The European Space Agency鈥檚 Rosetta spacecraft has been hanging out around comet 67P/Churyumov-Gerasimenko for over six months, and in November unleashed probe Philae to successfully touch down, captivating the world. Despite that, the mission researchers had so far only released a handful of scientific findings.
Now, the team have published seven reports in the journal Science covering data from August and September. Here are our favourite bits:
Egyptian gods rule 67P
The comet鈥檚 duck-like shape makes it difficult to come up with a system of latitude and longitude as used on other, more spherical solar system bodies. So the Rosetta team have split 67P into 19 regions named after ancient Egyptian deities, like Imhotep and Anubis.
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Pain in the neck
The Hapi region of 67P鈥檚 鈥渘eck鈥� hosts the only visible crack in the comet鈥檚 surface, which is around a kilometre long and a few metres wide. An on-going mystery is whether the two halves of 67P were once separate comets that merged, or the result of a larger comet eroding over time.
Comets have goosebumps
Some parts of 67P, particular steep slopes, are dotted with lumps that , who runs Rosetta鈥檚 OSIRIS camera, and colleagues have dubbed 鈥済oosebumps鈥�. All of the bumps are around 3 metres wide, which suggests something is limiting their growth. One possibility is that tiny grains of dust and gas floating in space are drawn together into 鈥減ebbles鈥� of this size, but can only grow larger by merging with others, says Sierks, eventually forming a larger body like 67P. The goosebumps would be the pebbles which survived this process intact, but the whole comet could be riddled with them.
Fluffy duck
New measurements of the comet鈥檚 mass and volume peg its density at roughly 500 kg/m鲁, or around that of cotton wool. This fluffy material is hard to hold on to 鈥� 67P loses around 4 billion kilograms, a ten-thousandth of its mass, every time it orbits the sun in six and a half years. That鈥檚 the equivalent of spitting out the Great Pyramid of Giza every orbit. In its first few months, Rosetta has managed to grab 353 grains of dust shed by the comet and found that it spits out around four times as much dust as it does gas.
Sniffing out the seasons
The comet rotates around an axis that is angled relative to the sun, giving it seasons. It鈥檚 currently 鈥渟ummer鈥� on 67P鈥檚 head, leaving some parts of the base of the body in permanent darkness. That means the comet鈥檚 coma 鈥� its transient atmosphere 鈥� varies from place to place.
Rosetta鈥檚 ROSINA spectrometer sniffed the coma and found higher concentrations of water from the head, and more carbon dioxide from the body. Kathrin Altwegg, who runs ROSINA, says they are still figuring out whether this is because the two halves have a different origin, or whether temperature differences caused by the comet鈥檚 seasons mean they are releasing different gases.
Dust in the wind
Dune-like structures and other surface features seemingly formed by wind were a bit of a puzzle when pictures of 67P first arrived, as its barely-there atmosphere shouldn鈥檛 be able to support even a slight breeze. But it seems that the low-density gas released by the comet is blowing fast enough to shift tiny particles around. It鈥檚 also possible that charged dust is being levitated across the surface by low-level electrical fields, a process that .
Black as night
Data from another Rosetta spectrometer 鈥� VIRTIS 鈥� reveals 67P reflects just 6 per cent of the sunlight that hits it, making the nucleus of the comet one of the blackest objects in the solar system 鈥� the greyish photographs you鈥檝e seen have been contrast boosted to reveal hidden details. This darkness is partly due to its carbon-rich surface, says VIRTIS lead researcher Fabrizio Capaccioni, which includes organic compounds like carboxylic acid. This is a component in amino acids, molecules necessary for life. VIRTIS also sees no reflective icy patches on 67P鈥檚 surface, meaning the first millimetre or so contains very little water 鈥� unsurprisingly, as it was likely stripped off during previous passes by the sun.
Finding Philae
The Science papers don鈥檛 include an update on attempts to spot the Philae lander, but Sierks told New 杏吧原创 that a dedicated imaging campaign in December was unsuccessful, and Rosetta鈥檚 busy science schedule leaves no time to search again until May. That鈥檚 also when the seasons on 67P will shift, illuminating the shadowy part of the comet where the probe, which has solar panels, landed. The hope is it will be reactivated and resume communication. 鈥淚 fear we will have to wait for Philae to wake up,鈥� says Sierks. But even if Philae slumbers on, the new view of 67P鈥檚 dark side is something to look forward to, he says.
Journal reference: Science, DOI:
