Abstracts

What can we learn on the Solar nebula from cometary volatiles and dust

Akiva Bar-Nun, Tel Aviv University, Dept. of Geophysics,Atmospheric and Planetary Sci. Tel Aviv University, Ramat Aviv Tel Aviv, Israel, akivab@post.tau.ac.il

Comets contain in their water ice both trapped gases and dust grains. The trapping of gases at their observed mixing ratios suggests that the ice grains which agglomerate to form comet nuclei were formed at 25-27 K. On the other hand, some of the dust grains collected by Stardust and IDPs suggest a high formation temperature, either near the young sun, from where they migrated outward, or in the outflow from a nearby red giant star. The organics in the dust were formed in the solar nebula and in the interstellar medium from which the nebula was formed.

Exploring the Early Bombardment of the Inner Solar System

William Bottke, Soutwest Research Institute, Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, CO 80302, United States, bottke@boulder.swri.edu 

The Late Heavy Bombardment refers to a period ~4 billion years ago in which the large lunar basins with known ages were produced. The nature of the LHB is debated. One view is that the LHB marked the end of a steadily decreasing bombardment of the inner solar system due to leftover planetesimals. A second view is that the LHB was a short-lived cataclysm of dramatically increased impact rates, possibly produced by a rearrangement of the giant planets. Here I argue that both schools are probably correct in some fashion, with late-forming lunar basins made by asteroids destabilized by late giant planet migration. I will show that many LHB-era impactors came from an unexpected source, and that they continued to hit the inner worlds well after ~3.8 Ga. In fact, this late late bombardment probably pummeled the Earth throughout the Archean and early-Proterozoic eras, a formative time for early life and our biosphere. 

Mantle dynamics and magnetic field evolution of rocky exoplanets

Doris Breuer, DLR, Institute of Planetary Research, Rutherfordstr 2, 12489 Berlin, Germany, doris.breuer@dlr.de

The discovery of rocky exoplanets has increased the quest to study the habitability of these planets. In that context the interior dynamics and the potential of super-Earths to operate in the plate tectonics mode and to generate a magnetic field are of interest. In particluar plate tectonics has been suggested to be essential for life due its role in the stabilization of the atmosphere temperature through the carbon silicon cycle. Present models dealing with the interior dynamics differ significantly in their prediction; for instance both an increase and a decrease in the propensity of plate tectonics with increasing planetary mass have been suggested. Similar, the mantle viscosity, which plays a critical role for the mantle dynamics and consequently also the interior cooling and magnetic field evolution, is controversially discussed. In the present talk I will give a review on the various models and their assumptions and discuss their consequences on the habitability of exoplanets.

Current state of knowledge about planetary origins from spacecraft exploration

Julie Castillo-Rogez, JPL/Caltech, 4800 Oak Grove Drive, Pasadena, CA, United States, jccastil@jpl.nasa.gov

The last decade of planetary exploration has led to breakthrough discoveries about the early Solar system history and dynamical evolution. This presentation will review the current state of the art in terms of planet and planetary system formation inferred from spaceborne exploration as well as returned samples. Specific case studies will be developed, including a detailed review of the system science achieved at the Saturnian system with the Cassini-Huygens mission.

Acknowledgement: This work has been carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA, and supported by an award from the Outer Planet Research Program. Government sponsorship acknowledged.

Origin of Giant-Planets and terrestrial planets' moons from tidal rings

Sebastien Charnoz, Universite Paris Diderot, CEA Saclay, Service d'Astrophysique, Centre de l'Orme Les Merisiers, bâtiment 709, 91191 Gif-sur-Yvette Cedex FRANCE, France, charnoz@cea.fr

Sébastien Charnoz & Aurélien Crida

Giant planet's moons and terrestrial planets' moons are thought to originate from different processes However, some recent works on the origin of Saturn's moons have shown that they may have formed from the rings themselves (Charnoz et al., Nature 2010, Canup, Nature 2011). This bridges an unexpected gap between giant-planet and terrestrial planets moon formation. Using numerical simulations, wz show how this process of moon formation explains well the main properties of Saturn's inner moons as well as is compatible also with the known properties of Saturn's rings, as observed by the CASSINI spacecraft.For the case of terrestrial planets suffering a giant impact, we will show why a single moons is preferentially formed . For giant planets, we show how it explains also the orbital architectures of Uranus and Neptunes' satellite.

Extreme Space Weather on Close-in Planets

Ofer Cohen, Harvard-Smithsonian CfA, 60 Garden St., MS-67, United States, ocohen@cfa.harvard.edu

Planet habitability is defined by its surface temperature. However, other factors should be considered. In particular, the role of terrestrial magnetic fields in shielding planets from high radiation by cosmic-rays and the solar wind has been well known. Since the dawn of the space era, a great detail of information about the Sun, the interplanetary environment, and planetary geomagnetic effects has been gathered. In the last two decades, the increasing amount remote-sensing and in-situ data has been used to develop state-of -the-art computer models to simulate the space environment. In particular, Magnetohydrodynamic (MHD) models have been developed to capture electromagnetic effects. These computer models are now mature enough, so that they can be implemented to study exoplanets. Here I present a numerical work to study the geomagnetic effects of a close-in planet and the ability of the planetary magnetic field to shield the planet from erosion by a space weather event.

Are Apollo Zircons Witness to a Lunar Cataclysm?

