Opportunity, the older (and smaller) rover cousin of Curiosity made the headlines last week when it discovered more conditions that could have supported life on Mars in its past. But for our best chance of finding life elsewhere in the Solar System, we may need to look beyond the dusty plains, vast mountains and deep canyons of Mars, and travel past the scattered cosmic debris of the asteroid belt. There, in the shadow of the bloated stripy gasbag Jupiter, could be actual living organisms – not the desiccated and irradiated remnants of long dead microbes that scientists hope to find on the red planet.
Jupiter has just under 70 documented moons, the four largest of which are the Galilean moons Io, Callisto, Ganymede and Europa. Io is a fiery world of volcanoes, molten lava and billowing clouds of toxic sulphur; Callisto, an ancient pockmarked body covered in a crust of icy rock. But beneath the vast cracked pancakes of ice on Ganymede and Europa, there are oceans of water. And where there is water, you have the potential for life.
This intriguing possibility has led to the development of a new internationally supported mission to Jupiter’s Moons, Juice, being put together by the European Space Agency. Juice, rather tenuously, stands for JUpiter ICy moons Explorer – an acronym that, I am told by a reliable source, was arrived at after quite a few late-night drinks.
The probe will set off for Jupiter in 2022. After it arrives in 2030, it will spend at least three years studying the Jovian system, flying past the planet and its icy moons and ultimately ending up in orbit around the massive Ganymede, the largest moon in the Solar System.
“It’s a fabulous mission,” says Andrew Coates from University College London, one of the lead scientists on the project. “It will compare all three [icy] moons, look at the habitability of all three and the formation processes.” By “habitability”, he means the right conditions to find life. Or, at least, life as we know it.
“You need a source of energy, you need liquid water, carbon, nitrogen, oxygen, phosphorous and sulphur,” says Coates. “Then you need enough time for life to develop.”
Both Ganymede and Europa are in with a fighting chance of possessing all these attributes. They certainly have liquid water and could easily have the molecular building blocks for life. When it comes to energy, Europa has traditionally been the favourite among astrobiologists. It is the only one of the Jovian moons likely to have a rocky ocean floor, meaning there could be hydrothermal vents. These underwater chimneys support thriving communities of plants and animals on Earth. With no significant energy from the Sun, hydrothermal vents could provide chemical energy for life.
As almost everything we know about Europa comes from Nasa’s Galileo mission [LINK TO: http://solarsystem.nasa.gov/galileo/ ] of the mid-1990s, which spent eight years studying Jupiter and its moons, hard evidence for habitability is hard to come by. However, new research adds weight to the claim that Europa is indeed where ET will be hanging out.
Based on what we know about Europa today, we have good reason to believe that it is habitable – by Earth based standards – for life as we know it,” says Kevin Hand, an astrobiologist at Nasa’s Jet Propulsion Laboratory in Pasadena, California.
Using data from Earth-based telescopes, Hand and his colleagues at the California Institute of Technology recently confirmed a widespread abundance of hydrogen peroxide across much of Europa’s surface. This substance could help provide the chemical energy needed for life in the ocean below. And, unlike on Mars, there might be enough energy for larger multi-cellular organisms, rather than just microbes.