“We don’t know that much about the evolution of complex life forms on Earth and so it’s hard to make a prediction about Europa,” Hand explains. “That said, some of our work indicates that compounds like hydrogen peroxide and oxygen, which are produced by the irradiation of Europa’s surface ice, could lead to a chemically and energy rich ocean that might be capable of powering complex organisms.”
So if life is out there, what form is it likely to take?
“Anything is possible when you consider a second, independent origin of life,” Hand says. “I’d bet it would likely be heavily dependent on acoustic and sonar sensory perception, since it would live in a vast ocean and have the ice sheet above cracking and creaking, day in and day out, as the moon is tidally tugged and pulled by Jupiter.”
Although it is exciting to imagine a sea full of fearsome alien fish with giant ears, this is, of course, just speculation. The evidence for habitability is growing but just because somewhere is habitable doesn’t mean that there is life. In fact Coates reckons Ganymede is a better candidate.
“It’s got a magnetic field that helps protect it from radiation,” he says. “One of the problems with Europa, in particular, is that the radiation environment is higher there, so the deflection by the magnetic field of radiation could play a key role in making the chemistry right at Ganymede. I think Ganymede is more interesting than Europa in fact.” The ice covering Ganymede’s liquid ocean also has a thicker crust, which may help with shielding from radiation.
The frustrating thing about all this is that, even if everything goes to plan, we will have to wait at least 17 years until Juice gets to Jupiter, and 19 years until it orbits Ganymede, before we get close to any answers. But Coates looks on the bright side: “It’s remarkable to think that two-year-olds now could potentially be doing their PhDs, just as Juice goes into orbit around Ganymede.”
It is also maddening that there is not enough money in the mission budget to include a lander to investigate the surface of either moon. Nevertheless, if results from Juice produce compelling evidence that these Jovian satellites are indeed habitable, you can bet there will be a scramble to build one.
If it turns out that there is life on such weird worlds as Europa and Ganymede – even in an insignificant solar system in the outer reaches of the galaxy such as ours – then there is a good chance that life is widespread in the universe.
And that is very exciting indeed.