Inside the Hartley 2 comet

As we were talking yesterday about the Hartley 2 comet, we wanted you to find out more about this interesting space object. A few years ago a study on the comet Hartley 2, analyzing data from ground integrated with those of the NASA EPOXI mission revealed unexpected aspects on different “flavors” of ice of its heart.
It’s easy to define the comets “icy bodies” or “dirty snowballs”. It is true that in a comet prevails precisely the frozen component, but there is ice and ice and in the core of the Hartley 2 there would be more than one type. This is revealed by the results of the study, published in Astrophysical Journal Letters, the result of an international collaboration between universities and research institutes.


Credit: NASA/JPL-Caltech/UMD

The work was carried out starting from the analysis of data from ground-based telescopes supplemented by those collected as part of NASA’s EPOXI mission that has recycled the Deep Impact probe just to make a close encounter with Hartley 2 in November 2010.
Since we need, in the case of comets, to understand what’s inside we must study also what’s around. And the international group of researchers led by Michael Mumma of NASA’s Goddard Space Flight Center has focused the analysis of the crown, the “clothing” made of gas, dust and icy particles, which surrounds the core. It was thus possible to determine that the water ice is effectively a dominant component in Hartley 2 and that there are traces of many other molecules. The release of these ingredients in the hair depends on the exposure to the Sun and the fact that the core of the Hartley 2 rotates faster on itself and it ensures that each portion of the surface is affected in turn by the solar radiation. The group of Mumma noted that increasing the emission of water vapor, it will also increase that of other molecules. At this point, given that the overall composition of the gases of the crown does not change, it may be concluded that even that of the core is uniform.
However, we must deal with the data obtained from EPOXI, which intervene to complicate the picture. The pictures, taken during the close meeting, clearly show the jets of carbon dioxide and water ice emitted from only one of the ends of the comet. The jets are produced when the radiation of the Sun turn into gas the frozen carbon dioxide which is located below the surface. So, in addition to ice water, in the heart of Hartley 2 there is also that of carbon dioxide. And the variety of ice does not end here because, according to Mumma, probably in the nucleus another kind of ice is also present, namely the ethane ice. The ethane gas is released in a specific direction and this is what leads us to believe that it is, frozen, in a precise region of the nucleus.
These revelations about the composition of the heart of Hartley 2 have important implications on the study of comets, considered a kind of fossils of the solar system. Whether it’s a special case, or that this uneven nature is common to other comets, is a matter to be clarified. What matters is that Hartley 2 is now an important reference point for comparison.

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