MARS

MARS, KNOWN AS THE RED PLANET, is the fourth planet from the Sun and the outermost rocky planet. In the 19th century, astronomers first observed what were thought to be signs of life on Mars. These signs included apparent canal-like lines on the surface and dark patches that were thought to be vegetation.

It is now known that the “canals” are an optical illusion, and the dark patches are areas where the red dust that covers most of the planet has been blown away. The fine dust particles are often whipped up by winds into dust storms that occasionally obscure almost all the surfaces. Residual fine dust in the atmosphere gives the Martian sky a pinkish hue. The northern hemisphere of Mars has many large plains formed of solidified volcanic lava, whereas the southern hemisphere has many craters and large impact basins. There are also several huge, extinct volcanoes, including Olympus Mons, which, at 370 miles (600 km) across and 15 miles (25 km) high, is the largest known volcano in the solar system. The surface also has many canyons and branching channels. The canyons were formed by movements of the surface crust, but the channels are thought to have been formed by flowing water that has now dried up. The Martian atmosphere is much thinner than Earth’s, with only a few clouds and morning mists. Mars has two tiny, irregularly shaped moons called Phobos and Deimos. Their small size indicates that they may be asteroids that have been captured by the gravity of Mars.