We’re off the moons of Jupiter…in 2022

I’ve been waiting a long time for this and I’m pretty sure all planetary scientists have been waiting a long time for this too. It’s regarded as the most important destination(s) in the solar system. That’s right, we’re finally off to the moons of Jupiter. Well we will be in 2022 anyway.

After a brief competition with two other space mission proposals JUICE (JUpiter ICy moons Explorer) will head off to Jupiter in 2022 and arrive in 2030 and spent a minimum of 3 years studying Jupiter’s moons. And it’s a European mission too!

JUICE and the Jupiter System

Why the moons of Jupiter? Well, the moons here are exceedingly interesting. Io, first of all, is the most volcanic object in the solar system (although Io won’t be studied much with this mission). The other 3 main moons are the really exciting ones though. Callisto is a fairly large moon and its surface is incredibly old, peppered with craters. It’s holding clues as to the formation of the Jupiter system some 4.5 billion years ago. Europa, the most famous of the moons, has a liquid ocean beneath it’s icy surface, and a very bizarre looking surface. Could there be life in the ocean? It’s a distinct possibility. The mission is mainly focusing on Ganymede though, the largest moon in the solar system, so large it’s bigger than Mercury! It generates it’s own magnetic field. How? Through a salty sub-surface ocean or a molten iron core?

Ganymede

The spacecraft itself looks quite interesting too. It’s going to be operating at the limits of what’s possible. It’ll be using solar power where there isn’t much solar power. Previous missions have used nuclear generators which are far more efficient this far out, but there’s a shortage of the plutonium required for such endeavours at the moment. We’re likely to get an advancement in solar power technology through the efforts of this mission though.

In my opinion NASA have really mucked up. With all their budget cuts they’re not planning a mission to launch to study Jupiter’s moons until well into the 2030’s despite having been told it is the utmost priority of planetary science at the moment. There’s a possibility they’ll add some hardware to the JUICE mission, but we’ll have to really wait and see. What we’d like to see is a Europa lander and ocean explorer (as outlined in NASA’s JIMO mission, now cancelled).

There’s one certainty though, we’re going to find out some truly exciting stuff and we’re going to be surprised with what we find!


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What’s going on on Europa?

The bizarre surface of Europa

Europa is an intriguing little place. It’s the second innermost of the 4 Galilean satellites (there are actually more than 60 moons around Jupiter but these are all much, much smaller than the 4 big, Galilean, ones) and it has a very interesting and bizarre surface.

When we look at most moons in the Solar System we find that there are an awful lot of craters on them. Some of these are very small whilst others are very big. What’s useful about this is that through looking at the craters we can tell how old the surface is. When we look at the cratering record on the Moon we find that it is about 4 billion years old. Europa is a different story altogether. In the image above you can see very few craters, if any at all. What this means is that the surface of Europa is very, very young. After careful analysis it appears that the surface of Europa is, on average, only 65 million years old (that’s considered very young in geologic terms). Therefore there must be a process on Europa that is working to erase the evidence of these craters. What could it be?

The secret to Europa’s resurfacing lies in Jupiter’s massive gravitational field and interactions with 3 of the other big Galilean satellites. Through this process (tidal heating) the interior of the inner two moons are kept warm. This leads to the spectacular volcanoes of Jupiter’s innermost moon, Io. Io looks kind of like a pizza and is the most volcanically active body anywhere in the Solar System. Europa is under these same processes but to a lesser extent.

The Galileo mission to Jupiter, launched in 1989, found that Europa had a magnetic field about it. This inferred that Europa either has a salty ocean beneath the ice or that there is motion in its core. It is now accepted that this is probably due to the presence of an ocean. Further evidence for the existence of this ocean comes from one of Europa’s few impact craters, Pwyll. The crater is unusual in that its base isn’t any lower than the surrounding terrain and shows the hallmarks of the impact having been into thin ice (about 20km thick). It would be useful here to note that lots of different models come up with different thicknesses for the ice shell, some as little as 3km and some up to 100km. This is where the problems starts. Some features on Europa are explained by there being a thin ice shell and others only by a thick ice shell.

A new theory, published in the journal Nature, sets out to put aside some of these problems and explain how what’s called chaos terrain can form. It was previously suspected that you need a very thin layer of ice for them to form, but this theory explains how shallow sub-surface lakes may be responsible.

Thera Macula (false color) is a region of likely active chaos production above a large liquid water lake in the icy shell of Europa. Color indicates topographic heights relative to background terrain. Purples and reds indicate the highest terrain. Credit: Paul Schenk/NASA

The new theory states that phenomena similar to mantle plumes here on Earth heat the base of the ice. Convection occurs and ice lower in impurities slowly rises and melts forming a lens of water a few kilometers below the surface. This would cause the surface to subside and lead to cracks forming from the top of the lens and surface. Eventually these cracks would end up creating rafts, water would then freeze in between and the lens would slowly refreeze and then causing a dome to form at the surface. This process would take millions of years.

It has been speculated that these lakes would be ideal habitats for life. I’m not so sure though. As these lakes would eventually freeze over the only life they could sustain would be some kind of extremophile. In my opinion it would seem that life would be better off living in the ocean beneath the ice. I don’t know enough on this area of astrobiology though to make a truly sound argument.

Europa is a bizarre, intriguing and beautiful place but the only way we’re going to learn more about it is sending a mission there. A review said a mission to Europa should be NASA’s second highest priority (I guess succumbing only to a Mars sample return mission?). Previous missions have been cancelled, like the Jupiter Icy Moons Orbiter (JIMO). Work going on in Antarctica at Lake Ellsworth and Lake Vostok will help us with a possible lander mission to Europa. These lakes in Antarctica are hidden beneath deep layers of ice, drilling technology being used will help us when we come to drill and venture beneath Europa’s icy shell.

Four step process for building “chaos terrains” on Europa

If I haven’t explained any of this adequately (and I probably haven’t, I’ve been up since 5am) or purely just if you’re interested I’ve put some links below this and also the video from the initial conference explaining the theory.

Links
Video: Jupiter Moon’s Subsurface Ocean of Water

NASA Probe Data Show Evidence of Liquid Water on Icy Europa

Active formation of ‘chaos terrain’ over shallow subsurface water on Europa

References
Greenberg et al (1999)
Schmidt et al (2011)
An Introduction to Astrobiology – C4 Europa – Dr David Rothery (OU study book)