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ASTR-1010
Planetary Astronomy
Day 40
The Chaotic Early Solar System
• Recent computer models are
challenging earlier views that
planets formed in an orderly way
at their current locations
• These models suggest that the
jovian planets changed their orbits
substantially, and that Uranus and
Neptune could have changed
places
• These chaotic motions could also
explain a ‘spike’ in the number of
impacts in the inner solar system
~3.8 billion years ago
The Moon and terrestrial planets were bombarded by
planetesimals early in solar system history.
Cosmic Billiards
• The model predicts:
100 Myr
20 AU
880 Myr
1. After formation, giant planet orbits
were affected by gravitational
‘nudges’ from surrounding
planetesimals
planetesimals
2. Jupiter and Saturn crossed a 1:2
orbital resonance (the ratio of orbital
periods), which made their orbits
more elliptical. This suddenly
enlarged and tilted the orbits of
Uranus and Neptune
3. Uranus / Neptune cleared away the
planetesimals, sending some to the
inner solar system causing a spike
in impact rates
883 Myr
~1200 Myr
N
U
S
J
The early layout of the solar system may have changed
dramatically due to gravitational interactions between
the giant planets. Note how the orbits of Uranus and
Neptune moved outwards, switched places, and
scattered the planetesimal population.
The Big Picture
• The current layout of our solar system
may bear little resemblance to its
original form
• This view is more in line with the
“planetary migration” thought to occur
even more dramatically in many
extrasolar planet systems
• It may be difficult to prove or disprove
these models of our early solar system.
The many unexplained properties of
the nature and orbits of planets,
comets and asteroids may provide
clues.
Artist’s depiction of Neptune orbiting close
to Jupiter (courtesy Michael Carroll)
For more information…
Press Releases
•
Sky and Telescope - “Chaos in the Early Solar System”
http://www.skyandtelescope.com/skytel/beyondthepage/8594717.html
•
Science News - 02/14/09 - ‘The Solar System’s Big Bang’
http://www.sciencenews.org/view/feature/id/40390/title/The_Solar_Systems_Big_Bang
•
Plan. Sci. Res. Disc. - 08/24/06 - ‘Wandering Gas Giants and Lunar Bombardment’
http://www.psrd.hawaii.edu/Aug06/cataclysmDynamics.html
Images
•
Impact on early Earth
2006 Pearson Education Inc., publishing as Addison Wesley
•
•
Computer simulation snapshots courtesy of Alessandro Morbidelli
Jupiter/Neptune art courtesy of astronomy.com / Michael Carroll
http://www.astronomy.com/asy/default.aspx?c=a&id=3320
Source Articles
•
(on-campus login may be required to access journals)
Gomes et al., ‘Origin of the cataclysmic Late Heavy Bombardment period of the
terrestrial planets’, Nature, 435, p. 466 doi: 10.1038/nature03676, 2005.
http://www.nature.com/nature/journal/v435/n7041/abs/nature03676.html
•
Tsiganis et al., ‘Origin of the orbital architecture of the giant planets of the Solar
System’, Nature, 435, p. 459 doi:10.1038/nature03539, 2005.
http://www.nature.com/nature/journal/v435/n7041/abs/nature03539.html
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 24 April 2009
Volcanoes on Mercury
• Mercury appears to be geologically
dead and is heavily cratered. There
are no large volcanoes like Mars’
Olympus Mons, but there are many
smooth, flat plains with few craters
• Scientists have debated whether
these ancient plains were formed
by erupting volcanoes driven by
internal heat, or simple melting
associated with impact processes
• The latest closeup images by
NASA’s MESSENGER support the
volcano theory
MESSENGER false color image of Caloris impact
basin (light orange is the basin interior). Extinct
volcanoes were imaged in several of the bright
orange regions just inside the southern crater rim.
Direct & Indirect Evidence for Volcanoes
• MESSENGER has found
shield volcanoes and vents
suggesting explosive
volcanism inside the large
Caloris basin
partly filled
crater
• The Mercury volcanoes may
be similar to the Hawaiian
Islands or Olympus Mons on
Mars
• Lava appears to have partly
filled impact craters both
inside and far from Caloris
basin (not shown)
vents
MESSENGER image (left) of a shield-like volcanic dome,
multiple vents and associated bright deposits, and partially
buried nearby features. Shield volcanism formed the island of
Hawaii (right).
The Big Picture
Alaska
Hawaii
• Volcanism appears to be
responsible for formation of
Mercury’s widespread plains
• Mercury’s ancient plainsforming, crater-filling volcanic
style was more similar to the
Moon than Mars or Earth
• MESSENGER will enter orbit
around Mercury in 2011,
offering abundant opportunity
to image volcanic features
and place Mercury’s
volcanism in a solar system
context
Mars
Mercury
Volcanic features in the inner solar system
Venus
For more information…
Press Releases
•
space.com - 7/3/08 - “Volcanoes on Mercury Solve 30-year Mystery”
http://www.space.com/scienceastronomy/080703-mercury-messenger.html
Images
•
Global view of Caloris basin and Mercury shield volcano courtesy of Science / AAAS
http://messenger.jhuapl.edu/gallery/sciencePhotos/pics/caloris_color_MB.jpg
http://messenger.jhuapl.edu/gallery/sciencePhotos/pics/Head_Fig1.jpg
•
Aerial view of Hawaii courtesy of NASA/JSC STS61A
http://tinyurl.com/maunaloashieldvolcano
•
Aerial view of erupting Mauna Loa in Hawaii courtesy of HVO/USGS
http://hvo.wr.usgs.gov/
•
Image of Alaska’s Redoubt Volcano courtesy of AVO/USGS, taken by Heather Bleick
http://www.avo.alaska.edu/image.php?id=17872
•
Image of Olympus Mons on Mars and Maat Mon on Venus courtesy of NASA/JPL
http://pds.jpl.nasa.gov/planets/captions/mars/olympus.htm
http://photojournal.jpl.nasa.gov/catalog/PIA00106
Source Article (on-campus login may be required to access journals)
•
Head et al., ‘Volcanism on Mercury: Evidence from the First MESSENGER Flyby’,
Science, 321(5885), p. 69, DOI: 10.1126/science.1159256, 2008.
http://www.sciencemag.org/cgi/content/abstract/321/5885/69
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 24 April 2009
Venus May Have Active Volcanism
• Venus has few impact craters, suggesting
the entire surface is younger than 1/2
billion years
• Venus has clouds of SO2 (a volcanic gas)
and many volcanoes - but active
volcanism has not been detected
• New infrared observations indicate some
regions were resurfaced in the last 100’s
to 10000’s of years. Venus was recently
(and still may be) volcanically active.
