Physical characteristics
Mars has a diameter of 6790 kilometers which is roughly half the size, and 15% of the volume, of Earth. Its small size and low density, relative to the Earth, give it a surface gravity only 38% as strong as Earth's.
The atmosphere on Mars consists mostly of carbon dioxide with only one percent of the gas pressure of Earth's atmosphere. Dust in the Martian atmosphere gives it a light pink color during the day, and at sunset it turns a very lovely teal. It's also cold as hell. The average temperature on Mars is -46° C.
The planet currently has no magnetic field, but geological (or, rather, archaeological) evidence suggests that it used to have a magnetic field some billions of years in the past. A magnetic field would have kept the solar wind at bay, which would have prevented the early Martian atmosphere from being stripped away into space. It is thought that the shutting down of this magnetic field eventually left us with only the thin ghost of an atmosphere that Mars currently has.
Mars has two small moons, Phobos and Deimos ("Fear" and "Dread," the sons of the war-god Ares in Greek mythology). Both are probably captured asteroids. Phobos has a surprisingly low density, leading some people to speculate that it may be hollow and artificial (and some nutters to believe that it is artificial), but the current understanding is that Phobos is a rubble-pile asteroid (an agglomeration of boulders bound by gravity). Another point of interest is the so-called "Phobos monolith," a bright rock jutting out of the surface that casts a long shadow (which suggests an unusual height-to-width ratio).
Jonathan Swift referred to two Martian moons in Gulliver's Travels (published in 1726, more than a century before their discovery in 1877). This has been used as evidence for claims of ancient astronauts and time travel, neglecting the fact that Kepler had speculated about a pair of Martian moons a century before.
 Life on Mars?
As a rocky planet similar to Earth, and massive enough to retain a thin atmosphere if gases were present, Mars has been a historical favorite of science fiction writers and others who speculate about extraterrestrial life. It is fairly obvious from geographical data and close up views of sedimentation on the surface that Mars once was home to vast quantities of water in large lakes and oceans. As water is one of the known prerequisites for biological life "as we know it", it could be possible that life once existed on Mars. With the relatively recent discovery of very dark patches on the surface that are thought to be extremely deep and dark sink holes and cave systems, the question about life existing now on Mars has been reopened to serious scrutiny. However, most serious exobiologists think life is more likely on the Jovian satellite Europa or Saturn's moon, Enceladus.
 Martian canals
During the 1877 opposition of Mars, the Italian astronomer Giovanni Schiaparelli noticed a network of features on the Martian surface that he called canali— Italian for "channels" but translated into English as "canals." His observations were collaborated by other astronomers and the hypothesis that these were artificial canals built by a Martian civilization started to gain followers. A prominent figure among them was the American astronomer Percival Lowell.
There was a slight problem, though - not all astronomers saw these canals. A vigorous scientific debate followed. Experiments demonstrated that canals can occur as an optical illusion. More powerful telescopes were pointed at Mars and found no canals and early spectroscopy found no significant amounts of water. Alfred Russel Wallace felt so strongly about the canal nonsense that he wrote a book, Is Mars Habitable? A critical examination of Professor Percival Lowell's book "Mars and its canals," with an alternative explanation. The idea started to fade out after the first decade of the 20th century, but it took the first "close-up" pictures of Mars, taken by NASA's Mariner 4 probe during its fly-by in 1965, to kill the canals for good.
 Probe-eating monster
A large proportion of (robotic) missions to Mars have failed, earning it the reputation of "the place where probes go to die". Some have blamed malevolent extraterrestrial intelligence, but a much more probable cause is shoddy terrestrial engineering. The probe-eating monster may have been squashed by a falling spacecraft, because all recent missions have been successful. (The cruelly-named Phoenix lander was not supposed to recover from the ice.)
