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Mercury
Mercury, the planet closest to the Sun, has almost no atmosphere, and its dusty
surface of craters resembles the Moon. The planet was named for the Roman god
Mercury, a winged messenger, and it travels around the Sun faster than any other
planet. Mercury is difficult to see from Earth—in fact, the famous astronomer
Nicolaus Copernicus, for all his years of research and observation, never once was
able to see Mercury.
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Size: Two-fifths the size of Earth in diameter; second smallest in the solar
system
Diameter: 3,032.4 miles (4,880 km)
Surface: Covered by a dusty layer of minerals (silicates), the surface is
made up of plains, cliffs, and craters
Atmosphere: A thin mixture of helium (95%) and hydrogen
Temperature: Mercury alternately bakes and freezes, depending on what
side is lit by the Sun. The sunlit side can reach up to 950° F (510° C) and the
dark side can drop as low as –346° F (–210° C)
Rotation of its axis: 59 Earth days
Rotation around the Sun: 88 Earth days
Your weight: If you weigh 100 pounds on Earth, you would weigh 38
pounds on Mercury.
Distance from Earth: 57 million miles, at the closest point in its orbit
Mean Distance from Sun: 36 million miles (57.9 million km)
Satellites: 0
Rings: 0
Venus
Venus is often called Earth's twin because the two planets are close in size, but
that's the only similarity. The thick clouds that cover Venus create a greenhouse
effect that keeps it sizzling at 864°F. Venus, named after the Roman goddess of
love and beauty, is also known as the “morning star” and “evening star” since it is
visible at these times to the unaided eye. Venus appears as a bright, white disk
from Earth.
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Size: About 650 miles smaller in diameter than Earth
Diameter: 7,519 miles (12,100 km)
Surface: A rocky, dusty, waterless expanse of mountains, canyons, and
plains, with a 200-mile river of hardened lava
Atmosphere: Carbon dioxide (95%), nitrogen, sulfuric acid, and traces of
other elements
Temperature: Ranges from 55°F (13°C) to 396°F (202°C) at the surface
Rotation of its axis: 243 Earth days
Rotation around the Sun: 225 Earth days
Your weight: If you weigh 100 pounds on Earth, you would weigh 88
pounds on Venus.
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Distance from Earth: At its closest, Venus is 26 million miles (41,840,000
km) away
Mean Distance from Sun: 67.24 million miles (108.2 million km)
Satellites: 0
Rings: 0
Earth
Earth is not perfectly round; it bulges at the equator and is flatter at the poles.
From space the planet looks blue with white swirls, created by water and clouds.
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Size: Four planets in our solar system are larger and four are smaller than
Earth
Diameter: 7,926.2 miles (12,756 km)
Surface: Earth is made up of water (70%), air, and solid ground. It appears
to be the only planet with water
Atmosphere: Nitrogen (78%), oxygen (21%), other gases
Rotation of its axis: 23 hours, 56 minutes, 4 seconds
Rotation around the Sun: 365.2 days
Mean Distance from Sun: 92.9 million miles (149.6 million km)
Satellites: 1
Rings: 0
Mars
Because of its blood-red color (which comes from iron-rich dust), this planet was
named for Mars, the Roman god of war. Mars is the fourth planet from the Sun,
situated between Earth and Jupiter. Three-quarters red, Mars also has dark blotches
on it and white areas at the poles—these are white polar ice caps.
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Size: About one-half the size of Earth in diameter
Diameter: 4,194 miles (6,794 km)
Surface: Canyons, dunes, volcanoes, and polar caps of water ice and carbon
dioxide ice
Atmosphere: carbon dioxide (95%)
Temperature: as low as –305°F (–187°C)
Rotation of its axis: 24 Earth hours, 37 minutes, 23 seconds
Rotation around the Sun: 687 Earth days
Your weight: If you weigh 100 pounds on Earth, you would weigh 38
pounds on Mars.
