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Mars

Mars is the fourth planet from the Sun in the Solar System. Mars is a terrestrial planet with a surface reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts, and polar ice caps of Earth and it has two small satellites. The rotational period and seasonal cycles of Mars are similar to those of Earth. It orbits the Sun in 686.971 days and its synodic period with respect to the Earth is 779.96 days. It is much smaller than the Earth, with radius almost ½ of the Earth, and surface 1/4th of the Earth, while its mass is only 1/10th of the Earth. It has very low mean density 3.93 g/cm³ and the gravity is 1/3rd of the Earth. It rotates around its axis in almost one day and its axial tilt is almost the same as the Earth’s although it varies much more than the Earth’s as our planetary axis is stabilized by the Moon. The average  temperature is 210 K, with extremes 186 K and 293 K. The apparent magnitude varies a lot from ?3.0 to +1.6, surpassed at maximum only by Venus, the Moon, and the Sun.

Mars probably lost its magnetic filed and magnetosphere 4 billion years ago, so the solar wind interacts directly with the Martian ionosphere, lowering the atmospheric density. Presently Mars has only some patchy magnetic fields. Compared to Earth, the atmosphere of Mars is quite rarefied. The atmospheric preassure is very low, only 0.6 kPa.   The surface pressure of Mars is equal to the pressure found 35 km  above the Earth's surface. The atmosphere is composed mainly of carbon dioxide (95.3%) and some nitrogen (2.7%) and argon (1.6%) and  minute amounts of oxygen (0.13%) and carbon monoxide (0.08%). There are traces of water, nitric oxide, molecular hydrogen, neon, HDO, krypton, formaldehyde, xenon, ozone and others in smaller quantities. The scale height of the atmosphere is about 10.8 km, which is higher than Earth's (6 km) because the surface gravity of Mars is only about 38% of Earth's.

Mars has many mountains and some volcanoes, including Olympus Mons, the the highest known mountain of the solar system, and Valles Marineris, the largest canyon. A very smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Surface features reveal that Mars probaly had large-scale water coverage. Even small geyser-like features (water or CO2) are present.

It is believed that Mars has a core 1,480 km in radius made of iron and 14–17% sulfur, that is partially in liquid form, surrounded by silicate mantle responsible for the tectonic and volcanic features on the planet, today inactive.

Mars two moons small satellites, Phobos and Deimos, irregularly shaped, look like captured asteroids, similar to 5261 Eureka a Martian Trojan asteroid.

Mars is currently host to three functional orbiting spacecraft: Mars Odyssey,Mars Express, and the Mars Reconnaissance Orbiter.

Many spacecrafts have been sent to Mars by Europe, USA, Soviet Union and Japan. The first successful mission was NASA's Mariner 4 (1964). Mariner 9  entered into orbit around the red planet in 1971  andis the first artificial satellite of a planet. Soviet probes, Mars 2 and Mars 3 followed the same yearand landed succesfully, followed by NASA’s Viking 1 and 2 with two orbiters and landers which touched down in 1976.  Soviet probe Phobos 2 successfully photographed Mars and Phobos. Mars Global Surveyor (1997), Mars Pathfinder (1997) and Sojourner are three very successful  missions NASA that studyied Mars, even with robotic exploration vehicle in the Ares Vallis on Mars, followed by Mars Odyssey (2001) that with its Gamma Ray Spectrometer detected large quantities of hydrogen which is thought to be contained in large deposits of water ice. In 2003, the European Space Agency (ESA) Mars Express mission, with Mars Express Orbiter and the lander Beagle 2. while at the same year NASA launched the twin Mars Exploration Rovers  Spirit (MER-A) and Opportunity (MER-B) that discovered that liquid water existed in the past at both landing places and in  2006 the NASA Mars Reconnaissance Orbiter probe conducted two year survey. The most recent mission to Mars was the NASA Phoenix Mars lander. The Dawn mission to Vesta and  Ceres, flew by Mars (February 2009) for a gravity assist on its way to the two dwarf planets.

In 2003, the European Space Agency (ESA) launched the Mars Express craft, consisting of the Mars Express Orbiter and the lander Beagle 2. Beagle 2 failed during descent and was declared lost in early February 2004. The Planetary Fourier Spectrometer detected methane in the Martian atmosphere and aurorae have been observed on Mars.

Links

http://www.space.com/missionlaunches/beagle_update_040126.html
http://www.nature.com/nature/journal/v435/n7043/abs/nature03603.html
http://adsabs.harvard.edu/abs/2008POBeo..85...19N
http://adsabs.harvard.edu/abs/1984JHA....15..211P
http://www.uapress.arizona.edu/onlinebks/mars/chap02.htm
http://solarsystem.nasa.gov/missions/profile.cfm?MCode=Mariner_09
http://web.archive.org/web/20060415081709/http://www.cnn.com/TECH/9706/pathfinder/surveyor/
http://mars.jpl.nasa.gov/odyssey/newsroom/pressreleases/20081009a.html
http://www.sciencenews.org/view/generic/id/33622/title/Impact_may_have_transformed_Mars_
http://www.guardian.co.uk/science/2008/jun/26/mars.asteroid?gusrc=rss&feed=science
http://www.space.com/missionlaunches/odyssey_update_030314.html
http://science.nasa.gov/headlines/y2001/ast31jan_1.htm
http://www.space.com/missionlaunches/beagle_update_040126.html
http://www.universetoday.com/2007/07/17/the-mars-landing-approach-getting-large-payloads-to-the-surface-of-the-red-planet
http://www.nasa.gov/mission_pages/mars/news/mgs-20061206.html
http://marsrovers.jpl.nasa.gov/science/
http://web.archive.org/web/20080419070652/http://edition.cnn.com/2008/TECH/space/03/03/mars.avalanche.ap/index.html
http://phoenix.lpl.arizona.edu/05_25_pr.php
http://www.jpl.nasa.gov/news/features.cfm?feature=2031

Pictures:

http://pds.nasa.gov/planets/special/mars.htm  

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