Carolyn Crow, University of California Los Angeles, 1330 S Centinela Ave #2, Los Angeles, CA 90025, United States, ccrow@ucla.edu 

It is generally agreed that there was a steep decline in the impact rate on the Moon after 3.9 Ga, but there the nature of bombardment before this time is controversial. Zircons are ideal for investigating the early lunar bombardment because (1) low initial Pb results in high precision U-Pb age measurements, (2) the crystallization ages of lunar zircons all predate the proposed cataclysm, (3) zircons incorporate both U and Pu, so we can measure fissiongenic Xe degassing ages and Pb-Pb crystallization ages for the same crystal. We measured Xe isotopic abundances of three large (~300 μm) individual Apollo 14 zircons using the University of Manchester Refrigerator Enhanced Laser Analyser for Xenon. Two of the samples produced sufficient xenon for precise xenon isotope ratios to be determined. All releases from these samples are consistent with the 238U end member suggesting little or no Xe contributed from 244Pu fission, which places a upper limit on the xenon degassing age of ~3.9 Ga. 

Sprite brightness on Earth, Saturn and Jupiter: laboratory simulations

Daria Dubrovin (POSTER), Tel Aviv University, P.O. Box 39040, Tel Aviv 69978, ISRAEL, Dept. of Geophysics and Planetary Science, dariad@post.tau.ac.il

Large electric discharges in the mesosphere, known as red sprites, are physically similar to streamer discharges in air at sea level, which can be reproduced in laboratory settings. Simple scaling laws relate physical properties of streamer discharges at sea level density with tendrils observed in sprites. We investigate the scaling with density of the brightness of streamers in artificial atmospheres of Earth, Saturn and Jupiter, and the ability to predict sprite brightness using experimental methods. Our method gives a lower bound of the brightness of sprites on Earth.
We provide an estimate for the lower bound of sprite brightness on Jupiter and Saturn. We predict that these discharges would be of comparable brightness as terrestrial sprites, and the emitted light is predominantly in the near UV. Extra-terrestrial sprites can be observed by orbiting space-craft.

Detection of transiting Jovian exoplanets by Gaia photometry

Yifat Dzigan, Department of Geophysics and Planetary Sciences, Tel-Aviv university, Ramat-Aviv, Tel-Aviv 69978, Israel, yifatdzigan@gmail.com

Gaia is a European Space Agency mission, to be launched at 2013. One can expect a milli-magnitude (mmag) precision of its photometry, with average of 70 measurements for each object. The mmag precision raises the question of whether Gaia can be used to detect exoplanetary transits, despite the low cadence and the small number of measurements. Using the updated design of Gaia we assessed the number of transits detectable by Gaia between a few hundreds to thousands.
The low cadence of Gaia suggests the possibility of a sophisticated detection approach, that will be optimized to low-cadence data. In Dzigan & Zucker (2011) we proposed a novel approach to utilize low-cadence photometric surveys, such as Gaia (and Hipparcos before), for exoplanetary transit search. Using our strategy we found that even if transits are undetectable in the survey alone, it can still be useful for finding preferred times for directed follow-up observations that will maximize the chances to detect transits.

Crusts and Atmospheres on Terrestrial Planets During and Just After Accretion

Linda Elkins-Tanton, Carnegie Institution for Science, DTM, 5241 Broad Branch Rd. NW, Washington DC 20015, United States, ltelkins@dtm.ciw.edu

Material delivered early to terrestrial planets is likely to have been processed through a magma ocean, which are assumed to occur one or more times during the first tens of millions of years of planetary formation because of accretionary impacts. Magma ocean models produce predictions for both earliest crusts and degassed atmospheres. An initial water content less than a half mass percent can produce a dense steam atmosphere, while a small change in chemistry can produce a carbon-based atmosphere, such as that on Venus. The planetary surface beneath this volatile layer may be created in several ways, including through flotation of buoyant minerals, such as the plagioclase crust on the Moon; through adiabatic decompression melting during magma ocean cumulate overturn, as has been suggested for parts of Mercury; or through later volcanism, as is apparent on Mars. Planetary size and bulk composition are controlling parameters in determining the earliest atmospheres and crusts. 

Origin and evolution of the giant planets

Therese Encrenaz, LESIA, Observatoire de Paris, 5 place Janssen, 92190 Meudon, therese.Encrenaz@obspm.fr

The four giant planets of the solar system belong to two different sub-classes: Jupiter and Saturn, with masses of 318 and 90 terrestrial masses, are believed to be mostly made of protosolar gas, while Uranus and Neptune, with respective masses of 14 and 17 terrestrial masses, are mostly made of ices. These different properties suggest different formation scenarios which will be discussed . This presentation will also review our current knowledge of the giant planets' atmospheric composition, thermal structure and cloud structure, derived from ground-based and space data. Abundance and isotopic ratios will be discussed and interpreted in terms of origin and evolution scenarios of the giant planets. Finally, we will discuss how our knowledge of giant planets' atmospheric composition can be extrapolated to try to understand what the possible nature of giant exoplanets could be.

