Although the connection failed repeatedly after that, it remained completely stable for those 12 minutes. “This sign of life from Philae proves to us that at least one of the lander’s communication units remains operational and receives our commands,” said Koen Geurts, a member of the lander control team at DLR Cologne.

The mood had been mixed over the last few days; Philae had not communicated with the team in the DLR Lander Control Center (LCC) since 24 June 2015. After an initial test command to turn on the power to CONSERT on 5 July 2015, the lander did not respond. Philae’s team began to wonder if the lander had survived on Comet 67P/Churyumov-Gerasimenko.

“We never gave up on Philae and remained optimistic,” said Geurts. There was great excitement when Philae ‘reported in’ on 13 June 2015 after seven months of hibernation and sent data about its health. The lander was ready to perform its tasks, 300 million kilometres away from Earth.
However, Philae has to communicate with the ground stations through Rosetta, which acts as a radio relay. Restrictions on the orbiter’s approach to and orbit around the comet have not permitted regular communication with the lander. The data sent on 24 June did not suggest that the lander had experienced technical difficulties. Now, Philae’s internal temperature of zero degrees Celsius gives the team hope that the lander can charge its batteries; this would make scientific work possible regardless of the ‘time of day’ on the comet.

The received data is currently being evaluated. “We can already see that the CONSERT instrument was successfully activated by the command we sent on 9 July,” explained Geurts. Even now, Philae is causing the team some puzzlement: “We do not yet have an explanation for why the lander has communicated now, but not over the past few days.”

The trajectory of the orbiter, for example, has not changed over the last three weeks. However, one thing is certain; Philae has survived the harsh conditions on the comet and is responding to commands from the LCC team. “This is extremely good news for us,” said Geurts.

Watch the latest video update from the LCC, here.

Rosetta is an ESA mission with contributions from its Member States and NASA. Rosetta's Philae lander is contributed by a consortium led by DLR, MPS, CNES and ASI.