WALL STREET JOURNAL

Rosetta Mission’s Probe Lands on Comet

European Space Agency’s Philae Is First Craft to Land on Comet in Historic Moment for Space Exploration

Scientists are nearing the crucial moment when the Rosetta space probe attempts to land on a comet.  Gautam Naik explains how this will be done. Photo: ESA

DARMSTADT, Germany—A robotic probe has become the first craft to land on a comet, a historic moment for space exploration and one that offers the promise of fresh insights into what comets are made of and how they behave.

Rocket scientists at the European Space Agency’s mission control here erupted in cheers as they received the first signal that the Rosetta mission’s probe, called Philae, had touched down on the forbidding landscape of a small comet known as 67P/Churyumov-Gerasimenko.

Rosetta’s lander, Philae, took this parting shot of its mothership shortly after separation.
Rosetta’s lander, Philae, took this parting shot of its mothership shortly after separation. ESA/Rosetta/Philae/CIVA

It is still not clear where exactly the probe has landed or if it was damaged.  Philae, which is about the size of a small fridge, was aimed for a relatively flat elliptical landing area about 550 yards in diameter, away from deep crevices, large boulders and sharp peaks.

If it landed intact, Philae is expected to quickly snap a few photographs and beam them back to Earth—in the first images ever taken from the surface of a comet.  (It takes nearly half an hour for a signal from the comet to reach earth.)

The comet has extremely low gravity.  To prevent the probe from bouncing back into space, it carries a pair of harpoons designed to fire immediately and fix the probe to the ground.  A thruster on the top was simultaneously expected to push the probe downward to help in the anchoring, but scientists discovered overnight that the thruster couldn’t be activated and that the harpoons would have to do the job alone.

Made of ancient ice, dust and other materials, comets are objects of scientific curiosity because they have survived virtually intact from the earliest days of the solar system, more than 4.6 billion years ago.

Because comets carry water and organic molecules, scientists also hope that the Rosetta mission will provide insights into whether comets could have brought water to Earth and possibly kick-started life here.

After a decadelong trek through the solar system, the spacecraft Rosetta made a rendezvous with the comet in August.

Corrections & Amplifications

Confirmation of the Rosetta probe’s successful touchdown on the comet is expected in a one-hour window around 1602 GMT (11:02 a.m. ET).  An earlier version of this article and a headline incorrectly said confirmation is expected around 1702 GMT (12:02 ET).  (Nov. 12, 2014)

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