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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.

WHAT IS THE TEMPERATURE ON MERCURY?

By day, temperatures on Mercury soar as high as

450°C (840°F). This is because Mercury spins round

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 –180°C (–290°F).

WHAT IS MERCURY’S SURFACE LIKE?

The Mariner 10 and Messenger spacecraft found

Mercury’s surface covered by craters, made mostly

by meteorite impacts billions of years ago. One huge

impact created the Caloris Basin, which is 1,300 km

Diameter (width) at Equator 4,880 km (3,032 miles) (800 miles) wide and ringed by mountain ranges.

Average distance from Sun 57.9 million km (36 million miles)

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 167°C (333°F)

Number of moons 0

Diameter (width) at Equator 12,104 km (7,521 miles)

Average distance from Sun 108.2 million km (67.2 million miles)

Time to orbit Sun 224.7 days

Time to spin around own axis 243 days

Mass 0.82 x Earth’s mass

Gravity 0.9 x Earth’s gravity

Average surface temperature 464°C (867°F)

Number of moons 0

HOW HOT IS VENUS?

Temperatures on Venus soar to over 460°C (860°F),

making it hotter than any other planet. Its carbon

dioxide atmosphere, which is 100 times heavier than

Earth’s, traps heat like a greenhouse.

WHY CAN’T WE SEE VENUS’S SURFACE?

Thick clouds in Venus’s atmosphere stop us seeing its

surface. Radar-carrying spacecraft, such as Magellan,

have scanned the surface, showing that it is dotted

with volcanoes and covered with rolling lava plains.

4 MESSENGER

The Messenger spacecraft

was launched in 2004

to go into orbit around

Mercury in 2011 after

making three fly-bys.

4 SCARRED SURFACE

Craters large and small cover

60 per cent of Mercury’s dark

surface. The rocky ground is also

crossed by cracks and ridges, and

smooth plains created by ancient

lava flows.

VENUS

Venus

MERCURY

Mercury

Rocky crust and mantle
cover an iron core that is
3,600 km (2,200 miles) thick

Mercury’s atmosphere is

so thin that it barely exists

MERCURY DATA

Seen from Earth shining brightly in the west at

sunset, Venus is called the evening star. It is a rocky

planet, and the second closest planet to the Sun.

4 TOWERING VOLCANOES

Maat Mons, one of Venus’s many

volcanoes, is about 9 km (5.6 miles)

high. Radar images show that it is

surrounded by lava flows from

repeated eruptions.

Thick sulphuric

acid clouds hide

Venus’s surface

VENUS DATA

Solar panel

Sunshade

Magnetometer

FIND OUT MORE. Earth 16 • Solar System 14 • Volcanoes 44

FIND OUT MORE. Interplanetary Spacecraft 29 • Meteors 23 • Volcanoes 44

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und

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Mercury

Venus