2008: a Martian odyssey
The terror lasted seven minutes. This was the time it took for Nasa's Phoenix spacecraft to slow down from a screeching 12,600mph to a sedate walking pace – its final speed when it landed safely early yesterday on the pebble-strewn surface of Mars.
During those seven minutes, the Phoenix had to endure temperatures of 1,500C as it slammed through the Martian atmosphere, before deploying its braking parachute, jettisoning a protective shell and firing the 12 small retrorockets that finally delivered the softest of landings. It was the first successful soft landing on the Red Planet for 32 years and made all the more momentous as it successfully used technology which might well, one day, allow humans to land on Mars.
The first signal from Phoenix that confirmed its safe landing on Mars took an excruciating 15 minutes and 20 seconds to travel at the speed of light the 171 million miles between Mars and its nearest neighbour, Earth.
At 00.53am British summer time on 26 May, scientists at mission control in California detected the first signal from a motionless Phoenix spacecraft, which had spent the past 10 months hurtling through 422 million miles of space. It was only then that tearful scientists at Nasa could breathe a massive sigh of relief.
"In my dreams it couldn't have gone as perfectly as it went. It went right down the middle," said project manager Barry Goldstein in Mission Control at the Nasa Jet Propulsion Laboratory (JPL) in Pasadena. "The hardest part is over. There's still a lot of drama left," said Dr Goldstein, who had kept up the JPL tradition of handing round "lucky peanuts" to his colleagues during tense moments, and who later tore up the contingency plans that would have been activated in the event of a mission failure.
The first pictures from Phoenix – the first from Mars's unexplored northern plain – showed a landscape of weird polygonal patterns woven into the Martian terrain like the stitches of a padded quilt – believed to be caused by the cyclical expansion and contraction of underground ice.
"We see the lack of rocks that we expected, we see the polygons that we saw from space, we don't see ice on the surface, but we think we will see it beneath the surface. It looks great to me," said Peter Smith of the University of Arizona in Tucson, the principal scientific investigator for the Phoenix mission.
Other images confirmed that the spacecraft's three feet were firmly planted on a stable surface and that its dust-free solar arrays had successfully unfurled to provide vital power. Only when the stereoscopic cameras panned to the distant horizon was it possible to envisage the flat enormity of this far north region of Mars, known as Vastitas Borealis.
Phoenix had risen from the ashes of a previous mission to Mars planned for 2001, which had to be abandoned because two earlier missions in 1999 had failed on two consecutive occasions. Indeed, only five of the previous 11 international attempts to land probes on Mars have succeeded, which made the success of Phoenix all the sweeter.
Ed Weiler, an associate administrator at Nasa headquarters in Washington, said that failure was always a possibility. "In exploring the universe, we accept some risk in exchange for the potential of great scientific rewards," he said.
The $457m (£231m) spacecraft is armed with an array of miniature science laboratories and instruments designed to detect the organic building blocks of life – substances containing carbon and hydrogen. But one of its most important tasks is to detect that most vital ingredient of all – water. Phoenix itself formed part of Nasa's strategy to "follow the water" in its search for the chemical evidence of microscopic life on Mars, whether it existed in the past or is still alive today.
"The main goal of the mission is to get below the surface of Mars to where we are almost certain there is water," said Dr Tom Pike of Imperial College London, a member of the British team involved with Phoenix. "Water, of course, is of critical importance because it is one of the building blocks – one of the essential habitats we need – for life."
Within the next day or so, Nasa intends to deploy the spacecraft's near-8ft-long robotic arm with a scoop that can dig into and under the surface and hopefully bring back frozen samples to the on-board instruments that can chemically analyse the material, convert the information into the digital language of computers and transmit the data back to Earth.
The three-month mission is the first on Mars to be conducted so far north, well into the "permafrost" region where underground ice deposits are believed to lie just near to the surface.
The last time man realised a soft landing on Mars was in 1976, when two Viking landers successfully landed on an equatorial region, where water is not thought to exist. Since then, all landings, including the highly successful Mars Exploration Rovers, Spirit and Odyssey, in 2004, have used inflatable balloons to cushion the final impact of descent.
Scientists said that the significance of a successful soft landing using retrorockets cannot be overestimated. This is the most likely technology to be used in any future manned mission.
Phoenix, the brainchild of scientists at the University of Arizona, was chosen from a short-list of 24 proposals to become Nasa first's mission in its "Scout Programme". It was launched from a Delta II rocket on 4 August 2007 and, when unfolded, it measures 18ft long and 7ft tall.
Missions to Mars
By David Hewitt
July 1965: Nasa's Mariner 4 completes the first successful fly-by of Mars. In total, 634kb of data, which would fit comfortably into a modern mobile phone memory, is beamed back to Earth, showing a crater-marked, lunar landscape, now known to be largely unrepresentative of Mars in general.
December 1971: The Soviet Union successfully lands its Mars 2 and Mars 3 probes. Although equipped with a surface rover and television cameras, the mission fails because the main parachute does not open and the descent module is destroyed on impact.
August 1976: Nasa launches its most ambitious mission so far, the Viking. After six years, Viking 1 fails to detect evidence of microbes on the planet, but the detail of the colour pictures sent back makes the mission a success. Still used today, the images returned include the famous "Face on Mars", taken by some conspiracy theorists as proof of extra-terrestrial life.
July 1988: The Soviet Union's exploratory efforts are again dealt a blow as its Phobos mission to Mars and its two moons is plagued by glitches. The Phobos 2 craft does manage to take some photos while in orbit but contact with Phobos 1 is lost before it can release its surface probes.
November 1996: Following the resounding failure of its Mars Observer orbiter four years before, Nasa launches the Mars Global Surveyor. Deemed a success, the mission comprehensively maps the surface of the planet before contact is lost at the end of 2006. The new images reveal that the "Face on Mars" is nothing more than a trick of the light, created by shadows.
October 2001: Nasa's Mars Odyssey, named after the science fiction film, enters orbit. In addition to detecting large amounts of hydrogen, thought to be contained in water ice deposits, the Odyssey also serves as a relay between Earth and the space agency's Mars rovers and Phoenix lander.
2003: The European Space Agency attempts its first planetary mission, the Mars Express. While the Mars Express Orbiter has been successfully undertaking high-resolution imaging and mineralogical mapping of the planet since 2004, the landing craft Beagle 2 crashes near the Martian South Pole.
May 2008: Nasa's Mars Phoenix lander touches down on and sends back historic pictures of its northern plain. Over the coming months, it will dig for sub-surface water ice which could prove that Mars once supported life.