Mars was among the first bodies in the Solar System to be viewed through a telescope. Early astronomers saw faint surface features along with evidence of changing seasons and speculated about an advanced Martian civilisation. Though these ideas are comical today, the search for more primitive life continues.
More recently, six-wheeled rovers have confirmed that water ice exists below the surface.
Photo: Mars taken by Mars Global Surveyor (NASA/JPL/MSSS)
The Red Planet continues to fascinate mankind.
The Viking orbiters see evidence of past water on Mars.
Viking orbiters mapped Mars in unprecedented detail and returned strong evidence of past flowing water. This finding suggested that the Red Planet may have once supported life.
American probes look for microbes in Martian soil.
The first spacecraft to land on Mars were the American Viking 1 and 2 probes in 1976. Their mission included testing the planet's soil for life. However, despite promising early test results, life was not found.
A wealthy Bostonian is intrigued by talk of canals on the Red Planet.
The American astronomer Percival Lowell popularised the idea that an advanced civilisation built canals on Mars, and he drew elaborate maps of their irrigation network. Many astronomers at the time were sceptical. It is now thought that surface features were mistaken for canals by well intentioned pioneers.
US spacecraft return the first photos taken from Mars's surface.
In 1976 the United States Viking spacecraft successfully returned the first complete photographs taken from the Martian surface.
A series of missions finds astonishing features on the Red Planet.
The unmanned Mariner missions gradually revealed Mars's extreme landforms. Perhaps most impressive was Olympus Mons, a volcano three times the size of Mount Everest.
Mars is the fourth planet from the Sun and the second smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is often described as the "Red Planet" because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. Mars is the site of Olympus Mons, the second highest known mountain within the Solar System (the tallest on a planet), and of Valles Marineris, one of the largest canyons. The smooth Borealis basin in the northern hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two known moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids, similar to 5261 Eureka, a Martian trojan asteroid.
Until the first successful Mars flyby in 1965 by Mariner 4, many speculated about the presence of liquid water on the planet's surface. This was based on observed periodic variations in light and dark patches, particularly in the polar latitudes, which appeared to be seas and continents; long, dark striations were interpreted by some as irrigation channels for liquid water. These straight line features were later explained as optical illusions, though geological evidence gathered by unmanned missions suggest that Mars once had large-scale water coverage on its surface. In 2005, radar data revealed the presence of large quantities of water ice at the poles and at mid-latitudes. The Mars rover Spirit sampled chemical compounds containing water molecules in March 2007. The Phoenix lander directly sampled water ice in shallow Martian soil on July 31, 2008.
Mars is currently host to five functioning spacecraft: three in orbit – the Mars Odyssey, Mars Express, and Mars Reconnaissance Orbiter – and two on the surface – Mars Exploration Rover Opportunity and the Mars Science Laboratory Curiosity. Defunct spacecraft on the surface include MER-A Spirit and several other inert landers and rovers such as the Phoenix lander, which completed its mission in 2008. Observations by the Mars Reconnaissance Orbiter have revealed possible flowing water during the warmest months on Mars. In 2013, NASA's Curiosity rover discovered that Mars' soil contains between 1.5% and 3% water by mass (about two pints of water per cubic foot or 33 liters per cubic meter, albeit attached to other compounds and thus not freely accessible).
Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude reaches −3.0, which is surpassed only by Jupiter, Venus, the Moon, and the Sun. Optical ground-based telescopes are typically limited to resolving features about 300 km (186 miles) across when Earth and Mars are closest because of Earth's atmosphere.