Entering orbit around an M-Class (Minshara-class) planet leaves even the most casual observer with little doubt that abundant water is present on the surface. Such was the case in the Enterprise episode "Strange New World." Majestic oceans, abundant clouds and expansive forests (i.e. life) can be seen with the naked eye.

Not all planets reveal their potential for supporting life this easily.

Mars is a perfect example. In the 1960s the Mariner IV probe sent back images that looked more like Earth's moon than the inhabited world we had imagined it to be. Subsequent probes showed that this resemblance was superficial. (Photo courtesy NASA.)

Each successive mission arrived armed with better instrumentation. In 1976 the twin Viking missions placed two orbiters above and two landers on the surface of the planet. The Viking probes revealed much about Mars. Its photos often gave it a pseudo-terrestrial desert appearance complete with dunes, dried up riverbeds, and carbon dioxide frost. Yet the most anticipated experiment — the ones looking for life — found little more than some exotic chemistry.

For several decades we turned our back on Mars, assuming that it was (perhaps) once alive, but now dead. Then, in the late 1990s, the Mars Pathfinder mission and the discovery of possible Martian fossils in the ALH84001 meteorite served to jump-start our interest in Mars as a possible abode for life.

The Mars Global Surveyor arrived several years later. True to form, this mission revealed new things about Mars. While many things on Mars are Earthlike, many things can only be classified as being "Marslike." As such one's familiarity with earthly explanations is both a help and a hindrance.

In the summer of 2000, SpaceRef first broke the news that liquid water may well exist under the surface of present-day Mars. Another jolt to our imagination. In the months that followed an ancient seabed and evidence of ancient salty oceans was detected. Yet another jolt. Now Mars was really starting to look like a place where life might exist. (Photo courtesy NASA.)

Flash forward to today: the Mars Odyssey spacecraft turned on its instruments just last week. The scientists operating this mission were stunned at the quality of the data they received as soon as they hit the switch. They were also stunned at what this data told them. Based upon various instruments carried on the spacecraft it would seem that a substantial amount of water ice lies just below the surface of Mars. Not in just one location, but all across the planet.

According to Dr. Steve Saunders, Odyssey project scientist at NASA's Jet Propulsion Laboratory, "Now we may actually see water rather than guessing where it is or was. And with the thermal images we are able to examine surface geology from a new perspective."

One of the things Mars Odyssey can do is observe the surface of Mars at night and take infrared measurements of its surface. Analysis of these images can show how different materials can hold or lose heat as the sun goes down. One of the tantalizing things this instrumentation could provide is the location of hot spots — geothermal springs. Perhaps "areothermal" is a better term to use. (Photo courtesy NASA/JPL/Arizona State University.)

There are many things required for life "as we know it" to exist on Earth. Until recently, Mars was thought to have all of the required conditions except one: the availability of liquid water. While much more data collection is required, this spacecraft is capable of both detecting heat sources and the presence of water, and correlating the two together.

If Mars has hot springs, this spacecraft can detect them. If Mars has hot springs, then the chances that it could harbor life go from theoretical to probable.

Whether Mars once had or still has life remains an open question. This spacecraft won't answer the question directly. Rather, it will simply make a better case for the possibility that it could exist. Readers of last week's Science Brief will know that life has been found in some rather harsh places on Earth. Many places on Mars are warm and cozy by comparison.

To find out whether there is life on Mars, we're just going to have to send our tricorders there. Indeed, NASA is already building them!

Say we discover life on Mars. Then what? Make your case at the Science & Technology message board!