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ASTR-1010 Planetary Astronomy

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

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ASTR-1010 Planetary Astronomy

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  1. ASTR-1010Planetary Astronomy Day 40

  2. 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.

  3. Cosmic Billiards 100 Myr 880 Myr 20 AU • The model predicts: • After formation, giant planet orbits were affected by gravitational ‘nudges’ from surrounding planetesimals • Jupiter and Saturn crossed a 1:2orbital resonance (the ratio of orbital periods), which made their orbits more elliptical. This suddenly enlarged and tilted the orbits of Uranus and Neptune • Uranus / Neptune cleared away the planetesimals, sending some to the inner solar system causing a spike in impact rates planetesimals 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.

  4. 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)

  5. For more information… Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 24 April 2009 • 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

  6. 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.

  7. Direct & Indirect Evidence for Volcanoes partly filled crater vents • MESSENGER has found shield volcanoes and vents suggesting explosive volcanism inside the large Caloris basin • 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) 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).

  8. The Big Picture Alaska Hawaii Venus Mars Mercury • Volcanism appears to be responsible for formation of Mercury’s widespread plains • Mercury’s ancient plains-forming, 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 Volcanic features in the inner solar system

  9. For more information… Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 24 April 2009 • 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

  10. 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.

  11. 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.

  12. 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.

  13. For More Information… Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 15 April, 2010 • 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

  14. Did Sulfur Affect Mars Climate and Geology? ~30 cm 1.3 cm • 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 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.

  15. 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 H2O • 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

  16. 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.

  17. Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 14 April 2009 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) • Halevy et al., ‘A Sulfur Dioxide Climate Feedback on Early Mars’, Science, 318, 1903 (2007), DOI: 10.1126/science.1147039. http://www.sciencemag.org/cgi/content/abstract/318/5858/1903

  18. 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.

  19. 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

  20. The Big Picture surface methane liquid water hot rock ~2 µm methane bacteria • Where can the methane come from? From analogy with Earth, there are two leading theories for the origin of recent subsurface methane at Mars: • Methane is produced by water-rock interactions • Methane is produced by bacteria, in regions where liquid water is found • Either theory implies that the Martian subsurface is dynamic • Future observations can test for trace chemicals associated with each process Methane on Mars could be produced chemically through liquid/rock interactions (top) or biologically (bottom)

  21. For more information… Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 24 April 2009 • 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

  22. Buried Glaciers at Mars • Radar observations made from orbit reveal that nearly pure ice “glaciers” covered by rock are common at mid-latitudes 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.

  23. Forming Protected Ice Reservoirs 1050 km • The tilt of Mars’ rotation axis was likely much greater (~45°) millions of years ago • 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 48° N 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.

  24. The Big Picture slope glacier 8 km • Debris-covered glaciers at mid-latitudes on Mars may contain enough ice to cover the entire planet in 20 cm of water • 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)

  25. For More Information… Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 15 April, 2010 • 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

  26. 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.

  27. Intensity Intensity Wavelengths where water absorbs light How was Water Detected? model with thermal radiation only • Lunar soil emits infrared thermal radiation. The amount of emitted light at each wavelength varies smoothly according to the Moon’s temperature. • H2O or OH molecules in the soil absorb some of the radiation, but only at specific wavelengths • All four infrared spectrographs measure a deficit of thermal radiation at those wavelengths, implying water is present model with thermal radiation and absorption by molecules An infrared spectrum measured by LCROSS (black data points) compared to models (red line)

  28. 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.

  29. For More Information… Prepared for the Division for Planetary Sciences of the American Astronomical Society by C. Runyon, David Brain, Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 03 December, 2009 • 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 M3 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

  30. 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.

  31. 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.

  32. 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 • 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 Tiger stripes Image of Enceladus showing the ‘tiger stripes’ region in the southern hemisphere, where the plumes originate

  33. For More Information… Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 03 December, 2009 • 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

  34. A Sunlit Lake on Titan reflected sunlight night side • The Cassini spacecraft recently recorded a flash of sunlight off a region of the northern hemisphere • 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 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.

  35. 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.

  36. 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.

  37. For More Information… Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 15 April, 2010 • 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

  38. 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.

  39. A Ring Creates a “Baseball” Moon Trailing Dust Iapetus Leading 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 Sun-warmed dust causes sublimation, driving ice to the poles and trailing side

  40. 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.

  41. For More Information… Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 15 April, 2010 • 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

  42. 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 (Corot-7b). Image from ESO / L. Calcada.

  43. How Can We Find a Planet’s Density? Amount of Light 0.04% -4 -2 0 2 4 Hours Star Radial Velocity -20 -10 0 10 20 Hours • Density = Mass / Volume • 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. Changes in the measured wavelengths of star light are caused by a planet with mass ~5 times Earth’s. Periodic decreases in light from the star are caused by a planet with diameter 1.7 times Earth’s passing in front.

  44. 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.

  45. For More Information… Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 3 December, 2009 • 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 Super-Earth 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

  46. 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.

  47. Inferring Composition from Density metallic core hydrogen/helium atmosphere ~2.7 x Earth mostly water ice core possible liquid surface water hydrogen/helium atmosphere • 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) Two possible interior structures of GJ 1214b.

  48. 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.

  49. For More Information… Prepared for the Division for Planetary Sciences of the American Astronomical Society by David Brain and Nick Schneider dpsdisc@aas.org - http://dps.aas.org/education/dpsdisc/ - Released 15 April, 2010 • 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

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