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Earth Astronomy - Planet Mars Jupiter

Mars Mass: 6.421 X 1023 kg (0.1075 Earths)
Radius (equatorial): 3397 km
Mean density: 3.94 g cm-3
Distance from Sun: 227 940 000 km
Rotational period: 24.62 hours (1.026 days)
Orbital period: 686.98 days
Escape velocity: 5.02 km s-1
Apparent magnitude: -2.01
Surface temperature: -63C (mean)
Atmospheric composition: carbon dioxide (95.32%), nitrogen (2.7%), argon (1.6%), oxygen (0.13%), carbon monoixde (0.07%)
Number of satellites: 2 (Phobos and Deimos)


It is the most visited planet after our own planet Earth. Mars is also commonly known as the Red Planet due to its orange-red appearance in the sky. Unlike Venus, Mars has more favorable conditions to be considered as possible candidate to harbor life. Nevertheless, Mars' orbit is significantly elliptical, meaning that temperature can vary wildly between -133C at the poles to about 25C during summer. Martian atmosphere contains a tiny amount of water, about a thousandth of water content in Earth's atmosphere. Even then, clouds can still form and are found to swirl around highlands and mountains.

Martian surface is rich with a variety of terrains that are very similar to Earth. Specifically, erosions, dry gorges, shorelines and riverbeds are found on the Martian surface. These terrain features are strikingly similar to those from Earth, suggesting that water may have once flown freely on the surface of Mars. This suggestion is further strengthened from the recent discoveries made by the Mars Global Surveyor that surface features indicating current sources of liquid water at or near the Martian surface were being discovered. In addition, the Mars Odyssey probe discovers large deposit of frozen hydrogen (and thus possibly ice) located near the southern polar region. Not surprisingly, numerous mission projects have been planned to study the planet in greater details, including survey probes, surface rovers, soil sample returns and even a possible future human exploration.

The Nasa's twin exploration rovers, Spirit and Opportunity landed on Mars at different location in early 2004. The rovers revealed temptation clues about the presence of water in the past. The rock features were highly altered and contained bromine, sulfur and chlorine, suggestive of watery past. Mars has two small, irregular-shaped satellites, Phobos and Deimos. Both may be composed of a mixture of carbon-rich rock and ice. Both are heavily cratered. Their origins are not known, but are widely regarded as the captured asteroids that may perhaps originate from the outer solar system.


HST image of Mars

Two dramatically different faces of Mars appear in these comparison images showing how a global dust storm engulfed Mars with the onset of Martian spring in the Southern Hemisphere. In June (left), the seeds of the storm were caught brewing in the giant Hellas Basin (oval at 4 o'clock position on disk) and in another storm at the northern polar cap. In September (right) the storm had already been raging across the planet for nearly two months obscuring all surface features.

Credit: NASA, James Bell (Cornell Univ.), Michael Wolff (Space Science Inst.), and the Hubble Heritage Team (STScI/AURA)

Panoramic view at Mars Pathfinder site

Panaromic view of Mars terrain at the Pathfinder's landing site. (Credit: NASA/JPL)

Gullies at Mars

Mars Orbiter Camera onboard the Mars Global Surveyor captured gullies and layers in crater wall in Newton (March 2001). Newton Crater and its surrounding terrain exhibit many examples of gullies on the walls of craters and troughs. The gullies are considered to have been formed by erosion - both from a fluid (such as water) running downslope, and by slumping and landsliding processes driven by the force of gravity.

Credit: NASA/JPL/Malin Space Science Systems

Gusev crater

Image taken by the Spirit rover while examining some bedrocks called 'Columbia Hill' at Mars' Gusev Crater. The evidence of the presence of water was found, which altered the rock structures.

Credit: NASA/JPL

Phobos, taken by Viking

Phobos, the larger of the two Mars' satellite, with a diameter of about 22 km. The most prominent feature on Phobos is the large crater named Stickney. The impact that created Stickney must have almost destroyed Phobos. The grooves and streaks on the surface were probably also caused by the Stickney impact. This image was taken by the Viking orbiter in 1977.

Credit: NASA

Deimos, taken by Viking

Deimos, the smaller satellite of Mars, with a diameter of about 13 km. Compare with Phobos, Deimos has a smoother appearance. This image was taken by Viking orbiter in 1977.



Because of its interesting geological features, questions of water at the surface and the possibility of extraterrestrial life, there are many missions to Mars. Quite a few, however, went disastrously wrong and ended prematurely.

Mariner Mission - The first spacecraft to visit Mars was Mariner 4, in 1965.

Viking Mission - Successful Mars landers in 1976.

Mars Pathfinder - First free-ranging robotic rover in planetary exploration.

Mars Climate Orbiter and Mars Polar Lander - Two missions that ended in total failure.

Mars Global Surveyor - Enduring mission to map globally surface topography, weather and mineral distributions.

Mars Odyssey - Probing hydrogen, elemental composition and radiation environment at Martian surface.

Mars Express - Mission to Mars planned by ESA and Italian space agency. Reached Mars in December 2003, but the piggybacked probe, Beagle ended in failure.

Mars' Twin Rovers - Nasa's successful twin rover mission, Spirit and Opportunity, which found strong past evidence of water.

The Mars Society - Society to encourage exploration of Mars.

Earth Jupiter


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