Walter S. Kiefer Lunar and Planetary Institute Next Stop: Mars! Walter S. Kiefer Lunar and Planetary Institute

Earth and Mars Earth and Mars at the correct relative size. The Earth view is of Africa (top) and Antarctica (bottom). Note the predominance of water, ice, and clouds on Earth, and the virtual absence of water on Mars.

Basic Facts about Mars Diameter: Mars Day: Mars Year: Mass: Gravity: Atmosphere: Atmospheric Pressure: Surface Temperature: 6,794 km (53% of Earth) 24 hours 37 minutes 687 Earth days 11% of Earth 38% of Earth 95% Carbon Dioxide < 1% of Earth at sea level -125 to +20 Celsius The image on the left is from the Hubble Space Telescope in 1999. Note the large storm system near the North Polar cap (1600 kilometers, or 1000 miles across).

Giant Volcanos Many of the geologic features on Mars occur on a very large scale, a fact that often fascinates school children. This three-dimensional perspective view shows the martian volcano Olympus Mons. It is the largest volcano known in the Solar System, at 640 kilometers (400 miles) across and 22 kilometers (14 miles) high.

Valles Marineris Valles Marineris is a giant trough on Mars, more than 4000 kilometers (2500 miles) long and up to 10 kilometers (6 miles) deep. It is long enough that it would reach from California to Washington D.C. on Earth! Valles Marineris formed in the middle part of martian history, roughly 2.5 to 3.5 billion years ago, when forces in the crust of Mars stretched the surface and created massive faults, resulting in the deep valley that crosses the center of this image.

An Impact Scarred Surface This image shows the Argyre impact basin, 1850 kilometers (1150 miles) across and 5 kilometers (3.1 miles) deep, which formed by the impact of a large asteroid or comet.. It has a deep, relatively smooth floor and is surrounded by a high, rough blanket of ejecta. Ejecta is the material which was blasted out of the basin by the impact and lands in the area surrounding the impact crater or basin. The Argyre basin probably formed around 3.8 to 4 billion years ago. Numerous smaller impact craters are also seen in this image.

Ancient Floods The surface of Mars has been scoured in many places by giant floods of water. This image shows Ravi Vallis, a region 300 kilometers (190 miles) across. The flood erupted from the depression at the left center and flowed to the right, creating the scoured channel floor seen in this image. 50 km

Phobos and Deimos Mars has two very small moons. Phobos (upper left) is 27 by 19 kilometers (17 by 11 miles) across. Deimos (lower right) is 15 by 11 kilometers (9.5 by 7 miles) across. Both moons may be captured asteroids. If so, they were probably captured early in martian history.

A Desert World Mars is a desert world, with no liquid water at its surface. This view, showing rust-colored dust and gray, basaltic (lava) rocks, was taken by NASA’s Spirit rover in early 2004.

A Geologic Time Machine Because rock layers are laid down bit by bit, the layer at the bottom of this cliff must be older than the layer at the top of the cliff. (This is similar to the stack of papers on your desk, or pile of clothes in your dirty clothes hamper – the papers at the bottom of the stack have been there longer than those at the top of the stack). By examining the rocks layer by layer, geologists can read the history of Mars. Because Mars has been geologically less active than Earth in the last 3 billion years, the early part of martian history is better recorded than the early history of Earth. In that sense, exploring Mars is like being in a geologic time machine.

Life on Mars? Look for evidence of respiration, response to nutrients. Results probably indicate unusual soil chemistry. No evidence for organic molecules at the parts per billion level. Claimed evidence for life in martian meteorite is not generally accepted. NASA looked for evidence of life in 2 places on Mars with the Viking spacecraft in 1976. Although a small number of the tests were ambiguous, the general consensus of scientists who have examined the data is that no evidence of life was found. Similarly, no evidence for organic molecules (the chemical building blocks of life) was found. A small number of scientists claimed in 1996 to have found evidence for fossil life in a meteorite from Mars (including the “fossil” shown in the image here), but these claims have not been generally accepted by the science community. For a summary of this issue see an article by Allan Treiman, “Microbes in a Martian Meteorite?” in the April 1999 issue of Sky and Telescope magazine. However, none of these findings are sufficient to prove that life does not (or did not) exist on Mars.