) grow from 1 in 1995 to more than 110 today. However, these epochal
discoveries outside our solar system have been made using indirect techniques. In
order to truly characterize their physical and chemical nature, more direct detection of
the light of the planets themselves is necessary. To this end, NASA and ESA have
embarked upon an ambitious plan of direct planet measurement that includes projects
with the KIA, LBTI, VLTI, SIM, GAIA, Kepler, COROT, MOST, MONS, WISE,
JWST, and the Spitzer Space Telescope.
I will review theoretical calculations of the atmospheres, spectra, and evolution of
irradiated EGPs as a function of mass, age, orbital separation, eccentricity, primary
star, and composition. Moreover, I will describe EGP albedos and orbital phase
functions, as well as transit physics. The predictions I summarize are predominantly
to inform the numerous direct discovery campaigns being planned for the next
decade.
Andres Carmona
European Southern Observatory. Garching. & Heidelberg University. Heidelberg, Germany
Observational studies of gas in circumstellar disks around YSO
Time when the process you describe started in the solar system: 0
The error bar on the start time: Time when this process ended: 5 Myr
The error bar on the end time: 1 Myr
Circumstellar disks around young stellar objects (YSO), where the process of planet
formation is thought to take place, consist nearly 99% of gas. However, until the
present, a great part of the observational effort in understanding YSO's disks has been
focused on the study of the dust. It is well known that dust causes
the bulk of infrared continuum radiation, as well as strong infrared spectroscopic
features. Interesting insights on the physics of the disks has been consequently
obtained even at low spectroscopic resolution. Unfortunately, dust does not provide
kinematic information that allow the detailed study of the dynamics of the disk.
Indeed dust observations don't permit a direct measure of the mass distribution as a
function of the distance to the star. On the theoretical arena, recent studies of planet
formation focused principally on the study of the dynamics of the gas in the
circumstellar disk. It appears that observational work aimed to study the gas is
necessary and fundamental for constructing a more accurate picture of the planet
formation process. Specifically, gas studies are vital to constrain and observationally
test theoretical scenarios proposed about giant planet formation and migration in
particular.Gas has weaker features, so observationally harder to study. However with
gas it is possible to obtain kinematic information. Only advanced technology allowing
extremely high spectral resolution would permit to resolve the weak spectral features
associated with circumstellar gas. Only 8m class telescopes are able to provide the
high angular resolution required to spatially resolve the disks around a close stellar
objects.The ESO-VLT capabilities combined with a new generation of high
resolution infrared spectrometers (VISIR and CRIRES) will allow astronomers for the
first time to study the gas and the dynamics circumstellar disks. However, even with
the best instrumentation available, to be able to resolve the disks and perform detailed
gas studies, young, close, ^Óbig^Ô and bright, stellar objects are required. Young
intermediate mass stars Herbig Ae/Be appear to be the more suitable targets for
effectuating this new and challenging research.
Brad Carter
USQ
www.usq.edu.au/users/carterb
The Anglo-Australian Planet Search
Time when the process you describe started in the solar system: 3Gyr (2 Gyr ago)
The error bar on the start time: 1 Gyr
Time when this process ended: 5 Gyr
The error bar on the end time: 1 Gyr
(The above figures represent the fact that the exoplanets to be
discussed are mature objects thought to be several billion years old to
roughly solar age or perhaps older.)
The Anglo-Australian Planet Search (AAPS) is currently surveying about 250
generally solar-type stars in the southern sky, to detect orbiting planets using stellar
reflex motion. Precision Doppler measurements of stellar radial velocity are made
with the Anglo-Australian Telescope (AAT) equipped with an echelle spectrograph
and an iodine absorption cell. The spectrograph point spread function and wavelength
calibration are derived from the iodine line spectra, resulting in a long term precision
of 3 metres per second. Because the magnetic activity of young stars produces a jitter
that affects precision radial velocity measurements, the target stars selected are older
than 3 Gyr and their planets are "mature" objects. The AAPS has revealed more than a
dozen planet candidates with minimum mass ranging from 0.2 to 10 times the mass of
Jupiter, and an additional four planet candidates have been confirmed. For the most
part the exoplanets detected are in eccentric or close orbits that are in marked contrast
to our solar system. Nevertheless, a recent result is the detection of a planet orbiting
the star HD70642 that suggests a planetary system architecture similar to our own.
Geoff Davies
Research School of Earth Sciences, Australian National University
Stratifying the Earth
Time when the process started: Magma ocean: during Mars-sized impact, late stage of
accretion, say 30 Ma after meteorite formation (4.56 Ga).
The error bar on the start time: 15 Ma
Time when this process ended: 5000 years later
The error bar on the end time: 3000years
OR
Time when the process started: Removal of excess accretional heat from Earth's
interior: late stage of accretion, 30 Ma after meteorite formation (4.56 Ga).
The error bar on the start time: 15 Ma
Time when this process ended: 400 Ma later (4.2 Ga)
The error bar on the end time: 200 Ma
The Earth's iron core probably began to segregate when the Earth was about half
grown, and would then have kept pace with the growth of the Earth, assuming Earth
formation lasted a few to a few tens of millions of years.
A magma ocean would freeze out in thousands of years, even if it were hundreds of
kilometers deep, unless there was a dense, opaque early atmosphere to keep the
surface hot. Thus a global magma ocean is only likely to have occurred after giant
impacts, and then only briefly. Transient magma seas or lakes would have formed
after lesser large impacts.
Basaltic crust would have begun to form as soon as melting began, during the later
stages of accretion, and this would continue to the present day through mantle
convection. Relatively thick basaltic crust (10-50 km) would have been forming as
the Earth approached its final size, and would have persisted through the early phase
of internal heat dissipation. The mantle strongly self-limits thermally at higher
temperatures.
The excess internal heat left from accretion would be removed by mantle convection
over a few hundred million years. Thereafter the internal temperature would have
slowly declined as the main radioactive heat sources (U, Th, K) decayed by a factor of
about 4.
Much of the early basaltic crust may have been subducted and settled to the bottom of
the mantle because under pressure it becomes denser than the mantle. It could have
formed a layer 100-1000 km thick, which could explain early geochemical depletion
of "incompatible" elements in the upper mantle.
Continental crust, closer to granitic composition, apparently accumulated only slowly
during the first billion years, more rapidly for the next billion years, and then more
slowly again.
U. Dyudina(1), P.Sackett(1), D. Bayliss(1), L Dones(2), H. Throop (2), A. Del
Genio(3), C. Porco(4), S. Seager(5)
(1)
(2)
(3)
(4)
(5)
Mount Stromlo Obs., Australian National University
Southwest Research Institute, Boulder, USA
NASA Goddard Institute for Space Studies, NY, USA
Space Science Institute, Boulder, USA
DTM, Carnegie Institute at Washington, USA
Disk-averaged phase light curves of extrasolar Jupiter and
Time when the process you describe started in the solar system: 106 y
The error bar on the start time: ranges from 105 to 106 y
Time when this process ended: continuing
Saturn.
We predict how the remote observer would see the brightness of the giant planets vary
as they orbit the star. The prediction is based on our empirical model of Jupiter,
Saturn, and Saturn's rings reflectivity. The planets' and rings' surface reflectivity and
the phase angle dependence of the reflectivity is derived from Pioneer and Voyagers
spacecraft observations. We model the planets and the rings at different planets'
obliquities and different viewing geometries. We derive the disk-averaged brightness
of the planet and rings depending on the orbital inclination and eccentricity.
