Humanity just landed a spacecraft on a comet

After 10 long years on Rosetta's back and a 7-hour fall toward its target, the Philae lander anchored itself to the surface of a comet

Just after 11AM ET, the European Space Agency's Philae lander made contact with the surface of a comet. The 250-pound probe settled on a patch of the 2.5-mile-long comet and sent a signal home, ESA said.

Philae left Earth a decade ago, hitching a ride on ESA's Rosetta orbiter. About seven hours ago, Rosetta released the washing-machine-sized probe, and it began to fall toward its target, a comet called 67P/Churyumov–Gerasimenko. Though the landing site was selected to ensure minimal debris, it was possible that Philae wouldn't stick the landing — especially after the head Rosetta lander, Stephan Ulamac, said yesterday that Philae's thrusters, meant to stabilize the craft as it landed, might not work.

"You have all heard Philae has landed," says Jean-Jacques Dordain, ESA's director general. "This is a big step for human civilization. This is terrestrial intelligence that makes a difference."

The harpoons meant to anchor Philae did not shoot, so although we know for sure it's on the surface, it may not stay there, ESA officials said on the livestream. The team is now looking at ways to reshoot the harpoons to make sure it stays on the surface. Based on the pressure of the landing gear when Philae touched, though, it was a gentle landing.

Philae in flight, as seen from Rosetta (ESA)

No spacecraft has ever before had a controlled landing on a comet, though NASA's Deep Impactslammed a probe into one in 2005 to find out what composed the comet's core.

After Rosetta launched in 2004, it orbited earth three times, using our planet's gravity as a slingshot to propel Rosetta to the speed required to catch 67P. Rosetta is powered by solar panels, but, at its farthest point from the sun, it got only about 3 percent of the sunlight we get here on Earth. To conserve power, scientists designed it to go into a kind of hibernation,with only the most vital functions running. In January, Rosetta woke up, and in August, it caught 67P/Churyumov–Gerasimenko.

COMETS ARE ICY CHUNKS OF ROCK LEFT OVER FROM THE PLANETS' FORMATIONComets are important to explore because the icy chunks of rock are left over from the planets' formation more than 4.6 billion years ago. "Comets have the beauty of having preserved the ingredients with which the solar system formed," Jean-Pierre Bibring, Philae's lead scientist, said last night. The complex molecules thought to be the initial building blocks for life may be preserved in 67P's ice, according to Bibring. Philae a little more than 60 hours at full power to run experiments using its 10 on-board instruments before its batteries drain. If the lander isn't stuck in a shadow, Philae's solar panels will recharge the craft.

Rosetta has already gathered an unprecedented amount of information about 67P; no comet has been followed as long. The orbiter has discovered the comet's personal scent,composed mainly of rotten eggs with notes of horse urine and formaldehyde. Rosetta has also been tracking 67P as the comet's surface temperature increases and it sprays off more water.

Rosetta, which cost €1.4 billion (about $1.75 billion), will accompany 67P around the sun and may supply more years of data. Its mission ends in December 2015, after it flies with the comet to its closest pass with the sun in August, according to ESA.

• SOURCEESA