The news that Philae had landed on the comet 67P/Churyumov-Gerasimenko arrived at the European Space Operations Centre in Darmstadt, Germany, right on schedule at just after 4pm GMT. The crowds of scientists and well-wishers erupted into cheers and hugs. Twitter was ablaze with congratulations for the European Space Agency (ESA) on its impressive achievement.
The next milestone should have been an image from Philae from the surface, around an hour after landing. But it never came. Tweets and messages started to fly around that there could be something wrong. Was Philae not properly anchored on the comet? Did it land at an angle? Was something broken?
At around 8pm, ESA called a press conference to tell us what they knew. Stephan Ulamec, manager of the Philae lander, said that his team thinks that Philae may have landed on the comet and then bounced off and landed again in a slightly different place. "Maybe today, we didn't just land once, we landed twice," Ulamec said to laughs in the room.
In addition, the flight engineers confirmed that the harpoons - meant to fire from the underside of the lander in order to anchor it into the comet - had not been engaged. That could mean that the lander might not be stable on the surface for long and might even slide around. Another niggle was that the communications between Philae and Rosetta seemed to be intermittent, suggesting that the lander might be moving on the surface.
On the plus side, the scientific instruments seem to be working - the Open University’s Ptolemy instrument even took its first data and sent it back successfully.
Rosetta is now no longer in the line of sight with the lander, so it can’t communicate with it at present. But contact should be re-established overnight. If Philae’s programming is working, it will have begin its first set of scientific experiments and Rosetta will be able to download the data in the morning. In that download, engineers will also get information from the lander’s sensors - including in its feet - to better establish what condition Philae is in.
Rosetta-watchers will have more information on all of this tomorrow afternoon.