Mars is the fourth planet from the Sun. It is about 1.5 times as far from the Sun as Earth is. Mars is about 6,780 kilometers (4,212 miles) across, which is about half the width of Earth.
Mars looks red because there is rusty iron in its ground. Mars is a cold, dry, desert world. Temperatures on Mars can drop to about minus 153 degrees Celsius and reach about 20 degrees Celsius on a warm day.
Air pressure at the surface of Mars is only about one hundredth of Earth's, about 6 millibars. The air on Mars is about 95 percent carbon dioxide. People cannot breathe the air on Mars.
Olympus Mons on Mars is the biggest volcano in the Solar System. It rises about 25 kilometers (16 miles) above the plains around it, much taller than Mount Everest. The Tharsis Rise is a huge bulge in the surface of Mars, about 4,000 kilometers wide and 10 kilometers high, near the equator.
Valles Marineris on Mars is the biggest canyon in the Solar System. It is a canyon system about 4,000 kilometers (2,500 miles) long, long enough to stretch across the United States.
In July 1965 Mariner 4 made the first successful flyby of Mars and took the first close-up pictures of it. Mariner 4 sent back 21 pictures of Mars in 1965. In 1971 Mariner 9 became the first spacecraft to orbit another planet. It orbited Mars. Mariner 9 sent back more than 7,000 pictures of Mars.
Scientists conclude that the solar wind and the Sun's radiation stripped away most of the air that Mars once had. Mars has no global magnetic field, so the solar wind hits its upper air directly. NASA's MAVEN orbiter studies how the solar wind and the Sun act on the upper air of Mars, to learn what happened to its once-thick atmosphere.
Mars has ice caps at its north and south poles. On the Mars polar caps, carbon dioxide ice builds up in winter and turns straight into gas in summer, leaving water ice behind.
Radar on the Mars Reconnaissance Orbiter found large amounts of ice buried under the ground, often under rubble. The Phoenix lander landed in the far north of Mars in 2008 and confirmed that there is water ice under the soil.
The Perseverance rover's MOXIE test made about 5.4 grams of oxygen from carbon dioxide in its first hour, a small amount but the first oxygen ever made on another planet.
A small helicopter named Ingenuity was the first aircraft to fly on another planet. It flew on Mars. Flying on Mars is very hard because the air there is only about one percent as dense as Earth's. Ingenuity flew 72 times on Mars, far more than the five test flights it was built for.
Words to know
- millibars: air pressure units
- magnetic: like a magnet
- flyby: a pass by
- orbiter: circling ship