Back-scattering effect of the real atmosphere makes the planet appear several times
brighter than Lambertian sphere at full phase. The rings make the planet appear
several times brighter at some geometries. A planet with rings produces complicated
non-symmetric light curve as it orbits the star and changes phase. The brightest point
on the curve may be different from the full phase geometry. This asymmetry together
with a specific shape of the light curve may allow detection of rings in the precise
photometry observations.
We will discuss detectability of extrasolar planets and the rings around the planets
using their phase light curves.
J. Freeman (1), L. Moresi (2) and D. May (3)
(1)
(2)
(3)
ANU
Monash University
VPAC, Monash University
Stagnant Lid Convection with a Water Ice Rheology
Numerical investigations of thermal convection with strongly temperature dependent
Newtonian viscosity (diffusion creep) and extremely large viscosity contrasts have
demonstrated the existence of three convective regimes. These are the small viscosity
contrast regime, transitional regime and the stagnant lid regime. The strong
temperature dependence of water ice suggests that convection operating within the
mantle of an icy satellite should be within the stagnant lid regime. We study the
evolution into the stagnant lid regime with a water ice rheology by solving the
equations of thermal convection for a creeping fluid with the Boussinesq
approximation and infinite Prandtl number. The viscosity is non-Newtonian
(dislocation creep). We fix the Rayleigh number at the base ($Ra_1$) to be $1\times
10^4$ and systematically increase the viscosity contrast (as determined by $\Delta
T$) over the region from $\Delta \eta = 1$ to $10^{14}$. The transition to the
stagnant lid regime occurs at a viscosity contrast greater than $10^4$ for Newtonian
viscosity convection, whilst non-Newtonian viscosity convection accommodates the
stagnant lid regime at larger viscosity contrasts.
For a stress exponent, $n$, equal to 3, the stagnant lid regime is achieved at a
viscosity contrast greater than $108$. Dislocation creep of water ice is characterized
by a larger stress dependence ($n=4$) than silicates ($n=3$), and with this water ice
rheology, the stagnant lid regime is attained at a viscosity contrast greater than $1010$.
Andrew Glikson
RSES, ANU
Early terrestrial maria-like impact basins: mineralogy and chemistry of early
Precambrian asteroid impact ejecta, Pilbara and Transvaal, may imply existence of
large
oceanic
impact
basins
on
the
early
Precambrian
Earth.
3.8 to 2.4 billion years interval
1.
Episodic Precambrian asteroid impacts, with which my abstract is
concerned, follow the major impact episode at 3.95-3.85 billion years,
generally referred to as the "Late Heavy Bombardment" (LHB).
2.
The error bar on the onset of the post-LHB era at about 3.85 billion
years ago would be about +/-20 or 30 million years.
3.
Impact by large asteroid clusters, with which the paper is concerned,
continue throughout geological history, the last being about 35 billion
years ago (late Eocene).
Asteroid impact fallout units, consisting of microkrystite (impact condensate)
spherules and microtektites, increasingly allow the deciphering of the early impact
history of Earth. In a paper of key importance, B.M. Simonson, D. Davies, M.
Wallace, S. Reeves, and S.W. Hassler, (1998, Iridium anomaly but no shocked quartz
from Late Archie microkrystite layer: oceanic impact ejecta?, Geology, 26:195-198)
point out the likely oceanic (mafic-ultramafic) crustal source of early Proterozoic
impact ejecta in the Pilbara Craton, Western Australia. Studies of mainly chloritic
microkrystite spherules from the Barberton greenstone belt, Transvaal, are consistent
with a mafic derivation of impact condensates (Lowe et al., 1989; Byerly and Lowe.
1994; Shukloyukov et al., 2000; Kyte et al., 2003; Lowe et al., 2003). Recent field and
geochemical studies of Archaean to early Proterozoic impact units in the Pilbara
Craton (Glikson and Vickers, 2003) lend support to Simonson et al.'s (1998)
suggestion, on the following basis:
[1]
[2]
Siderophile element (Ni, Co), ferroan elements (Cr, V) and Platinum Group
Element (PGE) patterns of least-altered microkrystite (impact-condensate)
spherules and microtektites from Archaean and early Proterozoic impact
fallout in the Pilbara Craton (northwestern Australia) and the Kaapvaal Craton
(Transvaal) (Table 1) indicate a mafic/ultramafic composition of impact target
crust.
No shocked quartz grains are observed in the impact fallout units.
Estimates of asteroid and crater sizes based on (a) Mass balance calculations of
asteroid masses based on the flux of Iridium and Platinum as measured from impact
fallout units, and (b) spherule size-frequency distribution using the method of Melosh
and Vickery (1991), provide evidence for asteroids several tens of kilometer in
diameter (Byerly and Lowe,1994; Shukloyukov et al., 2000; Kyte et al.; Glikson and
Vickers, 2003) and consequent oceanic (sima crust-located) impact basins with
diameters on a scale of several hundred kilometers.
The implications of these observations for the nature of the early Earth are
inconsistent with strict uniformitarian geodynamic models based exclusively on plate
tectonic processes. It is suggested the evolution of the early crust represents the
combined effects of mantle-driven convection, modified plate tectonic regimes, and
large extraterrestrial impacts which triggered deep faulting and adiabatic mantle
melting. The latter resulted, in turn, in a feedback mechanism which temporally and
spatially controlled the onset and loci of long term dynamic plate tectonic patterns.
A picture emerges of a post-3.8 Ga early Precambrian Earth, i.e. postdating the Late
Heavy Bombardment of 3.9-3.8 Ga, which consisted of sialic (SiAl-dominated)
continental nuclei composed of multiple superposed greenstone-granite cycles
interspersed within extensive tracts of simatic (SiMg-dominated) oceanic crust. The
latter included maria-like impact basins on scales of up to several hundred kilometer,
i.e. similar in size to the lunar Mare Crisium impact basin (~3.2 Ga; Ds ~ 400 km) or
even Mare Serenitatis (Ds ~ 600 km).
References:
Byerly, G.R., Lowe, D.R., 1994, Geochim. Cosmochim. Acta, 58, 3469-3486
Glikson, A.Y., Vickers, J., 2003, Geol. Surv. West Aust. Report
Kyte, F.T., Shukloyukov, A., Lugmair, G.W., Lowe, D.R., Byerly, G.R., 2003
Geology, 31, 283-286
Lowe, D.R., Byerly, G.R., Asaro, F., Kyte, F.T.1989, Science 245, 959-962
Lowe, D.R., Byerly, G.R., Kyte, F.T., Shukloyukov, A. Asaro, F., Krull, A., 2003,
Astrobiology, 3, 7-48
Melosh, H.J., Vickery, A.M., 1991, Nature, 350, 494-497; Shukolyukov, A., Kyte,
F.T., Lugmair, G.W., Lowe, D.R. and Byerly, G.R. (2000), Springer, Berlin, pp.
99-116
Simonson, B.M., Davies, D., Wallace, M., Reeves, S., Hassler, S.W., 1998, Geology,
26, p. 195-198
Karl E. Haisch Jr
University of Michigan
Circumstellar Disk Evolution in Young Stellar Clusters
Time when the process you describe started in the solar system: 200,000 yr
The error bar on the start time: 100,000 yr
Time when this process ended: 6 Myr
The error bar on the end time: 1 Myr
We report the results of the first sensitive infrared and millimeter continuum surveys
of the young clusters NGC 1333, NGC 2071, NGC 2068, and IC 348 to obtain a
census of the circumstellar disk fractions in each cluster. Our observations reveal that
the variation in the fraction of detected millimeter sources from cluster to cluster is
similar to the variation in the fraction of infrared sources for these clusters, implying
that the inner and outer disks are coupled.
