Mars

Mars is the outermost of the rocky planets that dominate the inner solar system – it is larger than Mercury, but considerably smaller than Earth or Venus. Mars is a complex world that has been shaped by all the same forces as our own planet. Today the two planets look remarkably different, but in the past Mars was probably much more Earth-like.

OUR OUTER NEIGHBOUR

Mars orbits the Sun once every 687 Earth days, at an average distance of nearly 228 million km (142 million miles). Unusually among the major planets, its orbit is noticeably elliptical (stretched), so at one end it comes as close to the Sun as 207 million km, while at the other extreme it is 249 million km away. Only tiny Mercury’s orbit is more elongated.

The Martian orbit interacts with Earth’s so that the distance between the two worlds is constantly varying. Because of this, close approaches between Mars and Earth, which occur every 26 months or so, vary between 57 million and 99 million km. The closest approaches take place every 16 years.

While the Martian year is notably different from Earth’s, the day and pattern of seasons are surprisingly similar – the planet rotates in 24 hours 37 minutes, and is tilted on its axis at 25.2 degrees from “straight up” – slightly more than Earth’s own 23 degree tilt. This means Mars goes through its own cycle of seasons, as first one hemisphere and then the other is exposed to more sunlight.

Can MARS Sustain Life?

Today two white polar caps stand out against the otherwise dark surface of the Red Planet. Composed of permanent deposits of varying amounts of water ice and shifting frosts of carbon dioxide, they are a stark reminder that Mars was, at some point in its geological past, home to both liquid water and, later, frozen glaciers. Both liquid and solid water have been fundamental in shaping the surface features of Mars.

Some of the giant valleys and the channels running off them were cut by fast-moving water during floods; others were created by water flowing gently through river valleys, and others still were carved a little later by slow-moving glaciers. Surface features such as the regular beds of sediment, shown in images taken by the Mars Global Surveyor in 2000, testify to the presence of seas or oceans on Mars in the distant past.