Still No Response From the Lost Comet Lander

For the past week, comet-chasing spacecraft Rosetta has been attempting to get a response from Philae, the lander it jettisoned onto the comet surface back in November.

But Philae remains silent.

The German Aerospace Center (DLR), which is working with the European Space Agency on the project, has today turned off Rosetta's co​mmunication unit—for now.

"From today onwards, the geometry between Rosetta and Philae is not favourable any more for communication," Koen Geurts, part of the DLR team, told me. They have to wait for Rosetta's orbit to line up such that a signal can be transmitted to the lander, and the window they had has now closed. The next opportunity will be in April.

So why no response from the little lost lander? Philae touched down on Comet 67P/Churyumov-Gerasimenko four months ago, but went into hibernation afte​r it stumbled on landing and ended up in a spot that didn't get enough light to keep its solar power going.

But as the comet is headed towards the Sun, ESA hopes the lander will reawaken before meeting its fiery demise. That's not happened yet.

The communication unit on Rosetta has​ been sending signals—Geurts characterised it as a message along the lines of "Hello, here I am, I want to talk to you"—towards the comet. If Philae's onboard computer picks up the message, it'll verify if it has enough power to switch on the transmitter and respond.

Geurts said that from their predictions, it looked like Philae would have enough power to respond, and they're pretty sure it's in an OK position too. But Philae's silence could be down to the fact that it's simply too cold. "The thermal predictions look a bit more pessimistic," he said.

Philae needs to reach a temperature above -45 Celsius to turn on. Below this, the switch is disabled in order to protect the lander's hardware.

But all is not lost; there are more opportunities before the comet gets closest to the Sun in August, and Geurts said the team is confident. Their predictions suggest various potential windows for communication. "Only the very optimistic ones had a wake-up already in March," he said.

Every day the comet is getting closer to the Sun—"so the chances are increasing by the day."

The team is currently working with ESA to figure out what exact date and time to next turn on the communication unit. For now, it's a game of patience.

"If we haven't heard anything by, let's say end of August, then our chances are rapidly decreasing," said Geurts.