Robotic vehicles set to unlock secrets of space
Several scientific discoveries prove that earth's neighbours in our solar system are more than gas giants and rocky worlds
At the end of last month came news that Nasa has ideas for a novel robotic space vehicle. Dubbed a "super ball bot" by the US space agency, this would be roughly spherical, built of interlocking rods and cables that would allow it to compress and bounce when landing on another world, before regaining its shape and rolling around to explore. Dozens of the bots could be folded and packed together for a single mission.
It seems a weird concept for space exploration, but our solar system is a weird place, as recent discoveries have shown. Several of these discoveries involve moons, but planets yield surprises too. Mercury, the planet nearest the sun, has a thin atmosphere despite relatively feeble gravity and daytime temperatures soaring to around 450 degrees Celsius. This might be formed by particles from the solar wind, which reach the surface thanks to vortex-like magnetic "tornadoes", forming windows in the overall magnetic field that otherwise deflects them. And despite the intense heat, in 2012, Nasa's Messenger satellite made observations consistent with ice on Mercury - in polar craters shaded from the sun.
Two scientists have suggested that diamonds form in the atmospheres of Saturn and Jupiter. Their scenario involves lightning zapping methane molecules apart to form hydrogen and carbon, with the latter clumping together to become soot particles that fall and experience increasing pressures to become diamonds. These in turn become so hot they liquefy, and turn to diamond rain. Nature quoted one of the researchers, Kevin Baines of the University of Wisconsin-Madison, as saying, "If you had a robot there, it would sit there and collect diamonds raining down," while also noting some are sceptical about the story.
At the south pole of a Saturn moon, Enceladus, there's a cryovolcanic area reaching a relatively toasty minus 116 degrees. It's known as the Tiger Stripes, for four almost parallel ridges that are 130 kilometres long, and split by central fractures. In 2005, observations by the Cassini spacecraft included a plume of icy material extending 500 kilometres above these stripes. Further research has shown that this is mainly water vapour and ice crystals, together with other chemicals including ammonia and carbon dioxide. The plume is brightest when Enceladus is at the furthest point in its orbit from Saturn, probably as the fractures become wider as Saturn's influence weakens a little.
The observations suggest that there may be a watery ocean beneath Enceladus' icy shell.
Last month came news of another moon that might similarly have a sub-surface ocean with extraterrestrial life - Europa, which orbits Jupiter. Europa had been considered one of the most intriguing objects in the Solar System since 1995, when observations by the Galileo orbiter led to theories it has a watery ocean beneath ice, and above a rocky interior.
Europa is criss-crossed by scars, and recent research bolsters notions that these arise from plate tectonics - with new material forming along some lines where ice plates are pulling apart, and other boundaries where plate material is pushed below the surface. "Having that mixing seems to be pretty important for establishing life," commented planetary scientist Alyssa Rhoden, a Nasa post-doctoral fellow who co-founded Destination Europa to promote plans for a new mission to this moon.
The plans were given added impetus by findings from Nasa's Hubble Space Telescope that were reported last month. Water vapour had been discovered above Europa, providing the first strong evidence that it has cryovolcanoes erupting water plumes. These may be vented by the linear cracks, much like the plumes from Enceladus' Tiger Stripes.
Also like Enceladus, the jets were only seen when Europa was furthest from Jupiter, perhaps as the vents open as Jupiter's gravitational influence fades. "The presence of the water has led scientists to speculate that the Europa we know today harbours life," Nasa's planetary science chief Dr James Green told BBC News.
But though such observations excite and tantalise scientists, budget constraints are holding back plans advocated by the Destination Europa team. Instead, the next mission to include Europa will be the Jupiter Icy Moon Explorer (JUICE), planned by the European Space Agency. This will assess the potential of three moons to support life, though will only pass close over Europa's equator, rather than its southern pole where the plume activity has been seen.
Even if all goes to plan with JUICE, we'll need patience to learn if it detects signs there could be aquatic aliens within Europa - as it's not due to launch until 2022, and will fly past the moons in the 2030s.
Martin Williams is a Hong Kong-based writer specialising in conservation and the environment. He holds a PhD in physical chemistry from Cambridge University