SPACE exploration is a serious scientific business. But ever since the beginning of the Space Age in the 1950s, it has been accompanied by a hefty dose of glitz and PR. Two years ago Earthlings watched with bated breath as a two-tonne, nuclear-powered, laser-armed robot rover fizzed through the Martian atmosphere, before being deposited gently on the surface by a rocket-powered 'skycrane'. The distance between Mars and Earth meant that the mission's controllers had to wait seven agonising minutes to find out whether the rover had survived re-entry. Their fingernail-biting was broadcast live by NASA. When news arrived of a successful landing, they whooped, hugged and lit cigars.
Now, it the European Space Agency's turn to put on a show. In August, after ten years blazing a circuitous trail through the solar system, including three fly-bys of Earth, one of Mars, two trips through the asteroid belt and a two-and-a-half year hibernation in the chilly void beyond Jupiter, a spacecraft called Rosetta caught up with its quarry, a 4km-long comet called 67P/Churyumov-Gerasimenko. Then, at 08.35 GMT on November 12th, a boxy probe the size of a washing machine, called Philae, separated from Rosetta and began a careful, nerve-jangling descent towards the comet's surface. Seven and a half hours later, at 16:05 GMT, Philae reported that it was down. The Europeans were more restrained in victory than NASA had been, confining themselves to a couple of cheers and an enthusiastic ripple of applause.
Philae's success marks the first time people-or, rather, their robotic representatives-have made a soft landing on anything other than a planet or a moon. It raises the number of objects on which this has been accomplished to five (besides 67/P, the others are Earth's Moon, Venus, Mars and Titan, a satellite of Saturn).
Engineers are reasonably comfortable with sending probes to big targets like planets and moons, which have useful features like an atmosphere to slow their descent, and gravity strong enough to ensure that once a probe reaches the surface, it stays there. Comets have neither, and that makes things tricky. Philae was nudged gently away from Rosetta at a speed of about 80 centimetres a second, and left to drift towards the comet under the influence of that object's feeble gravity.
Ensuring the probe landed on the relatively smooth area of the cometary surface chosen by ESA's scientists was tricky. Philae had no ability to control its own descent, which meant that everything depended on the accuracy of Rosetta's initial shove. That meant luck played an uncomfortably large part in the landing: the mission's scientists had been worried Philae would come down on top of a boulder, or on the edge of a rocky cliff, causing it to tumble over uselessly onto its back.
Once it reached the surface, the next trick was making sure it stayed there. The comet's gravity is so low that even a slight bounce could have sent the probe careering back into space. The failure of a small stabilising jet, designed to prevent just such a bounce, did not help anyone's nerves. In the event, though, everything else went to plan. At touchdown Philae fired a pair of harpoons into the comet's surface, anchoring itself in place.
The mission is more than a bravura display of deep-space engineering. Rosetta's genesis dates back to 1986, when Halley's Comet made one of its regular forays into the inner solar system and Europeans, Soviets and Japanese alike sent fly-by probes to take a look. Instead of a fly-by lasting a few days, Rosetta will spend a year in orbit around 67/P, hitching a ride as the comet plunges towards the sun. Philae will not be so long-lived, but its controllers hope it will last for several months. It will drill into the comet, taking samples of its crust and attempting to work out exactly what it is made of (is it mostly rock and ice with a few pockets of gas, or is it a loose pile of rubble held together by gravity?).
Researchers are interested in comets because they are space-going fossils, the builder's rubble left over from the construction of the solar system 4.5 billion years ago. That means they should preserve fascinating information about just how the solar system came together. One theory, for instance, holds that it was cometary impacts which seeded the newly formed Earth with much of its water. Another holds that comets are the source of the complicated, carbon-based molecules that were the building blocks of life on the primitive Earth. Instruments aboard Rosetta and Philae should be able to address those questions directly. After ten years, the nail-biting engineering is over, and it is time for the science to begin.
Entities 0 Name: Rosetta Count: 4 1 Name: Earth Count: 4 2 Name: NASA Count: 2 3 Name: Rosetta and Philae Count: 1 4 Name: Philae Count: 1 5 Name: Earth 's Moon Count: 1 6 Name: Jupiter Count: 1 7 Name: Halley Count: 1 8 Name: ESA Count: 1 9 Name: European Space Agency Count: 1 10 Name: Venus Count: 1 11 Name: Saturn Count: 1 Related 0 Url: http://ift.tt/1EsMned Title: It's Showtime! Philae Probe Revs Up for Historic Comet Landing - NBC News Description: An electronics-filled box about the size of a washing machine is gearing up to make the first-ever controlled landing on a comet - and you can watch the drama unfold on the Web.
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