Modeling Optically Thick Cometary Comae

Alan Gersch, University of Maryland, Department of Astronomy, College Park, MD 20742-2421, United States, agersch@astro.umd.edu

Recent space missions (e.g. Deep Impact & EPOXI) have provided spectra from comets of unprecedented spatial resolution of the regions of the coma near the nucleus. Currently active missions (e.g. Rosetta) and hopefully more in the future will continue the trend and demonstrate the need for better modeling of comae with optical depth effects included. We have adapted the Coupled Escape Probability method of radiative transfer calculations for use in asymmetrical spherical situations and applied it to modeling molecular emission spectra of potentially optically thick cometary comae. Here we present a brief description of our model and results of interest for cometary studies, especially for space based observations. Although primarily motivated by the need for modeling comets, our (asymmetric spherical) radiative transfer model could be used for studying other astrophysical phenomena as well, including (exo-)planetary atmospheres.

On the formation of Enceladus' hemispheric dichotomy

Lijie Han, Planetary Science Institute, 1700 E Fort Lowell, Suite 106 Tucson, AZ 85718, United States, han@psi.edu

We performed 3D spherical numerical simulations of thermal convection in Enceladus' ice shell with plasticity to understand the formation of Enceladus’ hemispheric dichotomy. Our simulations with circular core topography tend to produce global (even if locally initiated) episodic overturning. These models fail to explain the regional confinement of Enceladus' current activity to the South Polar Terrain. Models with various non spherical core topography tend to produce episodic overturning confined to the South Polar Terrain or regionally confined episodic overturning. These models can explain the tectonic dichotomy and local age differences on Enceladus. Our models can predict heat flow up to 10-15 GW at the high peak and 3-5 GW at the low peak in one episodic overturning. The high peak value of heat flow is consistent with the Cassini observations.

Spacecraft observations and laboratory constraints on the chemistry of ocean worlds of the outer solar system

Kevin Hand, JPL/Caltech, MS 321-653, JPL, 4800 Oak Grove Drive, Pasadena, CA 91109, United States, khand@jpl.nasa.gov

The water ice lithospheres of ocean worlds of the outer solar system serve, to varying degrees, as windows into the subsurface ocean chemistry. In this talk I will focus on Europa, Ganymede, Callisto, and Enceladus and review what is known with a high degree of certainty about the surface chemistry, sputtered atmospheres, and plumes. Much has been reported about known constituents of endogenous materials but as I will show, the evidence for such conclusions is sometimes overstated. Using results from lab simulations of ice chemistry and radiation processing I will provide a comparison to Galileo NIMS and Cassini VIMS/INMS data. Our results also serve as a guide for which species to expect given the observed chemistry (e.g. carbonic acid). Finally, I will discuss the implications of the surface chemistry for subsurface habitability, and provide details on how best to advance our spectroscopic techniques so as to better reveal the chemistry of these worlds with minimal ambiguity.

Planetary surfaces as hosts for life: A geochemical perspective

Itay Halevy, Weizmann Institute of Science, Department of Environmental Sciences, Sussman Building, Rehovot 76100, Israel, itay.halevy@weizmann.ac.il

Much of the interest in understanding the environments that have existed on and within the terrestrial planets and icy satellites stems from interest in their potential to host life, either today or in the past. Life, as we know it on Earth, has specific requirements, not all of which are easily met. Among these are a source of carbon, the existence of exploitable energetic gradients, sufficient nutrients and trace elements required for the biological machinery, sufficient water, a temperature within a limited range, and time within which life can emerge and evolve. I will survey the potential existence of these in several planetary environments.

Effects of Topography on the Stability of Water Ice and other Volatiles on Ceres

Paul Hayne, California Institute of Technology, Div. of Geological and Planetary Sciences

MC 150-21, Pasadena, CA 91125, United States, phayne@gps.caltech.edu 

Observations of both Mercury and Earth's Moon suggest the presence of water ice and other volatile species with appreciable abundances in regions persistently shadowed by topography. This motivates investigation into whether similar thermal regimes may exist on the dwarf planet Ceres. Fanale and Salvail (1989) developed the theory for ice accumulation and loss on Ceres, concluding that a polar ice cap could exist at > 80 degrees latitude. Schorghofer (2008) showed that ice naturally migrates to the subsurface below diurnal temperature waves, forming a buried snow line. We investigated the effects of topographic shadowing using models for the temperatures inside simple craters at different latitudes, placing constraints on the latitudes and total surface areas that may be occupied by water ice and other volatile species. Our predictions are potentially testable by the Dawn mission during its 2015 encounter with Ceres. 

Giant Planets: Interior Structure, Formation, and Evolution, and the Connection between Solar and Extrasolar Planets

Ravit Helled, Tel-Aviv University, Dept. of Geophysics and Planetary Sciences, Tel Aviv 69978, Israel, rhelled@post.tau.ac.il

The fields of Extrasolar Planets and Planetary Sciences are flourishing. In order to improve our understanding of giant planets we first must combine our knowledge of planetary interiors with planet formation and evolution, and in addition, study solar and extrasolar planets simultaneously. The compositions and internal structures of giant planets can reveal important information on their formation and evolution. I will review my recent work on the internal structures of the giant planets in the solar system, and discuss the importance of understanding the limitations of the available data. I will then discuss how interior models can be used to improve our knowledge on planetary origin and evolution in our solar system and beyond. Finally, open questions and future investigations will be discussed.