• This new evidence may help resolve a
debate about how volcanism proceeded
on Venus
Radar and topography “image” from the Magellan
spacecraft of Idunn Mons on Venus, which was
recently volcanically active. Dark regions are
smooth, and bright regions are rough or steep.
Elevations have been exaggerated thirty times.
Interpreting Surface ‘Hot Spots’
• Thermal emissivity indicates how
efficiently a material radiates heat
• Some volcanic regions of the Venus
surface have higher emissivity than their
surroundings
• Lower emissivity regions have reacted
chemically with CO2 and SO2 in the
atmosphere, forming a thin crust over
the lava
• High emissivity indicates younger
material that has not been substantially
weathered by Venus’ thick atmosphere
Infrared observations from the Venus Express
spacecraft overlaid on the image from the Slide 1
show that Idunn Mons (red) has higher thermal
emissivity than its surroundings (blue). This
indicates a compositional difference between the
two regions.
The Big Picture
• Scientists debate whether the entire
planet was resurfaced in a large global
event, or gradually over time
• The new observations of localized
recent volcanism suggest that the global
hypothesis can not be the entire story.
Some scientists believe the results
strongly support the gradual hypothesis
• The three regions in this study are all
geologically similar to Hawaii, where hot
material from deep inside the planet
causes uplift and volcanism at the
surface.
Global radar image of Venus from Magellan.
The approximate location of Idunn Mons, from
previous slides, is indicated.
For More Information…
Press
•
Space.com - 04/08/10 - “Volcanoes on Venus May be Young and Active”
http://www.space.com/scienceastronomy/venus-volcano-hotspot-100408.html
•
Planetary Society Blog - 04/09/10 - “Venus Express evidence for recent hot-spot volcanism on
Venus”
http://www.planetary.org/blog/article/00002434/
•
BBC - 04/09/10 - “ Venus 'still volcanically active’ ”
http://news.bbc.co.uk/2/hi/science/nature/8611195.stm
Images
•
Slide 1 image courtesy NASA / JPL-Caltech / ESA
http://photojournal.jpl.nasa.gov/catalog/PIA13001
•
Slide 2 image courtesy NASA / JPL-Caltech / ESA
http://photojournal.jpl.nasa.gov/catalog/PIA13001
•
Slide 3 image courtesy Magellan / JPL / NASA
http://antwrp.gsfc.nasa.gov/apod/ap050903.html
Source Articles
•
(on-campus login may be required to access journals)
Smrekar et al., ‘Recent Hot-Spot Volcanism on Venus from VIRTIS Emissivity Data’,
Sciencexpress, 8 April 2010, 10.1126/science.1186785, 2009.
http://www.sciencemag.org/cgi/content/abstract/science.1186785
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 15 April, 2010
Did Sulfur Affect Mars Climate and Geology?
• Mars missions suggest that
Mars once had a thick CO2
atmosphere and liquid water
• On Earth these conditions lead
to formation of carbonate rocks
(like limestone)
• But Mars missions detect very
little carbonate rock; instead
Mars rovers find sulfate rocks
~30 cm
1.3 cm
This rock outcrop studied by the Opportunity rover,
contains the sulfur-bearing mineral jarosite. The
inset shows a close-up of a hematite ‘blueberry’
believed to form due to water.
Discoveries in Planetary
Science
Why does Mars have more sulfur-rich rocks?
On Earth
• Volcanic SO2 rapidly
reacts with oxygen
and water vapor
• CO2 absorbed in
water, forms
carbonate rocks
• Little CO2 left in our
atmosphere - just
enough for a mild
greenhouse effect
Volcanoes on Earth and
Mars spewed out CO2
and SO2 along with
H 2O
On Ancient Mars
• Less oxygen and water
vapor in atmosphere, so
some SO2 absorbed in
surface water
• Water too acidic for
carbonate formation,
CO2 stays in atmosphere
• Sulfur-bearing minerals
form in water and make
sulfate rocks
The White cliffs of Dover,
composed of carbonate
Endurance Crater, Mars, with
countless ‘blueberries’ formed
due to acidic liquid water
Discoveries in Planetary
Science
The Big Picture
• A minor gas (SO2) can radically
change Mars chemistry, preventing
the major gas (CO2) from forming
carbonate rock as on Earth
• CO2 in the atmosphere (instead of
in rocks) plus H2O and SO2 gases
provided lots of greenhouse
warming for ancient Mars
• Planetary scientists continue to
investigate why the paths of these
two planets diverged billions of
years ago
Sulfur gases may have affected the geology and
climate of Mars enough to make it habitable in
the past.
Discoveries in Planetary
Science
For more details…
Press Releases
•
Marsdaily.com - 12/24/07 - “How Mars Could Have Been Warm And Wet But Limestone-Free”
http://tinyurl.com/marswarmwetnolimestone
•
Marsdaily.com - 12/24/07 - “Sulfur Dioxide May Have Helped Maintain A Warm Early Mars”
http://tinyurl.com/marsearlysulfur
Images
•
El Capitan and blueberry images courtesy of NASA/JPL
http://photojournal.jpl.nasa.gov/catalog/PIA05478
http://photojournal.jpl.nasa.gov/catalog/PIA05474
•
White cliffs of Dover image:
http://www.ippnw-students.org/OTT/DoverWhiteCliffs.jpg
•
Blueberries in Endurance Crater image courtesy of NASA/JPL
http://marsrover.nasa.gov/gallery/press/opportunity/20040727a.html
•
Volcanic eruption diagram
Adapted from “The Cosmic Perspective”, by Bennett et al., Addison Wesley, Inc.