In addition, we conclude that our published estimation of disk lifetimes (t ~ 6 Myr)
from infrared excesses provides accurate upper limits to the lifetimes of massive outer
disks. This is the timescale for essentially all the stars in a cluster to lose their disks,
and should set a meaningful constraint for the planet building timescale in stellar
clusters. The implications of these results for current theories of planet formation are
discussed.
Masahiko Honda
Research School of Earth Sciences, Australian National University
The origin and evolution of planetary atmospheres - implications from noble
gases
Time the formation of the terrestrial atmosphere started: unknown
Time the formation of the terrestrial atmosphere finished: 100 Ma relative to the
formation of solar system
Error bar: 40 Ma
The differences in noble gas elemental abundances between the Earth's atmosphere
and the solar abundances lead to the recognition that the Earth's atmosphere was
formed secondarily by extensive degassing of volatiles from the Earth's interior,
rather than by directly acquiring a primary atmosphere from the surrounding solar
nebula.
Models of degassing of volatiles from the Earth based on the differences of
40Ar/36Ar ratios in the Earth's atmosphere (=295.5; 40Ar produced from the decay of
radioactive isotope 40K in the Earth and 36Ar is primordial) and in mantle-derived
samples (>40,000) suggest that the Earth atmosphere was formed during a short
period within ~100 million years of the formation of the solar system; namely by
catastrophic degassing. Excess 129Xe, relative to the atmospheric 129Xe/130Xe ratio,
observed in mantle-derived samples is believed to be attributable to the radioactive
decay of the extinct nuclide 129I (half life 16 million years) once present in the Earth;
this requires that the Earth's atmosphere must have separated from the mantle before
all the 129I had decayed (another powerful argument in favour of early catastrophic
degassing of the Earth).
The observation of primordial solar neon, distinctly different from present-day
atmospheric neon, in mantle-derived samples implies that the Earth's atmosphere has
not evolved in a closed system. This can be explained by postulating that isotope
fractionation occurred in the Earth's atmosphere as a consequence of hydrodynamicescape processes, possibly associated with the rupture of the Moon, or, that volatilerich meteoritic material accreted at a late stage in the Earth's formation.
Similarities between the noble gas elemental abundances of the atmospheres of the
terrestrial planets (Venus, Earth and Mars), and between the neon isotopic
compositions of the Earth's atmosphere and Mars-derived meteorites, suggests that
insights to the formation of the Earth's atmosphere may be generally applicable to the
atmospheres of the other inner "terrestrial-type" planets.
Ing-Guey Jiang
Institute of Astronomy, National Central University, Taiwan
The Eccentricity Outburst and Resonance Sweeping
Time when the process started in the solar system: 0 Myr
The error bar on the start time: 0.9 Myr
Time when this process ended: 1.0 Myr
The error bar on the end time: + 1.0 Myr, - 0.9 Myr
The dynamics of asteroids within planetary systems is studied and the role of protostellar discs is discussed. We found that the orbital eccentricities of test particles near
the resonant region can be amplified significantly. The disc depletion could lead to
the migration of resonant region, which would definitely affect the resulting observed
dynamical properties of the asteroid belts for any planetary systems in general.
Ray Jayawardhana
University of Michigan
Timescales of Disk Evolution and Planet Formation
Most newborn stars are surrounded by disks of dust and gas. It is out of these disks
that planetary systems form. Studies of disk evolution can provide valuable insight
into the timescales and processes of planet formation. Recent observations at infrared
and millimeter wavelengths of young stars spanning a range of ages suggest that their
(inner) dusty disks evolve relatively rapidly, on timescales of 10 million years or less.
I will review the current evidence and discuss the constraints on planet formation
models.
Gareth Kennedy
Monash U., Australia
The Influence of a Binary Companion on Planetary Formation
The timescale for terrestrial planets, or giant planet cores, to form by accretion
depends on the balance between excitation in the early planetesimal disk caused by
self-gravitational interactions, and de-excitaton caused by inelastic collisions.
However, since approximately 48% of local galactic field stars have binary
companions, we investigate the disruption of this balance when a binary companion is
included. The method used to study this problem removes the effect of the interaction
between planetesimals, thus allowing the "tidal stirring" effect on the disk caused by
the binary to be examined. A summary of results will be given from computer
simulations investigating additional excitation caused by a binary companion, and the
implications for planetary formation.
Warrick Lawson
UNSW@ADFA, Australia
Long-lived accretion in nearby T Tauri stars
Time when the process started in the solar system: 0 Myr
The error bar on the start time: 0.9 Myr
Time when this process ended: 1.0 Myr
The error bar on the end time: + 1.0 Myr, - 0.9 Myr
The nearest young stellar populations share a kinematic origin with the nearest OBstar population (the Oph-Sco-Cen association) and have inferred ages of 5-15 million
years. These stars are prime targets for all early stellar and planetary evolution issues,
including the issue of circumstellar disk longevity. Optical/infrared study finds a
small fraction of these stars still possess inner disks and are undergoing active diskstar accretion at 10 Myr, a timescale comparable to that demanded by planet
formation theory to grow Jovian planets to near their final masses.
Laurie A. Leshin(1) and Steven J. Desch(2)
(1)
(2)
Geological Sciences/Meteorite Center, Arizona State University
Physics and Astronomy, Arizona State University
Making Waterworlds: The Importance of 26Al
In order to understand the possibility of discovering life elsewhere, we seek to explore
factors that affect the likelihood of forming "waterworlds" like the Earth in other solar
systems. Here, we consider the effect of the astronomical setting of a forming solar
system, and specifically its effect on the abundance of the short-lived radioisotope
26Al. If the source of 26Al in our solar system and others is a nearby supernova, the
essentially random distance to the supernova explosion sets a solar system's initial
abundance of 26Al. Recent models for the delivery of water to the forming terrestrial
planets indicate that most of Earth's water was carried in by hydrated asteroids. In
solar systems with more initial 26Al, asteroids would be drier, and dry Earths would
result. In fact, solar systems with less 26Al than our own are more likely, and this
could result in much wetter Earths. Clearly this is only one factor that could affect the
habitability of an extrasolar Earth, but it demonstrates the need to bring together
astronomers, planetary scientists, and geoscientists to consider which factors are
likely to be the most critical to forming and sustaining life.
Kurt Liffman
Monash University & CSIRO
Particle Size Sorting in the Solar Nebula
Time when the process you describe started in the solar system: 2 Myr
The error bar on the start time: 1 Myr
Time when this process ended: 7 Myr
The error bar on the end time:+ 3Myr, - 5 Myr
We wish to examine size sorting of chondrules and metal grains within the context of
the jet flow model for chondrule/CAI formation. In this model, chondrules, CAIs,
AOAs, metal grains and related components of meteorites are formed in the outflow
region of the inner most regions of the solar nebula and then ejected, via the agency of
a bipolar jet flow, to outer regions of the nebula.
We wish to see if size sorting of chondrules and metal grains occurred in the outflow
formation region or after the particles had left the outflow and were moving above or
into the solar nebula.
Doug Lin
UC Lick Observatory, USA
The ubiquity of planets and the diversity of planetary systems
Based on the core-accretion scenario, we consider the emergence of planetesimals,
growth of cores, accretion of gas, and migration of gas giants in an evolving
protostellar disks. We outline the condition which lead to the dynamical architecture
of our own Solar System. We discuss the mass and period distribution of gas giant
planets and show their dependence on the metallicity of their host stars. Based on
these results we infer the time scale for gas giant planet formation is a few Myr and
that for terrestrial planets and ice giants is a few times longer.
