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New bid to help get Rosetta talking to lander Philae

Paul Sutherland, Feature writer
Jul 4, 2015, 2:16 UTC

Sen—Rosetta space scientists are to try a new approach to get their spacecraft talking to its revived lander Philae on the surface of Comet 67P/Churyumov-Gerasimenko.

As Sen reported last week, initial elation that the probe had woken up, after being dormant for seven months, turned to frustration at the lack of a stable link. Nothing has been heard from Philae since June 24, following a number of intermittent communications.

The comet scientists are anxious to get Philae working and transmitting data about 67P as it reaches its most active phase around perihelion, its closest point to the Sun, next month on August 13. 

Experts at the Lander Control Center, at the German Aerospace Center (DLR) in Cologne, have now come up with a plan to get Philae and its mothership Rosetta communicating again by using a separate antenna that forms part of one of the lander’s science instruments.

The instrument in question is an experiment called CONSERT (COmet Nucleus Sounding Experiment by Radiowave Transmission). It was designed to use twin instruments to learn about the deep interior of the comet by sending radio waves from Rosetta and Philae through the nucleus.

Rosetta project scientist Matt Taylor told Sen: “We haven’t heard from the lander for a bit, but that doesn’t mean it’s not still alive. So we are looking to ‘command in the blind’ to get CONSERT going. Why CONSERT? Well, it’s an instrument that uses radio signals so has another antenna, so if we hear from CONSERT, it means the lander is well, but that there are issues with the comms link between the lander and orbiter. So it will provide useful info for us to try to improve the current situation.

“The main issue is that we haven’t had a stable link with the lander since it came back. So we have to join the dots a bit based on what we do know. Apparently, flying a spacecraft around a comet, deploying a lander on one and keeping in stable communications with it approaching perihelion, it's a helluva tough job!”

The DLR team will send a command on Sunday, July 5, to Philae to switch on the experiment in a bid to check that Rosetta can still talk to the probe it sent to a bounced landing on Nov. 12, 2014.

Announcing the move, Koen Geurts, Philae Lander Technical Manager at DLR, said today: “Since the last status report, there has been no new contact with Philae. We’re working hard to try to understand the situation. 

“Usually Philae uses bidirectional communications to talk with Rosetta but on this Sunday we’re going to send commands to Philae in a one-way mechanism telling it to switch on the CONSERT instrument on the lander. It has its own antenna to communicate with Rosetta so if it is successful, we can verify to Rosetta that at least the communication direction to Philae is working.”

Meanwhile, scientists studying 67P’s surface have identified a number of deep and circular pits on the nucleus’s surface as sinkholes, or collapsed areas similar to features found on our own planet. They believe the pits, ranging from tens to hundreds of meters wide, are formed when ice within the comet sublimates, or turns directly to gas, before disappearing into space. The ceiling of the void then left collapses under its own weight, leaving a hole.

Astronomer Dennis Bodewits, of the University of Maryland, is co-author of a paper about the findings published in the journal Nature this week. He said in a statement: “These strange, circular pits are just as deep as they are wide. Rosetta can peer right into them.

“We propose that they are sinkholes, formed by a surface collapse process very similar to the way sinkholes form here on Earth. So we already have a library of information to help us understand how this process works, which allows us to use these pits to study what lies under the comet’s surface.”

The researchers used Rosetta’s Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS) narrow angle camera, to image the surface of the nucleus in detail. They found two distinct types of pits—deep ones with steep sides and shallower pits more like those seen by passing space probes on other comets, such as 9P/Tempel 1 and 81P/Wild. Jets of gas and dust were seen to stream from the sides of the deep, steep-sided pits, but not the shallower ones.

The Rosetta team does not believe the deep pits are produced by the jets because explosive outbursts would not be enough to produce such large sinkholes. An outburst witnessed on April 30, 2014, allowed them to gauge how much material had been ejected.

Bodewits said: “The amount of material from the outburst was large—about 100,000 kg—but this is small compared to the size of the comet and could only explain a hole a couple of meters in diameter. The pits we see are much larger. It seems that outbursts aren’t driving the process, but instead are one of the consequences.”

Update, July 7, 2015: The attempt to get Rosetta's CONSERT instrument to switch on Philae's antenna on Sunday, July 5, failed. Another attempt will be made on Thursday, July 9.