Download How we think the planets were born

How we think the planets were born
Oliver Gressel (NBIA)
Folkeuniversitetet
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I. Solar system inventory
Print: Verónica Olivera Gómez
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Origin of the word “planet”
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ἀστέρες πλανῆται
(asteres planetai)
“wandering stars”
objects which apparently
move across the sky
eight “modern” planets:
Image: NASA
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Ages of discoveries
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Mercury, Venus, Mars,
Jupiter & Saturn known by
Babylonian times (2000 BC)
1577: Tycho Brahe
showed that comets were not
atmospheric phenomena
1608: Invention of the
telescope in Holland
Galileo discovers Jupiter's
(inner) moons in 1650s,
Cassini Saturn's in 1670/80s
Uranus (the 7th planet) found
by William Herschel in 1781
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Planet discoveries
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Ceres (the “8th” planet) first
announced by Piazzi in 1801
Galle & LeVerrier 1846:
Neptune (8th planet since 1851)
Clyde Tombaugh,
Pluto, discovered 1930
in search for “Planet X”
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Our solar-system planets
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Our solar-system planets
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Trans-Neptunian objects
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Asteroid belt
Asteroids are minor planets, especially those of the inner Solar System.
The main Asteroid Belt lies between the orbits of Mars and Jupiter.
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Asteroid belt
Asteroids are minor planets, especially those of the inner Solar System.
The main Asteroid Belt lies between the orbits of Mars and Jupiter.
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Kuiper belt
The Kuiper belt lies outside the orbit of Neptune (~30au) and extends out
to a distance of 50au from the Sun. Objects composed of frozen volatiles.
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Extrasolar debris discs
Images: NASA, Hubble Space Telescope
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II. Meteorites: cosmic heralds
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Comets
Icy-rocky bodies originating from the outer solar system.
Heating produces coma and tails when passing near the sun.
67P/Churyumov–Gerasimenko as seen
September 2014 by esa Rosetta mission
Comet Hale-Bopp. Image: NASA
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Geminids meteor shower
The Geminids can be annually observed in the first
half of December, with its
peak activity being around
December 14. The shower
owes its name to the constellation Gemini from
where the meteors appear
to emerge from in the sky
(the so-called “radiant”).
Unlike most other meteor showers, the Geminids
are associated not with a comet but with an asteroid
- the 3200 Phaethon, which was discovered in
1983 by NASA's IRAS. It resembles main belt asteroid Pallas so much, it might be a 5-kilometer
chip off that 544 km block.
An artist's concept of an impact event on Pallas.
Credit: B. Schmidt and S. Radcliffe of UCLA.
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Meteoritics
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Radiometric dating
Mineralogy
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Pristine meteorites
Chondrites/Achondrites
Iron meteorites (from ~50
differentiated bodies)
Agpalilik (“the man”) outside the
Geological Museum in Copenhagen
Agpalilik, when transported from its
original location in Greenland in 1963
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Chondrules
Pinhead-sized grains formed from (partly) molten droplets, then accreted
onto the surface of larger bodies. From Greek “χόνδρος” (chondros), grain.
The individual chondrules are from 1-4mm
across. Photo: Bob King
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Centre for Star and Planet formation
Multidisciplinary research center for cosmochemistry, astrophysics and
astronomy funded by the DNRF and located at the Natural History
Museum of Denmark, University of Copenhagen.
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Chondrule chonology
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III. New horizons: extrasolar planets
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The ancient view
"There cannot be more worlds than one.” - Aristotle (384-332 BC)
"There are innumerable worlds which differ in size. In some worlds
there is no sun and moon, in others they are larger than in our world,
and in others more numerous. They are destroyed by colliding with
each other. There are some worlds without any living creatures,
plants, or moisture.” - Hippolytus of Rome (c. 170 - 236) on
Democritus (460-370 BC)
“There is an infinite number of worlds, some like this world,
some unlike it… For the atoms out of which a world might arise,
or by which a world might be formed, have not all been expended
on one world or a finite number of worlds, whether like or unlike this
one. Hence there will be nothing to hinder an infinity of worlds."
- Epicurus of Samos (342-270 BC)
“Now since there is illimitable space empty in every direction, and
since seeds innumerable in number in the unfathomable universe
are flying about in many ways driven by everlasting movement
it cannot by any means be thought likely that this is the only round
earth and sky that has been made…” - Lucretius (99-55 BC)
“And if their force and nature abide the same,
Able to throw the seeds of things together
Into their places, even as here are thrown
The seeds together in this world of ours,
'Tmust be confessed in other realms there are
Still other worlds, still other breeds of men,
And other generations of the wild.” - Lucretius (99-55 BC)
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Image: xkcd.com/1298
Census
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Image: xkcd.com/1298
Census
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The radial velocity method
Image: esa
Image: esa
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The transit method
planethunters.org
The transit method is a powerful tool for detecting
planets with low enough orbital inclination so that
they pass in front of their host star.
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Planet microlensing
Planet microlensing captures the gravitational deflection of
light, or “lensing”, for extremely rare events where a star
with a planet passes right in front of a background star.
Has been described as the task of
“detecting a planet we cannot see,
orbiting a star we cannot see either...”
Images: OGLE website
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Direct imaging of planets
Gemini Planet Imager’s first light
image of the light scattered by a disk of
dust orbiting the young star HR4796A
The challenge in imaging
planets directly lies in their
extreme faintness compared to
their much brighter host stars.
