(Image: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)
Comet-chaser Rosetta has lucked out with a two-for-one deal. Pictures from the European Space Agency (ESA) probe suggest that its target comet, Churyumov-Gerasimenko, is actually two icy rocks stuck together in an arrangement known as a contact binary.
鈥淭his is the reason we organise these missions, to find surprises,鈥� says of the Max Planck Institute for Solar System Research in G枚ttingen, Germany, who has set up a team to analyse results from Rosetta.
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Launched 10 years ago, Rosetta鈥檚 mission is to make the first-ever landing on a comet. This latest discovery could complicate the mission.
It鈥檚 not yet clear whether these are two different comets that have come together, or parts of a single comet that fractured but remained gravitationally bound.
Conjoined twin
Alternatively, the two components could have formed together, but been joined at an angle because of rotation during the formation process. 鈥淭hree of the five comets we鈥檝e flown past seem to be made of two chunks, so maybe there is a trend,鈥� says Lacerda.
The plan is for Rosetta to reach the comet this August and then land a smaller probe, Philae, on its surface in November. ESA will need to carefully assess possible landing zones, but Churyumov-Gerasimenko鈥檚 unusual shape might rule out some locations. Lacerda says he would like to land close to the contact point to explore. 鈥淔rom an engineering point that may actually be quite tricky,鈥� he says.
Checking out both parts might have benefits, however. Comets are frozen remnants left over from when planets formed 4.6 billion years ago, so studying them can reveal the early era of our solar system. If the two parts of Churyumov-Gerasimenko do indeed have different origins, Rosetta will get to study two ice balls for the price of one and get a better look at the past.
鈥淚t was chosen as a comet that is interesting but not too crazy,鈥� says Lacerda. 鈥淭he fact that it is a binary adds a little bit to the crazy side of things, and that鈥檚 good.鈥�
