Philae, the first spacecraft to land on a comet, delighted scientists this weekend by waking up and reestablishing contact with Earth, seven months after running out of power. It “spoke” for more than a minute, according to the European Space Agency, and it’s expected to be able to continue gathering information and sending it home.
Here's a look at what the lander has done so far and what will happen next.
What is Philae?
Philae is a mobile laboratory the size of a washing machine. It was launched in March of 2004 from the Guiana Space Center in French Guiana, strapped to the side of the European Space Agency’s Rosetta orbiter. The pair was tasked with studying the mountain-sized comet 67P/Churyumov-Gerasimenko as it made its way toward the sun.
Together, they flew a looping trajectory through the inner solar system that lasted 10 years and covered nearly 4 billion miles. In August, they finally met up with 67P, which orbits the sun once every 6.5 years along a path that takes it roughly between Earth and Jupiter.
Rosetta spent a few months circling the comet, sending back images that would help scientists determine the best place for Philae to land. After a site was selected, Philae descended onto the comet’s surface in November.
Is Philae’s awakening a surprise?
After Philae’s first touchdown on the surface of the comet, it bounced twice before eventually settling into a shady spot where its solar panels were not able to receive sufficient sunlight to keep the lander operating. Scientists had hoped that as the comet approached the sun, the lander would get enough charge through its solar panels, but they didn’t know when or whether that would happen.
Why did Philae wake up now?
The comet finally brought it close enough to the sun. If Philae had landed at the intended site, it probably would have overheated and become useless by March, according to the ESA. But since Philae is in a shadowy spot, being nearer to the sun is what’s enabling it to power up.
The comet will travel closer and closer to the sun until August, when its orbit will pull it away again.
Where is Philae?
The lander’s exact location on the comet’s surface is unclear. Philae is so small that images taken by its mother ship, Rosetta, which is orbiting the comet, have not revealed its position.
What has Philae accomplished?
During its first 60 hours on the comet, when it was operating on battery power, Philae scooped up material from the comet's surface, took its temperature, sent radio waves through its nucleus and went hunting for hints of organic material.
Because comets are believed to be relics from our solar system’s earliest days, they can provide clues about the solar system’s formation. Scientists wonder, for example, how big a role magnetic fields played in causing the gas and dust that surrounded the young sun to clump together into objects such as planets and moons.
Measurements from Philae helped scientists find that the nucleus of comet 67P is not magnetized. If that’s representative of all comets, they concluded, “magnetic forces are unlikely to have played a role in the accumulation of planetary building blocks greater than one meter in size,” according to a study published in Science in April.
Philae also took the first panoramic images from the surface of a comet.
Philae’s first panorama from its point of final touchdown, with a superimposed sketch of the lander in what scientists believed was its position. (European Space Agency)
What did scientists find over the weekend?
On Saturday, Philae communicated for 85 seconds with the ESA team, sending a message to the Rosetta orbiter, which in turn beamed it across 190 million miles of space to Earth. However, the lander must have come out of hibernation before then, because there are more than 8,000 data packets in its memory, according to the space agency.
Philae phoned home again on Sunday, but this time the communication was just a few seconds long and less stable. Still, mission officials said this brief second contact was enough to confirm that the lander is in good condition.
“Philae is doing very well,” Stephan Ulamec, the space agency’s Philae project manager, said in a statement. “The lander is ready for operations.”
ESA officials are already working on new orbit trajectories for Rosetta that will optimize its ability to hear from Philae. Scientists also hope to find out exactly where on the comet it’s located.
After the health of the lander has been fully analyzed, engineers will slowly start turning on instruments, beginning with those that use the least energy and send the smallest bits of data back to Earth. The instruments that hammer and drill into the comet will be last on the list.
As it turns out, Philae’s unplanned bounce may have a silver lining: It should be operational during the time the comet is closest to the sun, a point called perihelion.
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