* Astronomy

As the first rays of summer sunshine glint off the frosted surface of Mars, scientists in California are preparing an ambitious search effort to locate a spacecraft that went missing there as it prepared to land six years ago.
If all goes according to plan, the carbon dioxide frost over the martian landscape will melt enough to leave a clear view of the ground as Nasa's orbiter, Mars Global Surveyor, approaches the intended landing site. As it hurtles overhead, the orbiter will roll in the sky, giving its camera the best chance to snap the missing spacecraft, or remains of it.
If the team is successful in taking a picture of the missing probe, the Mars Polar Lander, it will help to lay to rest a big question that has been hanging over all of those involved in the mission: what went wrong? The answer will help to ensure that future missions do not suffer the same fate.
The search for Mars Polar Lander is only the latest in what has become an intriguing sideline. Mars and the moon, especially, are littered with machines that were lobbed from Earth and lie scattered across the coldest of landscapes. Once the pinnacle of technology, they have become exhibits in a celestial museum of human space exploration.
The team operating the camera on Mars Global Surveyor (MGS) were asked by Nasa officials to hunt for Mars Polar Lander shortly after it disappeared in December 1999. Last month, they said they might finally have spotted it. Images from a previous orbit show what looks to be a parachute and a bright speck surrounded by a dark stain, conceivably the probe lying in the blast zone created by its landing rockets. But the images are poor and far from conclusive. "We don't know if it is the Mars Polar Lander, but it's a good candidate," says Ken Edgett, from Malin Space Sciences.
In an attempt to nail down whether they have located the missing lander, in a few months, when the Martian summer is at its peak, the scientists will use a new technique that enables MGS to take sharper pictures. As the orbiter flies by, it is instructed to pitch over, allowing the camera to dwell on its target for longer. Instead of only spotting objects 1.5m across, it should pick out anything larger than half a metre.
For Rich Zurek, a scientist at Nasa's Jet Propulsion Laboratory in Pasadena, the search has particular significance. Zurek worked as lead scientist on Mars Polar Lander and devoted five years to the project. "It's unfinished business, both emotionally and scientifically," he says. "If we knew where it was on the surface, that alone would rule out some of the failure mechanisms that have been hypothesised."
The leading theory is that the deployment of the lander's legs triggered a software glitch that fooled the probe into thinking it had touched down when it was still high above the surface. "When it started firing its rockets to slow its descent, it thought, 'oh, I'm already down', and shut them off, so it probably fell 50m or more," says Zurek.
Hopefully, any pictures MGS can grab of Mars Polar Lander will confirm what went wrong, and prevent the same mistakes happening again. "We already have another lander based on the same design, so understanding where it went wrong is crucial," says Zurek. "If our idea of what happened is right, it really amounts to the inversion of a few lines of software code and to have come so close, that's a frustration, but it's also motivation to do it right next time."
The group at Malin Space Sciences is already building a reputation for finding old spacecraft on Mars. Last month, they released images of Viking 2, the probe that touched down on the planet in 1976 and took some of the most recognisable images of its landscape. "It was spine chilling to see it," says Edgett. "Not only is this the lander, but you can see its shape and it's been sitting there nearly 30 years."
The position of Viking 2 is invaluable to scientists, as it puts all of the images it took in context. "Once you know where it landed, where those pictures were taken from, you can better interpret them. All of a sudden, all the things it saw from the ground fall into place," says Edgett.
Of course, among the lost probes on Mars is Britain's own Beagle 2, and the possibility that the Malin scientists might be able to find it was not lost on Beagle's lead scientist, Colin Pillinger. Hope was that Mars Express, the European Space Agency probe that flicked Beagle 2 towards Mars before going into orbit itself, would be able to join the hunt, but its cameras have not yet been any help. "When Beagle went missing we got in touch with Malin and they've been exceedingly helpful. Remember, though, we're looking for a few pixels out of three billion," says Pillinger.
So far, the group at Malin Space Sciences has searched about 70% of the region in which Beagle 2 should have landed. Last August, they thought they might have found it, but it turned out to be a false alarm. "We used the new technique with the camera and found it wasn't hardware, but a tiny sand dune that was out of place," says Edgett.
Finding Beagle 2 is going to be a tougher job than many, simply because it is so tiny. If it is still in its capsule, if the parachutes didn't come out, or if the airbags didn't deploy, it could well be beyond the capability of the MGS camera, says Edgett. If the Malin team can find Beagle 2, it will give the team behind the probe the excruciating knowledge of just how close they got. "A lot of the team who designed the engineering took a lot of the flak. If we could find it, we could at least say, well, we got so far, so close, and we could do it if we were given the opportunity again," says Pillinger. He may not have too long to wait. "We don't know if we're going to find anything, but we are still looking. The search will go on," says Edgett.
While Mars has become a sparse junkyard of modern space technology, the moon is more of an attic, home to discarded machines that were put up there decades ago, and now aged enough to achieve iconic status. There are the landing stages of the Apollo missions that first put man on the moon. There are dusty Soviet Lunokhod rovers. Alan Shepard's golf balls are still lying around somewhere on the moon, and what could beat the original moon buggies as an insight into the priorities of the early US space programme?
"There's a lot of junk up there. One of the last things the astronauts did before heading back to their command module before blasting off was to empty their garbage and toss out all sorts of things, particularly when they were returning with a lot of lunar rock samples," says Peter Golkin, at the Smithsonian Institute's National Space and Air Museum in Washington DC. There are also more poignant items among the junk. Many astronauts took pictures of their families to the moon and left them behind. There is a small memorial to fallen astronauts.
Much of the moon junk is testimony to the ingenuity of the scientists behind the early space missions. Apollo astronauts took experiments to the moon that were set up and left running on power from small nuclear batteries. One of the experiments used seismometers to monitor vibrations in the moon, to pick up any internal geological activity or detect the impact of any meteorites or asteroids that hit. The snag was how to calibrate the seismometers. The solution scientists hit on was effective, if blunt. On blasting off, the astronauts would fire the spent booster stage directly at the moon. "They knew its mass and velocity, so they'd crash it into the moon and know exactly what sort of impact it should register," says Dave Williams, at Nasa's Goddard Space Flight Centre.

