New surprises from the comet 67P/Churyumov-Gerasimenko

A section of the comet 67P/Churyumov–Gerasimenko’s smaller lobes seen by the Rosetta space probe (Image ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)
A section of the comet 67P/Churyumov–Gerasimenko’s smaller lobes seen by the Rosetta space probe (Image ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)

A special edition of the journal “Science” shows the results of the research done so far on the comet 67P/Churyumov-Gerasimenko using 7 of the 11 instruments of ESA’s Rosetta spacecraft. The various detections conducted between August and December 2014 have mostly confirmed the first impressions but reserved some surprises. Meanwhile, the comet is slowly approaching the Sun and its activity is increasing due to the higher heat that receives and causes more and more ice sublimation.

The various instruments of the Rosetta space probe allowed to otbain quite precise measurements of the comet 67P/Churyumov-Gerasimenko. Its mass was measured at around 10 billion tons with a volume of 21.4 km3 and a density of 470 kg/m3. The nucleus is formed by two lobes whose measures are 2.6 × 2.3 × 1.8 km (1.6 x 1.4 x 1.1 miles) for the small one and 4.1 × 3.3 × 1.8 km (2.5 x 2 x 1.1 miles) for the big one.

The observations had already uncovered the remarkable variety of geological features existing on the surface of the comet 67P/Churyumov-Gerasimenko. In some cases, it’s still difficult to explain their origin and in particular there’s still no definitive answer to the problem of its dual nucleus. The two lobes seem to have a very similar composition and this suggests that it’s a single nucleus which over time suffered a very strong erosion.

However, it’s not possible to rule out that the two lobes were initially two different comets whose nuclei merged creating the curious shape of the current nucleus. If this were the case, the two comets must have had a common origin to have a composition so similar.

The surface of the comet 67P/Churyumov-Gerasimenko had already turned out to be abnormally dark for a comet but the measurements were still some astonishing. The albedo, which is the amount of light reflected, of the surface turned out to be only 6%. Even the Moon has an albedo twice as much and this comet is one of the darkest objects existing in the solar system.

This means that the water ice, a substance normally present in large quantities in comets that greatly influences its albedo, is limited on its surface. The comet 67P/Churyumov-Gerasimenko still contains a lot of water but that on the surface probably has already been lost in space during previous trips in the inner solar system.

Other interesting results concern the chemical analysis of complex substances present on the comet 67P/Churyumov-Gerasimenko. Preliminary results showed the presence of compounds that made it smelly and left open the possibility that there were also organic materials. The spectroscopic analyzes showed the presence of polymers of carboxylic acids, which are present in amino acids. The fact that they were abundantly detected all over the surface suggests that they were abundant in the materials that formed the nucleus.

Because thouse compounds get formed elements such as methanol, methane or carbon monoxide must be present and they become solid at very low temperatures and get dispersed very easily as gases. This suggests that the comet 67P/Churyumov-Gerasimenko was formed at a great distance from the Sun when the solar system was in the early stages of its formation. This means that this comet contains trace of extremely ancient components, precisely what many scientists wanted to verify.

Other chemical elements are present much less homogeneously and this was discovered in the coma of the comet 67P/Churyumov-Gerasimenko that is forming due to the ice sublimation. In different areas there are different chemical compounds and there are also variations with the comet’s rotation.

The RPC (Rosetta Plasma Consortium) instrument of the Rosetta space probe was able to observe the development of an ionosphere and even a magnetosphere with the development of the coma of the comet 67P/Churyumov-Gerasimenko. Sublimated water molecules get ionized by the Sun’s ultraviolet light and these ions get accelerated by the solar wind’s electric field, creating the magnetosphere.

The discoveries made so far are very interesting but the Rosetta space probe keeps on working orbiting the comet 67P/Churyumov-Gerasimenko. The growing activity due to its getting closer to the Sun could allow to make other surprising discoveries, especially if there will be enough energy to awaken the lander Philae.

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