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FOCUS jean-pierre.bibring@ias.u-psud.fr dominique.bockelee-morvan@obspm.fr 7 WINTER 2015 N° 36 “We’ve succeeded in detecting water, as well as following the activity of the comet, and locating the main sources of the outgassing from the nucleus,” she explains. Bockelée- Morvan expects that as the comet draws nearer to the Sun, and starts producing its atmosphere of vapor, the data will start streaming in even faster. It will then take years— possibly decades—to process it all. “Fly-bys of comets which took measurements for one hour have produced up to three or four years of work. With Rosetta, we have one and a half years of measurements from ten different instruments—it’s amazing,” she enthuses. Sleep tight and wake up bright On landing, Philae bounced away from its intended resting spot, eventually settling into the shadow of a cliff. There, its primary batteries ran out and its solar array was starved of sunlight. Before it went to sleep, the multi-camera array of CIVA (pronounced “Shiva,” like the three-eyed Hindu deity) managed to capture an image of the cracked and icy “Perihelion Cliff” next to the lander. “The images that I am responsible for are a trove of new information. For instance, the building blocks for the ice and organics are very mixed up,” says Bibring. This, he adds, gives us essential insight for understanding the comet’s structure, especially when combined with data from the other instruments on board. “We already have results on the comet’s magnetization, showing that there is no magnetization at all. That is important because it sheds light on how the solar nebulae—the material from which the Solar System was formed—was composed very early on.” As comet 67P approaches the Sun, Philae should become active once more. At that point, Bibring says that the CIVA-M micro-cameras will be deployed to analyze pristine samples from below the surface. Water, water, everywhere One hypothesis about the origin of water on Earth is that it might have come from ancient comets. One of the first questions the Rosetta team set out to answer was whether this was possible. Bockelée- Morvan explains that much of the “water outgassing” from comet 67P appears at its “neck” where VIRTIS suggests there may also be surface ice. Somewhat disappointingly perhaps, the ROSINA mass spectrometer debunked the myth that Earth’s water was comet-borne—the ratios of deuterium to hydrogen isotopes on 67P are three times those of our oceans.11 On the other hand, we discovered that comet 67P originated in the Kuiper Belt, beyond Neptune. The migration of the giant planets perturbed other material in the interplanetary primordial soup. “Because of this shake-up of smaller bodies in the Solar System, you can expect some of these objects to have different compositions.” As comet 67P gets closer to the Sun and starts shedding vapor visible as a comet’s characteristic tail, Bockelée- Morvan expects to see much more. The comet is likely to release a number of gases, including carbon dioxide and noble gases. Much of this activity, and the interaction of the comet’s plume with the solar wind, are also of interest to the Rosetta team. “Most of the observations made from ROSINA were meant to prepare for the Philae landing. Now the escort phase is beginning—and so, actually, is our scientific work.” ii 1. Comet Infrared and Visible Analyzer, developed by the Institut d’astrophysique spatiale (CNRS / Université Paris-XI). 2. COmet Nucleus Sounding Experiment by Radio wave Transmission, developed by the Institut de planétologie et d’astrophysique de Grenoble (CNRS / Université Joseph Fourier). 3. Institut d’astrophysique spatiale (CNRS / Université Paris-XI). 4. Optical, Spectrocopic and Infrared Remote Imaging System, developed with the Laboratoire d’astrophysique de Marseille (CNRS / Aix-Marseille Université). 5. Visible and Infrared Thermal Imaging Spectrometer, developed with the Laboratoire d’études spatiales et d’instrumentation en astrophysique, and the IAS. 6. Cometary Secondary Ion Mass Analyser, developed with the Laboratoire de physique et chimie de l’environnement et de l’espace (CNRS / Université d’Orléans) and the IAS. 7. Many of these through the Centre national d’études spatiales (CNES). 8. Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (Universität Bern, Switzerland). 9. Microwave Instrument for the Rosetta Orbiter, (Jet Propulsion Laboratory, US). 10. Laboratoire d’études spatiales et d’instrumentation en astrophysique (CNRS / Observatoire de Paris / Université de Paris-VII / UVSQ / UPMC / CNES). 11. K. Altwegg et al., “67P/Churyumov-Gerasimenko, a Jupiter family comet with a high D/H ratio,” Science, 2014. DOI: 10.1126/science.1261952. Rosetta’s OSIRIS wideangle camera image of 67P shows jets of cometary activity along the body of the comet. © ESA/ROSETTA/MPS FOR OSIRIS TEAM MPS/UPD/LAM/IAA/SSO/ INTA/UPM/DASP/IDA


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