Mars is the first planet beyond Earth, away from the Sun. Mars's diameter is about 4,213 mi. Although Mars's orbit is nearly circular, it is somewhat more eccentric than the orbits of many of the other planets, and Mars is more than 25 mil mi farther from the Sun in some parts of its year than it is in others. Mars takes 687 Earth days to make one circuit of the Sun, traveling at about 15 mi a second.
Distance from Sun
Perihelion 128.4 mil mi
Semi-major axis 1.52364 AU
Aphelion 154.8 mil mi
Period of revolution around Sun 686.98 d (1.88 y)
Orbital eccentricity 0.09342
Orbital inclination 1 deg 51m 0s
Synodic day (midday to midday) 24h 41m 58s
Sidereal day 24h 37m 22s
Rotational inclination 25.19 deg
Mass (Earth = 1) 0.1075
Mean radius 2,106 mi
Mean density (Earth = 1) 0.713
Natural satellites 2
Average surface temperature 76 deg F
Hindi Name : Mangal Grah
Planet rotates upon its axis in almost the same period of time as Earth 24 hours and 37 minutes. Mars's mean distance from the Sun is 141 mil mi, so its temperature would be lower than that on Earth even if its atmosphere were not so thin. Mariner 4, in 1965, reported that atmospheric pressure on Mars is between 1% and 2% of Earth's atmospheric pressure.
As is the case with Venus, the thin atmosphere appears to be composed largely of carbon dioxide. No evidence of free water was found by Mariner 4. The planet is exposed to an influx of cosmic radiation about 100 times as intense as that on Earth.
Deductions from years of telescopic observation indicate that about 5/8 of the surface of Mars is a desert of reddish rock, sand, and soil. The rest is covered by irregular patches that appear generally green, in hues that change through the year. These were formerly held to be some sort of primitive vegetation, but with the findings of Mariner 4 of a complete lack of water and oxygen, it appeared that such growth would not be possible.
The nature of the green areas became a mystery. They may be regions covered with volcanic salts whose color changes with changing temperatures and atmospheric conditions, or they may be gray rather than green. (When large gray areas are placed beside large red areas, the gray areas appear green to the eye.)
Mars's axis of rotation is inclined from a vertical to the plane of its orbit about the Sun by about 25 deg, and therefore Mars has seasons as does Earth. White caps form about the winter pole of Mars, growing in the winter and shrinking in the summer. These polar caps are now believed to be both water ice and carbon dioxide ice. It is the carbon dioxide that is seen to come and go with the seasons.
The water ice is apparently in many layers with dust between them, indicating climatic cycles. Markings forming a network of fine lines, crossing much of the surface of Mars, have been seen by diligent observers. A few of the 21 photographs sent back to Earth by Mariner 4 covered areas crossed by canals; the pictures show faint, ill-defined, broad, dark markings, the nature of which could not be positively determined.
Mariners 6 and 7 in 1969 sent back many photographs of higher quality. These showed cratering similar to the earlier views, but in addition showed other types of terrain. Some regions seemed featureless over large areas; others were chaotic, showing high relief without apparent organization into mountain chains or craters. Mariner 9, the first spacecraft to orbit Mars (1971), transmitted more than 10,000 photographs covering 100% of the surface.
Although these photos and other data show that Mars resembles no other planet we know, scientists using terrestrial terms describe features that seem to be clearly of volcanic origin. One of these features is Olympus Mons, apparently a shield volcano whose caldera is more than 50 mi wide and whose outer slopes are more than 300 mi in diameter; it stands more than 15 mi above the surrounding plain the tallest known mountain in the solar system.
Some features may have been produced by cracking (faulting) of the surface and the sliding of one region over or past another. Many craters seem to have been produced by impacting bodies that may have come from the nearby asteroid belt. Features near the S pole may have been produced by glaciers no longer present. Valles Marineris, a huge series of interrelated canyons, stretches more than 3,000 mi.
Although the Russians landed a probe on the Martian surface in 1971, it transmitted for only 90 seconds. In 1976, the U.S. landed 2 Viking spacecraft on the Martian surface. The landers had devices aboard to perform chemical analyses of the soil in search of evidence of life; results were inconclusive. The 2 Viking orbiters returned the best pictures up to then of Martian topographic features.
Scientists believe many of these features can be explained only if Mars once had large quantities of flowing water. In 1997, 2 more U.S. spacecraft the Mars Pathfinder and the Mars Global Surveyor went to the red planet to continue exploration aided by monitoring with the Hubble Space Telescope. Preliminary geological results from the Pathfinder, which landed July 4, indicate that in its beginning stages Mars melted to a sufficient extent to separate into dense and lighter layers.
The Surveyor, which went into orbit around Mars on Sept. 11, has already reported the presence of a very weak magnetic field that may have been stronger in the distant past. Mars's position in its orbit and its speed around that orbit in relation to Earth's position and speed bring the planet fairly close to Earth on occasions about 2 years apart and then move Mars and Earth too far apart for favorable observation.
Every 15-17 years, the close approaches are especially favorable for observation. Mars has 2 satellites, discovered in 1877 by Asaph Hall. The outer satellite, Deimos, revolves around the planet in about 31 hours. The inner satellite, Phobos, whips around Mars in a little more than 7 hours, making 3 trips around the planet each Martian day.
Since it orbits Mars faster than the planet rotates, Phobos rises in the W and sets in the E, opposite to what other bodies appear to do in the Martian sky. Mariner and Viking photos show these satellites to be irregularly shaped and pitted with numerous craters. Phobos also exhibits a system of linear grooves, each about 1/3 mi across and roughly parallel.
Phobos measures about 8 by 12 mi and Deimos about 5 by 7.5 mi. Of the tens of thousands of meteorites found on Earth, approximately a dozen of them may have originated on Mars. In 1996, a NASA research team concluded that a meteorite found in 1984 on an Antarctic ice field not only might be a rock blasted from the surface of Mars but also might contain evidence that life existed on Mars more than 3.5 bil years ago.
The meteorite has been age-dated to about 4.5 bil years. The scientists theorize that 3.5 bil years ago, Mars may have been warmer and wetter, and microscopic life may have formed and left evidence in the rock, including possible fossilized microscopic organisms. Then, 16 mil years ago, it is believed that a huge asteroid or comet struck Mars, blasting material, including this rock, into space.
The rock may have entered Earth's atmosphere about 13,000 years ago, landing in Antarctica. The evidence is intriguing, but not conclusive, and even if the above conclusions are correct they indicate the presence only of microscopic life, at a time far in the past.
Mercury Planet Information (Budh Grah)
Venus Planet Information (Shukra Grah)
Jupiter Planet Information (Guru Grah)
Saturn Planet Information (Shani)
Uranus Planet Information (Arun Grah)
Neptune Planet Information (Varuna Grah)
Pluto Planet Information (Yama Grah)
Moon Planet Information (Chandra)
Sun Planet Information (Surya)