The planet Mars is a glutton for punishment.

Scientists have found no less than 20 new craters etched into the red planet's surface from space rocks that pummeled Mars within the last seven years.

"If you were to live on Mars for about 20 years, you would live close enough to one of these events to hear it," said researcher Michael Malin, who led the study. "So there'd be a big boom, and you'd know there was an impact crater."

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Malin, chief scientist at Malin Space Science Systems in San Diego, and his team used the Mars Orbiter Camera aboard NASA's now-silent Mars Global Surveyor to photograph about 30 percent of the planet between January and May of this year.

They compared the new images with photographs taken by MGS during earlier surveys to find new impact sites.

In the same study, researchers found evidence that liquid water may have flowed out of Martian gullies within the last five to seven years.

"It was just amazing that we could even do that," Kenneth Edgett, a Malin Space Science Systems researcher who spotted the first of the new craters, told SPACE.com. "And it was really a whirlwind, from that first one all the through the 20th."

Malin said that it was only by chance that Edgett spotted an image with a new crater and recalled a similar view taken years earlier by the MGS orbiter.

Their subsequent survey found the new craters, which ranged in diameter from seven feet (two meters) to 486 feet (148 meters), and suggested an average rate of about 12 impacts per year.

A few months after Malin and his team performed their survey, the MGS probe went silent. It is now thought to have been lost after 10 years of spaceflight.

The research is detailed in the most recent issue of the journal Science, and validates crater-impact models of Mars that until now were based solely on theory, Malin said.

The new craters also suggest a potential hazard for future astronaut explorers on long-duration missions to the Red Planet, he added.

"There is a hazard — it's probably a low hazard," Malin said. "But it's one we need to think about in terms of these objects hitting Mars at a fairly substantial rate."

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