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Now, since Rosetta touched down on "Tschurri", as the comet is called in the german speaking world, I am asking myself how firmly does Rosetta sit on its comet?
Since on the comet very little gravity is acting due to the comets low mass, it would probably not take too much effort (force) to lift Rosetta from the comet's surface.
So could during one of the comet's next active periods Rosetta be blown from the comet's surface by e.g. outgassing?
Sadly, we just don't know what happened to it, and we probably never will.
Rosetta may have come gently to rest in the snow-drift texture of the comet’s surface or bounced back into space, as the Philae lander did when it was dispatched in 2014. Rosetta’s precise fate will never be known, because it was pre-programmed to shut down all communication on contact and there are no telescopes on Earth powerful enough to see it. (Source)
Philae hit the surface around 1m/s and bounced quite high (twice) (at 38 cm/s for the first bounce). Rosetta hit the surface at 90 cm/s (same source as the quote above). Its possible Rosetta did the same and took damage when it landed. But this is just speculation. We won't know unless we send another probe to 67p to take pictures of the remains.
I have no clue if Rosetta could be blown off the surface by outgassing.
It's very unlikely that the force of outgassing would be sufficient to shift Rosetta or Philae's position on the comet. When Rosetta was initially approaching 67P, the comet was estimated to be losing about a liter of water every second; averaged over a sun-side surface area of roughly 50 square kilometers, this amounts to something like .02 milligrams of water per square meter per second evaporating. The exact force exerted would depend on the velocity of the departing water molecules, but it's obviously not going to amount to much. Further, note that evaporation will be much slower directly beneath the spacecraft, because the surface will be shadowed.
Note that Philae has been at rest on the surface of 67P for about two years, a period which included 67P's closest approach to the sun, and therefore its most furious outgassing. It is not known for certain that it hasn't shifted position significantly, but its position in pictures taken from Rosetta in September of 2016 is consistent with its estimated position in mid-2015.
