That’s one small step ... on Mars?

Alan Boyle Science editor • Profile • E-mail

Do Martians wear size-11 shoes? Or do we have evidence that the Mars rover missions are merely a hoax — an "X-Files" conspiracy as far-reaching as the fake trip to Mars portrayed in the movie "Capricorn One"?

One of the pictures in our latest "Month in Space" roundup led some readers to ask those kinds of questions. Toward the left edge of the 10th image in the set, you can make out a waffle-shoe kind of pattern in the sands of Meridiani Planum.

"I would like to know if anyone at MSNBC can explain why there is a footprint in the photo called 'Ripples on the Road' on the slide show?" one reader asked. "The caption states that the picture is from NASA's Opportunity rover on Mars. Last I checked, humans haven't been to Mars yet."

Some folks even thought that we were in on the conspiracy:

K.W.: "Maybe it's just me, but I think you guys are full of [expletive]. I can distinctly make out on the left-hand side of this photo a shoeprint ... a size 11 maybe. This photo was staged, as the Mars Rover runs on tracks and does not walk (in shoes, for that matter). You see, the mark does not indicate a continuous run as a wheeled or tracked vehicle would leave behind. Who do you think you're foolin' with this [expletive]?"

A closer look at the picture, such as the shot we've included here or the larger-resolution version from NASA, shows more clearly that the "footprint" is indeed the track of a rover wheel going over the rugged Martian terrain. The track doesn't appear continuous because it goes over bedrock, and because the rover's turns, stops and starts spoil the smooth impressions of the wheel tracks. The shades of Martian soil can also vary between light and dark — a phenomenon that geologists are still puzzling over.

You can see the footprint effect more clearly in this "stretched-color" photo of Opportunity's trail toward Victoria Crater. Crank the view up to full resolution for an even sharper view.

The footprints thus take their place among the alien-looking but not really alien features that have shown up in pictures sent back from the rovers, including bunny ears, rover rotini and blueberries.

Whenever we publish a new "Month in Space" slide show, we get plenty of messages from folks asking how they can save copies of the images. This e-mail from Peru is typical:

"My name is Jorge Anchante, I'm writing from Peru. I've seen your NBC picture stories and I like a lot the picture about Cleveland Volcano, taken from space, and I'd wish you send me this photo, it's excellent."

It may be a little inconvenient for us to send photos to the many thousands of people who click through the slide shows each month, but this list of links to source imagery may be helpful:

• Study in shadow
• Red Spot and son
• Comet with a ring
• Red Planet's White Rock
• Three Gorges, before and after
• Otherworldly stone
• Potato chip galaxy
• Waves of sand
• Cracking the code of a Martian crater
• Ripples on the road
• Teardrop canyon
• Cosmic fireworks
• Mimas and its mama
• Thar she blows

The image titled "Dark Launch" can be found by going to the Corbis Web site and searching for "CALIPSO."

This report originally appeared as a Cosmic Log item on May 31, 2006.

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