Basic Data

• Mean Distance from Sun: 227.9 million km.
• Equatorial Radius: 3396 km. (0.53 Earth)
• Mass: 6.42 x 10²³ kg. (0.11 Earth)
• Surface Gravity: 24.8 m/s² (2.53 Earth)
• Length of Year: 687.0 days
• Length of Day: 24h 37m
• Surface Air Pressure: 0.6 kPa (0.006 Earth)

Wikipedia - Mars

About Mars

Aside from Earth, Mars is the world that has been the subject of more speculation—and in modern times, more robotic exploration—than any other planet in our solar system. Although it is actually quite cold, it nevertheless lies just inside the outer edge of the so-called "habitable zone" around the sun. If it had a thicker atmosphere, it could conceivably be a cool, but livable world. In fact, until modern observations showed that its atmosphere was too thin and lacking in oxygen, many writers of speculative fiction assumed that it was inhabited.

The surface of Mars is largely barren and covered with rocks. Craters pock the face of the planet. Nevertheless, aside from Earth, Mars has the friendliest environment in the solar system for visiting probes. The Mars Exploration Rovers have been wandering around, peeking at rocks, taking pictures and performing tons of science for around five years at the time of the writing of this article. Although night temperatures drop well below freezing (down to -140° C in the polar regions) probes properly equipped with heaters can survive. And Mars is close enough to the sun to use solar panels.

Olympus Mons

Mars is subject to dust storms. No doubt, these dust storms account for much of the variations in the surface that were seen in telescopes before space probes ever went to investigate. And when one orbiter arrived, it found the entire planet blanketed in dust, a phenomenon previously unimagined. Only four spots showed through the haze, which turned out to be the tops of four enormous volcanoes. One of them, Olympus Mons, is the largest volcano in the solar system. None of these volcanoes appears to be active today; in fact, there does not appear to be any active volcanism on the planet. This does not mean that there is no geologic activity at all. Recently, one of the orbiters observed a large, 700 meter high avalanche.

The overall elevation of the entire northern hemisphere of Mars is notably lower than the southern hemisphere. This has recently led to the theory that an immense asteroid—or even a planetoid around the size of Pluto—once smashed into the northern polar regions, i.e. the northern hemisphere is one titanic impact crater. There are a couple of problems with this—objects in the solar system tend to orbit in the plane of the ecliptic, and if something that big really had hit Mars in the north pole, it should have knocked its orbit somewhat askew. However, it is also possible that the crust of the planet gradually shifted into a more dynamically stable configuration after the impact.

Scientists had long suspected that Mars once had large amounts of water, and were pretty certain that it still has water today, in the form of permanently frozen polar caps and permafrost. Both of the Exploration Rovers discovered strong evidence of past water at their respective sites, and in 2008 the Phoenix lander arrived in the northern polar regions and quickly found large quantities of ice only inches below the surface. However, because of the extremely thin atmosphere, liquid water is impossible; it would immediately evaporate. So today Mars is drier than the driest desert on Earth. And the thin atmosphere and lack of magnetic field also provide practically no protection against solar ultraviolet radiation and cosmic rays, both of which are deadly to the complex molecular structures that make up living organisms.

Mars is an interesting place. Mars may someday be our best bet for setting up human colonies, although they would still have to be under pressurized domes that would also provide protection from radiation. Nevertheless, in its own right Mars is a dead, hostile world, without life.

Mars' Moons

Mars has two small moons, Phobos and Deimos, which are believed to be captured asteroids. Phobos is close enough and big enough (26.8 km x 18.4 km) that it appears about a third the size of Earth's Moon from the surface. Deimos (15 km x 10.4 km) never appears larger than a bright point of light in the Martian sky. Photos taken from orbiting probes reveal a pair of irregular, crater-pocked rocks.

Observation from Earth

The ancient Babylonians called Mars Nergal, after their god of fire, war and destruction. The Greeks picked up on that and called it Ares, after their war god, whose Roman equivalent was Mars. To the Hindus it was Mangala, and to the Hebrews it was Ma'adim, "the one who blushes".

Early telescopic observations showed what appeared to be a series of straight lines across the surface of Mars, and the Italian astronomer Giovanni Schiaparelli called them canali, which can be translated either as "channels" or "canals". It was the latter translation that fired the imaginations of those who believed Mars to be inhabited by advanced creatures. Additionally, surface features were seen to vary, including the so-called "summer darkening" that occurred fairly regularly, which added fuel to the idea that there was at least some kind of vegetation present. Only when spacecraft began actually taking close-up pictures did astronomers finally realize that both were illusory.

Exploration of Mars

Martian Sunset seen by the Spirit rover

Mars has been extensively visited by space probes from the United States, the Soviet Union and the European Union. Japan also sent a single orbiter, but it failed, as have nearly two thirds of all probes sent to the red planet. However, enough craft have arrived safely and either gone into orbit or else landed to make Mars the most studied of all the other planets in our solar system.

In 1976, Viking 1 sent back the first pictures from the surface of Mars. It was quickly followed by Viking 2, and then many years passed before the next lander was sent. A number of orbiters, such as Mars Global Surveyor and Phobos 2 were sent in the 80's and 90's. Finally, in '97 Pathfinder landed, which carried a small prototype rover called Sojourner, which paved the way for the Mars Exploration Rovers Spirit and Opportunity, both of which landed in 2004.

The most recent lander was Phoenix, which set down in the northern polar regions to look for water ice. It also carried a microscope capable of resolving objects a thousandth of the width of a human hair. Due to the harsh polar nights and increasingly shorter days, Phoenix only lasted a few months before going silent. But they were very fruitful months.

Currently, in addition to the still-functioning rovers, there are three orbiters in operation: Mars Odyssey (US), Mars Express (EU) and Mars Reconnaissance Orbiter (US). A number of future missions are also planned.