After almost two years’ of searching, the European Space Agency’s Rosetta spacecraft has shown scientists what happened to the Philae lander when it bounced onto the surface of a comet – and why it went out of contact.
The answer to the mystery comes less than a month before the $1.4 billion Rosetta mission’s end.
Rosetta’s OSIRIS camera spotted the boxy, 3-foot-wide Philae lander stuck in a dark crack on Comet 67/Churyumov-Gerasimenko, more than 420 million miles from Earth.
The comet has been the object of Rosetta’s study since August 2014. Philae was pushed out from the main spacecraft and descended to the surface that November. The lander was supposed to beam up a stream of data about the comet’s composition. It did provide three days’ worth of data, but then the solar-powered probe fell silent.
Rosetta’s scientists determined that the lander had bounced on the surface, and spent months analyzing radio data and imagery from the main spacecraft in an attempt to figure out where it ended up. They assumed that Philae had fallen someplace dark where it couldn’t recharge its batteries.
Long-range pictures weren’t sharp enough to show Philae. The lander did send out some brief radio transmissions in June and July of last year, but not enough to let scientists nail down its location. Finally, on Sept. 2, Rosetta solved the mystery – and the explanation turned out to be just as scientists guessed.
In a picture taken on Sept. 2 from a distance of 1.7 miles, the lander shows up clearly, wedged in a crevice in a region known as Abydos. The picture shows two of the spacecraft’s three landing legs extended toward the rugged sides of the crevice.
The key to the discovery was that Rosetta is circling closer to the comet in preparation for its final data-gathering descent on Sept. 30, which will end with its own crash onto the surface.
“With only a month left of the Rosetta mission, we are so happy to have finally imaged Philae, and to see it in such amazing detail,” OSIRIS team member Cecilia Tubiana said today in a news release. ESA says Tubiana was the first person to see the images when they were downlinked from Rosetta on Sunday.
“It is incredible we have captured this at the final hour,” said Patrick Martin, ESA’s Rosetta mission manager.
Matt Taylor, ESA’s Rosetta project scientist, said there’s significant scientific value in figuring out precisely where Philae fell.
“This wonderful news means that we now have the missing ‘ground-truth’ information needed to put Philae’s three days of science into proper context, now that we know where that ground actually is!” he said.
Philae found that the ground where it landed was covered with coarse material such as pebbles and rocks rather than the dust deposits that scientists had expected. The lander tried to drill into the surface but soon encountered solid ice. Those observations make perfect sense, now that scientists are seeing the rugged crevice on Rosetta’s imagery.
Readings from Philae also told scientists that the comet contained lots of water ice and frozen carbon dioxide, along with a mix of 16 carbon-containing organic compounds. Under the right conditions, such chemicals could serve as the building blocks for life.