Europe's Rosetta comet probe has revealed that its target, Comet 67P/Churyumov-Gerasimenko, has a Siamese twin, a thrilling discovery for scientists preparing for Rosetta's August rendezvous and a huge challenge for engineers figuring out how to land a small probe onto the comet in November.
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Technically, the comet is what's called a "contact binary," comprised of two differently sized nuclei joined together.
France's Centre National d'Etudes Spatiales (CNES) released the images - prematurely, apparently - because they have since been removed from its website. But not before sharp-eyed Planetary Society blogger Emily Lakdawalla nabbed them, along with a press release estimating the comet's twin nucleus measures about 2 miles by 2.5 miles.
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Philippe Lamy, with the Laboratoire d'Astronomie Spatiale in France, apparently calculated that the comet bodies would have had to come into contact with each other at a relatively slow speed of 6.7 mph to meld together the way it has.
Like any parent confronting the prospect of twins, the surprising discovery presents complications.
Rosetta includes a small lander named Philae that is designed to harpoon itself to the comet's body several months after the mother ship reaches orbit in August. The comet's odd shape, however, could make finding a suitable landing spot more difficult.
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"This form restricts potential landing zones," Philae navigator Eric Jurado is quoted as saying in a CNES press release.
At the time of landing, slated for November 2014, the comet will be about three times as far from the sun as Earth and heading inward. After about three months, heating from the sun most likely will end Philae's mission.
The Rosetta mothership, however, which will be conducting both independent and collaborative studies with the lander, is expected to remain operational at least until the end of 2015.