Take a look at the Spirit and Opportunity slide shows.

The data is in: water did flow on Mars in the past. What's more is that water is still on Mars mixed with the soil in the northern aortic region. Soil analysis from the Phoenix lander also shows that Mars had a warmer, wetter past.

And to NASA's surprise, the MER's Spirit and Opportunity are still studying Mars as of August 10, 2009!

Mars - A Quick Summary: (More information can be found on the Mars Fact Sheet)

	Average Distance from Sun:	2.279 x 108 km
	Eccentricity of Orbit:	0.093
	Average Orbital Speed:	24.1 km/s
	Orbital Period:	686.98 days
	Rotational Period:	24h 37m 22s
	Inclination of Equator to Orbit:	25.19º
	Diameter:	6794 km
	Mass:	6.418 x 1023 kg
	Average Density:	3934 kg/m3
	Escape Speed:	5.0 km/s
	Albedo:	0.15
	Maximum Surface Temperature:	20º C
	Minimum Surface Temperature:	-140º C
	Average Surface Temperature:	-53º C
	Atmospheric Composition:	95.3% Carbon Dioxide
		2.7% Nitrogen
		0.03% Water Vapor
		2% Trace Elements

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The Martian Atmosphere:

The atmosphere on Mars contains the same levels of of carbon dioxide as Venus, but does not demonstrate the runaway greenhouse effect that Venus has. Water vapor is also present in the Martian atmosphere but at 30 times less than the level in Earth's atmosphere. The dry atmosphere is mostly due to the lack of ozone on Mars and the lower escape velocity so small particle within the atmosphere is free to escape.

The Mars Pathfinder took this photograph of a Martian sunset. Even though the atmosphere is thin, refraction of light and reflective atmospheric particles are still present enough to give the sunset a nice color. The red an blue colors would not be present if Mars had no atmosphere.

The presence of the atmosphere, no matter how thin, still allows for weather patterns to occur. The most common weather pattern on Mars are dust storms - sometimes on a global scale.

The Mars Global Surveyor photographed a dust-devil on the surface. A dust-devil is like a mini-tornado without the associated storm patterns.

The above Hubble image demonstrates a dust storm on a global scale. These storms can last several months.

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Martian Surface Features:

Mars contains a number of fascinating surface features, mostly as a result of the Mars Global Surveyor and Mars Exploration Rovers. While I could cover these here, I will leave that as a resource link or subjects for Advanced Topics.

The three major features on Mars are:

• The Polar Caps
• Valles Marineris
• Volcanoes

Using data from the Mars Orbital Laser Altimeter (MOLA), Paul Bourke of the Center of Astrophysics and Supercomputing created a video of Mars Topology. Click on the image on the left to view the video. You may want to download it as the file is 98MB in size!

(images care of Swinburne Astronomy Online)

The Polar Caps of Mars contain mostly carbon dioxide, but some water is present underneath. The seasons on Mars are similar to that on Earth in that there is a defined spring, summer, autumn, and winter. This is evident by the changing appearance of the polar caps:

Polar Caps - Spring	Polar Caps - Summer	Polar Caps - Winter

The carbon dioxide is transferred to the atmosphere during seasonal changes. Just like Earth, there is a Northern Polar Cap and a Southern Polar Cap.

• The Northern Polar Cap is mostly water with carbon dioxide on the outer rims
• The Southern Polar Cap is mostly carbon dioxide with water underneath

Canyons are another prominent feature. The Valles Marineris is similar to our Grand Canyon, and was the first evidence of possible water formation on Mars (since the Grand Canyon was formed by gradual erosion as a result of the Colorado River - and plate tectonics played a role as well). The second image from the top clearly shows this region. Valles Marineris is named after the Mariner orbiter.

Two of the three main volcanoes are visible in this same image - on the right hand side. The largest volcano is called Olympus Mons.

The image above shows Olympus Mons in comparison to the Hawaiian Islands (in red). This volcano is the largest in the Solar System.

This type of volcano is called a shield volcano and forms not by tectonics but by upward pressure from the mantle. Because plate tectonics is absent from Mars, these volcanoes are free to grow to very large diameters.

The geologic periods of Mars (or any planet) can be determined by crater counts. Using this technique, there are three ages, or periods, of Mars:

• Noachian Era - 4.6 to 3.7 billion years ago, dating back to the heavy bombardment period (where debris in the newly formed Solar System was prominent)
• Hesperian Era - 3.7 to 1 billion years ago, also know as the Martian middle period
• Amazonian Era - 1 billion years ago to the present, represents the least cratered areas on Mars (like the northern lowlands)

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