This week was the first anniversary of the Philae landing on 67P/Churyumov–Gerasimenko! Has it been a year already? ESA has an interesting postmortem on the Philae landing misfire (literally, a failure to fire)., with a video reconstruction of the cometfall.
With the unplanned and uncontrolled crash landing, Philae completed only the first few hours of exploration before running out of power and settling into hibernation. No effort to contact Philae has succeeded, but now, as the comet recedes from the sun, Rosetta is closing in on the rapidly cooling comet for one last close up look and a final deliberate plunge to the surface http://blogs.esa.int/rosetta/2015/11/12/from-one-comet-landing-to-another-planning-rosettas-grand-finale/. If Philae has survived the cold and then the heat and turmoil of perihelion, we may get one last bit of information about her.
As noted last week, a special issue of Astronomy & Astrophysics is devoted to reports of results from the Rosetta mission to 67P/CG. Many of these papers are based on data collected as Rosetta approached 67P/CG last spring, so there will be many more reports from the close observations this summer.
The Rosetta blog discusses two of the papers which explore surface features, boulders and dust, seen in imagery from the OSIRIS instrument. OSIRIS is two cameras (wide and narrow) that can capture visible, near IR and new UV light.
In the Thomas et al. paper the most interesting thing for me, is how mundane but alien the low gravity, thin atmosphere, very cold surface is. The imagery shows, for instance, ripples that resemble wind blown dust or sand on Earth. In this, we recognized that 67P/CG is a world just like where we live.
But the analysis indicates that these familiar looking formations probably formed through different processes than where we live. The spewing gasses from the boiling comet are very thin, but may reach 500m/s: powerful enough to ‘blow around” dust, at least close up.
Even more interesting, the investigators hypothesis that “On Earth, the major force to overcome when sculpting wind-blown ripples is gravity holding the grains in place. On the comet, where gravity is minuscule, the major hurdle is the cohesive forces between the dust grains holding them together.” We see something familiar, but the physics is completely different.
See the paper for more details on the careful thought, the methods and evidence, and discussion of uncertainties. It’s actually really cool. (You local library can help you get access to the paper.)
- Thomas, N., B. Davidsson, M. R. El-Maarry, S. Fornasier, L. Giacomini, A. G. Gracia-Berná, S. F. Hviid, W. H. Ip, L. Jorda, H. U. Keller, J. Knollenberg, E. Kührt, F. La Forgia, I. L. Lai, Y. Liao, R. Marschall, M. Massironi, S. Mottola, M. Pajola, O. Poch, A. Pommerol, F. Preusker, F. Scholten, C. C. Su, J. S. Wu, J. B. Vincent, H. Sierks, C. Barbieri, P. L. Lamy, R. Rodrigo, D. Koschny, H. Rickman, M. F. A’Hearn, M. A. Barucci, J. L. Bertaux, I. Bertini, G. Cremonese, V. Da Deppo, S. Debei, M. de Cecco, M. Fulle, O. Groussin, P. J. Gutierrez, J. R. Kramm, M. Küppers, L. M. Lara, M. Lazzarin, J. J. Lopez Moreno, F. Marzari, H. Michalik, G. Naletto, J. Agarwal, C. Güttler, N. Oklay, and C. Tubiana, Redistribution of particles across the nucleus of comet 67P/Churyumov-Gerasimenko. A&A, 583 11// 2015. http://dx.doi.org/10.1051/0004-6361/201526049