麻豆传媒

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DESPITE the fantastic success of the European Space Agency鈥檚 Rosetta spacecraft, which has been hanging out around comet 67P/Churyumov-Gerasimenko for over six months, mission researchers had until now released only a few findings.

Now, the team has 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 hard to use a latitude and longitude system, so the Rosetta team has split the 4-kilometre-long comet 67P into 19 regions named after ancient Egyptian deities, like Seth and Anubis.

Pain in the neck

The Hapi region on 67P鈥檚 鈥渘eck鈥� hosts the only visible crack in the comet鈥檚 surface, which is about 1 kilometre long and a few metres wide. An on going mystery is whether the two halves were once separate comets that merged, or a larger comet that eroded slowly.

Comets have goosebumps

Some parts of 67P are dotted with lumps that Holger Sierks, who runs Rosetta鈥檚 OSIRIS camera, and colleagues call 鈥済oosebumps鈥�. They may be formed when tiny grains of dust floating in space get drawn together into 鈥減ebbles鈥� about 3 metres wide. These pebbles can only grow larger by merging with others, eventually forming a larger body like 67P.

Fluffy duck

New figures for the comet鈥檚 mass and volume peg its density at roughly 500 kilograms per cubic metre, about the same as cotton wool. This fluffy material is hard to hold onto 鈥� 67P loses around 4 billion kilograms, 0.01 per cent of its mass, on each six-and-a-half-year orbit around the sun.

Sniffing out the seasons

The comet鈥檚 rotation gives it seasons. It is currently 鈥渟ummer鈥� on 67P鈥檚 head, so some parts of the body are in 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 near the head, and more carbon dioxide around 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 because they release different gases seasonally.

Dust in the wind

It was a bit puzzling to find dune-like structures and other features seemingly formed by wind when pictures of 67P first arrived, because its scant atmosphere shouldn鈥檛 be able to support even a slight breeze. But it seems 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.

Black as night

67P reflects just 6 per cent of the sunlight that hits it, so the comet鈥檚 nucleus is one of the blackest objects in the solar system. This darkness is partly due to its carbon-rich surface, which contains organic compounds like carboxylic acid 鈥� found in the amino acids needed for life. Also, Rosetta hasn鈥檛 seen any reflective icy patches on 67P鈥檚 surface, meaning the first millimetre or so contains very little water 鈥� unsurprisingly, as it probably would have been stripped off during previous passes by the sun.

All change

A paper published this week in the journal Nature suggests the comet may be shedding this surface (). Remote observations during 67P鈥檚 last jaunt around the solar system in 2008 suggest that, when it comes within 400 million kilometres of the sun, it starts kicking off its outer dusty layer to reveal a mixture of ice and dust. This probably happened again within the past month. The dust particles Rosetta has collected so far have crumbled after hitting its COSIMA instrument, meaning they don鈥檛 contain ice. The team is still waiting for new data to confirm the wardrobe change.

Finding Philae

The Science papers give no update on attempts to spot the Philae lander, which touched down in November before its batteries died a few days later. But Sierks told 麻豆传媒 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 67P鈥檚 seasons will shift, illuminating the shadowy part of the comet where the probe landed. The hope is that light will fall on Philae鈥檚 solar panels, letting it reactivate and resume contact. But even if the lander slumbers on, the view of 67P鈥檚 dark side is something to look forward to, Sierks says.

This article appeared in print under the headline 鈥淪ummer holiday around a comet鈥