•
Mars & Earth composite image courtesy of NASA/JPL
http://photojournal.jpl.nasa.gov/catalog/PIA02570
Source Article
(on-campus login may be required to access journals)
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
• Halevy
et al., ‘A Sulfur
Dioxide Climate Feedback on Early
Mars’,
[email protected]
- http://dps.aas.org/education/dpsdisc/
- Released
14Science,
April 2009318, 1903
(2007), DOI: 10.1126/science.1147039.
Discoveries in Planetary
Science
http://www.sciencemag.org/cgi/content/abstract/318/5858/1903
Methane in the Martian Atmosphere
• Methane gas was recently
detected in Mars’ atmosphere
using groundbased telescopes
• The methane gas distribution is
patchy and changes with time
• Most methane in Earth’s
atmosphere is produced by life,
raising questions about its origin
on Mars
View of Mars colored according to the methane
concentration observed in the atmosphere. Warm
colors depict high concentrations.
Recent Release of Methane
• Methane in the atmosphere
should be destroyed by UV
light within a few hundred
years
• Methane observed now must
therefore have been produced
recently
• Variations in space and time
suggest that it was recently
released from the subsurface
in localized areas
UV photons have enough energy to break molecules apart
The Big Picture
• Where can the methane come
from? From analogy with
Earth, there are two leading
theories for the origin of recent
subsurface methane at Mars:
1. Methane is produced by waterrock interactions
surface
methane
liquid water
hot rock
2. Methane is produced by
bacteria, in regions where liquid
water is found
~2 µm
Either theory implies that the
Martian subsurface is dynamic
• Future observations can test for
trace chemicals associated with
each process
methane
bacteria
Methane on Mars could be produced
chemically through liquid/rock interactions
(top) or biologically (bottom)
For more information…
Press Releases
•
space.com - 1/15/09 - “Mars Methane: Geology or Biology?”
http://www.space.com/scienceastronomy/090115-mars-methane-news.html
Images
•
All images (and accompanying animations) can be found at:
http://www.nasa.gov/mission_pages/mars/news/marsmethane_media.html
Source Article (on-campus login may be required to access journals)
•
Mumma et al., ‘Strong Release of Methane on Mars in Northern Summer 2003’,
Science, 323, p. 1041 DOI: 10.1126/science.1165243, 2009.
http://www.sciencemag.org/cgi/content/abstract/323/5917/1041
Related Articles
•
(on-campus login may be required to access journals)
Formisano et al., ‘Detection of Methane in the Atmosphere of Mars’, Science, 306,
p.1758 DOI: 10.1126/science.1101732, 2004.
http://www.sciencemag.org/cgi/content/abstract/306/5702/11758
•
Krasnopolsky et al., ‘Detection of methane in the martian atmosphere: evidence for
life?’, Icarus, 172, p.537, doi:10.1016/j.icarus.2004.07.004, 2004.
http://tinyurl.com/krasnopolskyIcarus2004
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 24 April 2009
Buried Glaciers at Mars
• Radar observations made from orbit
reveal that nearly pure ice “glaciers”
covered by rock are common at midlatitudes on Mars
• Previous spacecraft images indicated
glacier-like features next to steep
slopes and filling some craters, but
could not see through the overlying
rock to confirm their presence
• The layer of rock protects the ice from
subliming (evaporating) in Mars’ cold
dry climate
(Left) Perspective image of craters in the southern
hemisphere of Mars, created using NASA Mars
Reconnaissance Orbiter images; (Right) Artist
conception of ice underlying a surface layer, based
on radar observations.
Forming Protected Ice Reservoirs
1050 km
• The tilt of Mars’ rotation axis was
likely much greater (~45°) millions of
years ago
48° N
• During that epoch glaciers could
form more easily at mid-latitudes on
Mars
• Overlying debris transported from
nearby steep slopes would prevent
some glaciers from subliming, even
after Mars’ tilt changed
36° N
Topography map from Mars Global Surveyor
showing the locations of buried glaciers (blue)
in a northern hemisphere region of Mars,
inferred from many radar observations obtained
by Mars Reconnaissance Orbiter (yellow).
Buried glaciers are always found near steep
slopes.
The Big Picture
slope
• Debris-covered glaciers at mid-latitudes
on Mars may contain enough ice to
cover the entire planet in 20 cm of water
glacier
8 km
• These ice reservoirs are covered by
only a few meters of material - easily
accessible for future human and
scientific exploration
• Buried ice may record the history of
Mars’ climate, as ice cores from Earth’s
glaciers do
Debris covered glaciers on Mars (top, imaged by
the Mars Express spacecraft) and in Beacon Valley,
Antarctica (bottom, photo courtesy Jack Holt)
For More Information…
Press
•
Space.com - 03/04/10 - “Hidden Glaciers are Common on Mars”
http://www.space.com/scienceastronomy/mars-ice-glaciers-100304.html
•
National Geographic News - 11/20/08 - “Buried Mars Glaciers May Be Remnants of Past Ice Age”
http://news.nationalgeographic.com/news/2008/11/081120-buried-mars-glaciers.html
Images
•
Slide 1 image courtesy NASA / Caltech / JPL / UTA / UA / MSSS / ESA / DLR
http://www.jsg.utexas.edu/galleries/mars_glaciers112008/
•
Slide 2 image courtesy NASA / JPL / ASI / U. Rome / SwRI
http://photojournal.jpl.nasa.gov/catalog/?IDNumber=pia12861
•
•
Slide 3 Antarctica image courtesy Dr. Jack Holt (U. Texas)
Slide 3 Mars image courtesy ESA / DLR / FU Berlin
http://www.jsg.utexas.edu/galleries/mars_glaciers112008/
Source Articles
•
(on-campus login may be required to access journals)
Holt et al., ‘Radar Sounding Evidence for Buried Glaciers in the Southern Mid-Latitudes of Mars’,
Science, 322, doi:10.1126/science.1164246, 2008.
http://www.sciencemag.org/cgi/content/full/322/5905/1235
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 15 April, 2010
Water Found on the Moon
• Analysis of lunar rocks collected by Apollo
astronauts did not reveal the presence of
water on the Moon
• Four spacecraft recently reported small
amounts of H2O and/or OH at the Moon:
• India’s Chandrayaan mission
• NASA’s Cassini mission
• NASA’s EPOXI mission
• NASA’s LCROSS mission
The first three measured the top few mm of the
lunar surface. LCROSS measured plumes of
lunar gas and soil ejected when a part of the
spacecraft was crashed into a crater.
• How much water? Approximately 1 ton of
lunar regolith will yield 1 liter of water
This false-color map created from data taken
by NASA’s Moon Mineralogy Mapper (M3) on
Chandrayaan is shaded blue where trace
amounts of water (H2O) and hydroxyl (OH) lie
in the top few mm of the surface.
How was Water Detected?
model with
thermal
radiation only
Intensity
• Lunar soil emits infrared
thermal radiation. The
amount of emitted light at
each wavelength varies
smoothly according to the
Moon’s temperature.
model with thermal
radiation and
absorption by
molecules
• All four infrared spectrographs
measure a deficit of thermal
radiation at those
wavelengths, implying water is
present
Wavelengths where
water absorbs light
Intensity
• H2O or OH molecules in the
soil absorb some of the
radiation, but only at specific
wavelengths
An infrared spectrum measured by LCROSS (black data
points) compared to models (red line)
The Big Picture
• Lunar water may come from ‘solar wind’
hydrogen striking the surface, combining
with oxygen in the soil. It may also
arrive via meteorite and comet impacts.
Both processes are likely.
• Lunar water may be ‘bounced’ by small
impacts to polar regions, forming ice in
permanently shadowed craters
• Similar processes may occur on other
airless bodies (e.g., Mercury, asteroids)
• Water-laden lunar regolith may be a
valuable resource, possibly supporting
future lunar exploration activities
Discovery of water on the moon may support
future activities on the lunar surface and
beyond. Artwork from NASA / Pat Rawlings.
For More Information…
Press Releases
•
NASA – 9/24/09 - “NASA Instruments Reveal Water Molecules on Lunar Surface”
http://www.nasa.gov/topics/moonmars/features/moon20090924.html
•
Space.com – 09/23/09 - “It's Official: Water Found on the Moon”
http://www.space.com/scienceastronomy/090923-moon-water-discovery.html
•
NASA Ames – 11/13/09 - “LCROSS Impact Data Indicates Water on Moon”
http://www.nasa.gov/mission_pages/LCROSS/main/prelim_water_results.html
•
Space.com – 11/13/09 - “'Significant Amount' of Water Found on Moon”
http://www.space.com/scienceastronomy/091113-lcross-moon-crash-water-discovery.html
Images
•
Image from Slide 1 courtesy of [NASA/ISRO/BROWN University/R.N. Clark, USGS]
http://www.nasa.gov/topics/moonmars/features/moonm3-images.html
•
Images from Slide 2 courtesy NASA
http://www.nasa.gov/mission_pages/LCROSS/main/LCROSS_results_images.html
•
Image from Slide 3 from NASA / Pat Rawlings
http://www.patrawlings.com/
Source Articles
•
•
•
(on-campus login may be required to access journals)
Pieters et al., ‘Character and Spatial Distribution of OH/H2O on the Surface of the Moon Seen by M 3 on
Chandrayaan-1’, Science, 326, p. 568, doi: 10.1126/science.1178658, 2009.
Sunshine et al.., ‘Temporal and Spatial Variability of Lunar Hydration as Observed by the Deep Impact
Spacecraft’, Science, 326, p. 565, doi: 10.1126/science.1179788, 2009.
Clark R.N., ‘Detection of Adsorbed Water and Hydroxyl on the Moon’, Science, 326, p. 562, doi:
10.1126/science.1178105, 2009.
All articles available at http://www.sciencemag.org/content/vol326/issue5952/index.dtl
Prepared for the Division for Planetary Sciences of the American Astronomical Society by C. Runyon, David Brain, Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 03 December, 2009
An Ocean Below Enceladus’ Icy Crust?
• NASA’s Cassini spacecraft has
observed plumes of material
escaping from Saturn’s small icy
moon, Enceladus
• The plume is mostly water vapor,
with tiny ice particles and other
gaseous molecules mixed in (e.g.
CO2, CH4, C2H6)
• The plume supplies ice particles to
one of Saturn’s rings
• Some ice particles contain salt,
which may indicate they originate in
an ocean deep below the icy crust
Image mosaic of Enceladus taken by Cassini, showing
individual plumes of gas and ice escaping from the
surface. The plumes extend 100’s of km into space from
the ~500 km diameter moon.
What Process Creates the Plume?
• Plumes may be material escaping
through surface cracks from an
internal salty ocean or lake
• Alternatively, ice along cracks may
sublime or melt, followed by escape
of water vapor and icy particles
• Many scientists find the salty ocean
model most convincing, but others
favor combinations of alternative
explanations
Left: Enceladus may have a salty subsurface ocean
that releases material to space through cracks in the
moon’s icy shell. Right: The walls of icy cracks in the
surface may melt or sublime, venting gas and icy
particles to space.
