The hunt for water on Mars goes nanoscale
Small packages on Phoenix
If space, as Douglas Adams said, is mind-bogglingly big and the nanoscale is mind-bogglingly small, it seems incongruous to hear that Swiss scientists are going to use the latter, in the form of atomic force microscopy, to explore the former.
Yet that's exactly what the team, led by Urs Staufer, an associate professor at the Institute of Microtechnology at the University of Neuchâtel, will be doing when NASA's Phoenix Mars Lander launches this week*. It is due to land on the Red Planet in March 2008.
It makes more sense when you find out what they're looking for: water. Or, more precisely, signs of past life. In addition, analysing the soil samples should indicate the kind of environment future missions, manned or unmanned, will have to contend with. Of particular concern are quartz particles, which pose a health hazard to humans and can damage machines. Studying Martian dust and its interactions with its surroundings will also help scientists model Mars's climate and geology.
In building the Microscopic, Electrochemistry and Conductivity Analyser (MECA), Staufer and his team had to take into account parameters they don't usually have to deal with in normal operation in the lab. The device has to work at temperatures ranging from -60°C to +2°C. It has to operate at atmospheric carbon dioxide pressures of one to 10 mbar. It has to be radiation tolerant, use less than 10 watts of electricity, and cope with shock and vibration during the start, flight, and landing, and it had to have a mass of under 250g because each gram costs $50,000 to get to Mars.
Finally, on Mars, at least for this mission, there will be no on-site operator. Changes to the robot arm's programming will have to be made from Tucson in the narrow window of time each day during which communication is possible.
The key piece of machinery is a two metre robot arm, which will dig through the top soil layer and scoop up samples of buried soil and water-ice to the lander platform for scientific analysis. Riding inside the robot arm, MECA will examine soil samples to determine chemical properties (acidity, saltiness, and composition) and examine the soil grains through a microscope to determine their mineralogy and origin. Needles sunk into the sample will determine its water and ice content.
The atomic force microscope that forms the heart of MECA is the piece supplied by Staufer and his team. It is made up of three parts: a microfabricated silicon sensor chip, an electromagnetic scanner, and the controller electronics. As much of the necessary functionality as possible has been built into the chip.
The microscope itself, which will work down to the 20 nanometer scale the mission needs, collects the data from which it forms images from a sharp tip mounted on a tiny cantilever whose deflection in response to stress provides additional feedback. Since there will be no operator available to change tips, the chip has eight cantilevers mounted on it. If the tip in use becomes broken or damaged, the chip is pushed against a support beam that will break off that cantilever, moving the next one into use. Staufer describes the process as "like using a match box".
Soil samples collected by the robot arm will be poured onto a sample wheel and rotated in front of the microscope. If an interesting area is found, scientists will be able to direct it to zoom in and send images. Once the images arrive in Tucson, Staufer and his team will have about four hours to look at them, decide what else they want to look at, compile commands, and send them up to Mars for the next moves. Staufer and his team will spend three months in Tucson living on Mars time – the Red Planet's days are 40 minutes longer than ours.
The device had to pass a number of qualification tests – for example, vibration, and shock. However, it avoided the more stringent qualification tests it would have had to pass if it were going to come into direct contact with the Mars surface. ("We don't want to contaminate the ground on Mars," Staufer explains. ) Besides, keeping the instrument inside the robot arm provides better protection for the delicate cantilevers (although, Staufer notes, they tested it and proved the instrument can survive the autoclave).
The idea that there might be life on Mars has waned and waxed in popularity since the 16th century, when astronomer Tycho Brahe first observed the planet. In the 17th century, Dutch astronomer and watchmaker Christian Huygens spotted the polar caps. In the 19th century, French astronomer Honoré Flaugergues observed the polar caps more closely and concluded there must be seasons.
Later that century, Italian astronomer Giovanni Schiaparelli named the seas and continents and identified "canali", the Italian word for channels. Widely misreported as canals, these structures were eventually shown to be artefacts of the lenses Schiaparelli had available. Just before the turn of the 20th century, H G Wells wrote War of the Worlds, which had the intelligent aliens living on Mars invade Earth because they had run out of water. At that time, the existence of life on Mars was debated by serious scientists.
But by 1975 the images from Mariner 4 and Viking 1 and 2 had changed our view of the planet: no life was detected and, given the high levels of ultraviolet radiation and highly active oxidants, scientists concluded that life was impossible in the layers close to the surface. The idea of life on Mars became part of fringe science.
Then, in 2002, the Mars Odyssey Orbiter discovered large amounts of subsurface water-ice in the northern arctic plains. The Phoenix Mars Mission uses components of two more recent, unsuccessful Mars missions to study this region – hence the name "Phoenix", as the mission has literally risen from the ashes of its predecessors. ®
*There is a three week launch window which opens on Friday, 3 August.
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