Low temperature crystallization of ferric sulfate hydrates

Erik Hennings (POSTER), TU Bergakademie Freiberg, Leipziger Str. 29, 09599 Freiberg / Germany, Erik.Hennings@chemie.tu-freiberg.de

Structure and atmospheric dynamics of giant planets

Yohai Kaspi, Weizmann Institute of Science,311 Sussman, Israel, yohai.kaspi@weizmann.ac.il

Atmospheric dynamics on giant planets are dominated by strong east-west jet-streams at the observable cloud level. In this talk we will review current knowledge of atmospheric dynamics on giant planets, focusing on the depth to which these jets extend into the planets' fluid interior. Determining this depth has implications for understanding giant planets interior structure and origin. Using idealized general circulation models for giant planets, we will show how angular momentum constrains the properties of the interior flow, and how the compressibility of the gas affects the depth to which atmospheric circulation may extend. This topic will be in the frontier of planetary research in the next decade as two of NASA's space missions, Juno and Cassini, will probe the deep dynamics of Jupiter and Saturn via high order gravity measurements. We show that while low order gravity harmonics are dominated by the oblateness of the planet, high order harmonics (n>10) have a strong signature by the density perturbations arising from the flow field. We use the dynamical relations between the fluid velocity and the dynamical density gradients to give relations between the measurable gravity signal and the depth of the circulation. On Uranus and Neptune, due to the smaller mass of the planets and strong broad zonal jets, the gravity signature of internal dynamics appears even at low gravity harmonics. We show that using current knowledge of J4 allows to constrain the dynamics to the uppermost 0.4% of the mass on Uranus and 0.2% on Neptune.

New Evolution Model of Enceladus Including Serpentinization and Anti-Freeze

Uri Malamud (POSTER), Tel Aviv University, Hazait Street, 22, Omer , Israel, urimalam@post.tau.ac.il

We present a 1-D adaptive-grid thermal evolution code suited for small and medium sized icy bodies of the Solar System, with application to Enceladus. The code is used to investigate the multiphase flow of water through a porous medium, thus giving us a detailed look on the internal distribution of mass and energy, spanning 4.6 Gyrs of evolution.

Heating by radionuclides is taken into account. Several values of thermal conductivity and structural properties of the porous medium are used, and a hydrostatic structure is considered.

We introduce a new mechanism for heating via Serpentinization chemical reactions. This heating mechanism works on a much shorter timescale than radioactive heating, yet releases significant amounts of energy in that short period, and is strictly dependent on the flow of liquid water.

We also introduce anti-freeze to modify the thermo-dynamical properties of water, and study the degree to which the lowering of the melting temperature affects these processes.

Possible magnetic fields of Super Earths (SEs) generated by metallic oxides and universal equation of state of metals

William Nellis, Harvard University, Department of Physics, United States, nellis@physics.harvard.edu

Metallic fluid H has minimum metallic conductivity (MMC) at conditions in Jupiter; the magnetic field of Earth implies fluid Fe has MMC. Extrapolation of measured Al2O3 conductivities suggests Al2O3 reaches MMC. Since H2 and probably Al2O3 have MMC, insulators with intermediate strengths probably do also. Since MMC can stabilize a dynamo and many SEs have MMCs, many SEs probably have magnetic fields. Hugoniots of fluid metals at high pressure and temperature lie on or near a universal us-up Hugoniot, which suggests a simple scaling relationship of EOSs exists for many planetary materials off the Hugoniot, as well. Thus, EOSs and conductivities might be modeled with scalable EOSs and common electrical conductivities. However, there is little likelihood of refining interior chemical compositions using only mass distributions and external magnetic fields.

Modeling Uranus and Neptune

Morris Podolak, Tel Aviv University,Dept. of Geophysics and Planetary Sciences, Tel Aviv 69978, Israel, morris@post.tau.ac.il

To zeroth order Jupiter and Saturn consist of a solar mix of hydrogen and helium plus a small amount of high-Z material. From the standpoint of equations of state, this is a relatively simple material, yet despite this the interiors of these planets are still incompletely understood. The bulk of the mass of Uranus and Neptune is high-Z material of undetermined composition, and that makes these planets even harder to model. I review the history of the modeling effort, and point out some of the major difficulties in computing detailed interior models. I will argue that the observational parameters for these planets are insufficiently well known and will attempt to use general arguments (independent of equation of state details) to reach conclusions about the interior structures of these planets. I will then speculate how the process of planet formation may lead to such structures.

Search for small KBOs

Eran Ofek, Weizmann Institute of Science, Physics faculty, Israel, eran@astro.caltech.edu

The Kuiper belt is a remnant of the primordial Solar System. Measurements of its size distribution constrain its accretion and collisional history, and the importance of material strength of Kuiper belt objects (KBO). Small, sub-kilometre-sized, KBOs elude direct detection, but the signature of their occultations of background stars should be detectable. I will present preliminary results from a search for sub-km KBOs using the fine guidance system on board of the Hubble Space Telescope, and I will discuss the implications of this results for the material strength of KBOs.

The Dead Sea: microbial community dynamics at low water activity and implications for astrobiology

Aharon Oren, Department of Plant and Environmental Sciences, The Institute of Life Sciences, The Hebrew University of Jerusalem, 91904 Jerusalem, orena@cc.huji.ac.il

The Dead Sea, with about 350 g/l total salts, magnesium being the main divalent cation, is one of the harshest environments for life on Earth. Currently conditions are too extreme for massive growth of microorganisms, but blooms of unicellular green algae and red halophilic Archaea develop in the lake when the upper water layers become sufficiently diluted by flood waters after rainy winters. In the past decades conditions for life in the Dead Sea have become ever more extreme due to the precipitation of halite and the increase in concentrations of divalent cations. The Dead Sea is thus an ideal environment to study the limits of life in low water activity environments. Such studies are highly relevant in view of the recent discovery of seasonal flows of liquid water, probably brines, on Mars.