The Big Picture
• Enceladus is surprisingly active for such
a small body - likely a consequence of
tidal heating
• Future flybys of Enceladus by Cassini
may help to resolve whether Enceladus
joins the growing “club” of solar system
bodies believed to have oceans
Tiger stripes
• If Enceladus has an ocean, then it
contains all of the ‘ingredients’ known to
be important for life: liquid water,
molecular building blocks, and energy
Image of Enceladus showing the ‘tiger stripes’
region in the southern hemisphere, where the
plumes originate
For More Information…
Press Releases
•
Space.com - 06/14/09 - “Ocean Hidden Inside Saturn's Moon”
http://www.space.com/scienceastronomy/090624-enceladus-ocean.html
Images
•
Enceladus plume image courtesy NASA/JPL/Space Science Institute/E. Lakdawalla
http://antwrp.gsfc.nasa.gov/apod/ap091124.html
•
Europa plume cartoons adapted from image courtesy NASA/JPL
http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=2944
•
Enceladus image courtesy NASA/JPL/Space Science Institute
http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=2032
Source Articles
•
(on-campus login may be required to access journals)
Postberg et al., ‘Sodium salts in E-ring ice grains from an ocean below the surface of Enceladus’,
Nature, 459, p. 1098, doi: 10.1038/nature08046, 2009.
http://www.nature.com/nature/journal/v459/n7250/full/nature08046.html
•
Schneider et al., ‘No sodium in the vapour plumes of Enceladus’, Nature, 459, p. 1102, doi:
10.1038/nature08070, 2009.
http://www.nature.com/nature/journal/v459/n7250/full/nature08070.html
•
•
•
Porco et al., Science, 311, p.1393, 2006. http://www.sciencemag.org/cgi/content/abstract/311/5766/1393
Nimmo et al., Nature, 447, p.289, 2007. http://www.nature.com/nature/journal/v447/n7142/full/nature05783.html
Kieffer et al., Science, 314, p.1764, 2006. http://www.sciencemag.org/cgi/content/abstract/314/5806/1764
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 03 December, 2009
A Sunlit Lake on Titan
• The Cassini spacecraft recently
recorded a flash of sunlight off a region
of the northern hemisphere
reflected
sunlight
• The reflection comes from a dark,
smooth region suspected to be a large
lake or sea
• Infrared and radar observations
previously revealed hundreds of likely
lakes near the north pole, and a few
lakes near the south pole
• The lakes are filled with ethane, and
probably methane
night side
Cassini infrared image of Saturn’s moon Titan
taken from above the night side of the planet. The
bright region in the sunlit northern polar region
was predicted, and results from sunlight reflected
off a methane lake.
Lakes without Water
• Titan is 94 K - too cold for liquid surface water,
but not too cold for liquid methane and ethane
• Sunlight should rapidly convert atmospheric
methane to ethane and other species. But
methane is abundant, so must be replenished.
• Methane and ethane should be exchanged
between the atmosphere and lakes through
evaporation and precipitation (similar to water
on Earth)
• These processes can help maintain the high
atmospheric methane abundance and
contribute to observed seasonal variations in
the lakes
False color Cassini image showing the
amount of radar signal reflected from a
region of Titan’s northern hemisphere.
Dark regions are likely lakes.
The Big Picture
• Earth and Titan are the only two objects
in the solar system that have stable
bodies of liquid at the surface
• Similar processes help maintain surface
liquids and atmospheric compositions,
despite very different temperatures and
materials at each body
• Surface liquids facilitate erosion, and
can create ‘Earth-like’ landscapes
(e.g. sedimentary layers, river beds, …)
• Surface liquids may exist on a variety of
bodies orbiting other stars, and not be
restricted to ‘Earth-like’ bodies
Photograph taken from the space shuttle of
glinted sunlight from Earth’s oceans.
For More Information…
Press
•
NASA - 12/17/09 - “Sunlight Glint Confirms Liquid in Titan Lake Zone”
http://www.nasa.gov/mission_pages/cassini/whycassini/cassini20091217.html
•
Planetary.org - 12/17/09 - “Cassini VIMS sees the long-awaited glint off a Titan lake”
http://www.planetary.org/blog/article/00002267
Images
•
Slide 1 image courtesy NASA/JPL/U. Arizona/DLR
http://photojournal.jpl.nasa.gov/catalog/PIA12481
•
Slide 2 image courtesy NASA/JPL/USGS
http://www.nasa.gov/mission_pages/cassini/multimedia/pia09102.html
•
Slide 3 image courtesy NASA/JSC
http://tinyurl.com/DPSDisc-TitanLakes-Slide3
Source Articles
•
(on-campus login may be required to access journals)
Stofan et al., ‘The Lakes of Titan’, Nature, 445, doi:10.1038/nature05438, 2007.
http://www.nature.com/nature/journal/v445/n7123/full/nature05438.html
•
Brown et al., ‘The identification of liquid ethane in Titan's Ontario Lacus’, Nature, 454 ,
doi:10.1038/07100, 2009.
http://www.nature.com/nature/journal/v454/n7204/full/nature07100.html
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 15 April, 2010
One Moon Coats its Neighbor in Dust
• The trailing face of Saturn’s moon Iapetus
is ~10 times brighter than its leading face
• For 300 years, astronomers debated
whether the cause was internal (e.g.
eruption of dark material on one face) or
external (e.g. debris from a nearby impact)
• The discovery of a giant ring around Saturn
and close-up Cassini images confirm an
external cause: dust particles coat one side
and drive ice to the other by sublimation
Saturn’s moon Iapetus has a dark leading side,
while its polar regions and trailing side are
bright. The dividing line follows a pattern like the
stitching on a baseball.
A Ring Creates a “Baseball” Moon
Phoebe
• Impactors strike one of several distant
dark Saturn moons (such as Phoebe),
supplying a ring of dark particles that orbit
Saturn ‘backwards’, like Phoebe
• Sunlight pushes the ~10 micron particles
inward over thousands of years
• Particles collide with Iapetus and other
inner moons, making their leading face
slightly darker
• The darkened ice absorbs more sunlight,
warms up, and sublimes, recondensing as
bright frost on the trailing side and poles
Dust from backwards-orbiting (captured)
Phoebe coats the leading side of Iapetus
Trailing
Dust
Iapetus
Leading
Sun-warmed dust causes sublimation,
driving ice to the poles and trailing side
The Big Picture
• Planetary moons can be “painted” at a
global level by external causes such as
dust and even charged particles
• Dark dust and bright ice can segregate
on a moon’s surface, as sun-warmed
dust drives ice to brighter, icier regions
• New telescopes and instruments keep
discovering new phenomena: The
“Phoebe ring” is the largest and most
distant from its parent body
Artist’s conception of huge ring around Saturn,
discovered at IR wavelengths by the Spitzer Space
Telescope. The inset indicates scale by showing
an enlarged ground-based IR image of Saturn.
