Mercury Diameter=4,878 km or 38% that of Earth

Mercury, closest planet to the sun, is an airless cratered world, its face still showing scars of bombardment by asteroids and comets during the solar system's youth. For at least the last three billion years, it has remained essentially unaltered. Until recently when spacecraft were sent there, Mercury had been extremely difficult to study because its small size and its close proximity to the sun made it difficult to see through even the most powerful telescopes. Until 1965, it was believed as fact that Mercury did not rotate but that one side constantly faced the sun. The truth is that Mercury turns so slowly it is difficult to tell that it is turning at all; it orbits the sun twice while it rotates on its axis three times. Mercury's day is 58.6 Earth days long and its year 87.97, with temperatures on the day side reaching up to 450 degrees C, and on the night side dipping to -180 C.

Venus Diameter=12,104 km or 95% that of Earth's

Venus is often referred to as Earth's "sister planet" because of its similarities in size, mass, and surface gravity. However, there is little else in common. A human standing unprotected on the surface would be simultaneously sizzled by the heat, asphyxiated by carbon dioxide, crushed by the density of the planet's atmospheric cloak, and scorched by hydrochloric-acid vapours. Venus' surface pressure is 90 times that of Earth's and equivalent to the pressure at a water depth of 900 meters on Earth. Venus is a hot desert world, with a surface temperature of 464 C, topped by an unbroken layer of acid clouds. These reflective clouds make it one of the brightest objects in the sky, exceeded only by the Sun and Moon. It can be seen for a few hours each night, when it rises before dawn or sets after sundown. A day on Venus is longer than it's year, taking 243 Earth days to rotate (in the opposite direction to Earth's) but only 224.7 days to orbit the Sun.

Earth Diameter=12,756 km

Earth is the largest of the terrestrial planets and the only planet to support life as we know it. It's surface is a wrinkled layer of solid rock called the crust, which is between 10 and 32 km thick; the oceans, comprising about 2/3 of the Earth's surface, fill the crust's deepest basins. The areas not covered by water are the seven continents of Africa, North and South America, Asia, Australia, Europe, and Antarctica. Our atmosphere, composed of 78% nitrogen and 21% oxygen, is the only one in the solar system which provides the oxygen that humans need to breathe. Earth' s day is 23.hours and 56 minutes, its year 365.25 days. The moon is the Earth's partner in space. About 1/4 the size of Earth, it is an airless, waterless world which circles the Earth once every 27 days at an average distance of 384,000 km. The moon is Earth's nearest neighbour in space and the only celestial body on which humans have landed.

Other views of the Earth:

Earth from Apollo 17

Earth and Moon

Mars Diameter=6,794 km or 53% that of Earth

The last of the terrestrial planets and fourth from the sun, Mars is the second closest in similarity to Earth. It's day is almost the same length, at 24 hours and 37 minutes, and it has many similar surface features including enormous volcanoes, vast canyons, dune fields, and dry channels. The planet's most distinguishing feature is the Valley Marineris, a canyon complex that stretches 5,000 km, far longer than any similar feature on Earth. On a summer day Mars' temperature rises no higher than 0 degrees C and at night most areas cool to -100 C. The only sign of water on Mars are the now dry channels, and the currently existing northern polar ice cap. Mars is called the Red Planet because of its reddish appearance in the night sky, as well as on its surface. Exploration of the Martian surface revealed no signs of life, only boulder-strewn fields, sand dunes, and a weird pink sky. Mars has two satellites, Phobos and Deimos.

Home Stars

Constellations Terrestrial Planets Gaseous Planets

Asteroids The Sun