* Astronomy

Blobrana · L

RE: Comet 67P/Churyumov-Gerasimenko

Blobrana · L

Title: Summer fireworks on comet 67P
Author: J.-B. Vincent, M. F. A'Hearn, Z.-Y. Lin, M. R. El-Maarry, M. Pajola, H. Sierks, C. Barbieri, P. L. Lamy, R. Rodrigo, D. Koschny, H. Rickman, H. U. Keller, J. Agarwal, M. A. Barucci, J.-L. Bertaux, I. Bertini, S. Besse, D. Bodewits, G. Cremonese, V. Da Deppo, B. Davidsson, S. Debei, M. De Cecco, J. Deller, S. Fornasier, M. Fulle, A. Gicquel, O. Groussin, P. J. Gutierrez, P. Gutierrez-Marquez, C. Guettler, S. Hoefner, M. Hofmann, S. F. Hviid, W.-H. Ip, L. Jorda, J. Knollenberg, G. Kovacs, J.-R. Kramm, E. Kuehrt, M. Kueppers, L. M. Lara, M. Lazzarin, J. J. Lopez Moreno, F. Marzari, M. Massironi, S. Mottola, G. Naletto, N. Oklay, F. Preusker, F. Scholten, X. Shi, N. Thomas, I. Toth, C. Tubiana

During its two years mission around comet 67P/Churyumov-Gerasimenko, ESA's Rosetta spacecraft had the unique opportunity to follow closely a comet in the most active part of its orbit. Many studies have presented the typical features associated to the activity of the nucleus, such as localized dust and gas jets. Here we report on series of more energetic transient events observed during the three months surrounding the comet's perihelion passage in August 2015.
We detected and characterized 34 outbursts with the Rosetta cameras, one every 2.4 nucleus rotation. We identified 3 main dust plume morphologies associated to these events: a narrow jet, a broad fan, and more complex plumes featuring both previous types together. These plumes are comparable in scale and temporal variation to what has been observed on other comets.
We present a map of the outbursts source locations, and discuss the associated topography. We find that the spatial distribution sources on the nucleus correlates well with morphological region boundaries, especially in areas marked by steep scarps or cliffs. Outbursts occur either in the early morning or shortly after the local noon, indicating two potential processes: Morning outbursts may be triggered by thermal stresses linked to the rapid change of temperature, afternoon events are most likely related to the diurnal or seasonal heat wave reaching volatiles buried under the first surface layer. In addition, we propose that some events can be the result of a completely different mechanism, in which most of the dust is released upon the collapse of a cliff.

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Blobrana · L

Comet 67P/Churyumov-Gerasimenko makes its closest approach to the Earth (1.485 AU) on the 15th February 2016.

Blobrana · L

Inside Rosetta's comet

There are no large caverns inside Comet 67P/Churyumov-Gerasimenko. ESA's Rosetta mission has made measurements that clearly demonstrate this, solving a long-standing mystery.
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Blobrana · L

Exposed ice on Rosetta's comet confirmed as water

Observations made shortly after Rosettas arrival at its target comet in 2014 have provided definitive confirmation of the presence of water ice.
Although water vapour is the main gas seen flowing from comet 67P/ChuryumovGerasimenko, the great majority of ice is believed to come from under the comets crust, and very few examples of exposed water ice have been found on the surface.
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Blobrana · L

First public release of Rosetta science camera images of comet 67P

It has been a long wait, but so worth it: the Rosetta OSIRIS science camera team has delivered the first pile of data from the rendezvous with comet 67P to ESA's Planetary Science Archive. I have spent a good chunk of the last three days playing with the data, and it's spectacular. Most cameras that have been sent to the outer solar system have detectors that are about 1000 pixels square; the OSIRIS detectors are 2048 by 2048, and breathtaking in their detail.
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Blobrana · L

Rosetta reveals comet's water-ice cycle

ESA's Rosetta spacecraft has provided evidence for a daily water-ice cycle on and near the surface of comets.
Comets are celestial bodies comprising a mixture of dust and ices, which they periodically shed as they swing towards their closest point to the Sun along their highly eccentric orbits.
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Blobrana · L