Charles Lineweaver
UNSW, Australia
Galactic prerequisites for the formation of other Earths
(I will be talking about a paper by Lineweaver, Fenner and Gibson that will appear in
Science Magazine on Jan 2, 2004.)
The process I will be describing is the formation of other Earths in the galaxy within
the Galactic Habitable zone. This started about 8 +/- 1 billion years ago and
continues today.
As we learn more about the Milky Way Galaxy, extrasolar planets, and the evolution
of
life
on
Earth,
qualitative
discussions
of
the
prerequisites
for life in a Galactic context can become more quantitative. We modelled the
evolution of the Milky Way to trace the distribution in space and time of four
prerequisites for complex life: the presence of a host star, enough heavy elements to
form terrestrial planets, sufficient time for biological evolution, and an environment
free of life-extinguishing supernovae. We identified the Galactic habitable zone and
obtain an age distribution for the complex life that may inhabit our Galaxy
Jonathan Lunine
The University of Arizona
Making worlds habitable - the delivery of water and
Time when the process you describe started in the solar system: 106 years
The error bar on the start time: 0-107 years
Time when this process ended: 30 million years
The error bar on the end time: +/- 20 million years
organics
The formation of terrestrial planets may have been the final stage in the formation of
our solar system, one that was encouraged by the growth of Jupiter and the
consequent stirring of orbits. Water, if unavailable locally at 1 AU, was not primarily
provided by comets but rather by large bodies in what is now the asteroid belt. This
statement is supported by both isotopic evidence and dynamical modelling. However,
the organic compounds necessary for the origin of life could have been delivered by
comets, at least in part, and may have come to the Earth after our water was obtained.
The possibility of multiple sources for water and organics for terrestrial planets leads
to the speculation that considerable variety exists from one planetary system to
another in the abundance of water and organics on rocky planets around 1 AU, and
dynamical studies bear this out.
A-Ran Lyo
ADFA , Australia
Disk fraction in the ~10Myr-old pre-main sequence Eta Chamaeleontis cluster
Time when the process you describe started in the solar system: ~10 Myr
The error bar on the start time +/- 1Myr
Time when this process ended:
The error bar on the end time: +/- 1Myr
The study of disk longevity and the duration of the accretion phase in low-mass premain sequence (PMS) stars is important for planet formation and the growth of protoplanets to their final masses. Studies of the disk fraction in PMS clusters - the
majority based on K-band surveys - suggest most disks and star-disk interactions
disappear in a few Myr. This is in apparent conflict with planet formation theories
demanding Jovian planet formation timescales > 10 Myr. This issue has been difficult
to resolve owing to a lack of older PMS sample. To date only three ~10 Myr-old
groups have been discovered; the TW Hya Association, the Beta Pic moving group,
and the Eta Chamaeleontis cluster. We analysed JHKL observations of the stellar
population of the Eta Chamaeleontis cluster. Using IR colour-colour and colour
excess diagrams, we found that the fraction of stellar systems with near-IR excess
emission is ~ 0.60. We also obtained an accretion fraction of ~ 0.27 for this cluster
from their IR excesses Delta(K-L) > 0.4mag and broad H_alpha line profiles. The
result for Eta Cha cluster implies considerably longer disk lifetimes than found in
some recent studies of other young stellar clusters.
Sarah Maddison (1), James Murray (1), Laure Barriere-Fouchet (2), Robin
Humble (3) and Jean-Francois Gonzalez (2)
(1)
(2)
(3)
Swinburne
ENS Lyon
CITA
Predicting Dust Distribution in Protoplanetary Disks
Time when the process you describe started in the solar system: Just post cloud
collapse.
Time when this process ended: About a million year later
The error bar on the end time: +/- a few 10,000 yrs
We present hydrodynamic calculations and analytical models that follow the
evolution of distributions of dust (solid material of order microns to meters in size) in
the solar nebula. We find that a quasi-stable end state is reached in which the dust comoves with the nebula gas. The innovation of our approach lies in the use of a three
dimensional smoothed particle hydrodynamics code that represents the gas and dust
as two inter-penetrating fluids that interact via gravity and drag. Thus for the first time
we are able to predict the three dimensional structure of the dust distribution in
protoplanetary disks. The final density structure in these discs gives insight into
likely zones for planet formation.
Rosemary Mardling
CSPA, Monash U., Australia
Gravitational Instability and Planet Formation: From Planetesimal Collisions to
Free Floaters
Gravitational instability is fundamental to planet formation from the smallest scales
(planetesimal collisions to form terrestrials and giant cores) to the largest scales
(ejection of large bodies to form free-floaters; collisions of large bodies to form
planet-moon pairs; long-term stability). It is fundamental to understanding how
protoplanetary disk populations of bodies dynamically evolve, with resonances
playing an important role in energy transport. Hence gravitational instability is very
much at the heart of understanding timescales in the planet formation process. Until
now people have studied stability numerically, or analytically using the circular
restricted three-body problem, the latter being very successful for small bodies in the
Solar System. Here we will describe a new formulation which allows one to
analytically study stability in the general three-body problem, that is, there are no
restrictions on mass ratios, eccentricities or orientations. It is then clear how stability
depends on all these parameters without having to cover parameter space numerically.
This is particularly useful for understanding the extrasolar planet configurations
which are so different to the Solar System.
Marco M. Maldoni (1), M. P. Egan (2), Robert G. Smith (1), Garry Robinson (1),
C. M. Wright (1)
(1)
(2)
UNSW@ADFA, Australia
Air Force Research Laboratory, Pentagon, Washington, USA
Poster: Dust and Water Ice in Highly Evolved Oxygen-rich Stars
Tell-tale signs of ice mantles on dust grains in dust shells (DS) of O-rich stars are
infrared bands at 3, 44 and 62 micron. The laboratory spectrum of ice also displays a
band located between 11.5 and 13 micron (hereafter the 12 micron band) depending
on the structural phase. Surprisingly, this has only been detected towards two stars,
OH32.8-0.3 and OH231.8+4.2. The profile of the 3 micron band is a diagnostic of the
structural phase of ice. The observational evidence suggests that the crystalline phase
is the dominant one in DSs containing ice. OH231.8+4.2 stands out as the only object
in its class having largely amorphous ice in its DS.
The salient questions are:
1a.
Why is the 12 micron ice band not easily detected?
1b.
Why is it only detected towards OH32.8-0.3 and OH231.8+4.2?
2.
Why is ice in the DS of OH231.8+4.2 amorphous?
Radiative transfer modelling has been used to tackle the above questions. The results
indicate that radiative transfer effects in the 9-15 micron region severely hinder the
detection of the 12 micron ice band. The 11.5 micron bands detected towards
OH32.8-0.3 and OH231.8+4.2 are likely due to dust components. The 11.5 micron
band in OH231.8+4.2 may be due to Al2O3 grains. If this interpretation is correct it is
the first instance of the detection of a population of Al2O3 dust grains in a very
evolved star. The results also indicate that the ice mantles in OH231.8+4.2 are
crystalline, the previous assignment being based on unrealistically thick ice mantles.
Kevin D. McKeegan
University of California. Los Angeles
Short-lived radioactivity in the solar nebula: interstellar inheritance and local
irradiation
Time when the process you describe started in the solar system: time zero (formation
of Calcium-aluminum-rich inclusions, 4567 Ma). "Process"; is collapse and high
temperature evolution of the inner regions of the solar nebula.
