Without water, life as we understand it would be impossible. It is the one substance upon which our existence depends. And now it has been found streaking down the red, dusty slopes of the hills of Mars.
The discovery, announced by Nasa last week , that the Red Planet has running water has provided scientists who are seeking life there with a major boost. As Jim Green, Nasa’s director of planetary science, put it: “If you look at Earth, water is an essential ingredient. Wherever we find water, we find life.”
Hence the international acclaim for the discovery, although the hunt for water, and life, in the solar system is not restricted to Mars. Indeed, astronomers have recently found that our solar system is awash with tantalising pools of the stuff, including several moons of both Jupiter and Saturn. Now researchers are competing for funds to back projects to study these very different, remarkable worlds, even though some are found more than a billion miles from the nurturing warmth of the sun.
It is a tour of the solar system that takes us deep into space, though it begins at Mars, one of our nearest planetary neighbours. As a result, there are now five satellites in orbit round Mars, all returning data, while two robot rovers continue to trundle across its surface.
One bold effort will be made by Europe’s ExoMars lander mission in 2018. Launched on a Russian Proton rocket, it is designed to set down a robot rover that is under construction at Astrium’s construction plant in Stevenage, Hertfordshire. The rover will be fitted with a long drill that will allow samples to be taken from depths of two metres. These will then be analysed for signs of biological activity.
This alien ocean is also considered to be a likely place to find life and two separate missions – to be launched around 2020 – are now being designed to study Europa: the US Europa mission and the European Juice – Jupiter Icy Moon Explorer – mission. The latter will also investigate Jupiter’s moons Ganymede and Callisto. By contrast the US mission will concentrate on Europa, making dozens of sweeps over its surface in an attempt to detect any complex, organic material that might evaporate from its surface.
Titan is remote, and drilling down through its surface to an underground ocean will be extraordinarily difficult. One idea is to land a spaceship on one of Titan’s lakes of methane, where it could sail around searching for complex organic chemicals, the precursors of life. However, the mission – the Titan Mare Explorer (TiME) – was recently vetoed by senior Nasa officials, although Zarnecki and others hope it will be resurrected.
Titan is not the only moon of Saturn to attract attention, however. Observations by the robot craft Cassini, which has been orbiting Saturn since 2004, have shown that, at the south pole of Enceladus, an underground ocean appears to rise close to the surface. And at a few sites cracks have developed, allowing water to bubble to the little moon’s surface before being vented into space. In addition, complex organic chemicals appear to have built up in its sea. The importance of this combination of factors is stressed byNasa astrobiologist Chris McKay. “Enceladus is a small world with an ocean below its icy surface. Even better, plumes from that ocean are vented into space and that means easy access. This is the place to go,” he insists.
Detailed plans have been prepared to launch a probe that would sweep across Enceladus’s surface to gather droplets of water in its plumes. Instruments in the spacecraft, called the Enceladus Life Finder, would then analyse those droplets for amino acids, carbon isotopes and other features that would indicate biological activity. “We would also study Enceladus’s ocean in detail as well as the plumes of water it produces,” said the project leader, Jonathan Lunine. “It may be a sterile ocean – or it could clearly be a place where there is life.” If the latter, then a later mission would be designed to bring samples back to Earth.
The project has been backed by several leading scientists, but recently suffered a major setback when Nasa removed it from its list of forthcoming planetary missions. “We will redesign the project and resubmit, but there is no doubt this has set us back two or three years,” said Lunine. It is doubtful that a mission could reach Enceladus before 2030. Nor is there much prospect, at present, for a mission to Titan to get there any earlier.
“Mars and Europa are the two frontrunners now,” Lunine acknowledged. “Whether it stays that way is another matter.”
