Return to Mars

After a break in Martian exploration of almost two decades, the late 1990s saw the beginning of a new wave of more sophisticated probes - orbiters, landers, and rovers that have transformed our view of the Red Planet.

MARS GLOBAL SURVEYOR

The thrusters on MGS were able to tilt the probe 30° in any direction to photograph the Martian surface at oblique angles, and even look at objects close to Mars such as its two small moons and other orbiting spacecraft.

SOJOURNER ROVER

The Sojourner Rover was a small but robust vehicle, just 65cm (26in) long and weighing 10.6kg (23.3lb). With a maximum speed of 60cm (24in) per minute, it could range up to 500m (1,650ft) from the Pathfinder lander.

Alpha Proton X-ray

Spectrometer

The 1980s and early 1990s were a bad time for Mars-bound spaceprobes. NASA's immediate plans to follow up on the success of Viking were shelved as the rising cost of the Space Shuttle programme forced cutbacks elsewhere, and a series of Soviet probes fell victim to a variety of accidents and mishaps. For example, two sophisticated Phobos probes were lost in the late 1980s - the first when a faulty signal from Earth accidentally ordered the probe to shut down, the second for unexplained reasons shortly after Phobos 2 had entered orbit.

Even when NASA did finally launch a new mission to Mars, it proved to be a false dawn, as Mars Observer, sent on its way in September 1992, mysteriously lost contact shortly before entering orbit. With such bad luck, some people even started to joke about a "curse of Mars".

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Alpha Proton X-ray

Spectrometer

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Rocker-Bogie^ Mobility System warm electronics box

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The long wait ends

It was not until 1997 that a relatively small spacecraft, Mars Pathfinder, finally touched down in the Ares Vallis region. As the probe unfolded its triangular, petal-like solar panels, it released a small rover called Sojourner, which trundled onto the Martian soil on 4 July and immediately began to explore the rocky landscape around it. Sojourner operated for 83 Martian days, well beyond its expected lifetime, and even while it was still roaming the surface, another mission slipped into orbit above it. Mars Global Surveyor (MGS) brought with it sophisticated, high-resolution cameras that could distinguish objects just a few metres across. In order to slow itself into a lower orbit, however, the probe used the aerobraking technique rehearsed by the Magellan Venus mission (see p.266), slowly spiralling inwards until it was ready to begin its serious work in April 1999. MGS provided a stunning new view of Mars, sending back detailed pictures for some seven-and-a-half years -six years beyond its primary mission. Perhaps its most important revelation was the presence of eroded gullies on some canyon slopes and crater walls, which many experts believe are evidence of liquid flowing on Mars in the very recent past. Elsewhere, the presence of near-pristine lava flows suggested that Mars may still have volcanic activity too.

PRESIDENTIAL PANORAMA

A mosaic of photographs from the Mars Pathfinder lander, this so-called Presidential Panorama includes ten separate images of the Sojourner Rover investigating the nearby londscope. The londer itself is surrounded by the deflated airbags that cushioned its landing.

4 January 2004

The Spirit Mars Exploration Rover lands in Gusev Crater.

25 January 2004

The Opportunity Mars Exploration Rover lands in Meridiani Planum.

MARS IN STEREO

The stereoscopic camera on Mars Express produced spectacular 3-D images such as this one of ice trapped in a deep crater. The probe itself (right) was rapidly designed using the same basic spacecraft as the Rosetta comet probe.

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THE ILL-FATED BEAGLE

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Beagle 2 (named after the ship on which naturalist Charles Darwin travelled) was a small probe designed specifically to look for signs of life on Mars. The probe separated from the Mars Express orbiter on 19 December 2003 and entered the atmosphere on Christmas Day. It was supposed to touch down in the equatorial region of Isidis Planitia, open up, and use a robot arm to collect rock samples for analysis in various instruments. But nothing was heard from the Martian surface - it seems likely that Beagle 2 was disabled by hitting a crater wall as it landed.

Beagle 2 (named after the ship on which naturalist Charles Darwin travelled) was a small probe designed specifically to look for signs of life on Mars. The probe separated from the Mars Express orbiter on 19 December 2003 and entered the atmosphere on Christmas Day. It was supposed to touch down in the equatorial region of Isidis Planitia, open up, and use a robot arm to collect rock samples for analysis in various instruments. But nothing was heard from the Martian surface - it seems likely that Beagle 2 was disabled by hitting a crater wall as it landed.

MARS IN STEREO

The stereoscopic camera on Mars Express produced spectacular 3-D images such as this one of ice trapped in a deep crater. The probe itself (right) was rapidly designed using the same basic spacecraft as the Rosetta comet probe.

As NASA accelerated its programme of Martian probes, bad luck struck again - Mars Polar Lander, which should have investigated the planet's southern ice cap, was lost just before entering the atmosphere in December 1999, while Mars Climate Orbiter hit the planet after an embarrassing navigational error.

Two years later, 2001 Mars Odyssey reached orbit successfully. Designed to complement MGS, Odyssey included imagers and spectrometers to study Mars at different wavelengths and probe the chemicals in its rocks. Its most important finding was probably the presence of huge amounts of hydrogen (probably in icy permafrost) around both poles.

Europe goes to Mars

ESA's first interplanetary probe, Mars Express, arrived at the Red Planet on Christmas Day 2003. The probe had two parts - the Mars Express Orbiter and a small, and ultimately doomed, British-built lander called Beagle 2 (see panel, above). The orbiter carried spectrometers to investigate the chemistry of the Martian surface and atmosphere, a ground-penetrating radar to study buried features, and a camera that produced three-dimensional views by photographing areas of the surface from two slightly different angles. Mars Express's most important finding so far is the presence of methane in the Martian atmosphere. It seems this gas can come from only two sources - either active volcanoes or some form of life.

In 2004, two new NASA rovers arrived on Mars (see over). Larger and more robust than Sojourner, these Mars Exploration Rovers, Spirit and Opportunity, sent their data back to Earth directly or relayed through the MGS and Odyssey orbiters. Spirit's landing site in Gusev Crater had a broad, river-like channel flowing into it, and scientists hoped that the terrain might be covered in sedimentary rocks laid down by dust settling out of a standing lake. But surprisingly, the rocks turned out to be mostly volcanic.

Opportunity's landing site in Meridiani Planum was thought to lie near the shore of an ancient shallow sea, and when the probe visited a small nearby crater its operators were delighted to find sedimentary rocks in its walls and traces of minerals that probably formed under water. Despite gradual deterioration due to a build up of fine Martian dust, the rovers were still functioning three years after their arrival.

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TECHNOLOGY

NASA'S SPIRIT AND OPPORTUNITY

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