What do the moons of terrestrial planets tell us about their origins?

Kaveh Pahlevan, Institution Yale University, Mailing address P.O. Box 208109, New Haven, CT 06520, United States, kaveh.pahlevan@yale.edu

Here, I review what the satellites of terrestrial planets tell us about their origins. Mercury, having been despun by solar tides, hosts no stable orbital niches for massive satellites, and the absence of satellites carries no information about the formation epoch. Venus, while affected by solar tides, is too far from the Sun to have been despun from rapid rotation, and its slow rotation points to the past presence of a satellite that rapidly despun Venus and was subsequently lost. For the Earth, the presence of the Moon points to the occurrence of a giant impact between two planets but the Moon's "terrestrial" composition argues for an episode of turbulent mixing between the proto-lunar disk and the terrestrial magma ocean immediately after the impact. For Mars, the presence of two satellites in nearly circular, uninclined orbits points to an accretion disk, but the tidal collapse of Phobos in ~30 Myrs remains an enigma whose only explanation is an unlikely coincidence.

Icy Satellite Tectonics: More Primitive Than Thou

Robert Pappalardo, Jet Propulsion Laboratory, California Institute of Technology, Mail Stop 321-560, Pasadena, CA 91109, United States, robert.pappalardo@jpl.nasa.gov

The ubiquity and variety of tectonic features on outer planet satellites tells of a rich history of internal processes affecting the satellites through time. Notable examples occur on Jupiter’s Galilean satellites; several middle-sized icy satellites of Saturn and Uranus; and Neptune’s Triton. Extensional structures are especially ubiquitous; contractional and strike-slip structures are also recognized. Early work on icy satellite tectonics emphasized ancient processes in creating structures, but more recent evidence and analyses point to current and recent tectonic processes on some satellites. Absolute surface ages can be coarsely constrained through estimates of cratering rates in the outer solar system (Zahnle et al., 2003). Here I apply the concept of more primitive than thou to icy satellite tectonics, summarizing relative and absolute age estimates for icy satellite tectonic terrains, with implications for understanding whether ancient processes can be deciphered from them.

Rotational and dissipative behavior of Phobos and constraints on its origin

Nicolas Rambaux, Institution Université Pierre et Marie Curie, IMCCE, Observatory of Paris, 77 Avenue Denfert-Rochereau, 75014 Paris, France, Nicolas.Rambaux@imcce.fr,

N. Rambaux, J.C. Castillo-Rogez, S. Le Maistre, P. Rosenblatt

The origin of the martian moon Phobos is still a mystery and the knowledge of its internal properties will be helpful to discriminate between an in-situ or asteroidal origin. Here, we built and compare the dissipative properties for two end-models of Phobos as function of water ice and porosity. The presence of hydrated minerals and water ice can significantly increase tidal dissipation whereas the rubble-pile model leads to low tidal stress. Then, we investigate and describe the rotational motion of Phobos for each models of interior in order to extract possible signature that could be measure during future space mission. It appears that the librational spectrum is dense and hitertho couplings generally neglected can hide the signature of dissipative properties.

Detecting habitable planets and habitability

Heike Rauer, Institute for Planetary Research, DLR, and Center for Astronomy and Astrophysics, University of Technology Berlin, Rutherfordstr. 2, D-12489 Berlin, Germany, heike.rauer@dlr.de

The detection of terrestrial planets in the habitable zone (HZ) and the subsequent detection of habitable conditions and signatures for life on these planets are among the most interesting, but challenging, goals of exoplanet research. While the detection of super-Earths in the HZ around cool, M dwarf, host stars is already possible today, it is still out of reach for small terrestrial planets in the HZ of solar-like stars. Nevertheless, their detection is needed, not only for investigation of habitability, but also to extend the mass function of known exoplanets to small sizes to put further constraints on planet formation. Once planets in the HZ are detected, the question on their habitability needs to be addressed. Atmospheric biosignatures indicating the presence of an atmosphere have been investigated in a number of model simulations in the past to prepare for such observations. Here, we will first discuss the challenge to detect terrestrial planets in the HZ and then present the results of model simulations investigating the detectability of atmospheric spectral biosignatures under the influence of clouds, CO2-dominated atmospheres and for planets withdifferent host stars.

New tools for imaging exoplanets

Erez Ribak, Technion, Physics, Haifa 32000, Israel, eribak@physics.technion.ac.il

E. Ribak, S. Gladysz

Spectral detection of habitable exoplanets

Erez Ribak (POSTER), Technion, Physics, Haifa 32000, Israel, eribak@physics.technion.ac.il

E. Ribak, E. Schwartz , S. G. Lipson

Exoplanets are many orders of magnitude fainter than their own sun, and Earth-like exoplanets are even fainter. We are experimenting with a method of identifying bio-signature spectral lines in light from exoplanets. We employ Fourier spectroscopy in the infra-red, where we use an off-center part of a Fourier interferogram only. This results in superior sensitivity to narrower molecular-type spectral bands, which are expected in the planet spectrum but are absent in the parent star. We support this idea by numerical simulations which include photon and thermal noise, and show it to be feasible at a luminosity ratio of one million for a Sun-like parent star in the infra-red. We first carried out a laboratory experiment to illustrate the method, and have started telescope observations to validate it on astronomical objects of different line widths. The results suggest that this method should be applicable to real planet searches.