The error bar on the start time: <1 Ma
Time when this process ended: 5 Ma
The error bar on the end time: 4 Ma
I will review the record of short-lived, now-extinct radioisotopes that is preserved in
the earliest-formed solar system rocks. The goal is to understand the source(s) of
these newly synthesized isotopes, whether as debris from nearby mass-losing stars or
as a result of nuclear reactions during local energetic processes associated with
formation of the Sun. In fact, there is evidence to support both sources as
contributing to solar system matter: 10Be and (most likely) 7Be (as well as other
isotopic and petrogenetic evidence) indicate formation of refractory inclusions (CAIs)
in a high-radiation environment, probably near the proto-Sun, but 60Fe, which has
recently been found in chondrites, can only be produced in stars. Implications for
developing a high-resolution chronology of earliest solar system evolution will be
discussed.
Frank Mills
RSPhysSE and CRES, ANU
The photochemical stability of the Venus atmosphere
Time when process started: 400 million years before present
Uncertainty on start time: 100 million years
Time when process ended: Presently occurring
The primary constituent of the Venus atmosphere, CO2, dissociates into CO and O
when it absorbs ultraviolet radiation at wavelengths shorter than about 225 nm. In an
initially pure CO2 atmosphere, the O atoms preferentially would combine with each
other to produce an atmosphere that is approximately 90% CO2, 7% CO, and 3.5%
O2. The observed upper limit on O2 in the Venus atmosphere, however, is 0.3 ppm.
Catalytic cycles involving ClC(O)OO as an intermediary have recently been shown
capable of producing an O2 abundance that is within the observational upper limit if
the rates for specific reactions are varied within reasonable limits. The time scales
associated with these chemical processes will be discussed and compared with the
time scales for other relevant atmospheric processes, such as condensation (10-105
sec), modelled vertical mixing (105-107 sec), and horizontal transport (104-105 sec).
Charles Morgan
Monash University
Formation of the "Classical" Kuiper Belt
Start Time: 500,000 years
Error Bar on start time: 400,000 years
End Time: 200 million years
Error Bar on end time: 50 million years
I have simulated the orbital evolution of Kuiper belt. Most of the Kuiper belt we see
today took shape over a span of roughly 200 million years following the era of
planetesimal accretion. The orbital distribution of the Kuiper belt has turned out to be
a complex mixture of sub-populations. Just a couple of years ago most people
envisaged a vast planetesimal disk, like the disk of Beta Pictorus extending 900 AU
from the star. In fact, there are no trans-Neptunian objects (TNOs) whose orbits look
vaguely primordial beyond 48 AU from the Sun. The orbital evolution of this
complex distribution turns out to be surprisingly simple. The only processes at work
were gravitational scattering in TNO close mutual encounters and perturbation by the
planets in their present relative positions. The Kuiper belt appears to have expanded
from an initial population with a narrow range of orbits, just like the particulate ring
observed around the young star HR 4796A (age ~8 million years). The timescale of
orbital evolution is constrained by competition between weakly destabilizing
resonances due to Uranus and Neptune and to scattering by the most massive TNO.
All TNOs started within the zone of weak instability around 41 AU. The largest TNO
scattered some into adjacent stable orbits. These formed the core of what has been
called the "classical Kuiper belt". The eccentricities of those remaining in the unstable
zone were pumped up until they were scattered by Neptune, some outward into the
"scattered disk". The structure of the "classical Kuiper belt" was frozen in when the
dominant TNO was perturbed away after around 200 million years. The balance
between the various populations constrains the tenure of the largest TNO, as well as
its size to something like Ganymede.
Marc Norman
Research School of Earth Sciences, Australian National University
Timescales of Planetary Formation in the Inner Solar System: Constraints from
the Age of the Lunar Crust
Time when the process (planetary differentiation) started: 4.55 Ga
Error bar on start time: 0.1 Ga
Time when the process (planetary differentiation) ended: On active planets such Earth
the process continues today.
The crust of the Moon is composed of feldspathic igneous rocks thought to have
formed by crystallization of a global magma ocean. The compositions and ages of
lunar crustal rocks provide unique information about the early evolution of terrestrial
planets, and the timescales of planetary formation and differentiation in the inner solar
system. Large impact events have severely modified the primary compositions of
many lunar crustal rocks. However, unusually well-preserved samples yield
radiogenic isotopic compositions indicating a crystallization age of ~4.46 Gyr for the
earliest crust. The terrestrial planets must have formed, melted, and cooled no later
than about 100 million years after the formation of the first nebular phases such as
those preserved in primitive meteorites.
Allen P. Nutman (1), Clark R.L. Friend (2), Vickie C. Bennett (1), Masahiko
Honda (1)
(1)
(2)
Research School of Earth Sciences, ANU
Oxford Brookes University, U.K.
The World's Oldest Rocks: Extracting Useful Information on Early Terrestrial
Fractionation and Evolution from an Awful Geological Mess
Start time: 4.1 Ga
Error on start time +/- 0.4 Ga
End time: 3.6 Ga
Error on end time +/- 0.1 Ga
Earth is a dynamic planet. The hydrosphere attacks the surface. Mantle convection
constantly produces new igneous crust and keeps the crustal plates in motion. These
processes efficiently resurface Earth, so that only about a millionth of the accessible
planet now consists of >3.55 billion-years (Ga) rocks. This millionth contains record
of Earth's transformation from an inhospitable rock pock-marked by meteorites to a
watery planet with continents and probably life by 3.55 Ga (broadly like Earth
nowadays).
Surviving >3.55 Ga rocks are fragments that fortuitously escaped destruction in the
following three-quarters of Earth's history. These fragments occur in "gneiss
complexes", where >3.55 Ga igneous and sedimentary rocks were unfortunately
transformed almost beyond recognition by heating up to 800°C and distortion during
strong deformation. Extracting useful information out of this awful geological mess
is a task needing integrated geological observation, robust dating (particularly the
U/Pb zircon geochronometer) and cutting edge geochemistry.
Transformation of >3.55 Ga materials into gneisses can corrupt chemical and isotopic
tracers to the extent that they yield equivocal results. Employing geological and
mineralogical techniques to identify domains in >3.55 Ga materials least corrupted by
later geological disturbances maximises the success of geochemical studies.
Ultimately, less than a billionth of Earth's surface contains the most suitable
materials! Some key advances from this tiny part of the accessible Earth are:
*
The age of the hydrosphere pushed back from 3.5 Ga (1970) to definitely
>3.85 Ga (1990) and likely >4.0 Ga (this decade).
*
Ancient zircon (and atmospheric) noble gas geochemistry established the great
antiquity of the present atmosphere.
*
Growing acceptance of life at ca. 3.7 Ga, but controversy still surrounds
evidence for life by 3.85 Ga. Hence the Earth was benign with a retained liquid
hydrosphere before 4.0 Ga, something that would have been regarded unlikely only a
decade ago.
Craig O'Neill and Louis Moresi
School of Geosciences, University of Sydney
School of Mathematical Sciences, Monash University
The formation of crustal dichotomies on the terrestrial planets
Time when the process you describe started in the solar system: 4.55Ga
The error bar on the start time: 0.05
Time when this process ended: ongoing
The Earth's crust is a reworked composite of terranes that primarily forms as a result
of ongoing volcanic activity. Crustal formation has a first order effect on subsequent
planetary evolution, in that it concentrates a large proportion of heat producing
elements near the surface and forms a heterogeneous insulating blanket to the
convecting mantle.
Many of the planets exhibit marked variations or dichotomies in crustal thickness.
These variations arise due to the interplay between mantle convection patterns,
surface volcanism, near surface stress, buoyancy of the thickened crust, and the ability
of the lithosphere to support deviatoric stress. These features are continually evolving
while the surface of a planet retains some mobility; for example the Earth's continents
are continually evolving today. On 'one-planet' planets, such as Mars, Mercury and
the Moon, crustal thickness variations were locked in at the cessation of active-lid
convection.
