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]?"

NASA / JPL-Caltech

Marks on the left side of this image from the Opportunity rover look like a footprint.

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."

In the past, Bigelow Aerospace has been relatively hush-hush about its plans to test an inflatable space module that could someday be used as an orbital hotel. But in "Dispatches From the Final Frontier," Michael Belfiore provides lots of new details about Bigelow's plans for next month's test launch and beyond. And Bigelow's reworked Web site lays out the specifics for flying mementos in zero-G for less than $300, starting with its second test flight. The company even promises to post videos or photos that just might show your item floating inside the module — proving that you got what you paid for.

• Technology Review: Outward Bound for robots
• The Guardian: Top scientist gives up on creationists
• Christian Science Monitor: Evolution seen in a yogurt cup
• BBC: 'The Simpsons' as philosophy

Can we ever predict earthquakes? Seismic researchers are spending millions of dollars to get just a few seconds of advance warning of a major earthquake, and the catastrophic shock that hit Java over the weekend illustrates how much could be at stake.

With that background, Russia's launch of the Compass 2 satellite on Saturday promised to open up an avenue of research toward honest-to-goodness earthquake prediction, even though plenty of experts suspect it may be a dead end. The satellite was supposed to observe changes in Earth's magnetic field and determine whether those changes could serve as precursors of seismic events.

Researchers from NASA as well as Russia and China are debating whether such a seismo-magnetic connection exists. Unfortunately, it doesn't look as if Compass 2 will provide any evidence to settle the debate one way or the other. Russian mission controllers say they haven't been able to switch on the satellite's scientific equipment, and there are mounting reports that the loss is irretrievable.

In a classic example of swords being beaten into plowshares for space science, Compass 2 was launched from a Russian submarine in the Barents Sea, atop an intercontinental ballistic missile that was designed for delivering nuclear weapons.

By all accounts, the satellite was put into its proper orbit and was in contact with ground controllers — but something went wrong with the spacecraft's orientation or onboard equipment, preventing the start of science operations. Russia's Interfax news service as well as Itar-Tass passed along reports of the malfunction. The newspaper Kommersant quoted experts as saying Compass 2 would probably never be used for seismic studies (Russian-language report).

On the Hearsat mailing list, a gathering place for satellite radio trackers, veteran listener Bob Christy says he's had indications that Compass 2's science team "considers the situation irretrievable, as far as the science goes, and possibly the satellite itself." The satellite's predecessor, Compass 1, suffered a similar fate back in 2001.

Compass 2 is by no means the first submarine-launched space shot to go wrong. NBC News space analyst James Oberg minced no words in his e-mailed comments:

"This whole project, sub missile and all, is a desperate gambit by a bankrupt missile factory that lost all Russian military contracts a decade ago and has been hemorrhaging its aging workforce ever since — it's called the Makeyev Bureau. They sold Lou Friedman his 'cut-rate' Cosmos 1 launch, and destroyed it — they sold launches to one of my favorite innovative space transportation gimmicks, ESA's 'Demonstrator' inflatable entry vehicle, and lost mission after mission from booster and payload processing errors. These guys are terminal losers."

Even if Compass 2 is lost, research into the seismo-magnetic connection will continue, based on data already gathered by France's Demeter satellite as well as readings that might be made by a future Chinese satellite.

Last week's report on the quest for invisibility sparked some pretty intriguing comments, including numerous claims that the military has already developed real-life invisibility cloaks. It sounds a little too much like "The X-Files" to me — but hey, sometimes the truth really is out there. A couple of readers also noted additional limitations on invisibility technology. Read on for a selection of the e-mail feedback:

David Reid, Denver: "Wouldn't a person inside an invisibility cloak be 'blind'? If light is bent around their eyes (so their eyes are invisible along with their body) then they wouldn't be able to see. At least that's my theory on it."

John Boyle (no relation): "I think you left out one more catch: No part of an invisible object, including the eyes, absorbs light.  So if you're covered by an invisibility sheath of some sort, you'll be just as blind as everyone else.  Although that only applies to the wavelength you block, so you could use infrared goggles or something."

You're both right on target. A total invisibility shield might be good for hiding objects you don't want found, but not so good for hiding observers who want to look out of the cloak. It's important to remember that, realistically, the shield would be invisible only to specific wavelengths. Therefore, you could have a ship or underwater monitoring station that was "cloaked" from radar soundings but still able to see out (and be seen) in other wavelengths.

Robert Cutshaw: "Several weeks ago, Military.com contained an article regarding a company, Advanced American Enterprise, that claims it has invented a cloaking device. I don't know if you have already seen this article and dismissed it, but thought that you might find it interesting.  This is a link to another article regarding the same device and other technologies developed for military use. ... While digital technology makes it very easy to create fake photographic evidence, Advanced American Enterprise also claims it has a video available that shows the device in action. So far I have been unable to locate a copy of that video on the Internet.  So at this point the jury is still out on this particular device."

