The Martian landscape.

MARS - THE RED PLANET

Mars, the fourth planet from the Sun, has intrigued humans throughout history. The ancient Egyptians called Mars Her Descher: "the red one". The Romans named the planet Mars, after their god of war. Mars has given its name to the month of March. At its closest approach, the distance between Mars and Earth shrinks to 55 million kilometres. Only Venus comes closer. Observers using ground-based telescopes can see light and dark variations on the surface, as well as bright polar caps. Mars is the seventh largest planet in the Solar System. Mars' diameter is about half that of Earth. Although Mars is much smaller than Earth, its surface area is about the same as the surface area of the land on Earth.

A Winter on Mars

The orbit of Mars lies between Earth and Jupiter, marking the outer limit of the inner solar system. As Mars orbits, it rotates once every 24.6 hours; the Martian day is therefore only 41 minutes longer than an Earth day. The spin-axis of Mars is tilted by nearly 25 degrees, very similar to Earth's tilt. As a result Mars, like Earth, has seasons.

The orbit of Mars.

The eccentricity of the Martian orbit causes the distance between Mars and the Sun to vary by over 40 million kilometres. The resulting variation in the amount of solar energy falling on Mars has a significant effect on Martian seasons and global temperatures.

More about the season of Mars

Mars compared with Earth

With a diameter of 6,794 kilometres, Mars is one of the smaller planets of the Solar System. Of the nine known planets, Mars' size places it seventh. Mars' diameter is about half that of Earth's, but, being less dense, it has one tenth the mass of Earth. Although Mars is much smaller than Earth, the lack of oceans means the surface area is about the same as the land surface area of Earth.

The lower mass of course gives Mars a gravity field weaker than Earth's. Should you visit the surface of Mars, you will find that you lose 60% of your weight. The weaker gravity causes the escape velocity to be lower, which in turn has an effect on the Martian atmosphere.

Solar irradiance, the amount of the Sun's energy falling on the surface of Mars, is reduced compared to Earth because Mars is further away - Mars receives about 60% less than the Earth. The Sun in the Martian sky is not as bright, and, despite the planet's warm red appearance, the whole planet is cold.

Mars compared with Earth.

Weak magnetism

Mars has a very weak magnetic field, over 5000 times weaker than Earth's. Mars therefore lacks protection from the incoming solar wind which is slowly removing the Martian atmosphere, at a rate of 2 kilogrammes per second. Indeed, most of the atmosphere may have already been driven off by the solar wind, and this could also explain the slow loss of water from the planet. The lack of a strong magnetic field could have played a vital role in the evolution of Mars.

More about the evolution of Mars

The Search for Life

Early observers believed that what they saw through ground-based telescopes were signs of irrigation and seasonal vegetation change. In the 1960s maps of Mars were still being produced showing canals and oases. The scientific view held that Mars was exciting, possibly covered with life, if not intelligent aliens. The public perception was that intelligent aliens most definitely lived on Mars; the question was whether or not they were hostile?

'The Face'.

More about life on Mars

A fascinating terrain

Mars has a highly varied terrain, and is home to Olympus Mons, the Solar System's largest mountain, along with Valles Marineris, a 4000km long canyon, and Hellas Planitia, a 2000km wide crater.

More about Mars craters

Huge volcanoes

The grandest volcanoes in the Solar System are to be found on Mars - some of them over twice the height of Earth or Venus volcanoes. The largest Martian volcanoes are bigger than some of the countries on Earth. Why are Martian volcanoes so tall, and why are they no longer active?

More about Mars Volcanoes

Mount Olympus.

Spectacular canyons

Mars is home to some of the most spectacular canyons in the Solar System. One canyon, Valles Marineris, dwarfs Earth's Grand Canyon. The formation and history of the canyons is a Martian puzzle. The canyon images returned by spacecraft provide clues to Mars' surface history and climate change. What is the link between Valles Marineris and the orbit of Mars around the Sun?

More about canyons on Mars

Valles Marineris.

Mysterious channels

Mars has a network of channels varying from small valleys to large-scale tributaries, looking as if they were formed by running water. The channels are yet another Martian puzzle - if formed by water, this implies that Mars used to be a warm, wet planet. How then, has Mars changed so much?

Furthermore, some of the channels are so large they could not have been formed by mere rivers, but by huge floods, greater than any Earth has ever had.

Channels on Mars.

More about channels on Mars

Ice and Water on Mars

In the past, astronomers reported observations of irrigation canals and seasonal changes in vegetation. Mars has an ice cap at each pole, visible through the smallest telescopes.

Polar ice cap.

More about Mars ice caps

The surface of Mars shows many examples of features similar to riverbeds, islands and coastlines, that suggest at some time during Martian history there may have been flowing water. If so, where has the water gone? Future human colonisation of Mars will need to be able to use Martian water - will this be possible?

Features on Mars.

More about Martian water

Of all the objects in the Solar System, Mars is the most Earth-like. It comes as no surprise then that Mars has been the destination of so many spacecraft. Although Mars has revealed many secrets, there remain even more unanswered questions. Future missions are designed to find the answers, so that we may obtain a greater understanding of the Martian system, and perhaps learn how a future human colony could live safely.

More on the exploration of Mars