We examine causes leading to the stagnation of terrestrial planets, and the effect of
the formation of crustal dichotomies on convective regime. We also explore the
implications of these factors on ongoing volcanism on rocky planets.
Andrew Prentice
Mathematical Sciences, Monash University
Origin and Bulk Chemical Composition of our Inner Planets and Jupiter
Time when the described process started in the Solar system: 0 yr
The error bar on the start time: 0 yr
Time when this process ended: 1 Myr
Error bar on the end time: 0.5 Myr
There is a growing body of evidence that the planets of the inner Solar system
condensed within narrow, compositionally-distinct annuli, close to their present
orbital radii (Drake & Righter, 2002, Nature, 416, 39). Such a picture is consistent
with the Laplacian nebular hypothesis whereby the planetary system had formed from
a concentric family of gas rings. These rings were shed by the contracting proto-Solar
cloud [hereafter PSC] as a means for disposing of excess spin angular momentum
(Prentice: 1978, Moon & Planets, 19, 341; Earth, Moon & Planes, 2001, 87, 11; 2001,
in URL: http://www.lpi.usra.edu/meetings/mercury01/pdf/8061.pdf). A new model
for the PSC has been constructed. It consists of an adiabatic convective core
surrounded by a superadiabatic envelope of negative polytropic index. This structure
is suggested by numerical simulations of supersonic thermal convection in a model
atmospheric layer (Prentice & Dyt, 2003, MNRAS, 341, 644). The cloud possesses a
radial turbulent stress whose ratio to the gas pressure achieves a maximum value ~15
at the core/envelope boundary. If the controlling parameters stay constant, the PSC
contracts homologously and sheds gas rings whose mean orbital radii R{n} (n =
0,1,2,) are nearly geometrically spaced. The ring mean temperatures T{n} vary with
R{n} as T{n} ~ C/R{n}^0.9, where C is a constant. Choosing iron-rich Mercury to
calibrate C, so that this planet forms at 1643 K and contains a mass fraction of 0.67 of
Fe-Ni-Cr metal, Venus forms at 917 K and contains 0.325 by mass of metal and is
totally anhydrous. The initial Earth (678 K) has 0.0023, by mass fraction, of water
tied up in tremolite. Mars (460 K) contains a water mass fraction of 0.00295 in
tremolite and 0.0027 in (Na,K)OH. Mars is thus the most water-rich of all the inner
planets. At Jupiter's orbit, where the pressure on the mean orbit of the gas ring is p{J}
= 0.0000063 bar, T{J} = 164 K lies just 5 K below the condensation temperature of
water ice. A process of rock/ice fractionation now takes place whereby only 33% of
the total water vapour condenses. A subsequent enhancement by a factor of ~2 in the
abundance of solids relative to gas, via gravitational sedimentation of solids onto the
mean orbit of the gas ring, accounts not only for the observed enhanced heavy
element abundance in Jupiter's atmosphere but also for the nearly equal proportions of
rock and ice in Ganymede and Callisto. I thank John D. Anderson [NASA/JPL] and
David Warren [Hobart] for much support.
Tamara Rogers
University of California Santa Cruz
Poster: 2D Semiconvection
Time when the process you describe started in the solar system: 106-107 yr
I will describe two dimensional numerical simulations of penetrative convection as
well as semiconvection. These simulations describe the nature of convection bounded
by a stable region and convection in the presence of a stabilizing compositional
gradient.
While general and basic at the moment these simulations will be applied to planetary
interiors and the possible erosion of (heavy element) planetary cores by overlying
turbulent convection during planet formation.
Raquel Salmeron (1) & Mark Wardle (2)
(1)
(2)
The University of Sydney
Macquarie University
Magnetorotational instability in protostellar discs
Time when the process you describe started in the solar system: 0
Error bar on the start time: 1 Myr
Time when this process ended: 6 Myr
Error bar: 4 Myr
We present a linear analysis of the vertical structure and growth of the
magnetorotational instability (MRI), a promising mechanism to explain angular
momentum transport in accreting systems. The method incorporates vertical
stratification and non-ideal MHD regimes appropriate for protostellar discs. This
study revealed that, for a weak magnetic coupling, the Hall effect causes perturbations
to grow faster and act over a more extended cross-section of the disc than those
obtained using the ambipolar diffusion approximation. As a result, considerable
accretion can take place in regions closer to the midplane, despite the weak magnetic
coupling, rather than in the surface regions, which have a much stronger coupling, but
significantly less fluid density. Results using a realistic height-dependent conductivity
indicate that the MRI can grow at a significant fraction of its ideal rate for a wide
range of magnetic field strengths and radial locations. At 1 AU, under the assumption
that dust grains have settled towards the midplane of the disc, unstable modes are
found for 1 mG < B ~ 10 G. These results are relevant for our understanding of disc
evolution and planet formation mechanisms.
Therese Schneck
Consulting Engineer, PhD.
Poster: Protoplanetary Disks
Time when the process you describe started in the solar system:4 billion years ago.
The error bar on the start time: 100 million years.
Time when this process ended: 3.9 billion years
The error bar on the end time: 100 million years
The behaviour of the trends in abundances of heavy elements in galactic halo stars
give us major clues about the conditions and populations of stars that existed early.
The iron epoch ended roughly 10 billion years ago in the fossil structure of the Milky
Way (1).ACS images from the Hubble Telescope provide a panchromatic atlas of the
inner region. The gas and dust in the centre of protoplanetary disks compressed by
gravity and density is such that it generates enough heat to balance the stream of
particles, moving at 4500 to 8900 miles per hour, from the star. In the Trapezium
region, several globules of gas and dust (about 5 -8 times larger than our solar system)
surround the main stars. In NGC 3603 ,the starbust cluster dominant source of
ionization, which has a projection of 1.3pc from the cluster, has the spectral
characteristics of an ultra compact HII region(2).The Protoplanetary Disks located
within NGC 3372, 7300 light years from earth, are 100 times the diameter of our solar
system (3). The giant star forming region in NGC 3372(Curtis Schmidt Telescope)
gather the light from 3 different filters tracing emission from O(blue and hot ionized
temperature), H(green) and S(red).Thermal bremsstrahlung and non thermal
synchrotron radiation are at work in the proplyd source studied(4) and magnetized
regions within the envelope of the proplyd-like nebulae exist. The interaction of the
jet outflow with the surrounding ambient medium generates both the target
electrostatic plasma waves and the radiating swept up relativistic electrons. It does
not reply on the existence of large intrinsic ordered magnetic fields to account for
strong emission due to the synchrotron radiation process(5).
References:
(1) Ancient Stars in Milky Way Reveal Colorful Epochs of Heavy Element Formation
NOAO 2000 November,14
(2) W.Brandner and al HST/WFPC2 observation of Proplyds in the giant HII region
NGC3603 Harvard Smithonian Center for Astrophysics.NASA.
