ARUN RATH, HOST:
Today, we're learning that there is life in space. The Philae lander was originally designed by the European Space Agency to send data back to Earth after landing on a comet. But before it could teach us much, it went radio silent. Some thought Philae was a goner. But the lander shocked everyone last night by sending its first message in seven months. Philae is alive. Mark McCaughrean is a senior science advisor at the European Space Agency. He joined us by Skype, and he explained what went wrong.
MARK MCCAUGHREAN: Well, Philae was landed on the surface and bounced a couple of times before it ended up in a gully and relied on its primary battery, which was charged up and lasted for 60 hours. But what we hoped for was that using the solar panels on Philae - that they were charging a secondary battery up, and we could use those batteries then to extend the mission for weeks, maybe even months.
That didn't happen, because we were in a shaded place. But what's happened now is as we've moved closer to the sun, the intensity of the sunlight is high enough now that we can charge the batteries.
RATH: When it went quiet, after it went quiet, did you have any expectation you'd be hearing from the lander again?
MCCAUGHREAN: Well, we always knew we were going to be moving closer to the sun. But there were two things going the other way. One was that we didn't really know - and we still don't know exactly where Philae is on the comet. And it's possible that as we move towards the sun, we actually - we see seasons on the comet. So the southern hemisphere is now being illuminated. And it was always possible that that gully might go into shade even more.
And the other downside - possible downside - was that by sitting cold for months at a time at minus 100 degrees or so or even colder, that the electrons might just freeze and break up. But we now know that that's not the case and it's warmed up far enough that everything's turned back on. And as of now, it's looking pretty good.
RATH: So tell us about how you first heard from the spacecraft and your reaction.
MCCAUGHREAN: The teams had first seen the signal appear on the incoming telemetry around 10:30 here. Of course, we were listening for it, but not expecting it at any given moment. So clearly there were people running around saying what have we seen? What is this? Is it what we hope it is?
I think we'd all - not began to write it off, but say, well, let's not get too excited about the prospects. So of course, you know, your heart rate goes up. And immediately, my wife - I woke her up and said look, you know, Philae's woken up. So it was great excitement. I let the kids sleep though. I waited for this morning for them.
RATH: You know, I can think of spacecraft that have overcome problems before, say, like, you know, a faulty antenna - something like that. But has one ever come back to life like this?
MCCAUGHREAN: In general, spacecraft, once they die, it's rare that they come back to life. In fact, there's a silver lining here, because if we had been on a flat piece of surface, full sunlight from November, we actually predicted the electronics would have warmed up to the point they would have broken from the heat from the sun by March. And so now we're actually at a more interesting time because the comet is approaching its nearest point to the sun on the 13th of August. And we're seeing the comet in a much more active time than we would've seen it between November and March.
RATH: So what's the future for Philae?
MCCAUGHREAN: We can actually study the comet now as it gets more active. And in the end, we're trying to piece together this whole puzzle, you know? What are comets made of? What kind of form of water is there in comets? Is it like the water we have on the Earth? Are there carbon-bearing molecules, things which actually are the building blocks of life?
The whole beauty of this mission is to try to understand the origins of the planet Earth and potentially of human beings and other life on the planet Earth.
RATH: Mark McCaughrean is a senior science advisor at the European Space Agency. Mark, congratulations and thanks very much.
MCCAUGHREAN: It's my pleasure. It's been great to talk to you. Transcript provided by NPR, Copyright NPR.