After the success of the toy-sized Sojourner rover, brought to Mars by the Pathfinder lander in 1997, NASA decided that they need more and bigger
cars rovers. The result was the Mars Exploration Rover program and its two adorable offspring - Spirit and Opportunity. Arriving in 2004, they were still operational as of 2010, greatly exceeding their design expectations. Spirit got stuck in soft soil in 2009. After attempts at extracting it failed, it switched to hibernation mode for the Martian winter in March 2010. Attempts to establish communication with it still fail and its operators fear the worst. NASA is taking the next step with the car-sized, laser-shooting, drill-swinging, nuclear-powered Curiosity (formerly the Mars Science Laboratory), launched in November 2011.
The latest victim of
Russian under-funding the "Mars Curse" is the Russian Fobos-Grunt probe which was supposed to land on Phobos and return a small sample of its "soil" to Earth. After being launched successfully into Earth orbit, it failed to move into Mars transfer orbit and later re-entered Earth's atmosphere, with its remains falling in the Pacific Ocean. In a rare case of a government-endorsed conspiracy theory, some Russian officials apparently think that the US might have had something to do with it. (No, they didn't mention HAARP, but apparently it was the first thing on other people's minds.)
The most likely reason that so many Martian probes have failed is that more probes have been sent to Mars than to any other planet in the Solar System. Every mission has a chance of failure -- the more missions you launch, the greater the odds are that at least one of them will fail. Worse, in terms of mission delta-V requirements, Mars is easier to get to than any of the other planets. (Venus's orbit is closer to Earth's than Mars's is, but a Venus rendezvous requires cancelling a lot of the kinetic energy you have in Earth's orbit around the sun; a Mars rendezvous requires adding substantially less kinetic energy than this.) Because of this, Mars is usually the "first choice" for new and experimental space probe technology. The very first Mars mission to fail, Mariner 3, was also the first probe ever sent outside the Earth-Moon system, for example. In a way, it's kind of amazing that so many Mars missions have succeeded.
 Mars pareidolia club
A picture made by NASA's Viking 1 orbiter in 1976 showing a hill that looks like a face started a new hobby - looking closely at images returned by Mars probes and trying to find as much "evidence for extraterrestrial life" as possible. Contrary to expectations, magnifying images to the pixel level and repeatedly applying the "sharpen" tool are not considered cheating. Notable participants in this quaint activity are Richard Hoagland and the Mars Anomaly Research team. Not only a 'face' but whole pyramids and causeways are claimed to be seem - with the 'face' being 'identical' to that on the Sphinx at Gizeh. Sci-fi pedants have been amused to note that long-running BBC sci-fi show Doctor Who broadcast a serial in 1975 called The Pyramids of Mars, featuring a baddie called Sutekh the Destroyer who was imprisoned in a pyramid. On Mars. "coincidence??" etc etc
 Mars and the Great Flood
 Mars in Silly Love Songs
Venus, similarly, was named for the goddess of love, and has a yellowish cast. When the two planets are visible from the Earth in the same area of the sky, it is said that "Venus and Mars are alright tonight". In this case they can be reasonably represented by the 1 and 3 billiards balls, respectively.
Apparently, it has been discovered by
scientists, Creation Scientists, some loony nut jobs, that men do not actually come from Earth, but are in fact from Mars. Women, the smarter, wiser, and apparently less inclined to do anything but bake brownies, are themselves from Venus.
 See also
- ↑ Shatner "sings" Rocket Man
- ↑ Kepler's logic: the Earth has one moon, Jupiter has four (only the Galilean moons were known at that time), therefore Mars should have two, as 1,2,4 is a progression.
- ↑ Is Mars Habitable? (1907), full public domain text at Project Gutenberg
- ↑ Springtime on Mars, a
- ↑ A nice infographic by Bryan Christie
- ↑ The "Mars Curse": Why Have So Many Missions Failed?, Universe Today
- ↑ Spirit, xkcd
- ↑ What it's supposed to look like in action
- ↑ Charles Creager, Jr, July 23, 2008. "Mars, a Testament to Catastrophe." Answers Research Journal 1 (2008): 89-94.