Distance from Earth: 35 million miles (56 million km) at the closest point in
its orbit
Mean Distance from Sun:141.71 million miles (227.9 million km)
Satellites: 2
Rings: 0
Jupiter
A belt of asteroids (fragments of rock and iron) between Mars and Jupiter separate
the four inner planets from the five outer planets.
Jupiter, the largest planet in our solar system, was named for the most important
Roman god because of its size. About 1,300 Earths would fit into it. Viewed through
a large telescope, Jupiter is stunningly colorful—it is a disk covered with bands of
blue, brown, pink, red, orange, and yellow. Its most distinguishing feature is “the
Great Red Spot,” an intense windstorm larger in size than Earth, which has
continued for centuries without any signs of dying down.
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Size: 11 times the diameter of Earth
Diameter: 88,736 miles (142,800 km)
Surface: A hot ball of gas and liquid
Atmosphere: Whirling clouds of colored dust, hydrogen, helium, methane,
water, and ammonia. The Great Red Spot is an intense windstorm larger than
Earth.
Temperature: –234°F (–148°C) average
Rotation of its axis: 9 hours and 55 minutes
Rotation around the Sun: 12 Earth years
Your weight: If you weigh 100 pounds on Earth, you would weigh 265
pounds on Jupiter.
Distance from Earth: At its closest, 370 million miles (591 million km)
Mean Distance from Sun: 483.88 million miles (778.3 million km)
Satellites: 63
Rings: 4
Saturn
Saturn, the second-largest planet, has majestic rings surrounding it. Named for the
Roman god of farming, Saturn was the farthest planet known by the ancients.
Saturn's seven rings are flat and lie inside one another. They are made of billions of
ice particles.
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Size: About 10 times larger than Earth in diameter
Diameter: 74,978 miles (120,660 km)
Surface: Liquid and gas
Atmosphere: Hydrogen and helium
Temperature: –288°F (–178°C)
Rotation of its axis: 10 hours, 40 min, 24 sec
Rotation around the Sun: 291/2 Earth years
Your weight: If you weigh 100 pounds on Earth, you would weigh 107
pounds on Saturn.
Distance from Earth: 744 million miles at the closest point
Mean Distance from Sun: 887.14 million miles (1,427 million km)
Satellites: 31
Rings: 1,000?
Uranus
Uranus is a greenish-blue planet, twice as far from the Sun as its neighbor Saturn.
Uranus wasn't discovered until 1781. Its discoveror, William Herschel, named it
Georgium Sidus (the Georgian star) after the English king, George III. Later its
name was changed to Uranus, after an ancient Greek sky god, since all the other
planets had been named after Roman and Greek gods.
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Size: 4 times larger than Earth in diameter
Diameter: 32,193 miles (51,810 km)
Surface: Little is known
Atmosphere: Hydrogen, helium, and methane
Temperature: uniform temperature of –353°F (–214°C)
Rotation of its axis: 17 hours
Rotation around the Sun: 30,685 days or 84 Earth years
Your weight: Not known
Distance from Earth: At the closest point, 1,607,000,000 miles
Mean Distance from Sun: 1,783.98 million miles (2,870 million km)
Satellites: 27
Rings: 11
Neptune
Neptune, named for an ancient Roman sea god, is a stormy blue planet about 30
times farther from the Sun than Earth. Neptune was discovered when astronomers
realized that something was exerting a gravitational pull on Uranus, and that it was
possible that an unknown planet might be responsible. Through mathematical
calculations, astronomers determined there was indeed an undiscovered planet out
in space—a year before it was actually seen for the first time through a telescope
(in 1846).
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Size: Almost 4 times the size of Earth in diameter
Diameter: 30,775 miles (49,528 km)
Surface: A liquid layer covered with thick clouds and with constant, raging
storms
Atmosphere: Hydrogen, helium, methane, and ammonia
Temperature: –353°F (–214°C)
Rotation of its axis: 16 hours and 7 minutes
Rotation around the Sun: 165 Earth years
Your weight: Not known
Distance from Earth: 2,680,000,000 miles at closest point
Mean Distance from Sun: 2,796.46 million miles (4,497 million km)
Satellites: 13
Rings: 4