Scientists are hunting for oceans in space. Why is the discovery of water so important?
FOR decades, researchers looking for life elsewhere in the solar system have stuck to a simple rule: “follow the water”. The stuff is essential to life on Earth, and its peculiar properties mean those hunting aliens think the same will be true elsewhere. This is one reason that Mars has received so much of their attention. Mars has water vapour in its atmosphere, and water ice in the shining cap at its north pole.
It is biochemistry—evidence of molecules made by life—that Mars has failed to provide. Four decades ago twoprobes landed and subjected samples of its surface to various chemical tests as a way of looking for life. The results were frustrating; not quite what was expected from lifelessness, but not seemingly compatible with life. For all the satellites and rovers that have studied Mars since, there has been no sign of so much as a bacterium.
That may sound odd. Jupiter and Saturn are much farther from the sun than Mars is. The average temperature on Europa is a chilly -171°C. But sunlight is not the only way to heat an astronomical body. Gravity can do it, too. To most Earthlings, the tides produced by the gravity of the moon and sun matter only to sea levels.
Whether they have actually given rise to life is, of course, another question. But the more researchers look, the more intriguing the Saturnian moon becomes. On March 12th, Sean Hsu of the University of Colorado and his colleagues published a paper inanalysing tiny silicate grains spewed out by the plumes.