Last year, NASA’s Dawn probe became the first spacecraft to orbit two bodies in the Solar System – the asteroid Vesta in July 2011, and then Ceres in March 2015. Now, there’s an even more ambitious proposal on the table, to send it to an unprecedented third destination.
According to New Scientist, the Dawn team are currently asking NASA for a mission extension, which would allow them to deorbit Dawn from Ceres, and head to another asteroid in the asteroid belt – although they’re being coy about when or where that might be at the moment.
“As long as the mission extension has not been approved by NASA, I’m not going to tell you which asteroid we plan to visit,” principal investigator Chris Russell told New Scientist. “I hope a decision won’t take months.”
It's not clear yet if Dawn would orbit this asteroid, or simply fly by. And of course, other spacecraft like the Voyager probes have visited more than three bodies before, although those were flybys of planets rather than orbits. But either way, heading to a third object – having already orbited two others – would be a significant step in showing how resourceful spacecraft like Dawn can be.
Visiting multiple destinations is possible for Dawn thanks to its revolutionary xenon ion engine. It provides a very small amount of thrust but over a long period of time, meaning that it requires very little fuel to move Dawn around the Solar System. There is not much fuel left on Dawn though, considering it has already been to two destinations, so this third stop would almost certainly be its last.
Dawn has been returning stunning images of the surface of Ceres. NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
But it would be a fitting conclusion to the mission. Most other spacecraft when they finish their mission are either left in a graveyard orbit, where the spacecraft dies a quiet death, or sent crashing into their orbiting body. The latter option was used for spacecraft such as Galileo and Venus Express, while Rosetta will be sent to gently touch down on Comet 67P Churyumov-Gerasimenko later this year.
This second option is not possible for Dawn, however, because it was not sterilized to a sufficient standard before it launched. Under planetary protection rules, no spacecraft can land or impact a body where there is a risk of contaminating it with Earth-based life. Thus, if the extension is not approved, Dawn will simply be left to orbit Ceres endlessly until it runs out of fuel.
Aside from limited funds in NASA’s planetary budget, there doesn’t seem to be any reason why this proposal wouldn’t be granted. Dawn’s mission is scheduled to end in the summer, and although there’s still plenty of interesting science to do at Ceres until then, with its numerous craters and bright spots still throwing up surprises, the opportunity to visit another destination is possibly too good to pass up.
Here’s hoping Dawn gets this final moment in the spotlight.