(3) National Optical Astronomy Observatory News release January 8,2003 NOAO
(4) A.Mucke,B.S.Koribalski,A.F.J.Moffat,M.F.Corcoran and I..R.StevensProplyds
like object in NGC 3603 APJ 571:366-377 2002
(5) R.Sclhickeiser.Non thermal radiation from jets of active galactic
nuclei:Electrostatic Bremsstrahlung as alternative to synchrotron radiation.A&A
410,397-414(2003)
T.G. Sharp (1), Z. Xie (1), C. Aramovich Weaver (1) and P.S. DeCarli (2)
(1)
(2)
Department of Geological Sciences, Arizona State University, Tempe AZ, 85287-1404
SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025-3493
Poster: Late Impacts on the L-chondrite parent body: Constraints from ShockVeins
Shock effects in meteorites provide a record of major impact events on meteorite
parent bodies. Nearly all type 5 and 6 chondrite show some evidence of shock
metamorphism. Based on radiometric dating, most of the shock metamorphism in
chondrites occurred at about 500 Ma (Bogard, 1995). Shock veins in chondrites,
which result from local melting during shock loading, record the high-pressure history
of impact events. The mineralogy and microstructures in shock veins provide a record
of crystallization pressures that can be used to constrain shock pressures and pulse
duration from impact events.
Ten L6 chondrites, ranging from shock stage S3 to S6, were investigated using
scanning electron microscopy, transmission electron microscopy and Raman
spectroscopy: RC 106 (S6), Tenham (S6), Acfer 040 (S6), Sixiangkou (S6) Umbarger
(S4-S6), Roy (S3-S5), Ramsdorf (S4), Kunashak (S4), Nakhon Pathon (S4) and La
Lande (S4). Igneous melt-vein assemblages, combined with published phase
equilibrium data (Agee et al. 1996), indicate crystallization pressures from less than
2.5 GPa to approximately 25 GPa. These crystallization pressures are about half those
based on calibration of shock deformation and transformation effects in shock
recovery experiments (Stöffler et al. 1991). Because shock veins quench primarily by
thermal conduction, crystallization pressure versus time can be estimated based on
melt-vein mineralogy and thermal modelling. Most samples appear to have
crystallized prior to shock release and therefore record the shock pressure. Tenham
and RC 106, (S6) crystallized nearly isobarically at approximately 25 GPa during
pressure pulses that lasted at least 50ms and 500 ms, respectively. These relatively
low pressures and long pulse durations suggest that the late impact on the L-chondrite
parent body involved a large impactor travelling at a relative velocity of only a few
km/s.
Frank H. Shu
National Tsing Hua University
Stellar Collapse from Molecular Clouds
We review the evidence and arguments, theoretical and observational, for the
timescales of the formation of sunlike stars in molecular clouds, starting from the
condensation of molecular cloud cores, to the gravitational collapse of such cores to
produce star/disk/pseudodisk/envelope structures, to the breakout of stellar jets and
bipolar outflows, to the T Tauri phase which has been traditionally identified with the
epoch of planet formation. We discuss the similarities and differences engendered by
star formation in clustered and dispersed environments, and we present a simple new
derivation for the stellar initial mass function that incorporates most of the modern
thinking about the process of star formation.
Dave Stegman (1), Mark Jellinek (2), Mark Richards (3), Michael Manga (3),
John Baumgardner (4)
(1)
School of Mathematical Sciences, Monash University, Bldg 28, Monash University, Clayton,
Vic 3800 Australia
(2)
(3)
(4)
Dept. of Physics, University of Toronto, 60 St. George Street, Toronto, Ont M5S 1A7 Canada
Dept. of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall,
University of California, Berkeley, Berkeley, CA 94720 United States
Theoretical Division, Los Alamos National Laboratory, Mail Stop B216, Los Alamos National
Laboratory, Los Alamos, NM 87545 United States
Model of mantle convection on Mars
Time when the process you describe started in the solar system:~ 4Ga
The error bar on the start time: +/- 400 Myr
Time when this process ended: ~ 4Ga
The error bar on the end time: +/- 400 Myr
Mars' large-scale physiography is dominated by a hemispheric dichotomy (thin
northern crust with low, smooth topography vs. thick southern crust with high, rugged
topography) and by the Tharsis rise (an enormous volcanic plateau), both of which
developed within the first ~1 Gyr of Martian history. Using a 3-D spherical mantle
convection model with temperature-dependent viscosity, we explore the effect of
hemispheric-scale crustal thickness variations on Martian mantle convection.
Thickened crust in the "southern" hemisphere of the model causes insulation of that
hemisphere which may effect the underlying mantle circulation. This leads to a
transient, regional-scale partial melting event sufficient to generate the Tharsis rise
during the first ~0.5-1.0 billion years following the formation of the crustal
dichotomy. Our model avoids some problems of timing inherent in plume models,
provides testable hypotheses regarding the history of Martian volcanism,
and suggests a causal link between the formation of the N-S dichotomy and Tharsis.
Ross Taylor
Dept. of Geology Australian National University
Earth-like planets: Common or rare in the galaxy?
Time when the process you describe started in the solar system: T zero 4566 Myr
The error bar on the start time: 5 Myr
Time when this process ended: 50-100 m.y. after T zero
The error bar on the end time: 50 m.y. (editor's comment by U.D.)
Earth-like planets: Common or rare in the galaxy? This problem, like astrobiology,
cannot be addressed directly at present in the absence of extra-solar examples.
However an examination of the processes by which the terrestrial-type planets formed
in our own system reveals, apart from the obvious requirements for metals, orbits of
low eccentricity and avoidance of giant planet migration into the inner nebula, that
rocky planet formation was essentially stochastic.
Following the formation of Jupiter, the inner nebula was dry, as revealed by the
anhydrous primary mineralogy of meteorites, while the water content of the Earth is
only 2 x 10-4 that in the primordial solar nebula. Not only do the inner planets mostly
lack the gas and ice components of the solar nebula, but they are also depleted in
elements volatile below about 1000K, including biologically significant elements.
Formation from differentiated planetesimals has also resulted in differences in
planetary compositions for the major elements (e.g., Mg/Si and Al/Si) from the
primordial CI abundances. While planets such as Earth and Venus, unlike Mars and
Mercury, are close in density, bulk composition and heat production, subsequent
collisional histories (e.g. lack of a Moon for Venus) and random late accretion of icy
planetesimals have produced startling differences in the geological histories of these
"twin" planets.
So the problem of forming Earth-like planets elsewhere would seem to depend on the
repetition in detail of the essentially random processes of planetary accretion and
subsequent geological evolution that has characterised the terrestrial planets.
Taylor, S. R. (1999) On the difficulties of making Earth-like planets. Meteoritics and
Planetary Science 34, 317-329
Taylor, S. R. (2000) Destiny or chance: our solar system and its place in the cosmos
Cambridge University Press, 229 pp.
Miguel
de
Val
Borro,
Pawel
Artymowicz
Stockholm Observatory
Poster: Instabilities in protoplanetary disks
(Times given with respect to the formation of solar
Time when the process you describe started in the solar system: 0 Myr
The error bar on the start time: 0 Myr
Time when this process ended: ~ 10 Myr
The error bar on the end time: 5 Myr
system)
We study hydrodynamic instabilities in protoplanetary disks caused by gaps opened
by giant planets. We consider wave-like perturbations to the initial disk in the linear
approximation and calculate the growth rate of the most unstable modes. The surface
density of the studied disks include analytical edges and bumps, as well as more
realistic gap profiles obtained from numerical simulations of disk-planet interaction.
We compare the results from the linear theory with two-dimensional non linear
hydrodynamic simulations. In particular, we address how the instabilities may
influence planet formation and migration in the disk.
Mark Wardle
Macquarie University
Magnetic activity in protoplanetary discs
Time when the process you describe started in the solar system: 0 yr
Time when this process ended: 5 Myr
The error bar on the end time: 4 Myr
Magnetic fields affect the dynamics and evolution of protoplanetary discs through
their influence on the rare charged species in the weakly ionised gas. In turn, charged
particle drifts induced by electric and magnetic fields determine the evolution of the
magnetic field and its degree of coupling to the bulk neutral material. If the coupling
is sufficient, the presence of magnetic fields strongly modifies disc evolution via
magnetically-driven turbulence and/or centrifugally-driven outflows. Preliminary
calculations of the degree of coupling of the magnetic field to the weakly-ionised
matter in protoplanetary discs indicate that magnetic activity influences disc evolution
and planet formation.
