Not everything worth doing can be done in four years. The Cassini-Huygens mission, currently beaming us pictures of Titan, Saturn’s largest moon, first hit the drawing board in 1982. It was a couple of years later that scientists conceived a comet rendezvous mission. The result was the Philae lander, which touched down on the comet 67P/Churyumov-Gerasimenko last year.
Nasa’s Voyager probes left earth in 1977 and only now is part of their legacy bearing fruit. Two years after their launch, when Margaret Thatcher had been in Downing Street just a couple of months, the Voyager 2 probe beamed back pictures of a scarred moon covered with what looked like ice floes. It was these images that made us decide to revisit Jupiter’s ice moon Europa.
A European mission, which will cost about €1bn (£740m) and is known as the Jupiter Icy Moons Explorer (or “JUICE”), is scheduled to make a couple of fly-bys of Europa in 2030. Now Nasa has greenlit a mission called Europa Clipper. This has been 15 years in the making so far and has now been allocated $255m (£167m) over the next five years. That is enough to get the next ball rolling.
The Voyager picture of Europa’s scarred surface suggests that it might be the best place in the solar system to look for aliens. The scars seem to be the consequence of tidal forces that arise from the gravitational pull of Jupiter. This stretches and squeezes the moon, creating an internal heat. Europa is thought to have a vast ocean under its ice crust with twice as much water as there is on earth.
The tidal heating causes currents of warmer water to move towards the surface. The result is that the surface ice melts then refreezes, in a perpetual cycle. The currents will also drag life-nurturing nutrients up from the ocean floor, creating the perfect conditions for sustaining life, if it exists. We don’t know how deep the ice crust is – estimates vary from a few kilometres to tens of kilometres. But, rather fortuitously, we might not even need to get beneath the crust to look for life. Geysers occasionally erupt from the surface, shooting jets of oceanic water into the moon’s thin atmosphere.
In 2013, data from the Hubble Space Telescope suggested that a cloud composed of hydrogen and oxygen – almost certainly water vapour – was ejected near Europa’s south pole. It was 200 kilometres high and seemed to be firing out 3,000 kilograms of water per second. The sighting has yet to be repeated. The geyser may have been a freak event. It may be regular but unpredictable and thus difficult to work with. Hubble’s observation is intriguing nonetheless and definitely worth a closer look.
You’ll have to be patient, though. Jupiter is half a billion kilometres away, so it’s going to take a while to get there. What’s more, these missions are deliberately slow in their development: you don’t get to do them twice, so you have to do them right. The European Space Agency and Nasa missions will carry cameras to take more photographs as well as instruments for analysing the moon’s internal composition and the chemicals in the atmosphere and on the surface. Even if they can’t capture a sample of life from a geyser, all this data will tell us a great deal about the likely existence – or not – of Europan life.
And there’s a certainty to that: the pressure on the missions sets a high bar for the performance of those technologies that make it on board. Everything has to be proven to work well in the harshest of conditions. So it won’t be the latest, whizziest ideas that end up on the launchpad; it will be stuff we know will do what we need it to do – in the long term and in unpredictable circumstances. If only politics worked half as well as space exploration.
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