Distance from the Sun: 227,900,000 km
Radius: 3,397 km
Mass: 6.42 x 1026 kg
Density: 3940 kg/m3
Mean Temperature at Solid Surface: 186 to 268 K (-86oC to -5 oC)
Major Atmospheric Constituents: carbon dioxide, nitrogen, and argon

Mars has inspired our imaginations over the centuries, and has been the focus of intense scientific interest for many years. Mars has shown itself to be the most Earth-like of all the planets; as it has polar ice caps that grow and recede with the change of seasons, and markings that appear to be similar to water channels on Earth.

Mars is a small rocky planet that has experienced volcanic eruptions, numerous impact events, and displays many atmospheric changes. Areas of layered soils near the Martian poles suggest that the planet's climate has changed more than once, perhaps caused by a regular change in the planet's orbit. Martian tectonics, the formation and change of a planet's crust, differs from Earth's. Where Earth tectonics involve sliding plates that grind against each other or spread apart in the seafloors, Martian tectonics seem to be vertical, with hot lava pushing upwards through the crust to the surface. Periodically, great dust storms occur that engulf the entire planet. The effects of the storms are dramatic, including dunes, wind streaks, and wind-carved features.

One of the early mysteries pondered by scientists was why Mars does not have oceans like Earth. Mars has an atmosphere that is now too thin and its temperature too cold to allow liquid water. Mars certainly had surface water and groundwater once. This liquid water shaped the valley networks in the highlands and the huge flood channels that cut from the highlands to the northern lowlands. Scientists are not certain of exactly how much water was present. Estimates range from the equivalent of an ocean 10 meters deep covering the entire surface to the equivalent of a layer kilometers deep. However much water there was, it is not now on the surface, except for a bit in the polar ice caps. One question that has been raised is where did the water go? It could be underground in pools of groundwater, either small or huge depending on how much water Mars started with. Or it could have escaped to space and been lost completely (the hydrogen from water can escape easily through Mars' low gravity and small magnetic field).

We don't know if there is or was life on Mars. There are currently no clear signs of any life on the inhospitable surface of Mars. We do know, however, that the climate of Mars was once quite different than today. We could imagine the past where Mars had a thicker atmosphere, flowing water, volcanoes, lava flows, open lakes, and perhaps even an ocean. These conditions could have supported life similar to that which develops in hot springs here on Earth.

In a recent study, scientists found a huge deposit of the mineral hematite. This discovery has led to speculation that there was water on Mars long enough for life to form. At a recent meeting of the American Geophysical Union, Arizona State University Prof. Phil Christensen suggested that the hematite deposit "is really the first evidence we have that hot water was around long enough for a geological period of time so that potentially life could have had an opportunity to form." Hematite is an iron oxide mineral that forms by a variety of ways that often involve water. The coarse-grained hematite spotted on Mars also occurs on Earth around volcanic regions such as Yellowstone National Park. It is evidence that a large-scale hydrothermal system may have operated beneath the Martian surface, said the scientists working on the Mars Global Surveyor Mission. "If you want to find out about possible life on Mars, the deposit is a good place to start," Christensen said. "You've got water, you've got heat, and you've got energy.