Looks like the Mars rover Opportunity has a few miles more to go before it can break the record for longest off-world driving distance of any rover from Earth. Scientists using NASA’s Lunar Reconnaissance Orbiter Camera have snapped images of the current record-holder, the Russian Lunokhod 2, and found that its meandering path was slightly longer than previous estimates.
Two months ago the scrappy Mars Exploration Rover Opportunity, which has been roaming the Red Planet since 2004, passed the NASA 22-mile distance record set by the Apollo 17 vehicle that astronauts drove around the moon in December 1972. But they had yet to break the international driving record, held by the unmanned Russian Lunokhod 2 rover that landed on the moon just a month after Apollo 17 and racked up an estimated 23 miles. That record has remained unbroken.
But the Russians' distance estimates -- which relied on measuring the number of wheel rotations -- were fuzzy at best, leaving some room for error. And now, scientists using the camera on the NASA lunar orbiter have taken high-resolution images of the tracks and found that the actual distance driven is probably closer to about 26 miles, said the camera’s lead scientist, Mark Robinson, a geologist at Arizona State University.
"It’s just really fantastic to be able to see that accomplishment as something real in front of you," Robinson said.
The finding backs an earlier estimate made by Russian scientists who were also using the NASA lunar orbiter's data -- though the estimate has yet to be refined, Robinson warned, and it's unclear exactly what acounts for the discrepancy.
"One possibility is that's just a rough estimate of how far they’d driven from the starting point to the end point," he said.
But the rover did not proceed in a straight line. Extra mileage on the odometer may come from the rover zigzagging back and forth, Robinson pointed out. Also, since the rover was unable to capture full panoramic images, it may have also driven in circles to take in the whole view, he said.
The lunar rover had some advantages over its Martian peer -- Lunokhod 2's top speed was about 1.2 miles per hour, roughly 10 times faster than Opportunity’s estimated flat-out top speed of 0.11 miles per hour. But Opportunity could still break the record, provided the scrappy rover continues rolling along. Perhaps the odds are in its favor -- it's lasted roughly 37 times longer than its predicted three-month lifetime.
This "competition" did little to enthrall Robinson, however.
"What is the utility or the usefulness of the comparison of how far the Mars rover drove and the lunar rover drove?" he asked, suggesting it was better to focus on the scientific achievements of each rover.
In the meantime, scientists may actually learn a thing or two about the moon’s surface using the new images of this decades-old trail, Robinson said. Light reflected by the Lunokhod 2 tracks and landing-spot halos should reveal some of the properties of the dust, soil and rock that make up the very top layer of the moon.