Exoplanets from supernova explosions

Erez Ribak (POSTER), Technion, Physics, Haifa 32000, Israel, eribak@physics.technion.ac.il

E. Ribak, S. Dado , A. Dar

We propose that high-speed gas blobs, which are observed in huge numbers in supernova remnants and planetary nebulae, could end up as exoplanets, or strongly affect planetary systems. These blobs grow in mass and slow down in the interstellar medium by accretion, while cooling by radiation. Once their mass exceeds the Jeans mass, they collapse into hot giant gas planets. It could be that significant galactic material has been swept into such free-floating objects. More condensed blobs could perturb stellar planetary systems, kick bound planets into misaligned orbits or be captured themselves into misaligned orbits. Extended blobs could then collapse or be tidally disrupted into a tilted gas disk to form planets, some of them misaligned. Giant floating Jupiters were occasionally detected by their microlensing effects and by radio scintillations of compact extragalactic sources such as quasars and gamma ray bursts, and the hotter ones could be observed in the future by deep photometry.

What topography can tell us: Understanding the power spectra of cratered terrains

Margaret Rosenburg, California Institute of Technology, 1200 E. California Blvd. MC 150-21

Pasadena, CA, 91125, United States, megr@gps.caltech.edu

Cratered surfaces are found throuhout the solar system, and their statistical properties contain a record of the processes that have created and modified them, dating back to the earliest formation of solid bodies in the solar system. The evolution of cratered terrains is not well understood, but the high resolution of the LOLA topography and ongoing advances in computing power together provide a new opportunity to correlate models with observed lunar features. We have developed a cratered terrain model to investigate the statistical properties of such landscapes and how they depend on the size-frequency distribution of impactors, crater shape, and competing surface processes. Working under simplified conditions, we can predict the slope of the power spectrum from the size-frequency distribution of craters and the depth-to-diameter ratio, and by understanding the components of the power spectrum, we begin to interpret the real topographic signatures present on the Moon. If an oral presentation slot is unavailable, I would also be happy with a poster presentation.

D/H Ratios of the Lunar Volcanic Glasses

Alberto Saal, Brown University, Geological Sciences, 324 Brook St, Room 038, Providence, RI 02912, United States, asaal@brown.edu 

We report the first in-situ measurements of δD values dissolved in primitive volcanic glasses and their melt inclusion samples recovered from the (74220; 15426; 15427). Our SIMS detection limits represent at least 2 orders of magnitude improvement over previous analytical techniques. δD measured in ~ 65 lunar glass beads range from +161‰ to +5420‰, and thus, are indisputably fractionated from terrestrial values. δD is inversely correlated with water content, and part of the D enrichment is the result of in situ spallation during interactions with solar and galactic cosmic rays. After correction for spallation the average δD of the highest-H2O glass bead is +340‰ (+180‰/-240‰). It is very likely that the original pre-eruptive δD value of these lunar magmas was significantly lower, affected by preferential loss of H during magmatic. A simple degassing calculation suggests that the δD of the lunar glasses might not have been that different from that of terrestrial basalts.

Planet formation and evolution

Reem Sari, Hebrew University of Jerusalem, Racah Institute, Jerusalem, 91904, Israel, sari@phys.huji.ac.il

We discuss the theory of coagulation of planetesimals, confronting it with information from the planets in our solar system, the Kuiper Belt, and extrasolar planets. Particularly, we discuss mechanisms that give rise to a flat size distribution as observed in the Kuiper Belt. We review the theory of planet disk interaction, thought to be the origin of short orbital periods in extrasolar planets, and perhaps also their large eccentricities. We speculate about the differences between our solar system and others.

Outer Planet Moons: Present States and Origins

Gerald Schubert, UCLA, Department of Earth and Space Sciences, University of California Los Angeles, CA 90095-1567, United States, schubert@ucla.edu 

The present states of outer planet moons are end points in their evolutions and therefore they constrain their origins and evolutionary paths. What we know about these satellites will be reviewed and the implications for their origins and histories will be discussed. We will focus on the Galilean moons of Jupiter and the Saturnian satellites Titan, Enceladus, Rhea and Dione. 

Frontiers in Understanding the Atmospheres of Extrasolar Planets

Adam Showman, University of Arizona, Department of Planetary Sciences, Lunar & Planetary Laboratory, Tucson, AZ 85721, United States, showman@lpl.arizona.edu

The pace of discoveries in the field of exoplanets is astounding. Ever since their first detection in the 1990s, exoplanets continue to be discovered at a fast pace. The past decade has seen a transition from an emphasis on exoplanet discovery to exoplanet characterization. This work has mostly focused on hot Jupiters--close-in giant planets--but the observational cutting edge is shifting toward smaller planets. At the same time, direct imaging is placing constraints on a wholly different class of exoplanet, namely young giant planets at great planet-star separations. I will highlight some of the recent major discoveries, open puzzles, and future work needed in our effort to understand the atmospheres and interiors of these planets.

The Kepler space mission: Looking for Earth-like planets

Avi Shporer, UCSB - LCOGT, 6740 Cortona Dr., Suite 102, Goleta, CA 93117, United States, ashporer@lcogt.net

To date, some 600 extrasolar planets have been discovered orbiting other stars. Of those, about 200 are transiting their host star, allowing a much more detailed investigation, including the measurement of their radius and mass, and the study of their atmospheres. Most of those exoplanets are gas giants the size of Jupiter and Saturn. Kepler is an ambitious NASA Discovery mission whose primary goal is to measure the frequency of small, Earth-like planets, orbiting Sun-like stars in their Habitable Zone, where liquid water can exist on the planet's surface. I will discuss the exciting new results recently obtained by Kepler, based on the large sample of about 2,300 transiting planet candidates and about 360 multiple transiting planet systems.

