The Rosetta Orbiter Might End Its Mission by Crashing into Its Comet

The European Space Agency's Rosetta probe has been chasing its target comet for a decade or so, including several years' hibernation. At the end of its mission, it might get closer than expected: Rosetta's project scientist told Motherboard the team is considering actually colliding the spacecraft with the comet (for science, of course).

British astrophysicist Matt Taylor said they were considering the move in an email response to a question about next week's flyby, which will see Rosetta swoop down to within 6KM of the comet. I asked Taylor whether this would be the closest Rosetta would get to its comet.

"At the moment yes," he responded, but added that they were now thinking about extending the mission and starting to think about its end. "We are currently considering putting the orbiter onto the surface of the comet," he wrote. "That will then be the closest it gets!"

Rosetta is currently orbiting Comet 67P/Churyumov-Gerasimenko, having released the Philae lander onto the surface earlier this year. Philae went into hibernation when it lost power, though ESA still holds hope that it will reawaken when its solar array is brought closer to the Sun.

Rosetta will eventually suffer the same fate. After August this year, it will start to travel with the comet away from the Sun, and will have to survive on limited fuel as its solar cells won't catch enough rays.

So what to do with an orbiter that's dying? One option is to just put it to sleep, like last time it hibernated, except this time there's no wake-up plan. "But a lot of people are keen on trying to push the spacecraft as close to the comet as possible to get the best information we can," Taylor told me in a quick phone call as he waited to board a plane from a meeting with Rosetta colleagues in the US.

He emphasised that this is just a thought for now; it is not confirmed and details have not been discussed. But the general idea would be to de-orbit the spacecraft and gradually spiral it down towards the comet at descending altitudes, "because you'd get a fantastic set of measurements really close up to the surface of the comet." Getting closer to the comet would give the team deeper insight into its "coma," the comet's atmosphere, which has been a focal point for some observations on the mission so far.

But Rosetta, unlike Philae, was not designed to land. "Basically, it will crash into the surface," Taylor said.

While it would really be a de-orbiting as opposed to a landing, he joked that it could be "our fourth landing on the comet." Philae "landed" three times, bouncing twice on the comet surface before settling down (albeit not quite in the right place).

Another option, Taylor said, would be to put Rosetta in hibernation for three to four years. But it would still have minimal fuel, and that would entail keeping teams together past the current mission timeframe.

The focus at the moment is on the main science phase of Rosetta's instruments, which will continue to collect the most detailed information we've had about the comet's coma and nucleus.

Over the next months, ESA will discuss whether to extend the mission (it's currently only funded until the end of this year). This will involve considering the end-of-mission scenario, which would occur around the beginning or end of next year depending on whether an extension is granted.

Either way, Taylor is enthusiastic about the de-orbiting suggestion.

"At the moment, the majority of people are looking at doing the spiralling, just getting these really close measurements," he said. "There are other options, but given the pros and cons I'm certainly more keen on doing the de-orbiting strategy."

Sending Rosetta on a (controlled) kamikaze finale could be a pretty cool finish to a pretty cool mission. And as Taylor said, "Basically, there's not much more you can do with a spacecraft once the fuel has run out."