TEMPE, ARIZONA -- There is a dark side to Mars. Experts studying the reddish globe in the infrared see a wonderland of nighttime surprise. Through the art of sunless science, researchers are trying to discern whether Mars is a percolating planet of still huffing volcanoes and hot shot geysers.

Since nudging itself into a science orbit around the planet in February, NASA's Mars Odyssey has been busily snapping images of martian terrain in both infrared and visible light. That job belongs to the probe's Thermal Emission Imaging System - better known in spectral splendor shorthand as THEMIS.

It is fitting that looking at Mars in an evenhanded way -- in both daytime and nighttime conditions -- is the task of THEMIS. After all, Themis is the ancient Greek Goddess of Justice.

Peering down on a long strip of fresh Odyssey imagery stretched across a large table, Christensen said his labor of love - THEMIS - is churning out spectacular data to unravel the planet's physical makeup. "This much detail and this much variability. I didn't expect Mars to be this interesting," he said.

Infrared sweeps of THEMIS during Mars' nighttime reveal telltale signatures of rocky surfaces, dust strewn and sandy stretches of landscape. Each cools differently during the nightly nosedive of temperature, yielding a unique thermal fingerprint of geology.

"Now we're off wondering what is causing all this variability. And we're just starting to scratch the surface," Christensen said.

A promising outcome of Odyssey is observing hydrothermal hot spots. A mix of water and heat would do wonders for martian life. Finding a Mars equivalent of Yellowstone National Park in Wyoming, or heat wafting up from a still active volcanic area can't be ruled out, Christensen said. "I don't think it is unreasonable. It's certainly unlikely, but certainly not unreasonable. I'm hoping we find something like that. That would be one of those 'wow' discoveries," he said.

In fact, THEMIS infrared data might have already spotted such heat anomalies. However, the wealth of heat signatures being picked up by the instrument may be masking them out. A needle in the proverbial haystack comes to mind.

"Finding a hot spring down there is like looking for Waldo," Christensen said.

To identify such heat sources will mean comparing images taken over a 6-month stretch of time. Just like searching for a comet against a starry background, Mars pictures will be judged against each other. The hope is to see what has changed, if anything, in the complex sea of thermal signatures, Christensen said.

"We've looked at Mars in the visible for 30 years. We've looked at Mars in the infrared for just a few months. We're just beginning to calibrate our brains as to what is normal, what's natural, and what's different," Christensen said.

To date, the output from THEMIS is but an overture of what's still to come. Great care is being taken to calibrate all the wavelength bands in which the instrument operates. Eventually, all of Mars through the eyes of THEMIS are in the offing.

"We can really get the global, big picturea deeper and larger understanding of what's going on. That's what THEMIS is going to do. Imagine hovering in a little chair above a map the size of a football field. Mars will be displayed at that resolution. It's spectacular stuff," Christensen said.

Christensen said that several things strike him in looking over Odyssey's ever-growing photo album of Mars shots.

"I see Mars as a far more active, interesting place than I thought it was 6 months ago. I envisioned a Mars mantled in dust. Those dust deposits would play a major role making it pretty hard in a lot of places to find rocks. THEMIS is saying there's a lot of rocky places on the planet. There are places where rock is exposed on the surface. You don't have to dig around to find it. Big outcrops of rock are sitting there. So I think Mars is getting more interesting," Christensen said.

Getting to know Mars is like earning a Ph.D., said Victoria Hamilton, a faculty research associate in ASU's Mars Space Flight Facility. "It's an exercise in learning not what you know, but what you don't know. The more we learn the more we don't understand," she said.

Hamilton said that having two well-instrumented spacecraft circling the red planet -- Mars Odyssey and the Mars Global Surveyor -- is incredibly beneficial. "There are times of the day when they cross over the same spot on the ground within a couple of hours of each other. Sometimes even within 45 minutes of each other," she said.

Using Mars Global Surveyor's Thermal Emission Spectrometer, Hamilton is building an intriguing case for having found a distinct area on Mars seemingly common in mineral makeup to that of the infamous "Mars rock" - meteorite ALH 84001. Odyssey's THEMIS should help sort out whether a site near Eos Chasma might be the meteorite's point of origin, she said.

Mars today is not the Mars of just a few decades ago.

"A lot of people are still stuck with the Viking view of Mars from the 1970s. Some of that view still stands, but the Mars Global Surveyor and now Mars Odyssey are both showing a new kind of Mars," Rice said. "I think there's a learning curve to try and catch up with. It takes a while to calibrate your eyeballs to what we see there now," he added.

Although Mars may never fail to surprise, it also frustrates at the same time, Rice said.

The "big story", Rice said, is likely to show up unexpectedly. "It would be great to find that needle in the haystack just sitting there on Mars and screaming out: 'Come see me.'"

"Every mission to Mars finds something stunning. We're definitely looking. The thing about exploration and discovery, you don't know what you're going to find. That's the fun part of all this," Rice said.