As 2004 was but a few days old, there was much cheering at NASA’s Jet Propulsion Laboratory as the two Mars landers touched down safely and unleashed the two Rovers to deploy their instruments. Celebrations at ESA were not so universal, as the Beagle-2 miniature geochemistry laboratory vanished without trace. Beagle could in principle have proved the existence or otherwise of Martian life, had it survived and landed on suitable ground. Still, ESA’s Mars Express orbiter was safe and promised oodles of highly detailed pictures and other data. What followed was an embarrassment of riches from both the US and EU missions, more or less throughout the year. Then ESA had real cause for partying as 2005 opened, as its Huygens probe landed on the largest and most enigmatic moon in the solar system, Saturn’s Titan, but that is a story that will run this year, and it was carried courtesy of NASA’s Cassini mission. New Scientist featured an excellent summary of the achievements on Mars in its 15th January 2005 issue (Chandler, D.L. 2005. Distant shores. New Scientist 15 January 2005, p. 30-39). Everything has worked better than expected, Rovers Spirit and Discovery having the benefit of sand blasts that cleared the dust off their solar cells. They are still functioning, though not exactly prancing – it has taken a year for them to travel just over 5 km between them. But the treasures they have unfolded have delighted lots of geologists. There is ample evidence at least for the former influence of liquid water at the surface, which has both weathered the Martian surface to produce iron minerals that witness both water and highly acid conditions and also laid down sediments in layer after layer. Some hint at the former existence of a large shallow, salty sea where Discovery landed. Mars Express’s imaging devices have produced high-resolution pictures that confirm the influence of water’s sculpting, seemingly late in its history, and the presence of recent glacial deposits. The orbiter also carries a deeply penetrating radar device (MARSIS) capable of finding water up to a kilometre beneath the surface, though it has yet to be deployed. Perhaps the most intriguing find is that Mars’ atmosphere has more methane in it than seems possible, unless something is continually emitting it. That “something” could be volcanism (2004 also revealed signs of previously unknown, recent eruptions), methane may be leaking from sub-surface gas-hydrates similar to those beneath Earth’s sea floor, it could be emitted by icy material from comet debris, and maybe it signifies some primitive, methanogen life forms that are respiring. The last needs to be tied down very rigorously before scientists get over excited. Even if it matches up with signs of emitted water vapour, which it does, that could still be an abiogenic phenomenon. There can be little doubt that Mars is proving irresistible as a political draw, riding on its kudos to hammer out the old message that “Man Must Go There!”. But consider this: had today’s robotic technology and analytical miniaturisation been possible 35 years ago we would know vastly more than we do about the evolution of our neighbour the Moon. Instead of carrying astronauts and their weighty life support systems, the Apollo missions would have brought back an equivalent mass of lunar rock. The same goes for Mars, surely, on the old basis of getting “more bangs for your buck”. But that is a scientific outlook, and maybe the bucks can only be raised by the romantic notion of some brave souls treading where Edgar Rice Burrough’s John Carter once rode astride his banth. But of course, robotic science can also ride on that “vision”, for what could be more catastrophic to whichever US president succeeds in making George W. Bush’s dream come true to find that it is not safe enough out there, and the astronauts do not come back.
Plotting meteorite falls
Museums host collections of thousands of meteorites donated by collectors over more than a century. Although they are the source of much of our understanding about the timing and processes involved in the origin of the solar system and of the Earth itself, the collections are biased towards those that are most easily spotted on the ground. Metallic meteorites show up much more readily than do those made of silicate minerals, which resemble ordinary terrestrial rocks in colour and density. Only when collectors pore over very uniform, light coloured surfaces, such as ice caps, deserts and bare limestone plateaux, can they be assured of a truly representative selection of types. Also, many meteorite samples are weathered and contaminated with earthly materials, because they have lain around on the ground for a long time. Improved precision and detection limits of the chemical analytical tools that meteorite specialists use demand fresh material, as do researchers interested in organic materials carried from space – the embarrassment of having an announcement of a fossil bacterium in a meteorite and then finding that it is some common bug from soil is career threatening. Most important are trying to overcome the compositional bias and to see from which part of the sky different kinds of meteorite come. Phil Bland of Imperial College, London is trying to solve all problems at a stroke. His idea is to set up a network of wide-angle sky cameras to record meteor trails, so that computer analysis of the film will triangulate the point of impact and also work out the precise orbit of the offending body. The ideal place – easy to get to, safe, flat, dry unvegetated and dominated by pale rock – is the infamous Nullarbor (“No Tree”) Plain of SW Australia, which is one of the most featureless places on Earth. Bland already has one sky camera in place that has sensors that only turn it on if the sky is clear, and an internet connection that e-mails him if something as malfunctioned. In one year it spotted 12 trails bright enough to have resulted in meteorites falling to the surface. With three cameras, he hopes that results will be sufficiently accurate to narrow search areas to a square kilometre. If funded, the extended project will even incorporate e-mail alerts to teams of local collectors, whenever a trail exceeds a certain brightness. They should then be able to pristine recover material in a few days.
Source: Muir, H. 2004. Catch a falling star. New Scientist, 25 December 2004, p. 45-47.