When something strange shows up on Mars, Jim Bell is the guy to call for answers. For the past decade he has watched Mars through the eyes of the Spirit, Opportunity, and Curiosity rovers. He's written popular books about Mars (including one in 3D), published extensively about the planet's geology and mineralogy, and he's president of the Planetary Society. As the Opportunity rover celebrates its 10th anniversary on the Red Planet, I spoke with Bell to get the consummate insider's impressions of what it is like living virtually on another world.

The "Jelly Donut" rock appeared on Mars during a 12-day period when Opportunity wasn't looking. Its appearance and composition are also odd. (Credit: MER/Cornell/JPL/NASA) Just as the anniversary celebrations were going on, Mars threw out a little surprise: an odd rock, nicknamed the Jelly Donut, that seemingly materialized out of thin Martian air right in front of Opportunity. Add that to the list of other strange sightings on Mars--the lizard, the rat, the mermaid, the bunny, etc--that eager sleuths have spotted in the Mars images (discussed in an earlier post). As you'll see, Bell has plenty to say about those as well. [For more updates, follow me on Twitter: @coreyspowell] You’ve probably seen as much of the Martian landscape as anyone. What’s your overall impression as you drive around and get to know the place? Probably the single most non-intuitive impression I get is that the place looks familiar. At the same time, it is phenomenally un-Earth like. The atmospheric pressure is 1 percent what it is here, and there’s no oxygen. You’d be dead in so many ways if you were hiking around out there. And yet it looks inviting because of the colors. It’s like you're in the Southwest or somewhere in the Southern California desert. What are the biggest difference between the scenery on Mars and equivalent locations on Earth? On Earth, we're used to seeing erosion happen relatively quickly. Only a tiny fraction of the surface is over a billion years old; the rest is constantly modified by wind and water and rain and glaciers, plate tectonics and all that. On Mars, most of the erosion has been just from the wind. When you've got three billion years, dust grains can carve gorges and canyons out of mountains. We see scoured outcrops and fragile mini-sculptures of rock formed by eddies and currents of the wind. The dust grains are very small—microns in size, like cigarette smoke. Imagine blowing smoke at a rock, nothing’s really gonna happen. But blow smoke at a rock for a billion years, something’s gonna happen, you know?

Self-portrait by the Curiosity rover captures its tread marks, the dusty Martian sky, and Mt. Sharp looming in the distance. (Credit: NASA/JPL-Caltech/Malin Space Science Systems) Also, the range of temperatures on Mars is much more extreme than on Earth. The rocks and soils expand and contract as the temperature swings come and go. Let that expansion and contraction go on for billions of years and if there’s fractures in the rock and there’s some sort of preferable place where the rock had fracture—those kinds of low likelihood events become really important. Rocks turn to rubble piles over a billion years. It’s a concept of time that we don’t experience on Earth. And yet you see things happening in real time, right now, on Mars. Yeah, we’ll drive over a place and make tracks with the rover wheels. Unlike footprints on the moon, tracks on Mars fade pretty quickly because of the dusting over of the surface. We’ve gone off on a detour and come back to our original path; we looked at our old tracks and they faded into the background. The changes that are happening quickly are very small, but it takes a tiny amount of dust or sand to dominate the color or brightness of the surface. What do you make of that bizarre Jelly Donut rock that showed up from nowhere in front of the Opportunity rover? We have seen so many strange and wonderful things in our 10-year adventure on Mars with the Opportunity rover (and 6-plus years with Spirit, and 1.5-plus years and going with Curiosity), that this funky little rock appearing out of nowhere wasn't really much of a surprise to me! The most reasonable story is that it was flicked into the field of view by the spinning and grabbing of the rover wheels. However it got there, it sure is fascinating as its underside appears to be exposed for the first time in who-knows-how-long, allowing us to study the weathering processes for a part of a rock perhaps not exposed to the sunlight. W e're in the middle of the investigation so we don't know what to expect yet, but it sure is fun working on it.What is the strangest thing you’ve seen on Mars? Gosh, where do I begin? The stream bed deposits that we almost landed on, that was unexpected. From orbit we saw evidence that water had flowed there in these channels, but seeing rounded, river rounded rocks actually there on what is today a bone dry planet, that was jarring. It brought home that water really did flow here, and significant amounts of it, because these rocks and pebbles are too large to have been moved by the wind. That was a bonus discovery just staring us in the face: watery evidence right there where we landed. But with Curiosity, it’s the layers in the giant mountain in front of us that is our goal. We're inside of a big hole in the ground [Gale Crater], a crater created by an asteroid three and a half, four billion years ago. For some reason, inside that crater, there’s a giant mountain in the middle, but the top of the mountain goes higher than the walls of the crater. How does that happen, how are all these layers formed? We've got evidence now from Curiosity that there may have been a lake in the floor of that crater, and maybe this is a giant pile of lake sediments from when the whole crater was filled up. Where did all that sediment go? Mount Sharp has been teasing us for a year now. It’s driving all of us a little bit batty. We see this promised land right in front of us and we want to get there. We're going as fast as we can. OK, so when will Curiosity reach the promised land? If everything is working well and we can restrain ourselves along the way, it might be six months; in other scenarios, maybe a year. Those predictions are based on the ability of the science team to resist the temptation to stop and look at every single rock, boulder, meteorite, and sand dune. But if we find a dinosaur bone or an abandoned shopping cart, we're not just gonna drive past it.