Dissipation of tidal energy in planetary satellites

Frank Sohl (POSTER), H. Hussmann, F.W. Wagner (DLR Berlin, Germany)

Most natural satellites are in synchronous rotation and subject to tidal forces exerted by their primaries. The ellipsoidal shape of their surfaces was acquired early after formation and tidal despinning, when their deep interiors were sufficiently hot and deformable and hardly overlain by thin lithospheres. The nonspherical part of their present low-degree gravity fields is predominated by spin and tidal contributions, which are related to the radial mass distribution. In addition, tidally-induced, time-variable surface distortion and gravity variation due to tiny radial and librational tides occur along slightly eccentric orbits, thereby causing the dissipation of tidal energy. This has important consequences for the thermal state and orbital evolution of planetary satellites. Based on interior structure models and assumptions on tidally-effective rheological properties of planetary materials (i.e. ice, rock, internal ocean), we will address the tidal response of some active satellites in the outer solar system and examine the role of tidal heating for their past or present geologic activity.

Structure, composition, and mass-radius relationships of rocky exoplanets

Frank Sohl, DLR Institute of Planetary Research Rutherfordstr. 2, 12489 Berlin, Germany, frank.sohl@dlr.de

F. Sohl, F.W. Wagner, H. Rauer (DLR Berlin, Germany)

The growing number of transiting planet discoveries will allow us to characterize rocky exoplanets in terms of internal structure and atmospheric composition with important implications for their formation, orbital evolution, and possible habitability. We construct structural models of solid exoplanet interiors by using equations of state for the radial density distribution, which are compliant with the thermodynamics of the high-pressure limit. To some extent, those structural models suffer from inherent degeneracy or non-uniqueness problems because of a principal lack of knowledge of light and heavy constituents, their degree of internal separation, and/or the possible presence of an optically thick atmosphere. We thereby will address the robustness of mass-radius relationships and their usage for the classification of low-mass exoplanets and their characterization in terms of interior structure and bulk composition.

Life and the Evolution of Planetary Interiors

Tilman Spohn, DLR Institute of Planetary Research, Rutherfordstrasse 2, 12489 Berlin, Germany, tilman.spohn@dlr.de

It is generally held that plate tectonics is a pre-requisite for (evolved) life on terrestrial planets, a presumption that motivates the intense discussion about plate tectonics on super-Earths. We are looking at the potential role of life in stabilizing plate tectonics. We note that microorganisms are known to increase weathering rates on continents and thus the transfer of sediments to sedimentary basins where most of the Earth's biomass is tob e found. We consider the catalytic effect of microorganisms on diagenic and metamorphic reactions in sedimentary basins and the capacity of these rocks at storing water. We follow the water along the downgoing slab to the depth where partial melting creates melt to rejuvenate continental crust and to greater depths where water is fed into the mantle. We consider the water budget of the mantle and discuss a feedback mechanism between growth of the continents and the biomass, water storage in the subducting crust and mantle convection.

Origin and Evolution of Giant Planets

David Stevenson, Caltech, MS 150-21, Pasadena, CA 91125, United States, djs@gps.caltech.edu

This talk will summarize our current understanding of giant planet structure (both gas giants and ice giants) at a level intended for those who are not experts in the subject. The emphasis will be on current ambiguities in the structure, especially the extent to which the three classes of materials (ice, rock and gas) are mixed rather than well separated. There are recent developments in this area, partly in condensed matter physics and partly in fluid dynamics (double diffusive convection). These ambiguities will be related to ideas about the formation of these planets. Possible resolution of these issues will be discussed (Juno, more observations , more modeling, exoplanet systematics, seismology...)

Growth of E. coli at Nanomolar Concentrations of Oxygen

Daniel Stolper, Caltech, 1200 East California BLVD, MC 100-23 Pasadena, CA, 91125, United States, dstolper@caltech.edu

Microbes transition from aerobic to anaerobic growth at the Pasteur Point, which generally occurs when the O2 partial pressure is ~.01 of the present atmospheric level (PAL) of O2 (Fenchel and Finlay, 1995). The Pasteur Point is often assumed to approximate the O2 level below which aerobic processes cease to be viable (e.g., Goldblatt et al., 2006) implying that aerobic respiration evolved only after the earth’s atmosphere reached O2 concentrations ≥ .01 PAL. To investigate whether the Pasteur Point is a valid proxy for the level at which aerobic metabolisms become non-viable, we designed an experiment in which the presence or absence of aerobic growth could be measured at O2 concentrations significantly below the Pasteur Point. Our main conclusion is that at least one aerobic organism (E. coli) can grow at O2 levels 3 orders lower than previously expected. This result may have implications for what it means to be an aerobe and for the timing of the evolution of aerobic respiration. 

