Astronomers have long suspected that Jupiter's moon Europe may have subsurface conditions that can support life. We have long known that its surface is a shell with ice over a sea of liquid water, but it has been difficult to see that water directly. The ice shell is miles thick, and all the evidence we have is indirect.
It looks like it has now changed: Astronomers have just announced that the direct discovery of water erupted from Europe in huge geysers!
The observations were made using the mammoth 10-meter Keck telescope. Keck can detect infrared light, far beyond the colors that our eyes can see, and this is critical: When water molecules are hit by sunlight, they can absorb it, vibrate (like weights on springs attached to each other) and release that energy at specific wavelengths for infrared light.
Astronomers observed Europe from February 201
This is exciting! Europe is a bit smaller than our own moon, but the amount of liquid water in Europe is more than all the oceans and rivers on earth! The moon's surface is clearly icy and dotted with cracks, but it has been unclear if that water can get through the thick ice shell.
The culprit here is serious. And when you talk about Jupiter is serious. Europe orbits Jupiter on a very little elliptical orbit, which means it is sometimes a little closer to Jupiter and sometimes further away. The gravity it feels from Jupiter is changing over its 3.5-day orbit, and this ends clamping and compressing the moon. This generates huge amounts of friction in Europe, manifested as heat (like rubbing hands together on a cold day warms them up). The heat melts the ice and creates the ocean's underground (this is exactly the same mechanism responsible for the geysers in the water Cassini saw eruptions from the Saturn moon Enceladus).
The surface temperature is so cold, about -170 ° C on average, that all water there is frozen to rock hard ice. That is why it has been so difficult to see the floating water directly. Still, it can apparently squeeze through the cracks and blast off into 200-kilometer-high geysers.
Evidence that these plumes have been built for a long time. The first observations of them, although not understood as such at the time, were from the Galileo spacecraft, which flew through a plum in 1997. Computer modeling of the day was not good enough to work out what the observations meant, but later analysis supported the idea the spaceship had flowed through a water geyser.
Since, 2013, Hubble Space Telescope observations strongly observed that water erupted in space; it saw a molecule called OH – which is what you get when ultraviolet light from the sun breaks apart water molecules (that, plus a hydrogen atom). These observations looked pretty good, but OH – molecules can be formed in other ways. Water is the easiest and most likely way, so that's pretty good evidence, but it's still indirect.
These new observations show water directly. This often happens in science; you get the hint of something, so you keep looking, and as technology and software get better, your chances of confirming or denying that idea grow. In this case, things went in a positive direction. Hurray!
So what does this mean for life in Europe? It has been a scientific opportunity for a long time now, and to be honest I do not think that for many researchers have any lingering doubts that the water is there. The good news here is that we now have direct evidence of that. So it's a step in the right direction.
However, the next step is a giant leap: Europa Clipper, a NASA mission to the moon. Equipped with instruments that can capture images, thermal scans, ultraviolet spectra, magnetic readings and more (one lot more), it is a measurement assignment that will circle Europe and try to answer some of the biggest questions we have about the moon: How deep is the sea? What other molecules are there besides water (like organic molecules)? What is the geography of the surface?
And, of course, is it possible that the chemistry that is right for life can exist? Clipper is now being built and should be launched to Jupiter in the middle of the next decade. It won't be too long before we have more close-ups of the moon and have a much better understanding of its surface … and what lies beneath.