Four spacecraft are about to be sent to Mars. Kevin Nolan explains why there's more interest than ever in our nearest neighbour.
The cosmos is vast. Our sun is but one star of four hundred thousand million in the Milky Way galaxy. The Milky Way is but one of a hundred thousand million galaxies. But there is still a cosmic context for Earth - and we are becoming aware of it because of the relentless progress of research as humanity begins to figure out the big picture for our planet. Yet the big picture is far from complete.
Many now regard life on Earth as a planetary phenomenon, but we have little idea how life started, what external forces affect life here and what the cosmic abundance of life is. Our long-term survival may well depend on knowing the answers to such questions.
Mars presents a unique opportunity in the search for answers. In all the vastness of the cosmos, we find next door the perfect planetary companion, a cosmic stepping stone. Might life have arisen on Mars also? Might there be life there today?
We have had various suggestions. Only 80 years ago, we thought there might be an advanced Martian race living on the planet. When the Mariner and Viking space probes visited Mars in the 1960s and 1970s to reveal a sterile planet, we concluded it harboured no life. Lately, however, we have developed more sophisticated ideas of the process of life. Since the Viking missions, we have discovered life on Earth thriving in conditions more severe than those on Mars.
We know there was life on Earth soon after its birth. We see planets throughout the Milky Way where water is forming by the oceanful every day. We know there are trillions of comets coated with the chemical building blocks of life.
We also know a lot more about Mars. Recent probes have verified that it has water in abundance. Dried river beds point to an ancient history similar to Earth's. It is plausible that life formed on Mars during its infancy. Only after a billion years did Mars take a different path. There may have been a thriving biosphere for millions of years, and there could even be life there today, hidden under the surface. This is why we want to re-examine Mars, now we have learned which questions to ask.
Numerous organisations are involved, from NASA and the European Space Agency to smaller groups, such as the Planetary Society. This worldwide programme began in 1996, with the Mars Pathfinder rover mission. More recently, two orbiters were sent, the Mars Global Surveyor and Mars Odyssey. Next month, four more probes embark on their six-month journeys: two rovers sent by NASA and the European Space Agency's Mars Express, a two-in-one probe that incorporates an orbiter and the Beagle 2 lander.
All these probes will analyse the geology and climate of Mars in detail and look for water and signs of life. They also lay a foundation for the next generation of probes. NASA envisages long-range rovers and a new class of "scout" mission, including airborne vehicles on Mars by 2009. A "sample-return" mission by 2014, which would bring back Martian rocks and allow us to tackle the question of life on the planet, is also possible.
In 2007, the European Space Agency will send six landers to Mars, each carrying microphones built by the Planetary Society. They will use surround-sound techniques to hear the soundscape of Mars, regarded as important in understanding the planet's climate.
Although neither the European Space Agency nor NASA plans to send people to Mars, this flurry of probes is regarded as laying the foundations for a human mission in the future.
Looking closely at Mars allows us to look at ourselves in a broader context - as one planet among many that are similar to our own. But the greatest discovery has yet to be made. If even one microbe is found on Mars, it will confirm that there is life elsewhere - that we are not alone. It will reveal Earth as one planet of many that harbour life.
• Kevin Nolan lectures in physics at the Institute of Technology, Tallaght. He is co-ordinator to Ireland for the Planetary Society, the largest space interest group
NASA's new rovers
NASA sends two powerful new rovers on their way to Mars next month. Far more mobile than the 1997 Mars Pathfinder Sojourner rover, these twin explorers will be able to trek up to about 40 metres each Martian day.
Rover 1, right, should be launched on Sunday week, with an expected arrival at Gusev Crater, 15 degrees south of the Martian equator, in early January next year. Rover 2 should leave on June 25th, targeted at Meridiani Planum, two degrees south of the equator but halfway round the planet from Gusev. It should arrive in late January.
The main role of these identical rovers is to search for evidence of water that may have been present in the planet's past. They also carry cameras and scientific instruments.
They will descend to the surface in much the same way as Pathfinder, back in 1997. They will deploy parachutes to slow the spacecraft, then air bags will inflate to cushion the landings. They will bounce across the surface perhaps a dozen times and roll for a kilometre or more before they halt. The air bags will then deflate and retract, and the landers will open up to reveal the rovers.
These are much larger than the Sojourner rover and have a more ambitious mission. Sojourner travelled about 100 metres during 12 weeks; the new rovers should cover 10 times that in the first three months of operation. They weigh about 180 kilograms each and will use radioisotope heaters to keep electronics and moving parts warm in the overnight cold of -105 degrees.
Infrared and visible-light colour cameras will come into operation first, to give mission controllers targets for exploration. The rovers will analyse rocks and soils, using a rock-abrasion tool to expose fresh material.
The scientific mission is to study the history of the planet's climate and to look for signs of water. The sites, both of which have clear evidence of ancient water, were chosen after analysing data from the Mars Global Surveyor satellite.
The rovers' instruments will study the geological record of the two sites. The cameras will provide a detailed view of the terrain and identify the most promising rock and soil samples.
Some of the experiments are deployed on a robotic arm with spectrometers, a microscopic imager and the abrasion tool. - Dick Ahlstrom
The lander Beagle 2
The Beagle 2 lander will leave the Mars Express orbiter as the two approach the Red Planet, then plummet to the surface on its own. It takes its name from HMS Beagle, the ship that carried Charles Darwin on the voyage of discovery that allowed him to formulate the theory of evolution.
When folded, the lander resembles a fob watch. A heat shield will protect the lander as it begins its descent, then a parachute will deploy to slow it further. Once close to the ground, the chute will be cut and the lander will bounce down to the surface, protected by large air bags.
Once the lander pops open, it will begin studying the geology and mineral and chemical composition of the landing site.
It will use onboard experiments to search for life and also report on the weather and climate.
It has a "paw", a robotic arm that carries stereo cameras, a microscope, two types of spectrometer and a light. The cameras will direct controllers to promising samples, then a grinder will expose fresh surfaces. The lander also has a "mole", a sampler that can crawl across the surface and dig its way under rocks or drill into the samples.
These can then be cooked in a gas analysis oven inside the shell of the lander, to reveal their chemical composition. - Dick Ahlstrom
The orbiter Mars Express
Mars Express and its piggyback satellite companion, Beagle 2, will be launched from the Baikonur space centre in Kazakhstan on Monday and should reach Martian orbit by Christmas Day.
The project, which was planned bythe European Space Agency, is Europe's first satellite mission to a planet in our solar system.
The orbiter will handle communications between Beagle 2 and Earth. It also carries a high-resolution stereo camera that will be used to image the surface at high resolution, down to two metres per pixel.
It will produce one map of the mineral composition of the surface and another of the composition of the atmosphere, determining its global circulation.
It also carries a powerful radar-based instrument that will be able to probe for structures beneath the surface, to a possible depth of five kilometres. This will allow researchers to extend their search for frozen water well beneath the surface.
The orbiter will study how the solar wind, particles from the sun, affect the upper reaches of the Martian atmosphere. It is thought the solar wind may have helped strip away the planet's ancient atmosphere.
The wider project also involves contributions from NASA and from the Italian Space Agency. - Dick Ahlstrom