• Mars is the fourth planet from the Sun, between Earth and Jupiter.
• Minimum distance from the Sun: 128.6 million miles.
• Maximum distance from the Sun: 154.8 million miles.
• Minimum distance from Earth: 35 million miles.
• Diameter (avg): 4,200 miles. Earth's diameter is 7,913 miles.
• Volume: approximately 15 percent of Earth's volume.
• Mass: approximately 11 percent of Earth's mass.
• Density (water=1): 3.94. Earth's density=5.52.
• Surface gravity: 38 percent of Earth gravity.
• Length of day: 24 Earth hours, 37 Earth minutes.
• Length of year: 687 Earth days.
• Temperature (mean avg on surface): -45 degrees Fahrenheit. Earth temperature is 60 degrees.
• Temperature range: -225 degrees F to 63 degrees F. (calculated)
• Atmosphere (major components): carbon dioxide, with small amounts of nitrogen, water vapor. Earth's atmosphere is made up of nitrogen and oxygen, with smaller amounts of water vapor, carbon dioxide, and argon.
• Albedo (percentage of light reflected back into space): 16 percent. Earth's albedo is 36 percent.
• Tilt of Axis: 25 deg, 12 min.
• Satellites: two, Phobos and Deimos.

PhobosDeimos

• Discovered by Asaph Hall, American astronomer, 1877.
• Named Phobos (fear) and Deimos (terror)
• Both irregularly shaped, heavily cratered.
• Phobos is about 5830 miles from the center of Mars. Deimos is about 14,580 miles from Mars' center.
• Phobos' diameter: about 14 miles. Deimos' diameter: about 7 miles.
• Phobos orbits Mars about once every 7 and a half hours. Deimos orbits Mars once every 30 hours, 19 minutes.
• both thought to be either pieces ejected from Mars during early formation, or captured asteroids.

A dust storm on Mars (look for red covering the ice cap in early image!)
• Much thinner atmosphere than on Earth.
• Atmospheric pressure is 0.1 pound/square inch, less than 1 percent of Earth's atmospheric pressure.
• Atmosphere mainly carbon dioxide.
• The wind is important on Mars: dunes and drifts of sand and dust have been observed, as have dust storms.
• Three types of clouds have been observed.
  • Pink clounds of dust covering large areas
  • Thin bluish clouds, thought to be made of ice crystals.
  • Thicker white clouds, possibly water vapor. (only occasionally seen)

• Two-thirds of the surface is covered with red-brown material. Some seems to be limonite, material found in Earth deserts.
• Dark bluish-gray or greenish-gray patches called maria (seas) cover about one third of the surface.
• The size and shape of the maria change, possibly due to blowing sand and dust.
• About half the planet, mainly the Southern hemisphere, is heavily cratered.
• The Northern hemisphere is more smooth, thought to be the result both of wind-blown sediments and volcanic activity.
• No evidence of plate tectonic activity beyond early stages. Possibly due to thick crust and mantle.
• Surface has canyons and gorges and features resembling dried riverbeds, supporting those who think that once Mars had lots of liquid water on its surface.
• What appear to be white polar ice caps, which shrink and grow with the seasons, add further support to the liquid water theory.
• The Tharsis region near the equator has many large extinct volcanoes.
• This includes the largest known volcano in the Solar System, Olympus Mons, which is about 27 km tall, and 550 km across.
• Nearby is a deep gorge called the Vallis Marineris, possibly an ancient fault line.
• The Vallis Marineris is over 4000 km long. Parts are over 150 km wide. It is between 2 and 7 km deep.

Though the Viking mission settled the idea of "canals" on Mars once and for all, the possibility that liquid water once flowed on Mars around 4 billion years ago still has people wondering: could there be some form of life on Mars? Was there life at one time? Speculation was driven into a frenzy last year with the analysis of the famous martian meteorite, found in Antarctica in 1984. Scientists found four types of evidence inside the meteorite:

• masses of carbonates, similar to those produced by microorganisms on Earth
• iron sulfides and magnetite, also produced by Earth microorganisms
• traces of polycyclic aromatic hydrocarbons (PAH) produced by the decay of Earth microorganisms
• tiny tube and egg-shaped objects, only 20 to 100 nanometers across, resembling fossilized Earth microorganisms (but smaller.)

Not everyone is so sure, though - many people have presented ways that the four clues could have been made without the help of microscopic life. Unfortunatly, the Pathfinder/Sojourner mission is not designed to analyze for traces of life. We'll have to wait for future missions to do that!