A rocky sphere, with a huge iron core, Mercury is the closest planet to the Sun. It can sometimes be glimpsed from Earth, near the horizon, in the east at dawn or in the west at sunset.
By day, temperatures on Mercury soar as high as 840°F (450°C). This is because Mercury spins around so slowly on its axis that one place is exposed to the hot Sun for 88 days at a time. At night, with little atmosphere, the planet cools rapidly, and temperatures drop to –290°F (–180°C).
The Mariner 10 space probe found Mercury’s surface covered in bowl-shaped craters, made mostly by meteorite impacts billions of years ago. One huge impact created the Caloris Basin, which is 800 miles (1,300 km) wide and ringed by mountain ranges.
Table 5. MERCURY DATA
|Diameter (width) at equator||3,032 miles (4,880 km)|
|Average distance from Sun||36 million miles (57.9 million km)|
|Time to orbit Sun||88 days|
|Time to spin around own axis||58.7 days|
|Mass||0.06 x Earth’s mass|
|Surface gravity||0.38 x Earth’s gravity|
|Average surface temperature||333°F (167°C)|
|Number of moons||0|