For More Information…
Press
•
BBC.com - 10/07/09 - “New ring detected around Saturn”
http://news.bbc.co.uk/2/hi/8291905.stm
•
Sky & Telescope - 12/11/09 - “Has Iapetus Finally Been Solved?”
http://www.skyandtelescope.com/community/skyblog/newsblog/79066992.html
•
CNN.com - 10/07/09 - “Scientists discover massive ring around Saturn”
http://www.cnn.com/2009/TECH/space/10/07/space.saturn.ring/index.html
Images
•
Slide 1 image courtesy NASA / JPL / Space Science Institute
http://photojournal.jpl.nasa.gov/catalog/PIA08234
•
Slide 2 Phoebe image courtesy Cassini Imaging Team / SSI / JPL / ESA / NASA
http://apod.nasa.gov/apod/ap060212.html
•
Slide 3 image NASA/JPL-Caltech/Keck
http://www.nasa.gov/mission_pages/spitzer/multimedia/spitzer-20091007a.html
Source Articles
•
(on-campus login may be required to access journals)
Spencer and Denk, ‘Formation of Iapetus’ Extreme Albedo Dichotomy by Exogenically Triggered
Thermal Ice Migration’, Science, 327, 10.1126/science.1177132, 2010.
http://www.sciencemag.org/cgi/content/full/327/5964/432
•
Verbiscer et al., ‘Saturn’s largest ring’, Nature, 461, doi:10.1038/nature08515, 2009.
http://www.nature.com/nature/journal/v461/n7267/full/nature08515.html
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 15 April, 2010
First Rocky Exoplanet Detected
• Most known exoplanets are large
and have low densities - similar to
jovian planets in our solar system
• A space telescope recently
discovered a planet with radius
only 70% larger than Earth’s
• Groundbased observations show
the planet’s mass is less than 5
times Earth’s
• Together, the observations reveal
that the planet’s density is similar
to Earth’s - the first confirmation of
a “rocky” exoplanet
Artist’s conception of the view of the rocky planet’s parent
star (Corot-7) from above the surface of the planet (Corot7b). Image from ESO / L. Calcada.
• The planet’s mass was determined
using the radial velocity method:
The planet gravitationally ‘tugs’ on
the star, shifting the wavelength of
light the star emits back and forth.
The amount of shift indicates the
planet’s mass.
• Volume = 4/3  R3
• The planet’s size was determined
using the transit method:
The amount of light measured from
a star decreases when a planet
passes in front. The amount of
decrease indicates the planet’s size.
QuickTime™ and a
decompressor
are needed to see this picture.
-20
-10
0
QuickTime™ and a
decompressor
are needed to see this picture.
10
20
Hours
Changes in the measured wavelengths of star light are
caused by a planet with mass ~5 times Earth’s.
Amount of Light
• Density = Mass / Volume
Star Radial Velocity
How Can We Find a Planet’s Density?
-4
0.04%
-2
0
2
4
Hours
Periodic decreases in light from the star are caused by a
planet with diameter 1.7 times Earth’s passing in front.
The Big Picture
• After discovering hundreds of
exoplanets resembling our jovian
planets, astronomers have found the
most Earth-like planet to date
• Although planet Corot-7b’s density is
close to Earth’s, differences abound:
it orbits its star in ~20 hours (faster
than any known exoplanet) - so close
that its rocky surface may be molten
• With the existence of Earth-like
planets now demonstrated,
astronomers have reason to hope
that the Kepler mission will discover
more
Detection of more rocky exoplanets (‘Super-Earths’) like
those in this artist’s depiction should come rapidly,
thanks to dedicated space telescopes and improving
ground-based detection capabilities. Image from D.
Aguilar, Harvard Smithsonian CfA.
For More Information…
Press Releases
•
Space.com - 09/16/09 - “First Rocky World Confirmed Around Another Star”
http://www.space.com/scienceastronomy/090916-rocky-exoplanet.html
•
Eurpoean Southern Observatory - 09/16/09 - ‘First Solid Evidence for a Rocky Exoplanet’
http://www.eso.org/public/outreach/press-rel/pr-2009/pr-33-09.html
Images
•
Artist depiction of Corot-7 system courtesy European Southern Observatory / L. Calcada
http://www.eso.org/public/outreach/press-rel/pr-2009/pr-33-09.html
•
•
•
Detection method cartoons - 2006 Pearson Education Inc., publishing as Addison Wesley
Transit and radial velocity data plots adapted from source articles below
Artist depiction of Super-Earth courtesy David Aguilar, Harvard Smithsonian CfA
http://www.cfa.harvard.edu/news/2008/pr200802_images.html
Source Articles
•
(on-campus login may be required to access journals)
Léger et al., ‘Transiting exoplanets from the CoRoT space mission VIII. CoRoT-7b: the first SuperEarth with measured radius’, Astronomy and Astrophysics, in press, 2009.
http://www.aanda.org/articles/aa/pdf/forth/aa11933-09.pdf
•
Queloz et al., ‘The CoRoT-7 planetary system: two orbiting super-Earths’, Astronomy and
Astrophysics, in press, 2009.
http://www.aanda.org/index.php?option=article&access=doi&doi=10.1051/0004-6361/200913096
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 3 December, 2009
Possible ‘Water World’ at 40 Light Years
• A configuration of 8 small telescopes
detected an exoplanet passing in
front of a nearby small star
• Observations provide estimates of
the planet’s size (~2.7 x Earth) and
mass (~6.5 x Earth)
• The density of ~1.8 g/cm3 implies
that the planet may be composed
primarily of water, which has density
of ~1 g/cm3
Artist’s conception of GJ 1214b - a ‘Super Earth’
orbiting a star ~40 light-years away. The planet orbits at
a distance of only ~15 stellar radii. Image from David
Aguilar.
