![]() Mars has two tiny moons, Phobos and Diemos, which were discovered in 1877 and appear to be captured asteroids. Microbial life may have evolved on Mars billions of years ago when it was far more Earth-like whether any microbial life still exists today is a matter for further exploration. Mars boasts the largest volcano in the solar system, Olympus Mons, which is 25 km tall (almost three times the height of Mt Everest) and one of the biggest canyon systems, the Valles Marineris, more than 4,000 km long. Mars has seasons, like the Earth, and polar caps composed of carbon dioxide ice and water ice. ![]() Orbiting spacecraft and rovers have provided considerable evidence that there was once water flowing on the surface of Mars water may even exist today, frozen as permafrost beneath the surface. Most of Mars’ atmosphere was either oxidised into its iron rich surface (forming the rusty red colour we see today) or lost to space over time due to Mars’ weak gravity. Mars may once have been Earth-like, but has now lost its surface water and possesses only a very thin carbon dioxide atmosphere and a surface pressure less than one percent that of Earth. A day on Mars is about 40 minutes longer than an Earth day, and it takes 687 days to orbit the Sun. Our planet has one large moon, with a radius about one quarter of the Earth’s, making it the largest satellite compared to its parent planet (although Charon, the moon of the dwarf planet Pluto, is about half the diameter of Pluto).Īt 6,799 km Mars is about half the diameter of the Earth, with a surface temperature range of -125 to -20☌. With surface temperatures ranging from -88 to 58☌, Earth is the only place in the solar system where water exists in all three forms – solid, liquid and gas. The Earth’s powerful magnetic field also protects us from bombardment by radiation from space. The atmosphere is composed mainly of nitrogen (78 percent) and oxygen (21 percent) and only allows a narrow slice of the electromagnetic spectrum (mostly visible light) to reach the surface, shielding us from harmful infrared, ultraviolet, X-rays and gamma-rays. With its vast oceans and protective atmosphere, our home planet has proved just right for the development of life and is the only world in the universe where life is currently known to exist. Seen from Earth, Venus is the brightest object in the night sky apart from the Moon.Įarth is the largest of the “terrestrial”, or rocky, planets (12,742 km in diameter), and has the greatest density of any planet in the solar system. The atmospheric pressure at the surface of Venus is a crushing 90 times that at sea level on Earth. ![]() Observations using radar to “see” through the clouds have revealed that there are thousands of volcanoes on the surface, some up to 240 km in diameter, and evidence strongly suggests that volcanic activity is still occurring. However, the clouds at the top of its atmosphere zip round the planet in only four days, driven by wind speeds around 360kph. Similar in size to Earth, with a diameter of 12,100 km, Venus is the hottest world in the solar system, its thick carbon dioxide atmosphere trapping heat like a greenhouse, so that the surface temperature reaches 462☌ – hot enough to melt lead.Ī “year” on Venus is 225 Earth days long, but the planet spins so slowly (and in the opposite direction to the spin of most of the other planets) that it takes 243 Earth days to complete one rotation, meaning that Venus’ day is longer than its year. Hidden under a blanket of clouds, Venus is a hellish world of crushing atmospheric pressure, high temperature and acid rain.
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