Life On Earth
Mars Probe May Have Spotted Lost Rover
The most powerful camera ever sent into orbit around Mars has spotted yet another lander lying lifeless on its surface: Mars Pathfinder, which operated for three months in 1997. It may also have found the mission's tiny rover, Sojourner, which appears to have crawled towards Pathfinder after the lander had already died.
NASA's Mars Reconnaissance Orbiter (MRO), which arrived at the planet in March 2006, has previously spotted four spacecraft on the planet's surface – the current rovers, Spirit and Opportunity, and the twin 30-year-old Viking landers.
Now, it has used its ultrapowerful camera, called HiRISE (High Resolution Imaging Science Experiment), to identify the Pathfinder lander and scattered hardware from the mission, including the parachute and backshell it used during its descent a decade ago.
The lander and some of these components had been seen before from orbit by NASA's now-lost Mars Global Surveyor spacecraft. But HiRISE can resolve details between two and five times as small, imaging objects just under 30 centimetres across.
"Before HiRISE came along, it was a lot like having a state road map to find a neighbourhood address," says geologist Tim Parker of NASA's Jet Propulsion Laboratory in Pasadena, California, US. "Suddenly, it was like having a residential street map, or maybe even photos showing houses so you can recognise them."
Such images will help researchers interpret the geology around the landing site by bridging the gap between what previous, lower-resolution orbiters have seen of the site and what the lander itself saw at close range, he says. MRO's eagle-eyed vision is also being used to choose landing sites for future missions, such as Phoenix, which is due to launch in August.
But despite MRO's sharp eyesight, it is still not clear whether it has spied Sojourner, the toaster oven-sized rover that hitched a ride to the planet's surface inside the lander, then struck out to explore its surroundings.
Unlike Spirit and Opportunity, Sojourner could not directly communicate with Earth and had to rely on the lander to transmit messages about its health and travels. So when contact with the lander, which was designed to last one month, was lost after three months, ground controllers were not sure what became of Sojourner.
Now, it seems the rover kept moving, apparently trying to reach its companion. "The rover was programmed so that if it didn't get commands from the lander, it would assume it somehow got out of radio contact behind a ridge or rock," Parker told New Scientist. "So it would drive to the lander as best it could and keep trying to re-establish contact", circling it as it got close, he says.
Around and around
When it was last seen, the rover was 13 metres away from the Pathfinder lander. Now, it appears to be about 6 metres away, according to the new MRO images. "I think the simplest explanation is it started to drive back, got about half way, and stopped for whatever reason – it may have thought it got there," says Parker. "The other possibility is it drove around and around for who knows how long and simply failed at that location."
Still, the images are not clear enough to definitively identify the rover, and Parker says what the team is seeing may just be a cluster of pebbles. So they have considered the possibility that the rover simply drove off on its own after its partner died.
"If you think about it, if it were still working and maybe only driving a metre a day, that's 3 kilometres over 10 years," says Parker. "But that's pretty optimistic. I've looked up to 300 metres away from the lander and haven't seen anything that looks like a rover twitching around. It probably really is close to the lander and hasn't moved in a long time."
Future observations with HiRISE may be able to settle the question. The camera usually only takes full-resolution images with its red colour channel, using its infrared and blue-green channels at a lower resolution. Parker has requested that these other channels be used at the highest resolution possible to study the landing site. "The hope would be that the solar panels on Sojourner would stand out in one of the other colours," he says.
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