The inner boundary of the habitable zone

Barbara Stracke, Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR) in der Helmholtz-Gemeinschaft, Rutherfordstr. 2, 12489 Berlin, Germany, barbara.stracke@dlr.de 

The Habitable Zone (HZ) is generally defined as the orbital region around a star, in which life supporting (habitable) planets can exist. Taking into account that liquid water is a basic requirement for the development of life as we know it, the HZ is mainly determined by the stellar insolation, which is sufficient to maintain liquid water at the planetary surface. This study focuses on different processes that can lead to the complete loss of a liquid water reservoir from the surface of a terrestrial planet to determine the inner boundary of the HZ. We investigate criteria, which determine the inner boundary of the HZ, with a one-dimensional radiative-convective model of a planetary atmosphere. The feedback processes for increased solar insolations between the surface temperature and the greenhouse effect of water vapor on the boundary of the inner HZ are calculated self-consistently. Modelling results are presented determining the inner boundary of the HZ affected by these processes. 

What are exoplanets made of?

Giovanna Tinetti, University College London, Dep. of Physics and Astronomy, Gower Street, United Kingdom, g.tinetti@ucl.ac.uk

Exoplanetary science is one of the fastest evolving fields of today's astronomical research. Ground-based surveys together with Kepler & CoRot, are delivering an ever-increasing number of exoplanets, now numbering at over 700. ESA's GAIA mission will escalate the exoplanetary census into the several thousands. Spectroscopic observations of transiting exoplanets are providing an unprecedented view of the atmospheres of planets around nearby stars. Most recent observations with Hubble and Spitzer or from the ground, have proved being possible to use the wavelength/time dependence of the combined light star-planet to identify key molecules and thermal structure of the planet’s atmosphere.

The European Space Agency is currently assessing a space mission that is fine-tuned to this purpose: the Exoplanet Characterisation Observatory (EChO). Using mid-resolution spectroscopy between 0.4 and 16 μm, this mission will study the chemistry and physics of gas and icy giants, and super-Earths.

On the Evolution and Survival of a Jupiter-Mass Protoplanet in a Disk

Allona Vazan (POSTER), Tel Aviv University, Hahavazelet 9 Binyamina 30500, Israel, allonava@post.tau.ac.il 

We model the evolution of a Jupiter-mass protoplanet at various radial distances accounting for the presence of the disk. It is found that at radial location of ~10 AU a protoplanet of one Jupiter-mass cannot undergo a dynamical collapse and evolve further to become a gravitational bound planet. We therefore suggest that giant planets, if formed by the gravitational instability mechanism, must remain in large radial distances during the first ~10^5 years. We find that the minimum radial distance in which protoplanets of 1 Saturn-mass, and 3 and 5 Jupiter-mass planets can form are 12, 9, and 7 AU, respectively. The effect of gas accretion on the evolution of 1 Jupiter-mass protoplanet is also investigated, and it is shown that gas accretion can shorten the pre-collapse timescale substantially. Our study suggests that the timescale of the pre-collapse stage does not only depend on the planetary mass, but is greatly affected by the presence of the disk and efficient gas accretion. 

Shaping of the inner solar system by the gas-driven migration of Jupiter

Kevin Walsh, Southwest Research Institute, 1050 Walnut St. Suite 300, Boulder, CO 80302, United States, kwalsh@boulder.swri.edu 

A persistent difficulty in terrestrial planet formation models is creating Mars analogs with the appropriate mass: Mars is typically an order of magnitude too large in simulations. A recent work found that a small Mars can be created if the planetesimal disk from which the planets form has an outermost edge at 1.0 AU. However, that work and no previous work can explain such a truncation of the planetesimal disk and preserve the asteroid belt. We show that gas-driven migration of Jupiter inward to 1.5 AU, before its subsequent outward migration, can truncate the disk and repopulate the asteroid belt. This dramatic migration history of Jupiter suggests that the dynamical behaviour of our giant planets was more similar to that inferred for extra-solar planets than previously thought, as both have been characterised by substantial radial migration.

Lunar magnetism: Impacts and dynamos

Mark Wieczorek, Institut de Physique du Globe de Paris, 4 avenue de Neptune 94100 Saint Maur des Fosses, France, wieczor@ipgp.fr 

The terrestrial planets, the Moon, and many of the meteorite parent bodies differentiated early in their history, forming metallic cores and silicate mantles and crusts. By the extraction of heat from their core many of these objects likely possessed dynamos that gave rise to strong magnetic fields on their surface. As a direct result of spacecraft observations, Mercury and Ganymede are known to possess internally generated magnetic fields today. In addition, these measurements have shown that Mars and the Moon have strong crustal magnetic anomalies, and these are often interpreted to reflect crustal rocks that were magnetized by ancient dynamo fields. In this talk, recent work on lunar magnetism will be reviewed. These studies show that the magnetized materials on the Moon may in fact be extra-lunar in origin, and that a core dynamo could have been powered by exotic mechanisms.

Updated review of planetary lightning

Yoav Yair, The Open University of Israel,1 University Road, Ra'anana 43107,Israel, yoavya@openu.ac.il

We present the latest observations from spacecraft and ground-based instruments in search for lighting activity in the atmospheres of planets in the solar system, and put them in context of previous research. Since the comprehensive book on planetary atmospheric electricity compiled by Leblanc et al. (2008), advances in remote sensing technology and telescopic optics enable detection of additional and new electromagnetic and optical emissions, respectively. Orbiting spacecraft such as Mars Express, Venus Express and Cassini yield new results, and we highlight the giant storm on Saturn in December 2010 that was probably the single most powerful storm ever observed in the solar system. We also describe theoretical models, laboratory spark experiments simulating conditions in planetary mixtures and map open issues.