Enigmatic mineral "blueberries" apparently formed under wet conditions on Mars. (Credit: NASA/JPL/Cornell/USGS) What else have you come across on Mars that totally stumped you when you first saw it? With Opportunity, back in 2004, when we saw the ground sort of littered with these little spherical, rocky grains about the size of BBs. Initially it was like, “What the hell? Why are these billions of years old rocks, spherical rocky balls all over the place? What’s going on?” That was a real alien moment. It took a while for folks to grasp that and then think, “Well, there are some places on the Earth where we've seen things sort of like this.” Then you build up this database of analogues from the Earth. They aren’t exactly the same, but maybe sort of close, and they kind of guide your ideas about what the things are. [Learn the answer about the blueberries, read about a new, related mystery, here.] And it didn’t stump us but—when we look up instead of down we can see Mars’ moon Phobos pass in front of the sun. It’s a “we're not in Kansas any more” moment, you know? You must get hounded all the time by the people who see the rats and the lizards those kinds of things in the Mars images, right? Actually no. Very little interaction with folks about that. Really? I’m shocked. I think our decision to put all of the pictures on the Internet as soon as they come in and let everybody just look at everything—that has fundamentally changed the nature of those kinds of reports. There used to be a group of self-described experts who were independently looking at the images, separate from NASA, which was, you know, part of big government bureaucracy trying to cover everything up. That doesn’t work any more, because we can point people to the actual data and say, “Hey, judge for yourself.” Anybody can go look and say, “Oh no, that’s not a lizard. That’s not a Yeti.” [The source image for the Mars lizard is here.] So to me, it’s become comedy. It’s not taken seriously by the general public. And I'm delighted to see so many people interested, even people who have kind of crazy ideas. It still represents an interest in their investment in the space program.

Look! A lizard on Mars (helpfully circled by the folks at UFO Sightings Daily). Credit: NASA-JPL/MSSS Despite that progress, there are still conspiracy theorists who believe you’ve seen things on Mars that you aren’t talking about. How do you feel about them? When I do interact with folks who are passionate about their beliefs, I say, “Look, you guys have to understand, my colleagues and I would be at the front of the parade if we found a tiny lizard on Mars. It would be the most spectacular discovery in the history of science. Don’t you think we would love to see that stuff?” Come on! Anybody who made that discovery would be famous, be on TV and write books and all that. Why the hell would we cover it up? We want it to happen. [Right on cue: One of the "passionate" folks has declared that the jelly-doughnut rock is a living fungus.] You wrote a lovely essay recently in which you described yourself as a landscape photographer working on Mars. Occasionally, something goes wrong with the rover and the engineers will say, “We need to stop and diagnose this issue.” Then it’s like—oh, we happen to be in a great location and you know what, if we can catch this slope at sunset, it’s going to be spectacular. When those opportunities come along, people jump on them. We aren’t thinking about it scientifically, we’re thinking about it artistically or aesthetically. Sometimes it doesn’t work out like you had imagined, just like for a real landscape photographer. And sometimes it does work out, and then I walk into a Starbucks and I see the photo as somebody’s background on their laptop. That’s incredibly rewarding. Are you disappointed that you'll never have the chance to go to Mars in person? You know, there is this fundamental misconception in the public that it’s the rovers that are exploring, that it’s robots off doing things and reporting results back to us. That’s not at all what’s happening. It’s people. It’s human exploration of Mars that is happening right now, through tools that allow us to extend our senses there. I make this argument all the time: It’s not robotic versus human exploration, it is human exploration using robotics.

A fading sunset on Mars, captured by the Spirit rover on May 19, 2005. (Credit: NASA/JPL-Caltech/Texas A&M/Cornell)