To say that 2015 has been a great year for planetary exploration would be an understatement, with fantastic new discoveries from around the Solar System. From our first ever close-up look at Pluto and its moons, to more evidence for ancient lakes and rivers on Mars (and current briny streams) to weird bright spots and mountains on Ceres, to the continuing study of Saturn and its moons, notably Enceladus, to spectacular close-up views of a comet, it has indeed been quite a year.
Comet 67P/Churyumov–Gerasimenko, or 67P, has been the focus of intense study by the Rosetta spacecraft since 2014. One of the key mysteries scientists have been trying to figure out is how the comet became the odd “rubber duck” shape that it is, with its two distinct lobes. Now they think they have the answer: Comet 67P was formed by the collision of two other, separate comets which fused together to form its distinctive shape.
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.