DARMSTADT, Germany — After a suspense-packed, seven-hour descent, the European Space Agency's Philae lander made an unprecedented touchdown on the surface of a comet Wednesday — marking the high point of a $1.3 billion, 10-year mission.
Officials confirmed early Thursday that Philae was sending data back from the comet — including images.
Paolo Ferri, the head of mission operations at ESA, said: "It was transmitting data from the moment we came around the horizon, we are getting all the science data we wanted and got pictures from the surface that we were waiting for. We know it is stable on the surface, it is transmitting data, it is doing what it is supposed to do."
Cheers erupted as the confirming signals were received at the European Space Operations Center in Darmstadt, Germany, at 11:03 a.m. ET onn Wednesday. The signals took 28 minutes to travel at the speed of light over the 317 million miles (510 million kilometers) between Comet 67P/Churyumov-Gerasimenko and Earth.
Philae was released for its descent seven hours earlier by ESA's car-sized Rosetta spacecraft, which has been keeping pace with the comet since August. The boxy lander, which is about the size of a washing machine, made its way to the comet's surface at a leisurely walking pace — roughly 2 mph (1 meter per second).
At the end of the trip, a cold-gas thruster system was supposed to be fired to hold the lander steady and keep it from bouncing off the surface, while harpoons were shot into the comet to secure it in place. But mission managers said readings from the lander suggested that the thruster system was not properly activated.
Let our news meet your inbox. The news and stories that matters, delivered weekday mornings.
After the landing, the team said telemetry data from Philae indicated that the harpoons did not engage. "Some of these data indicated that the lander may have lifted off again," said Stefan Ulamec, Philae lander manager at the DLR German Aerospace Center Ulamec. Although not conclusive, the readings suggested that the lander may have bounced a bit, turned slightly and settled back down in a different position.
'"So maybe today we didn't just land once, we landed twice," Ulamec said. Further data would confirm the sequence of events and help mission managers figure out what to do next, he said.
The landing served as the climax of a mission that was launched more than 10 years ago and involved a 4-billion-mile (6-billion-kilometer) journey to the comet.
The car-sized Rosetta spacecraft reached its rendezvous point in August. Since then, the mission team has been mapping the planned trajectory for the 220-pound (100-kilogram) Philae lander, which is about the size of a washing machine.
Dignitaries lined up at the Darmstadt mission control center to hail Wednesday's achievement:
"A small jump for a robot, a giant leap for mankind, and for Europe," said Roberto Battiston, president of the Italian Space Agency.
"Hollywood is good, but Rosetta is better," quipped David Parker, chief executive of the UK Space Agency.
"How audacious, how exciting, how unbelievable to be able to dare to land on a comet. ... It is the start of something very important: The solar system is mankind's. This mission is the first step to take it," said Jim Green, director of NASA's Planetary Science Division. NASA has provided several scientific instruments for the Rosetta mission.
As Philae descended toward the 2.5-mile-long (4-kilometer-long), rubber-ducky-shaped comet, it headed for a spot that was dubbed Agilkia. That name and the lander's name are both inspired by Egyptian islands that figure in the story of the Rosetta Stone, which archaeologists used in the 19th century to decipher ancient hieroglyphs.
Similarly, the Rosetta mission is aimed at deciphering the chemistry of the early solar system. Comet Churyumov-Gerasimenko is thought to preserve leftovers from the solar system's formation 4.5 billion years ago — and a detailed analysis of the comet's ice and dust could provide fresh insights into those origins.
The lead scientist for the Philae lander mission, Jean-Pierre Bibring of France's Institut d'Astrophysique Spatial, said the comet's chemistry could conceivably be compared someday with readings from other planetary systems. "This should tell us some clues as to whether we are alone in the universe," he said during an ESA webcast.
To gain those deep insights, the mission team intends to have Philae drill down into the comet, extract samples and analyze them using an array of scientific instruments. Cameras, sounding devices and a magnetometer will characterize the comet as well. The images and data are to be beamed up to Rosetta and relayed back to Earth.
Philae's journey was closely watched because it represented first attempt to make a controlled landing on a comet's nucleus. The best precedent for such a feat is NASA's Deep Impact mission, which sent a probe barreling into Comet Tempel 1 in 2005. That impactor probe was destroyed on impact. Two other space odysseys — NASA's NEAR Shoemaker mission and Japan's Hayabusa mission — sent spacecraft to make soft landings on asteroids (Eros and Itokawa, respectively).
Even if Philae's mission is cut short, ESA says Rosetta could still achieve most of its scientific objectives by studying Comet Churyumov-Gerasimenko from a distance. Rosetta is expected to monitor the comet for another year as it makes its way around the sun.
"The coming months will be incredible with the changes in the comet," said Ferri. Eventually, Rosetta itself may settle down to a resting place on the comet's surface.