Astronomers Cheer 'Audacious' Landing on Comet

TUCSON, Arizona—Scientists packed into a hotel conference room erupted in celebration Wednesday morning on word of the first soft landing of a spacecraft on a comet. Primed by early views of the comet, the successful landing promises answers to vexing mysteries about these icy visitors from deep space.

"You couldn't ask for a better crowd to watch a landing with," said planetary scientist Morgan Rehnberg of the University of Colorado in Boulder, who was among the scientists applauding at the ongoing American Astronomical Society's Division for Planetary Sciences meeting. (See "Touchdown! Comet Landing to Offer Clues to Solar System Origins.")

Scientists at the meeting weren't just delighted with the landing as a spectacle. They have already had an early taste of the science it will deliver.

Earlier in the week, Timothy Bowling of Purdue University in West Lafayette, Indiana, reported preliminary results about comet 67P/Churyumov-Gerasimenko that show how its gravity, hundreds of thousands of times weaker than Earth's, varies wildly over its surface. The variation is caused by the comet's odd shape, often compared to a rubber ducky in space.

That same weak gravity makes the harpoons to anchor Philae important. Even a slight bounce triggered by its camera's motion or other jostling might lift Philae off the comet's surface, or cause it to slide. (For more on the landing, also see our Viewing Guide.)

Shortly after the landing, the European Space Agency announced that those harpoons had failed to fire as Philae settled on the 4.1-mile-wide (6.7 kilometers) dual-lobed comet.

Other researchers had reported with surprise at the meeting that the surface of the "neck" of the comet connecting its two lobes appeared roughly 40 percent brighter than the rest of the space snowball. They speculated that ice percolating off the surface of the comet on its travels had collected to drape around its neck.

Rosetta scientist Nicolas Thomas of the University of Bern, Switzerland, had reported at the meeting that these ice particles sputter from the comet at speeds just under 1.2 miles (2 kilometers) per hour. Some of that ice may drift back down onto the comet and shift down to the thin neck of comet 67P.

Comet Cacophony

As befits the modern world, the scientists at the planetary meeting first learned the happy news from Twitter. Tweets announced the successful touchdown of the Philae lander on comet 67P/Churyumov-Gerasimenko at 11:03 a.m. EST.

"Everyone was very excited," said radar science expert Alessondra Springmann of the University of Arizona's Lunar and Planetary Laboratory in Tucson. "I think a lot of the people here understand how much work goes into a mission like this one."

Moments before news of the landing arrived at the science meeting, hundreds of experts had overwhelmingly indicated, by show of hands, their expectation that the landing would be successful.

"We know these guys. You don't root against your own team," Rehnberg said.

Along with the rest of the world, the scientists at the meeting are hungry for more news from Philae and its comet. Radar measurements of the surface should reveal the structure of the soft comet's interior. If all goes well, the lander will hold fast and reveal changes to the comet as it draws toward its point of closest approach to the sun, some 116 million miles (186 million kilometers) away, in August of 2015.

Soft Landing

The arrival of the Philae lander serves as the "cherry on the cake" of the $1.74 billion Rosetta spacecraft's ten-year mission to explore comets, said the European Space Agency's Alvaro Giménez, in comments before the landing.

ESA officials have also raised the possibility of landing the entire Rosetta orbiter on the surface of the comet in 2016, after it runs out of fuel, similar to the 2001 soft landing of a NASA spacecraft on the large asteroid Eros.

There it would join the lander, designed to report from the surface of the comet as it loops around the sun, observing changing conditions on the muddy iceball some 235 million miles (378 million kilometers) away from the sun.

"How audacious, how creative, how exciting to dare to land on a comet," said NASA's Jim Green at the ESA briefing on the landing. "It is the start of something important."

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