Title: Rapid temperature changes and the early activity on comet 67P/Churyumov-Gerasimenko
Author: V. Alí-Lagoa, M. Delbo', G. Libourel

The so-called "early activity" of comet 67P/Churyumov-Gerasimenko has been observed to originate mostly in parts of the concave region or "neck" between its two lobes. Since activity is driven by the sublimation of volatiles, this is a puzzling result because this area is less exposed to the Sun and is therefore expected to be cooler on average (Sierks et al. 2015).
We used a thermophysical model that takes into account thermal inertia, global self-heating, and shadowing, to compute surface temperatures of the comet. We found that, for every rotation in the August--December 2014 period, some parts of the neck region undergo the fastest temperature variations of the comet's surface precisely because they are shadowed by their surrounding terrains. Our work suggests that these fast temperature changes are correlated to the early activity of the comet, and we put forward the hypothesis that erosion related to thermal cracking is operating at a high rate on the neck region due to these rapid temperature variations. This may explain why the neck contains some ice --as opposed to most other parts of the surface (Capaccioni et al. 2015)-- and why it is the main source of the comet's early activity (Sierks et al. 2015).
In a broader context, these results indicate that thermal cracking can operate faster on atmosphereless bodies with significant concavities than implied by currently available estimates (Delbo' et al. 2014).

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Blobrana · L

Comet 67P/Churyumov-Gerasimenko makes its closest approach to the Earth (1.768 AU) in the constellation Gemini on the 23rd August 2015

Blobrana · L

Comet 67P/Churyumov-Gerasimenko is at perihelion (closest approach to the Sun)(1.243 AU) in the constellation Gemini on the 13th August 2015.

Ephemeris

Date    TT    R. A. (2000) Decl.     Delta      r    Elong.  Phase   Mag
2015 08 10    06 16 50.0 +24 14 07   1.7748  1.2438    43.0    33.8  13.2
2015 08 11    06 20 55.3 +24 16 56   1.7737  1.2435    43.1    33.8  13.2
2015 08 12    06 25 00.4 +24 19 20   1.7727  1.2433    43.1    33.8  13.2
2015 08 13    06 29 05.0 +24 21 21   1.7719  1.2433    43.1    33.9  13.2
2015 08 14    06 33 09.2 +24 22 58   1.7711  1.2433    43.2    33.9  13.2
2015 08 15    06 37 13.0 +24 24 12   1.7704  1.2435    43.2    33.9  13.2
2015 08 16    06 41 16.2 +24 25 02   1.7699  1.2438    43.3    33.9  13.2
2015 08 17    06 45 18.8 +24 25 29   1.7694  1.2442    43.3    33.9  13.2
2015 08 18    06 49 20.7 +24 25 33   1.7689  1.2447    43.3    33.9  13.2
2015 08 19    06 53 22.0 +24 25 14   1.7686  1.2454    43.4    33.9  13.2
2015 08 20    06 57 22.5 +24 24 33   1.7684  1.2462    43.5    34.0  13.2
2015 08 21    07 01 22.2 +24 23 30   1.7682  1.2471    43.5    34.0  13.2
2015 08 22    07 05 21.1 +24 22 04   1.7681  1.2481    43.6    34.0  13.2
2015 08 23    07 09 19.1 +24 20 17   1.7681  1.2493    43.6    34.0  13.2
2015 08 24    07 13 16.2 +24 18 08   1.7682  1.2505    43.7    34.0  13.2
2015 08 25    07 17 12.3 +24 15 38   1.7683  1.2519    43.8    34.0  13.2
2015 08 26    07 21 07.4 +24 12 48   1.7685  1.2534    43.8    34.0  13.2
2015 08 27    07 25 01.4 +24 09 37   1.7688  1.2550    43.9    34.0  13.2
2015 08 28    07 28 54.3 +24 06 05   1.7691  1.2568    44.0    34.0  13.2
2015 08 29    07 32 46.2 +24 02 14   1.7695  1.2586    44.1    33.9  13.2
2015 08 30    07 36 36.8 +23 58 04   1.7700  1.2606    44.2    33.9  13.2
2015 08 31    07 40 26.3 +23 53 35   1.7705  1.2627    44.3    33.9  13.3