Mars – the Red Planet – is our outer neighbour in the Solar System. It is a world known since ancient times, and is named after the Roman god of war.
Mars is at its brightest every couple of years when it shines with an orange hue that might resemble a drop of blood.
Mars grips the public imagination more than any other planet. That is hardly surprising. For the Red Planet resembles our own Earth in many ways. It is made of rock, plus it has an atmosphere and weather systems.
Mars will shine brightly in mid-2018 because it will be at its closest to us and on the same side of the Sun. This gives amateur astronomers their best opportunity to glimpse surface features with small telescopes.
At other times Mars shows a smaller disk and shines much more dimly because our orbits have carried us much further apart, and sometimes it can lie on the far side of the Sun.
Mars is much smaller than Earth, with a diameter of around 6,795 km (4,222 miles), but its day is just 40 minutes longer than ours and its axis is tilted by 25 degrees – a similar amount to Earth’s – giving it seasons like those we experience.
Early telescopes revealed surface features on the Red Planet, leading scientists and sci-fi writers to wonder if it might be inhabited. They also revealed that Mars has two tiny moons, named Phobos and Deimos. They are probably asteroids captured by Mars.
From the moment we got our first close views of Mars from passing spacecraft, it became clear that the old ideas about our neighbouring world would have to be revised. There was no sign of life. Instead, Mars more resembled the Moon, with the first photos showing a rugged, cratered landscape.
Thanks to space probes, we are learning more and more about what a dramatic world awaits the first explorers. Surveys from orbit picked our many features that have clearly been carved out by water, such as former lake beds and long dried-up river gullies.
Space studies have shown that reservoirs of water exist as ice at the martian south pole and evidence is overwhelming that the planet was once covered with oceans. Mars also has contrasting hemispheres. To the south are highlands, dotted with craters, while the north holds a vast low-lying plain that was probably produced by a collision with another large body four billion years ago.
Dramatic features on Mars include the biggest volcano in solar system, the 26 km (16 mile) high Olympus Mons, plus Valles Marineris, a vast chasm 4,000 km (2,500 miles) long that dwarfs the Earth’s own Grand Canyon.
We have known since 1965 that Mars is covered with craters from asteroid impacts. Surprisingly, recent monitoring of the surface shows that impacts are still happening today. But surface features are gradually eroded by the winds or covered by desert dust whipped up by martian whirlwinds.
Bigger dust storms, caused by seasonal changes in temperature, can occasionally envelop the whole planet. The latest planet-wide dust storm blew up in June 2018.
With historic evidence of water and other organic ingredients, it is natural to wonder whether life ever existed on Mars – and if it might be found there even today!
The human race is determined to find out. Mars has been put under greater scrutiny than any other planet. A large flotilla of spaceships have traversed the gulf of space to reach it, some with more success than others. But a number of probes have gone into orbit, robot rovers have landed to explore the surface and still more missions are on their way or are being prepared for flight.
Most excitingly of all, the world’s space agencies, and some private enterprises such as SpaceX, have set goals of putting men on Mars within the next few decades.