The fourth planet from the Sun, Mars is one of
Earth’s closest neighbours. Mars has a slight atmosphere (mainly carbon
dioxide), and ice caps at the poles. Channels on the surface suggest that water
may have flowed on the planet in the past. Although freezing now, some
astronomers think that Mars might once have been warmer and supported some form
of life.
Table 13. ESSENTIAL DATA
| Diameter at equator | 6,794 km (4,222 miles) |
| Average distance from Sun | 227.9 million km (141.6 million miles) |
| Orbital period | 687 days |
| Rotation period | 24.63 hours |
| Mass (Earth=1) | 0.11 |
| Gravity (Earth=1) | 0.38 |
| Average surface temperature | -63°C (-81°F) |
| Number of moons | 2 (Phobos and Deimos) |
Astronomers believe that the two tiny moons of Mars were asteroids
that Mars captured in its gravity long ago. The largest moon is Phobos, an
irregular lump around 26 km (16 miles) in diameter. Deimos is even smaller
– only about 16 km (10 miles) wide. Both moons are covered with craters
and are thought to be made up of rock rich in carbon.