David Wark
Earth Sciences, University of Melbourne, and A.C.R.C., Monash University
The Sequence of High Temperature Events in the Early Solar Nebula
Time when process started: 50,000 y
Error bar on start time: 40,000 y
Time when process ended: 5 million y
Error bar on end time: 4 million y
Ca-Al-rich Inclusions (CAIs) in meteorites define the 4.56 billion year age of the
Solar System. They are the oldest dated objects and contain isotopic anomalies due to
their formation from incompletely mixed stardust, and the effects of nuclear reactions,
in the early solar nebula. Their chemical and mineralogical composition was created
at high temperature, probably close to the protosun. CAIs must then have been
transported outwards where they accreted with other materials to make asteroids, the
"parent bodies" of meteorites.
CAIs reveal the following history of multiple, high-temperature processes, which
need to be accounted for by models of solar nebula evolution:
1.
Volatilisation, condensation and/or partial melting to produce CAIs from 16Orich material.
2.
"Flash-heating" of cm-sized CAIs to ~3000 K for a few seconds, producing a
thin, refractory, surface residue rich in Al oxide, Zr, Pt, etc.
3.
At lower temperatures (1400-1500 K), Mg, Si, Ca & O diffused into the
residue from nebular gas & dust to create microscopic (~0.05 mm) layers of
the minerals spinel, melilite and pyroxene known as ^ÓWark-Lovering (WL)
rims^Ô on the CAIs. WL rims probably formed very soon after the ^Ñflash
heating^Ò, because both they and underlying CAIs contain the same
anomalous, 16O-rich material.
4.
Slow infiltration and alteration of many CAIs at lower temperatures volatiles
(alkalis, Fe, H2S, etc) prior to their being accreted into asteroids.
The consistent layering and thickness of WL rims indicates that probably all coarse
CAIs passed through the same terminal sequence of extreme ^Ñflash heating^Ò, then
high temperature diffusion, before final cooling and accretion. This sequence needs
to be explained by nebular models.
Peter Wood
RSAA, ANU, Australia
Could long secondary periods in red giant light curves be due to close orbiting
companions?
Time when the process you describe started in the solar system: +5.5 x 109 yr AD
The error bar on the start time: 0.5 x 109 yr
Time when this process ended: +5.500001 x 109 yr AD
The error bar on the end time: (0.5 + 0.0001) x 109 yr
About 25% of variable red giant stars show evidence for long secondary periods (4001000 d) in their light curves. The long secondary periods (LSPs) are longer than the
radial fundamental mode of pulsation and therefore can not be due to radial, normalmode pulsation. An initial suggestion was that these long secondary periods could be
due to a close orbiting companion. Subsequent studies of radial velocity variations in
the largest amplitude examples of these stars show that they mostly have asymmetric
radial velocity curves which, if interpreted as binary orbit motion, suggest a close
companion of mass ~0.1 Msun in an eccentric orbit (a ~ 1.5 AU, e ~ 0.35). The
orbital decay and merger timescale for such a binary companion is only ~1000 years,
and the expected number density of such stars is only ~1/200 the observed number
density. In addition, 7 of the 9 stars with known radial velocity variations have an
argument of periastron from 180-360 degrees, a situation with only 7% probability.
Overall, the binary companion explanation for the LSPs does not seem very
plausible. A possible way of stopping the rapid orbital decay would be to have a
resonance between the orbit and a nonradial g-mode, although the details of such an
interaction have not been investigated. If the large light amplitude variations can be
explained as binary companions, then the lower amplitude stars would likely have
planetary-mass sized companions. In this case, the frequency of some orbiting body
around a typical solar mass star would be ~ 25%.
Christopher M. Wright (1), David K. Aitken (2), Alistair C. H. Glasse (3), Craig
H. Smith (4), Patrick F. Roche (5)
(1)
(2)
(3)
(4)
(5)
ARC ARF, School of Physical, Environmental and Mathematical Sciences, UNSW@ADFA,
Canberra ACT Australia
University of Hertfordshire, UK
Royal Observatory Edinburgh, UK
Electro Optical Systems, Queanbeyan NSW
University of Oxford, UK
Cosmic Dust Mineralogy Derived from Mid-Infrared Spectropolarimetry
Time when the process you describe started in the solar system: -10 to -1 million
years
The error bar on the start time: 1 million years
Time when this process ended:1 to 10 million years
The error bar on the end time: 1 million years
We will present astronomical mid-infrared polarisation observations, including newly
obtained data using the Michelle spectropolarimeter at the UKIRT telescope, of
various stellar environments. Modelling of the polarisation spectrum from 8-13 and
16-22 microns can yield important dust grain information, especially its mineralogy.
We will describe such modelling of several objects, including those i) lying behind
large columns of the interstellar medium, ii) embedded in molecular clouds, and iii)
with putative circumstellar disks. Assuming time zero corresponds to when a new star
begins its gravitational contraction, these phases might be approximately interpreted
as minus one million years, zero years and plus one million years. An evolution of the
dust begins to emerge for these different types of environments, proceeding from bare
amorphous silicate grains, to grains coated with ice mantles, and then mixtures of
amorphous and crystalline silicate. We look at what factors inherent in the evolution
of young stars might influence the detected spectral changes.
Li-Chin Yeh
Department of Mathematics, National Hsinchu Teachers College, Taiwan
On the Chaotic Boundaries of Disc-Star-Planet Systems
Time when the process started in the solar system: 0 Myr
The error bar on the start time: 0.5 Myr
Time when this process ended: 5 Myr
The error bar on the end time:+ 5Myr, - 4 Myr
The influence from a disc is included in the three-body problem and thus the orbits of
test particles in a disc-star-planet system are studied. We calculate the Lyapunov
Exponent of test particles' orbits for many different initial conditions and then
determine the boundaries between chaotic, regular and ejected orbits. The
implications on the resonant orbits of disc-star-planet systems will be discussed.
Bill Zealey
School of Engineering Physics, University of Wollongong
Syria Planum and Thaumasia Planum: Highland Lakes on Mars?
Time when the process you describe started in the solar system: 3.5By
The error bar on the start time: 500 My
Time when this process ended: 1By
The error bar on the end time: 500 My
The high altitude plains Syria, Solus, Sinai and Thaumasia Plani lie within the
contiguous volcano-tectonic province of Tharsis. Each plain forms a separate
catchment area sharing the Mariner Valley/ Labyrinthus Noctis rise as a common
boundary to the north and the Claritis and Thaumasia Highlands to the south.
Highlands are bounded to the east by the Coprates Rise. The Tharsis Montes ridge lies
to the west but the Syria mons boundary appears to be an extension to the
Labyrinthus Noctis Rise. Although there is some evidence for volcanic activity and
possible hydrothermal vents no major collapse features, similar to those associated
with flood channels, are found in this highland region. Evidence for flow channels
exist on the eastern flanks of Thaumasia Planum.
The following questions arise:
Are the flows sourced from hydrothermal vents or widespread rainfall over the
Highlands?
Was there standing water on the plains?
What drainage patterns would have resulted if there had paleolakes?
Do we see evidence for channels between the hypothesised catchment areas?
Can we estimate rainfall and flow volumes from altimetry data?
What is the timeframe for these events?