Coronagraphs are used to
block the light from the star.
HR8799 direct imaging planet detections
Credit: Marois et al (2010)
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The Kepler mission
launched in March 2009
earth-trailing helioc. orbit
photometric monitoring
of 150,000 stars
3277 planetary candidates
announced so far
Kepler spacecraft.
Image: NASA
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The harvest...
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The harvest...
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The Kepler 11 system
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The Kepler 11 system
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The “habitable” zone
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The “habitable” zone
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Exoplanet atmospheres
Transmission spectroscopy of planetary atmosphere
allows to get information about planet's “weather”.
Image: NASA, JPL/CalTech
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“Weather” forecasting
Cho, J. et al. (2003), Astrophysical Journal,
587, 117, The changing face of the extrasolar
planet HD 209458b
Time-dependent temperature
distribution on hemisphere facing
star for a model hot Jupiter
Simulated flows and vortices on an irradiated hot Jupiter
Harrington, J. et al, (2005), Science,
“The Phase-Dependent Infrared Brightness
of the Extrasolar Planet ʊ Andromedae b”
Varying infrared luminosity of
Upsilon Andromeda b as a
function of orbital phase
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Small fraction of starlight passes through
planet atmosphere during transit
Absorption features due to sodium observed
in the spectrum - in agreement with
theoretical predictions…
Using a similar techniques H2O, CH4, CO and
CO2 have been detected in atmospheres of the
planet HD 189733b
Recent observations using the Hubble Space
Telescope suggest that the atmosphere of HD
209568b is boiling off - producing a long
‘cometary tail’
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HD 209458b
Originally discovered using radial
velocity technique in 1996
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Found to transit in front of its star in
1999 – the first transiting planet
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Combining transit data and radial
velocity measurements gives the
planet mass and radius:
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mass=0.69 Jupiter masses
radius=1.347 Jupiter radii
gas giant planet with mean
density of about 1 g/cm3
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IV. Planetary birthplaces
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The nebular hypothesis
The Nebula Hypothesis for the
formation of the Solar System was
developed in the 18th century by
Emanuel Swedenborg (1734),
Immanuel Kant (1755) and
Pierre-Simon Laplace (1796).
Hypothesis: “The Sun and planets formed
from a rotating and flattened rotating cloud
of gas and dust - the Solar Nebula”
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dusty protoplanetary disc
Image: Hubble Space Telescope
Star formation regions
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The ALMA revolution
The ALMA site at the Atacama desert of northern Chile
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radio telescope array, sub-mm wavelength
unprecedented sensitivity and resolution
spirals or gaps associated with hidden planets
kinematic information via spectral lines
ALMA (ESO/NAOJ/NRAO), S. Casassus et al.
HD 142527 lies in the constellation Lupus, about 450 light years away
NASA/JPL-Caltech/T. Pyle (SSC)
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ALMA “first light” long-baseline
New high-resolution capabilities
achieved by spacing the antennas
up to 15km apart.
Most detailed image of the disc around HL Tau, a
million-year-old Sun-like star 450 light-years
from Earth in the constellation of Taurus.
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Gap formation
Simulation of a planet opening a gap in a protoplanetary disc. Video: Richard P. Nelson, QMUL
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A Saturn-mass planet opening a gap
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Gas giant formation
magnetic
field lines
magneticallycollimated jet
horseshoe
region
Synthetic image of
disc/gap/planet.
streamlines
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How to build a planetary system...
Take a disc of well mixed gas +
dust, make a snowline beyond
3au where temperature falls
below -100oC, dust + ice grains
collide and stick, forming
kilometre-sized planetesimals
Giant planets:
outside snowline, growth occurs
until massive planetary core
forms gaseous envelope settles
onto core after few million years
Terrestrial planets:
smaller rocky planets
form nearer the Sun
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Lab experiments on dust growth
Levitation of ice aggregates via the Knudsen “compressor” effect.
Study growth of dusty/icy aggregates into larger agglomerates.
Video: AG Wurm, Uni Duisburg
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Dust collision experiments
Collision of two dust agglomerates at a few tens of cm/s.
The volume filling factor is
higher on the hanging agglomerate, the "target", while the
more porous agglomerate, the
"impactor", is destroyed completely in this collision (catastrophic disruption). The overall result is a slight growth of
the target while a lot of small
particles are produced. Video:
AG Wurm, Uni Duisburg
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Jumping the metre-sized barrier
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The role of magnetic fields
Image: R. Moll, Garching
HH30, Image:NASA HST
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Defining the environment...
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Scenario A:
“Viscous” transport
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Turbulent flow
Strong particle stirring
Puffed-up dust disc
Broadened spectral lines
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Scenario B:
Magneto-centrifugal wind
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Laminar flow
Quiescent environment
Dust settled into thin disc
Double-peaked lines
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Defining the environment...

Scenario A:
“Viscous” transport
–
–
–
–
Turbulent flow
Strong particle stirring
Puffed-up dust disc
Broadened spectral lines
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Scenario B:
Magneto-centrifugal wind
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Laminar flow
Quiescent environment
Dust settled into thin disc
Double-peaked lines
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Effect of turbulence on particle collisions
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Back to the big picture...
The pale
blue dot.
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