In the short term, it falls to European scientists to grab pictures of space history on the moon. Earlier this year, the European Space Agency's Smart-1 probe, which is in orbit around the moon, took pictures of the original Apollo landing sites and spotted the places where two Soviet probes touched down. Right now, Smart-1 is probably in too high an orbit to pick out any hardware that is lying around.
Should Smart-1 fail to stumble across any of the old moon probes, the task may be passed on to another mission, the Lunar Reconnaissance Orbiter, which is due to launch in 2008. With higher resolution cameras, it should be able to take unprecedented images of the lunar surface and the technological detritus that litters it.
The sheer tonnage of historic junk left on the moon and Mars has prompted some to wonder who owns it all. Could someone ultimately salvage it for their own private collection? According to Golkin, UN guidelines are already in place to cover such an eventuality. Put bluntly, the UN's Outer Space Treaty states that any probe remains the property of its terrestrial owner regardless of where it ends up.
The Smithsonian Institute has a deal with Nasa that gives it first refusal on any old mission hardware. "Because there seems to be no impending visits to the moon by eager souvenir hunters, this hasn't been considered a very pressing issue," says Golkin.
As Malin Space Sciences prepares to search for the Mars Polar Lander, Rich Zurek is readying another probe that might join the hunt. On August 10, the Mars Reconnaissance Orbiter is due to blast off with a camera that can pick out objects as small as 30cm across. The satellite is due to arrive in Mars orbit in March 2006. "Maybe we'll find it, maybe we won't," he says. "There are a lot of things to look at on Mars, and at some point you have to accept that these old landers, well, they're just chunks of metal now."

Mars: the missing missions

USSR Sputnik 1962
Launched November 4, 1962. Mass 890kg
The Sputnik 24 is the first lander ever designed for Mars, but a delicate attempt to manoeuvre it onto the proper trajectory fails and the spacecraft drifts helplessly out of control. The US ballistic missile early warning system. later spotted spacecraft debris in the Earth's atmosphere in January 1963.

US Mariner 1964
Launched November 5, 1964. Mass 260kg
The US joins the race to Mars with a flyby of the red planet intended to study its environment and bring back photographs. A launch malfunction keeps the heat shield in place after launch and the added weight takes the probe off its 325m-mile path to Mars.

USSR Cosmos 419 1971
Launched May 10, 1971. Mass 4,650 kg
The first attempt to send both orbiter and lander to Mars. The payload fails to separate from the fourth stage of the launch vehicle, and Cosmos 419 re-enters Earth's atmosphere two days later. Supposed to overtake Mariner 8 (another US probe that failed on launch two days earlier).

USSR Mars 7 1973
Launched May 28, 1971. Mass 2,265kg
The Soviets release identical descent modules in attempted "soft landings". Mars 2 plunges too steeply. A fierce dust storm destroys Mars 3 but not before it transmits 20 seconds of data, including the first grainy television images of the Martian surface. Two orbiters return pictures.

USSR Phobos 1973
Launched August 9, 1973. Mass 1200 kg
A flyby bus and descent module packed with weather instruments and camera reaches Mars on March 9, 1974. Thanks to a computer chip error, the landing probe separates prematurely and misses the planet by 1300 km. Both vehicles then go into a long slow orbit around the sun.

US Mars Observer 1992
Launched September 25,1992. Mass 1018 kg
Mars Observer was designed study climate, topography and gravitational field. Three days before it is to enter orbit, it begins to spin out of control. Either it began to circle Mars, or is still orbiting the sun: nobody knows. Total cost $813m.

US Climate Orbiter 1998
Launched December 11, 1998. Mass 338kg
It reaches Mars in September 1999, begins its orbit, and never sends a message home. Later chagrined engineers discover that some navigation commands have been sent in Imperial rather than metric units. The spacecraft sails too close, and probably broke up in the atmosphere.

US Mars Polar Lander 1999
Designed to land just 1000km from the south pole of Mars. It is to release two probes (see below) and then land, turning on a microphone to relay for the first time the sounds of Mars, and then begin digging into the soil. No signal is ever received.

US Deep Space 2 1999
Launched 3 January 1999. Mass 3.57kg
Two little passengers, called Scott and Amundsen, should separate from Mars Polar lander and independently stab the dusty Martian icecap 15 to 20 seconds before the mothership touches down, and then send data to an orbiter. They too are silent.
Cost: $30m Launched January 3, 1999. Mass 290kg.

UK Beagle 2 2003
Launched 2 June 2003. Mass 33.2kg
Last seen on December 19, 2003, sailing away from its European mothership Mars Express. Beagle 2 - little lander with its own camera, excavator and chemistry set, should have landed on Isidis Planitia on December 25, 2003 and begun a search for evidence of bygone life. No signal was ever received.

http://www.guardian.co.uk/life/feature/story/0,13026,1501759,00.html