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, and 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, and people cannot breathe the air on 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.
Sometimes dust storms cover most of the planet Mars. Dust storms may have helped dry out Mars: dust-trapped water vapor may rise like an elevator to space.
InSight studied the inside of Mars. Its seismometer listened to marsquakes, and the waves told scientists how big the core is.
InSight's seismometer recorded more than 1,300 marsquakes in about four years. The largest was magnitude 4.7.
The core of Mars is large: InSight's marsquake data show it has a radius of about 1,840 kilometers. The rocky crust of Mars is about 10 to 50 kilometers thick. At the InSight landing site, the crust is 15 to 47 kilometers thick.
In 1976 Viking 1 became the first American spacecraft to land safely on Mars, and the Viking landers searched Mars soil for life in 1976. The results were mostly negative but not a clear answer.
The Phoenix lander landed in the far north of Mars in 2008 and confirmed that there is water ice under the soil, and Phoenix found the chemical perchlorate in the Mars soil.
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.
A small helicopter named Ingenuity was the first aircraft to fly on another planet, and it flew on Mars. Flying on Mars is very hard because the air there is only about one percent as dense as Earth's, yet Ingenuity flew 72 times on Mars, far more than the five test flights it was built for.
Words to know
- seismometer: quake listener
- marsquakes: quakes on Mars
- perchlorate: a soil chemical
- crust: rocky outer layer