Inferring Composition from Density
• Knowing the mean density of the planet
does not uniquely tell us its composition
• The planet may have a small, dense
metallic core surrounded by a massive
hydrogen atmosphere - but the star
should rapidly boil the atmosphere away
• More likely the planet has a core made
mostly of solid water (ice) and a small
hydrogen atmosphere (expected for a
planet orbiting so close to its star)
metallic core
hydrogen/helium
atmosphere
~2.7 x Earth
mostly water ice core
possible liquid
surface water
hydrogen/helium
atmosphere
Two possible interior structures of GJ 1214b.
The Big Picture
• The planet’s surface is hot, but high
pressures may allow for liquid or
solid water there
• The planet is so close (only ~40 light
years from Earth) that our radio and
TV transmissions have passed it
• The Spitzer Space Telescope will
soon conduct infrared observations
to measure conditions in the
atmosphere
Eight 16” telescopes monitor a few thousand stars
cooler than the Sun, searching for transiting planets
as part of the MEarth project. Similar ground-based
configurations may soon be able to detect Earth-sized
planets. Image from Dan Brocius.
For More Information…
Press
•
Harvard-Smithsonia Center for AStrophysics - 12/16/09 - “Astronomers Find Super-Earth Using
Amateur, Off-the-Shelf Technology”
http://www.cfa.harvard.edu/news/2009/pr200924.html
•
Wired Science - 12/16/09 - “Most Earth-Like Extrasolar Planet Found Right Next Door”
http://www.wired.com/wiredscience/2009/12/super-earth/
•
Space.com - 12/16/09 - “Nearby Super-Earth May Be a Waterworld”
http://www.space.com/scienceastronomy/091216-super-earth-water-atmosphere.html
Images
•
Slide 1 image courtesy David A. Aguilar, CfA
http://www.cfa.harvard.edu/news/2009/pr200924_images.html
•
Slide 3 image courtesy Dan Brocius, CfA
http://www.cfa.harvard.edu/news/2009/pr200924_images.html
Source Articles
•
(on-campus login may be required to access journals)
Charbonneau et al., ‘A super-Earth transiting a nearby low-mass star’, Nature, 462,
10.1038/nature08679, 2009.
http://www.nature.com/nature/journal/v462/n7275/full/nature08679.html
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 15 April, 2010
Another Impact on Jupiter
• Australian amateur astronomer
Anthony Wesley discovered a large
new dark spot near Jupiter’s south pole
• Hours later, U.S. astronomers alerted
by Wesley imaged Jupiter at other
wavelengths
• The spot appears to be debris in
Jupiter’s atmosphere leftover from a
comet or asteroid impact
impact scar
Visible wavelength image of a dark impact scar
near Jupiter’s south pole. Image from Anthony
Wesley, Murrumbateman Australia.
Information at Different Wavelengths
Hubble Space Telescope
storm
• Images at different wavelengths
provide useful information:
Visible - The impactor debris is dark
relative to Jupiter’s cloud tops
Infrared - Impactor debris reflects sunlight
at longer IR wavelengths. Nearby clouds
appear dark because they lie at lower
altitudes, and methane and hydrogen just
above them absorb IR radiation.
Other IR images show that the atmosphere
is warmed by the impact, and that
ammonia is present in the atmosphere
dark impactor
debris
visible
NASA Infrared Telescope Facility
methane and hydrogen
absorb IR light from
lower altitudes
impactor debris
reflects sunlight
infrared
Visible and infrared (2.23 microns) images of
the impact site taken 4 days after discovery,
and 20 hours after discovery, respectively
The Big Picture
incoming comet fragments
• Impact events allow scientists to study the
impact process, the atmospheric material
excavated by the impact, and upper
atmospheric motions
• A similar (but larger) impact event was
observed at Jupiter 15 years earlier. At
the time, it was thought to be a rare event.
Impacts on Jupiter are more common
than previously thought
OR
Improved monitoring of Jupiter,
particularly at infrared wavelengths, can
now capture smaller impact events
impact scars
Images of Comet Shoemaker-Levy 9 after
Jupiter’s gravity broke it into pieces, and the
resulting impact scars in July 1994.
For More Information…
Web Resources and Press Releases
•
The Planetary Society - 09/13/09 - “The Jupiter Impact”
http://www.planetary.org/blog/article/00002049/
•
University of Central Florida - ‘Jupiter Impact’
http://planets.ucf.edu/resources/jupiter-impact
•
Goddard Space Flight Center - ‘What Hit Jupiter?’
http://www.nasa.gov/centers/goddard/multimedia/largest/impact2009.html
Images
•
Slide 1 image from Anthony Wesley, Murrambateman Australia
http://jupiter.samba.org/
•
Slide 2 HST visible image from NASA/ESA/H. Hammel/Jupiter Impact Team
http://hubblesite.org/newscenter/archive/releases/2009/23/
•
Slide 2 IRTF infrared image from NASA/JPL/IRTF
http://www.jpl.nasa.gov/news/news.cfm?release=2009-112
•
Slide 3 SL9 fragments infrared image from H.Weaver/T.Smith/NASA
http://www2.jpl.nasa.gov/sl9/image2.html
•
Slide 3 SL9 impacts image from NASA/HST
http://apod.nasa.gov/apod/ap950714.html
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 3 December, 2009
Asteroid Detected Hours Before Impact
• A routine search revealed a small
asteroid hurtling toward Earth
2008 TC3
• Rapid international observations
predicted the object’s impact 19
hours later over Sudan
• The fireball from the asteroid
breaking up in the atmosphere was
observed by passing aircraft,
satellites and residents of Sudan
• This small impact tested NASA
warning procedures developed for
more ominous impact events
Image of F class asteroid 2008 TC3 in the hours
before it impacted Earth. Exposure time was 6
minutes, so the asteroid appears as a streak. Image
from La Sagra Sky Survey, Spain.
