Year in review: Rosetta mission hits its target

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With a hop and a skip, a robot called Philae bounded onto comet 67P/Churyumov-Gerasimenko, perhaps a bit too eager to explore the alien world.

The touchdown on November 12, amid cheers and tears on Earth, marked the first time scientists have set a probe on a comet. But the jubilation was short-lived. Philae’s boisterous bounces landed the robot slightly sideways in the shadow of a cliff, making it impossible for its solar panels to get enough sunlight to recharge its batteries. After about 50 hours of scratching and sniffing 67P’s surface, Philae transmitted its last batch of data and settled in for a long, potentially permanent, sleep.

If all had gone perfectly, Philae would have studied the comet’s surface until March 2015. But the lander’s apparent early retirement didn’t mark the end of the European Space Agency–led mission to get an in-depth look at the 4-kilometer-long hunk of dust and ice (SN Online: 11/13/14). The Rosetta spacecraft (illustration, inset) arrived at the comet on August 6 carrying Philae (SN: 9/6/14, p. 8). The craft is still zooming around 67P, doing its own set of studies, scrutinizing the comet’s hazy atmosphere, snapping images of the surface and trying to pinpoint the lander’s final resting place.

Even in its brief life on 67P, Philae offered hints about some of the comet’s secrets. The lander beamed back evidence supporting the idea that comets carried, and possibly even spread, organic molecules throughout the early solar system (SN: 12/13/14, p. 6). The robot also hammered just 10 to 20 centimeters into the surface of the comet and hit a surprisingly hard layer of material, thought to be ice. The discovery suggests that some of the dust ejected from 67P when it approaches the sun and heats up stays gravitationally bound to the comet and falls back to form a thin surface layer. The finding also hints that 67P’s core may be layered.

“There are a number of different ideas about how the nucleus of the comet could be structured — whether it’s layered, whether it’s one bound entity or a group of aggregated bodies together that are covered in a surface,” says Rosetta project scientist Matt Taylor, who is based in Noordwijk, Netherlands.

Understanding the comet’s structure and composition could give scientists clues to how the planets formed and whether comets brought water and other ingredients for life to Earth (SN: 11/1/14, p. 22). Observations may also reveal what’s in the cauldron of chemicals that’s created when the comet shoots out gas and dust as it nears the sun, Taylor says.

Rosetta is slated to stay with 67P until December 2015 and will be ringside for the comet’s closest approach to the sun, in August. Rosetta may also relay any messages that Philae ekes out as the comet nears the sun and exposes the lander’s solar panels to more light, potentially enough to revive it.

Data from 67P will force scientists to rethink what they know about comets, says ESA scientist Mark McCaughrean, who is also based in Noordwijk. This mission will certainly not be the last word on these unpredictable beasts, he says. “You can be damn sure that the people working off the back of this will be thinking of what to do next.”