ESA

Hubble Space Telescope images of Ganymede's aurorae colored blue overlaid on a Galileo space probe image of the moon (Image NASA/ESA)

The Hubble Space Telescope has been used to study Ganymede, the largest Jupiter’s moon, and in particular its aurorae. Analyzing their characteristics, it was possible to get the best clues found so far of the existence of a Ganymede underground ocean of liquid salt water. This ocean may contain more water than it exists on the surface of the Earth.

Montage of four pictures of the comet 67P/Churyumov-Gerasimenko taken by the Rosetta space probe's NAVCAM (Image ESA/Rosetta/NAVCAM)

After the flyby performed a few weeks ago, the Rosetta space probe moved away from the comet 67P/Churyumov-Gerasimenko and was able to observe its increasing activity. In late February, from a distance between 80 and 100 km (from 50 to 52 miles) its Navigation Camera (NAVCAM) instrument took several photographs that ESA processed to make the best observations of the jets of steam and dust emitted by the comet.

Image of the SOHO space probe showing the comet C/2015 D1 (SOHO) near the Sun (Image ESA/NASA/SOHO/Hill)

The SOHO (Solar and Heliospheric Observatory) space probe has the primary purpose of keeping an eye on the Sun but when a comet passes close to our star is also useful to track its trajectory. Last week, SOHO identified a new comet because passing near the Sun it’s become bright enough to be detected.

This comet was originally called SOHO-2875 because in the course of over 19 years of mission in a collaboration between ESA and NASA this is the 2875th comet identified by the SOHO space probe. Subsequently officially named C/2015 D1 (SOHO), it survived a flyby with the Sun and may also be visible from Earth in the coming weeks.