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Groussin O.,French National Center for Scientific Research | A'Hearn M.,University of Maryland University College | Belton M.J.S.,Belton Space Exploration Initiatives | Farnham T.,University of Maryland University College | And 7 more authors.
Icarus | Year: 2010

We present results on the energy balance of the Deep Impact experiment based on analysis of 180 infrared spectra of the ejecta obtained by the Deep Impact spacecraft. We derive an output energy of 16.5 (+9.1/-4.1) GJ. With an input energy of 19.7 GJ, the error bars are large enough so that there may or may not be a balance between the kinetic energy of the impact and that of outflowing materials. Although possible, no other source of energy other than the impactor or the Sun is needed to explain the observations. Most of the energy (85%) goes into the hot plume in the first few seconds, which only represents a very small fraction (<0.01%) of the total ejected mass. The hot plume contains 190 (+263/-71) kg of H2O, 1.6 ± 0.5 kg of CO2, 8.2 (+11.3/3.1) kg of CO (assuming a CO/H2O ratio of 4.3%), 27.9 (+25.0/-8.9) kg of organic material and 255 ± 128 kg of dust, while the ejecta contains ∼107 kg of materials. About 12% of the energy goes into the ejecta (mostly water) and 3% to destroy the impactor. Volatiles species other than H2O (CO2, CO or organic molecules) contribute to <7% of the energy balance. In terms of physical processes, 68% of the energy is used to accelerate grains (kinetic energy), 16% to heat them, 6% to sublimate or melt them and 10% (upper limit) to break and compress dust and/or water ice aggregates into small micron size particles. For the hot plume, we derive a dust/H2O ratio of 1.3 (+1.9/-1.0), a CO2/H2O ratio of 0.008 (+0.009/-0.006), an organics/H2O ratio of 0.15 (+0.29/-0.11) and an organics/dust ratio of 0.11 (+0.30/-0.07). This composition refers to the impact site and is different from that of the bulk nucleus, consistent with the idea of layers of different composition in the nucleus sub-surface. Our results emphasize the importance of laboratory impact experiments to understand the physical processes involved at such a large scale. © 2009 Elsevier Inc. Source

Brack A.,CNRS Center for Molecular Biophysics | Horneck G.,German Aerospace Center | Cockell C.S.,Open University Milton Keynes | Berces A.,Hungarian Academy of Sciences | And 22 more authors.
Astrobiology | Year: 2010

The ultimate goal of terrestrial planet-finding missions is not only to discover terrestrial exoplanets inside the habitable zone (HZ) of their host stars but also to address the major question as to whether life may have evolved on a habitable Earth-like exoplanet outside our Solar System. We note that the chemical evolution that finally led to the origin of life on Earth must be studied if we hope to understand the principles of how life might evolve on other terrestrial planets in the Universe. This is not just an anthropocentric point of view: the basic ingredients of terrestrial life, that is, reduced carbon-based molecules and liquid H2O, have very specific properties. We discuss the origin of life from the chemical evolution of its precursors to the earliest life-forms and the biological implications of the stellar radiation and energetic particle environments. Likewise, the study of the biological evolution that has generated the various life-forms on Earth provides clues toward the understanding of the interconnectedness of life with its environment. © 2010 Mary Ann Liebert, Inc. Source

Kaltenegger L.,Harvard - Smithsonian Center for Astrophysics | Eiroa C.,Autonomous University of Madrid | Ribas I.,Institute Of Ciencies Of Lespai Csic Ieec | Paresce F.,Istituto di Astrofisica Spaziale e Fisica Cosmica | And 21 more authors.
Astrobiology | Year: 2010

We present and discuss the criteria for selecting potential target stars suitable for the search for Earth-like planets, with a special emphasis on the stellar aspects of habitability. Missions that search for terrestrial exoplanets will explore the presence and habitability of Earth-like exoplanets around several hundred nearby stars, mainly F, G, K, and M stars. The evaluation of the list of potential target systems is essential in order to develop mission concepts for a search for terrestrial exoplanets. Using the Darwin All Sky Star Catalogue (DASSC), we discuss the selection criteria, configuration-dependent subcatalogues, and the implication of stellar activity for habitability. © 2010 Mary Ann Liebert, Inc. Source

Kaltenegger L.,Harvard - Smithsonian Center for Astrophysics | Selsis F.,University of Bordeaux 1 | Fridlund M.,European Space Agency | Lammer H.,Austrian Academy of Sciences | And 17 more authors.
Astrobiology | Year: 2010

We discuss how to read a planet's spectrum to assess its habitability and search for the signatures of a biosphere. After a decade rich in giant exoplanet detections, observation techniques have advanced to a level where we now have the capability to find planets of less than 10 Earth masses (MEarth) (so-called "super Earths"), which may be habitable. How can we characterize those planets and assess whether they are habitable? This new field of exoplanet search has shown an extraordinary capacity to combine research in astrophysics, chemistry, biology, and geophysics into a new and exciting interdisciplinary approach to understanding our place in the Universe. The results of a first-generation mission will most likely generate an amazing scope of diverse planets that will set planet formation, evolution, and our planet into an overall context. © 2010 Mary Ann Liebert, Inc. Source

Schneider J.,Laboratoire Of Lunivers Et Ses Theories | Leger A.,University Paris - Sud | Fridlund M.,European Space Agency | White G.J.,Open University Milton Keynes | And 17 more authors.
Astrobiology | Year: 2010

We describe future steps in the direct characterization of habitable exoplanets subsequent to medium and large mission projects currently underway and investigate the benefits of spectroscopic and direct imaging approaches. We show that, after third- and fourth-generation missions have been conducted over the course of the next 100 years, a significant amount of time will lapse before we will have the capability to observe directly the morphology of extrasolar organisms. © 2010 Mary Ann Liebert, Inc. Source

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