Meteorites Found from Asteroid
• The small asteroid was expected to
vaporize in the atmosphere but a joint
NASA-Sudanese team undertook a
search for fragments
• Surprisingly, ~280 fresh-looking
meteorites have been found spread
along TC3’s predicted ground track
• Analysis of the collected samples
enabled scientists to determine the
asteroid’s composition and type
• Meteorite composition and density
suggest TC3 was ejected from the
surface of a larger asteroid of rare type
meteorite
A meteorite from 2008 TC3 is discovered in
the Nubian Desert of Sudan by staff and
students of the University of Khartoum, led
by Dr. M.H. Shaddad (Univ. Khartoum) and
P. Jenniskens of SETI / NASA Ames.
The Big Picture
• 2008 TC3 was the first asteroid
observed from space to the ground
• For the first time, scientists can
study meteorite samples knowing
where the meteorites came from
• Global cooperation and
increasingly widespread
technology may make these
fortuitous events more common
Clockwise from top left: Telescope of the Catalina Sky
Survey where TC3 was discovered; Detection image of
2008 TC3; Cell-phone image of luminous trails left in the
atmosphere when TC3 disintegrated into dust; TC3
meteorite in the Nubian Desert of northern Sudan
Press Releases
•
For More Information…
Nature - 3/26/09 - “The Rock that Fell to Earth”
http://www.nature.com/news/2009/090325/full/458401a.html
•
The Planetary Society - 10/07/08 - “The full story of Earth-impacting asteroid 2008 TC3”
http://www.planetary.org/blog/article/00001684/
•
Space Daily - 03/30/09 - ‘NASA Team Finds Riches In Meteorite Treasure Hunt’
http://www.spacedaily.com/reports/NASA_Team_Finds_Riches_In_Meteorite_Treasure_Hunt_999.html
•
SETI Institute - 03/30/09 - ‘Surprise Recovery of Meteorites Following Asteroid Impact’
http://www.seti.org/Page.aspx?pid=1281
•
NASA / JPL - 11/04/08 - ‘Asteroid 2008 TC3 Strikes Earth: Predictions and Observations Agree’
http://neo.jpl.nasa.gov/news/2008tc3.html
Images
•
2008 TC3 pre-impact image courtesy of La Sagra Sky Survey, Spain
http://www.minorplanets.org/OLS/2008_TC3/
•
All remaining images courtesy of NASA, found at http://www.nasa.gov/topics/solarsystem/tc3/
- Catalina Sky Survey images courtesy of Catalina Sky Survey
- Atmospheric luminous trail image from M. Elhassan (Noub NGO), M.H. Shaddad (Univ.
Khartoum), and P. Jenniskens (SETI Institute/NASA Ames)
- Meteorite images courtesy P. Jenniskens (SETI / NASA Ames)
Source Article (on-campus login may be required to access journals)
•
Jenniskens et al., ‘The impact and recovery of asteroid 2008 TC3’, Nature, 458, p. 485 doi:
10.1038/nature07920, 2009. http://www.nature.com/nature/journal/v458/n7237/full/nature07920.html
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 3 December, 2009
Will the World End Before Finals?
• ‘Doomsday’ rumors have been
proliferating recently, fueled by
recent books, shows, and films
• Most rumors cite the ‘end’ of the
Mayan ‘long count’ calendar in
December, 2012
• Doomsday scenarios include:
• Collision of a rogue planet
with Earth
• Violent solar storms
• Sudden violent ‘shifting’ of
continents and poles
• Sudden reversal of Earth’s
magnetic field
• ‘Galactic’ alignment
Artist rendition of two planets undergoing a catastrophic
collision. Such collisions do happen in planetary systems,
but are highly unlikely after the system has formed.
No!
• The Mayan long calendar will partly ‘reset’,
but the world will not end
• Like New Year’s (when both day & month reset), 13 (of
at least 20) Mayan time increments will reset in 2012
• The Mayans recorded recurring astronomical events tied
to the Sun, Moon, and visible planets - but did not
predict natural disasters or undiscovered astronomical
objects
• There is no known ‘Planet X’ that will impact
Earth in the near future
Photo of a Mayan long count calendar
• A few Pluto-like dwarf planets have been discovered in
our outer solar system recently, but none have orbits that
bring them inside ~35 AU
• A planet headed toward Earth would be easily visible
• Conspiracies in astronomy are unlikely, especially given
the large number of skilled amateurs (who regularly
pioneer new discoveries)
• Other ‘doomsday’ scenarios are similarly farfetched, or based on poor science
Artist’s conception of dwarf planet
Eris. From NASA / ESA / A. Schaller
The Big Picture
• Many of these doomsday scenarios are not
new, but have been recycled for many years
• Ancient (and modern) astronomers could not
predict the future, beyond repeated events
(e.g. lunar cycles, eclipses, planetary
positions) based on observations
• One advantage of studying science at any
level is that one learns how to think critically
about any topic, such as the 2012 rumors
Movie poster for ‘2012’, released in November
2009. The movie features worldwide tectonic
activity and natural disasters, triggered by the
Sun.
For More Information…
Web Resources and Press Releases
•
Astronomy Society of the Pacific - Astronomy Beat on-line column on 2012 by David Morrison
http://www.astrosociety.org/2012/index.html
•
NASA Lunar Science Institute - Video by David Morrison - ‘The Truth about 2012’
http://www.vimeo.com/7463829
•
NASA - 11/06/09 - ‘2012: Beginning of the End or Why the World Won't End?’
http://www.nasa.gov/topics/earth/features/2012.html
•
National Geographic News - ‘2012: Six End-of-the-World Myths Debunked’
http://news.nationalgeographic.com/news/2009/11/091106-2012-end-of-world-myths.html
Images
•
Slide 1 image from NASA / JPL-Caltech
http://www.nasa.gov/mission_pages/spitzer/multimedia/spitzer-20090810.html
•
Slide 2 Mayan calendar photo from Wikipedia user ‘Maunus’, released to public domain
http://en.wikipedia.org/wiki/File:Lamojarra-inscription.jpg
•
Slide 2 Eris image from NASA / ESA / A. Schaller (STScI)
http://hubblesite.org/newscenter/archive/releases/2006/16/image/a
•
Slide 3 image from Sony Pictures 2012 Official Website
http://www.whowillsurvive2012.com/
Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider
[email protected] - http://dps.aas.org/education/dpsdisc/ - Released 5 December, 2009