Since August 2014, the Rosetta spacecraft has been orbiting Comet 67P/Churyumov-Gerasimenko, providing an unprecedented look at an active comet as it moves closer to the Sun in its orbit. As expected, the level of activity increased the closer the comet was to the Sun, with jets of water vapour, gas, and dust becoming bigger and more prominent. The comet reached perihelion, the closest point to the Sun on its orbit, on Aug. 13, 2015. For the first time ever, a spacecraft is observing this activity close-up, as it happens. But now, scientists have been noticing other dramatic and rapid changes on the comet’s surface as well, which haven’t been explained yet.
Great new OSIRIS images of individual dust jets coming off comet 67P/Churyumov–Gerasimenko, from the Rosetta spacecraft. They were taken about half an hour after the Sun had set in the region, and show many individual jets erupting from the comet’s surface.
A stunning view of the Hathor and Seth regions on the comet, taken by the Rosetta spacecraft. The cliffs of Hathor loom in the background. Some jet activity can also be seen in the closer foreground. See also the Rosetta blog post here.
The impact of comet Shoemaker-Levy 9 into Jupiter in 1994 was a spectacular event for astronomers. The scars in Jupiter’s atmosphere lasted for weeks afterward; while those have long since faded, there are still other features of the impact visible even now, it was announced last Tuesday.