The Philae lander makes its descent to comet 67P/Churyumov–Gerasimenko (Image: ESA)

Update 12 November 2015 20:31: In a press briefing, landing manager Stephan Ulamec confirmed that Philae’s anchoring harpoons did not fire. Some data indicates that the lander may have bounced and rotated before touching down again. “Maybe today we didn’t just land once, we landed twice,” Ulamec says. A press briefing is scheduled for 1300 GMT tomorrow.

Original article, published 12 November 2015 18:13

Cheers, hugs and an explosion of joy marked the announcement that the European Space Agency’s Philae lander had safely touched down on a comet – a world first.


“We are there and Philae is talking to us,” said landing manager Stephan Ulamec, from the European Space Operations Centre in Darmstadt, Germany. “We are on the comet!”

The landing was not perfect, though: an issue with a gas thruster and harpoons intended to help Philae grapple with the surface means that the craft may not be firmly anchored to the comet.

Paolo Ferri, head of mission operations, says that Philae might be moving around on the comet’s surface, perhaps even sliding – but it is unlikely to bounce off. “Frankly, given it has been on the surface for a few hours now, I would be very surprised,” he says.

Watch our live blog for further updates.

Philae and its companion spacecraft Rosetta have spent the last 10 years travelling to comet 67P/Churyumov-Gerasimenko, some 500 million kilometres from Earth, and that distance means it takes 28 minutes and 20 seconds for signals from the spacecraft to reach us.

Gentle descent

At 0835 GMT on 12 November, the Philae lander separated from Rosetta and began a 7-hour descent to the surface of the comet. It took so long because Philae moved at a slow walking speed of 1 metre per second. The craft had no way of manoeuvring once it was released, so gravity alone determined whether it reached the surface.

“It’s all down to Isaac Newton now,” said ESA senior science adviser Mark McCaughrean shortly after release.

After a long, tense wait, punctuated by the first images from the lander as it fell, the signal that Philae was on the surface finally arrived at 1603 GMT.

“We see the lander angled, sitting on the rocks,” said Rosetta flight director Andrea Accomazzo. “We can’t be happier than we are now.”

Scratch the surface

But not everything went as planned. The comet’s gravity is 10,000 times weaker than Earth’s – not enough to hold a lander down – so Philae was supposed to grapple on to the comet with harpoons. It also has a gas thruster designed to push it into the surface as it lands, but the night before landing, ESA discovered it had a problem, leaving the harpoons as the only way to tether to the surface.

About half an hour after landing, it became clear that Philae had only penetrated 4 centimetres into the surface of the comet, much less than ESA was expecting. That probably means that the anchors did not fire correctly.

Possibly worse, the telemetry link with Philae, which uploads the all-important science data, was unstable shortly after landing. Ferri says the unstable telemetry is not concerning, but it does need addressing.

Primordial soup

At some point tonight, ESA will need to move Rosetta, which will break the link with Philae in any case. This was always planned, but with the link currently unstable, it could cause problems.

Still, “this is a big step for human civilisation”, said ESA director Jean-Jacques Dordain. The science pay off from even a few images could be huge.

Comets are the building blocks left over from the formation of our solar system. That means they contain pristine samples of the material that went to make up Earth. Landing on a comet and drilling into its surface will let us touch and taste that material, giving us a glimpse at our origins.

Instruments on Philae will examine the comet’s water and other molecules important for life, to see how they compare to those found on Earth. If they match, Philae will essentially be scooping up handfuls of frozen primordial soup.

Correction: An earlier version of this story reported a landing time that was off by an hour.