David B. Buffalo: "Thirty years ago (yep, when I was at Georgia Tech), I knew two Air Force ROTC students who had been doing research in what was then the Electrical Engineering Department. One claimed, and I had no reason to doubt this guy (because he was no B.S. artist and he was incredibly intelligent), that the Department of Defense had developed four different refractive/reflective cloaking devices late in 1974. If someone in academia like Mr. Pendry [one of the researchers behind the latest studies] is just now discussing such ideas, I truly believe it is a smoke screen or he is just lost in the laboratory working on projects no one cares about.

"I have to believe that American and Russian scientists (who quite frankly have had superior optical research projects on the books when compared to the U.S.) have long since developed cloaking technologies and are probably deploying them now. The stealth bomber technology of the last decade was pretty much finished in the middle 1970s, and one Australian engineering outfit had already figured out how to defeat it within a couple of years of our deployment. One of the things that worries engineers currently with regard to 'Star Wars' anti-missile technology is that Chinese or Russian scientists have already begun testing radar and other kinds of cloaking that would make it impossible to knock down missiles or satellites, in ways similar to how thermal decoys are used to fool heat-seeking missile technology in anti-aircraft defenses.

"If we are not much farther along with cloaking technology than what Mr. Pendry is describing, then I am truly worried about American defense capabilities. Given the last few presidential administrations' penchants for giving away technological advantages to our enemies, your most recent article really gives me the chills. I don't listen to Art Bell either. I just know that in the past, we have had technological breakthroughs that did not emerge into the public domain for decades. If what Mr. Pendry is describing is the best the West has, we are in trouble deep."

Don't be surprised if Cosmic Log takes on a new look over the next few days — and a new Web address as well. The ID number for this old place may change, but even if you get lost, you can always find your way back to the log by typing in CosmicLog.com.

• Science News: A gripping tale of nanotubes
• N.Y. Times: Katrina was like four storms in one
• National Geographic: To hell and back in Peru
• Nature: Mini-fridge exploits molecular motion

Take one scary phenomenon, find the worst conceivable real-world scenario and scale it up a few notches  … that's the formula for disaster flicks ranging from "10.5" to "Armageddon" to "The Day After Tomorrow," and now for the "Poseidon" remake as well.

This week, the subject is rogue waves — giant walls of water that dwarf even your run-of-the-mill storm swells. These are distinct from the 33-foot-high, earthquake-generated tsunami waves we came to know all too well in 2004. For ages, mariners have told of much bigger midocean waves, rising  more than 200 feet to hammer the ships caught in their sights.

The plot of "Poseidon" posits a 150-foot-high rogue wave, big and bad enough to upturn a cruise ship. Although that's way over the top — kind of like Shelley Winters' acting in the original 1972 "Poseidon Adventure" — it turns out that real-life rogue waves can come closer to that mark than scientists once thought.

Rogue waves, also known as freak waves, have been the subject of more studies in recent years, due to the availability of ocean-monitoring satellites. The European Space Agency says its MaxWave satellite radar project detected more than 10 rogue waves measuring higher than 82 feet (25 meters) over a three-week period in 2001 — perhaps including the 100-foot whoppers that smashed the windows of the cruise ships Caledonia and Bremen.

A 70-footer washed over the Norwegian Dawn cruise ship last year, a nearly-100-footer was reported in 2004 during Hurricane Ivan, and there have been reliable measurements of a 112-foot (34-meter) wave that rose over the USS Ramapo in 1933. Could there have been bigger waves that people didn't survive to tell about? Maybe so: In "The Bird in the Waterfall," Jerry Dennis and Glenn Wolff report that computer models can produce theoretical waves as high as 219 feet (67 meters).

The big mystery has to do with the mechanism that causes the waves. A variety of studies, including the MaxWave observations, have shown that cross currents can "focus" the energy of wind-driven waves through constructive interference.

"At some point, the waves all march in lockstep together, and then again they go their own way," Vijay Panchang, a maritime engineering expert at Texas A&M University in Galveston, told me today.

But sometimes freak waves can arise without those cross currents. "Sustained winds from long-lived storms exceeding 12 hours may enlarge waves moving at an optimum speed in sync with the wind," the ESA reported.

Seabed topography may play a role as well, Panchang said. A "bump" on the seafloor, for example, could give an extra boost to a wave at just the wrong time.

One of Panchang's biggest contributions to the science of big waves is to develop a forecasting model for coastal waves. Currently, the model is being applied to waves off the coast of Maine as well as the Gulf of Mexico and the Gulf of Alaska. You can check out the predictions here.

"Our predictions are reasonable," Panchang said — nothing like the whoppers of "Poseidon," but big enough to catch the attention of mariners and oil-platform operators.

For much, much more on the real science of freak waves, check out archived articles from Science News and Discover magazine — as well as this tutorial from the National Oceanic and Atmospheric Administration and this "Savage Seas" Web site from WNET. You can even play around with a virtual wave generator. Here's an interesting safety angle from the Boston Herald, just in time for the debut of the Freedom of the Seas. (Think "Poseidon" will ever play in that ship's theater?)

Meanwhile, for an intriguing discussion of where the physics goes wrong in "Poseidon," check out this blog discussion. If you spot any other scientific howlers from the film — or other summer blockbusters, for that matter — feel free to leave a comment.