IN the early hours of Christmas morning a pale red dot visible just above the horizon in the evening sky will become the focus of extraordinary global attention. Shortly after 2 am GMT, Mars will receive a small visitor from Europe, followed shortly by two visitors from the US. And if that weren鈥檛 stretching the bounds of hospitality, Mars is already playing host to two American orbiters. Never has the Red Planet been so busy.
Back on Earth, the stakes for many scientists and engineers could hardly be higher. These missions have been designed to look for signs that Mars was once wetter and warmer, conditions that many believe would have made Mars ripe for the evolution of life. And the European lander, Beagle 2, is equipped to spot signs of life itself. It is just possible that in the next few weeks we will discover that we are not alone in the universe.
The first to arrive will be Mars Express, the European Space Agency鈥檚 maiden mission to another planet. It consists of the Beagle lander and an orbiter that will photograph the surface and relay data from Beagle back to Earth.
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On Christmas morning Beagle will enter the Martian atmosphere like a meteor and in the space of a few minutes will jettison its heat shields, deploy parachutes and finally, only a few metres above the surface, inflate a set of airbags that will absorb the force of impact. Almost immediately, its protective cover will open like a flower and the craft will get to work. 鈥淚t should basically start as soon as it鈥檚 on the surface and the petals are deployed. It works autonomously,鈥� says Don McCoy, an aerospace engineer working on the mission.
The lander consists of a base with solar panels and batteries to provide power, and a flexible robotic arm housing the most important instruments. Like a meerkat standing on its hind legs, the raised arm will survey the landing site with a stereoscopic camera to show scientists back on Earth which rocks merit further investigation. The arm will then bend over to examine any suitable targets. Its microscope will reveal the rock鈥檚 structure and two spectrometers will bombard it with gamma rays and X-rays and analyse the spectra of the reflected rays. This should give an accurate picture of the rock鈥檚 composition.
The robotic arm is also fitted with a corer to take samples for further analysis. The arm can even deploy a small, tethered jack hammer known as the mole that can crawl up to 3 metres away to collect samples or dig several centimetres beneath the surface before being reeled in with its load.
Whatever the mole and the corer find will be studied for signs of life by perhaps the most important instrument, the gas analysis package (GAP). This will heat the samples and analyse their carbon isotope content using a mass spectrometer. Molecules containing the lighter carbon-12 isotope tend to react more quickly than those containing its heavier carbon-13 cousin. Because of this, complex reactions tend to concentrate carbon-12 at the expense of carbon-13, so their ratio in a material is a good measure of the complexity of the chemical processes that created it. A relatively low ratio means the sample was created in a simple chemical process such as precipitation, but a high ratio points strongly towards a much more complicated genesis. On Earth, the highest ratios are produced by the complex reactions of life.
The GAP will also measure methane levels in the atmosphere. Methane is quickly broken down by sunlight, so even tiny levels must mean that it is being produced somewhere on the surface. If methane is present, one possibility is that it is slowly leaking from deposits beneath the surface. 鈥淚f there was life at one time there could be traces of methane left in the soils,鈥� says McCoy. But the gas could also come from living organisms.
During the lander鈥檚 180-day mission, its parent vehicle will play second fiddle, sending data back to Earth and slowly finalising its orbit over the Martian poles from where it will command a view of every part of the planet at every time of day and night. Then over the next two years, the orbiter will map the planet at resolutions down to 2 metres. It will study the density of the atmosphere and the pattern of Martian winds by broadcasting radio signals back to Earth just as the spacecraft passes behind the planet. These signals will have to pass through the atmosphere to reach Earth and the distortions this introduces can be used to determine atmospheric conditions. A radar system will even map the permafrost that is thought to lie below the Martian surface.
Almost two weeks after the Beagle has landed, the first NASA rover will arrive. The second is due on 25 January. The landings are timed so that NASA鈥檚 Global Surveyor will be overhead at the moment of impact. If something goes wrong, it could provide crucial information for coming up with a solution or at least providing useful lessons for future missions. If all goes well, the rovers will take their first pictures and transmit them just before sunset on their first day. Then they will shut down their instruments and turn on heaters to protect them through the cold Martian night.
The identical rovers 鈥� each the size of a quad bike 鈥� will roll across the surface on six wheels, examining rocks and photographing their surroundings. The dual approach is partly insurance in case one rover is damaged, and partly because of the advantage scientists will get from comparing identical measurements made at two different parts of the planet.
Unlike Beagle, they are not equipped to look for signs of life directly. Instead, they will trundle over the Martian surface searching for evidence that it might once have been much wetter than it is today. 鈥淭he scientific focus of our mission is to try to determine whether or not Mars ever had conditions at its surface that would have been suitable for life. The surface today is dry and barren, yet you have these tantalising clues that it might once have been different 鈥� river beds, mineral deposits associated with hot springs,鈥� says Steven Squyres, an astronomer at Cornell University in Ithaca, New York, and the lead scientist for NASA鈥檚 rover missions.
He says there鈥檚 no question that there was once water on Mars. 鈥淲hat鈥檚 an open question is whether or not water was present long enough to provide appropriate conditions for life. Was it just a brief flood? Or were there long-standing bodies of water, or persistent hot springs? What we鈥檙e after is not just whether there was ever liquid water, but what the environment was like.鈥�
The clues will be hidden in the rocks. Sitting atop a mast that rises 1.4 metres above the ground, the rovers鈥� cameras will allow scientists back on Earth to identify interesting targets from a distance. The vehicles will then move up close and begin studying them in more detail. What Squyres is after is a good idea of the size and shape of the grains that make up the rock, indicating whether it is volcanic, for example. Any layering might suggest it was laid down underwater.
Each rover has a small robotic arm fitted with a grinder that can remove the outer surface of any rocks to see what鈥檚 beneath. 鈥淭he rock-abrasion tool serves the same function as a rock hammer for a geologist in the field. After a rock has been exposed to the elements 鈥� sunlight and moisture 鈥� the outer layers may become non-representative.鈥� Then the detailed analysis begins. The arm is fitted with a microscope to photograph the exposed area and a couple of spectrometers to determine the rock鈥檚 chemical composition. 鈥淥ne of the things we would hope to get is a sense of whether water activity was brief, or whether it went on for some time,鈥� he says.
If it did, and if any of the Beagle鈥檚 experiments come up trumps, the number of spacecraft prospecting Mars today could be overwhelmed by a swarm of visitors from Earth in the not too distant future.
