Jupiter and Ganymede
Another gem from Hubble…
The Hubble Space Telescope caught Jupiter’s largest moon Ganymede just before it ducks behind the giant planet. Credit: NASA, ESA, and E. Karkoschka (University of Arizona).
Just look at the size of these objects – Ganymede is the largest of all moons in our Solar System; it’s even larger than Mercury! (For those who needs number to imagine the size, Ganymede measures 5268 km across and Mercury is 4878 km across). The only reason it’s called a moon and not a planet is because it doesn’t orbit our Sun, instead it orbits Jupiter.
And when this largest moon stands beside its mighty parent planet, it was totally dwarfed! Ganymede can’t even compete in size with the Great Red Spot (which is just only a feature on Jupiter), leave alone the whole planet.
A lot of features are visible on the Jupiter in the image above: the Great Red Spot (visible near the centre of the image) – a storm which has been on Jupiter for more than 3 centuries, texture of the clouds in the atmosphere and other smaller storms and vortices.
The most amazing thing here is not the features on Jupiter – Jupiter is big, so its features are easily visible. What is amazing is that Hubble’s view is so sharp that we can even see features on the moon’s surface, most notably is the white impact crater Tros.
No matter how beautiful a Hubble image is, it must be taken for a scientific reason. Observation time on Hubble is too precious to use only to take pretty pictures. In this case, astronomer Karkoschka uses these images to study Jupiter’s upper atmosphere.
As bright Ganymede goes behind Jupiter, it’ll first pass through Jupiter’s atmosphere and at the same time illuminate the atmosphere. If we compare how Ganymede looks like when alone in space and when it’s near the limb of the giant planet, we can get some clues about the properties of Jupiter’s high-altitude haze above the cloud tops.
And as if still image is not enough to take our breath away, the astronomers at Hubble took the series of these images and made them into an animation! Wow!
My Dark Sky 