Posted by: Kash Farooq | May 3, 2012

Space Scenery: Europa

Continuing the Space Scenery series

Europa is a moon of Jupiter. It is my favourite moon. Yes, I have a favourite moon. I’m fascinated by the very likely possibility that there is a liquid ocean beneath the icy shell. The huge gravitational force exerted on the moon by Jupiter, together with the orbital resonance with the other Galilean moons (Io, Ganymede and Callisto) ensure that Europa is constantly being kneaded. And just like a squash ball being hit around a squash court, it heats up – tidal forces generate enough heat to produce a liquid ocean.

It was discovered in January 1610 by Galileo Galilei and was not of particular scientific interest until the 1970s when spacecraft started flying by. They discovered active worlds completely unlike Earth’s Moon. One of the tell-tale signs of activity was the lack of craters. Many craters indicate an ancient surface that has been battered by meteorites. On Europa hardly any could be seen. This indicates that resurfacing events must regularly be taking place that erase any craters.

I’ll start with an image from the most recent fly-by. The New Horizons spacecraft took this arty image on its way to Pluto (click for the 1019 × 816 version):

Europa rising over Jupiter

Europa rising, with Jupiter in the foreground. Taken from the spacecraft New Horizons, which is on its way to Pluto and the Kuiper Belt. Credit: NASA/New Horizons.

Zooming in, here is an image by a Voyager probe. You can see what scientist were starting to get excited about. An icy moon had been discovered with what looked like a cracked surface. And hardly any craters could be seen. (Click for the 790 × 790 version):

Europa from Voyager

Europa from Voyager, at a distance of 246000 kilometres. Credit: NASA/Voyager.

And here is a full globe view captured by the Galileo spacecraft. This mission was dedicated to exploring the Jupiter system (click for 1006 × 1000 version) and obtained the best images we have of Jupiter and the moons:

Juipter's moon Europa

The bright white and bluish part of Europa’s surface is composed mostly of water ice, with very few non-ice materials. Credit: NASA/Galileo.

The Galileo spacecraft has captured lots of images of surface features (click for 1903 × 1864 version):

Dark bands on Europa

Dark crisscrossing bands on Europa demonstrate fracturing of the surface and the possible eruption of material from the interior. Credit: NASA/Galileo.

Here is a close up of the surface showing features known as “rafts”. You can also see that the ridges don’t line up – they are clearly older features that have been broken apart by newer melting episodes. (Click for 1710 × 1320 version):

Europa Ice Rafts

High resolution image showing features known as “rafts” – crustal plates ranging up to 13 kilometers across that have been broken apart and moved into new positions. They resemble pack-ice on polar seas during spring thaws on Earth. Credit: NASA/Galileo

And here we can see what appears to be evidence of liquid that has bubbled to the surface and then refrozen (click for 2150 × 1950 version):

Evidence of Internal Activity on Europa

Directly to the south of the “X” shape is a 75 by 100 km area where the icy crust of Europa has been disrupted by activity from below. It looks like something has bubbled up and then solidified. Icy blocks have been rafted from the edges of this zone. These features provide evidence of thermal activity below Europa’s surface. Credit: NASA/Galileo

Next step…a lander mission? (Please!)



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