Given the choice between hitting the off switch and landing the Rosetta space probe on a comet, well… it wasn't much of a choice for ESA scientists. Rosetta deployed the Philae lander on comet 67P in 2014.
The Rosetta spacecraft will likely end its life next September with a spectacular weeks-long descent toward Comet Chury, climaxing as the three-ton piece of machinery attempts an improvised landing on the spinning ball of ice and rock.
"It's very simple. As soon as there's contact, it is game over, it's finished," spacecraft operations manager Sylvain Lodiot told DW. "Rosetta is not designed to land, so as soon as there's contact with the comet, there won't be any communication anymore. That's the end of the mission."
In the weeks prior to final impact, Rosetta will orbit Comet 67P/Churyumov-Gerasimenko at distances never before attempted.
"We will attempt to go to distances of below one kilometer to the surface," Lodiot said.
Doing so presents a particular challenge, since the lopsided shape of the spinning comet means its gravity field is non-uniform. This will cause huge perturbations in Rosetta's trajectory as the space probe nears the comet. It will also cause Rosetta's "height" to change as the comet moves.
During the descent, Rosetta's 12 remaining onboard instruments will continue to collect information. The 13th, the Philae lander, is already on the comet.
The other instruments include remote sensing, imagery, gas and dust analysis to atomic force microscopes as well as a plasma consortium, which measures the plasma and interaction with the sun and solar wind.
"You could imagine that the Rosina instrument would maybe discover new traces of gases around the comet," Lodiot said.
But he acknowledges that what will likely attract the most attention next September are the potential close-up photographs of the comet.
In total, the Rosetta team considered three options for terminating the life of the Rosetta space probe: "Do nothing," crash it into Comet Chury, or a third option that proved unfeasible and that would have involved putting the spacecraft into hibernation mode as Comet Chury's elliptical orbit took it on a multi-year voyage away from the sun's energy-giving light.
The Rosetta spacecraft released the Philae lander onto Comet 67P last November, after a ten-year flight that took it 500 million kilometers away from Earth. It was the first ever soft-landing on a comet.
The Rosetta mission is the first to rendezvous with a comet, to accompany that comet as it orbits the sun, and to deploy a lander on its surface.