Many scientists and astronomers are happy to admit to believing that there is – or, at least, that there has been – life on Mars, even if the proof has yet to be found.

No firm evidence for the existence of microbes or even organic chemicals has yet been found on the Red Planet, but there is surprising faith among researchers who study it that such discoveries will be made just as soon as humanity can get the right technology to the right place.

Some base their confidence on tantalising hints of organic material among the data collected by the Viking missions of 1976, though nothing conclusive was found.

Others have been convinced by the recent successes of a flotilla of spacecraft sent to Mars over the past decade. The orbiters Mars Global Surveyor, Mars Odyssey and Mars Express, and the Spirit and Opportunity rovers, have proved beyond doubt that the cold and arid planet was once warmer and wetter.

Some water, frozen as ice at the poles and below the surface, is known still to exist, and it is even thought that it may sometimes still thaw and bubble up in sudden torrents. Pictures taken in 1999 and 2005 show fresh channels apparently cut by running water.

All this is significant because, wherever there is liquid water on Earth there is also life – and widespread presence of one on Mars could thus prefigure the discovery of the other. Such organisms may be extinct, or they could be in suspended animation and be periodically revived when melting ice makes water available.

So far all the evidence for water has come at one remove, sensed remotely from orbit or from the rovers’ geological examination of rocks that have been affected by the planet’s wetter past. Humanity’s robots have yet to get their feet wet in actual Martian moisture – which is where Phoenix comes in. It has been deliberately sent to the north polar region of Mars, a place where there is plentiful water ice just beneath the surface.

The first pictures sent back by the spacecraft seem to confirm this. Though no ice can be seen on the surface, there is a pattern on polygon shapes on the ground that had been spotted from orbit. These are thought to have been formed by the freezing and thawing of soil.

Phoenix is fitted with a 2.35metre robotic arm, with which it can dig up to 50cm into the ground. This should be deep enough to reach the icy permafrost layer and study Martian water directly for the first time. The probe is not equipped to hunt for past or present life, but it will be capable of detecting chemical signatures of a habitable environment in the permafrost. It will also be studying the Martian weather at the poles.

The safe arrival of the spacecraft is a triumph in itself. Mars is sometimes known as the “Bermuda triangle” of space, such is the poor record of past missions. Only five previous attempts to land on the planet were successful, and many orbiters have been lost too. In 2003 Britain’s Beagle 2 probe failed to make contact after entering the Martian atmosphere, and Nasa’s Mars Polar Lander was lost in 1999.

The latest probe is also important as a test of landing technology. The most recent landers bounced to the surface shielded by protective airbags, but Phoenix made a soft landing, cushioned by retro-rockets that slowed its descent.

Phoenix is designed to operate for 90 Martian days, each of which lasts for about 40 minutes longer than an Earth day, though if the performances of Spirit and Opportunity are anything to go by it may keep experimenting for much longer. The two rovers were supposed to work for six months after landing in January 2004, and are still going strong more than four years later.

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