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Planets: Facts

South Pole


We live in or on many places — a town or city, a region, a country, even a planet. We live on planet Earth, but there are seven other planets that are all a part of our solar system. These planets have a special relationship to each other because they all revolve around the sun.

More About the Solar System

Solar System

Our solar system has:

  • One central star called the Sun

  • Eight planets:
    • Mercury (closest to the sun)
    • Venus
    • Earth
    • Mars
    • Jupiter
    • Saturn
    • Uranus
    • Neptune (farthest from the sun)
  • More than 60 moons
  • Millions of rocky asteroids
  • Billions of icy comets
  • Four dwarf planets:
    • Pluto
    • Ceres
    • Makemake
    • Eris

Questions and Anwsers

How old is the solar system? About 4.6 billion years old.

How was it formed? All of the solar system except the sun are loose particles left over from the formation of the Sun. Find out more at Amazing Space.

How big is the solar system? The Oort Cloud, a collection of comets orbiting the solar system, is considered the boundary between our solar system and deep space. It lies about 50,000 astronomical units (or almost one light-year) away from the sun.

Do the planets have the same shaped orbit? No! All the planets have their own unique paths around the sun.

Can you see the planets? You can see Mercury, Venus, Mars, Jupiter and Saturn without a telescope but not Uranus or Neptune.

Where do the planet names come from? Every planet, except for Earth, was named for an ancient Roman god or goddess.

Wasn't Pluto once called a planet? Yes, but scientists reclassified it as a dwarf planet in 2006. Read about why at this Library of Congress Q&A page.

What Is An Orbit?

Orbits

An orbit is the path followed by an object in space as it moves moves around another object. Read more about orbits from NASA!

Earth takes 365 days to go around the sun, while Neptune takes 164 years.

The Rocky Planets

Rocky Planets

The rocky planets are the four closest ones to the Sun — Mercury, Venus, Earth, and Mars.

The Rocky Planets are small and similar in composition to Earth — they all have a solid, rocky surfaces and hot, molten cores. They do not have rings. Earth and Mars have moons.

A look at how the early solar system formed will help explain how the inner, rocky planets came to differ from the outer, gaseous ones.

The Gaseous Planets (or Gas Giants)

Saturn

The gaseous planets are the four furthest away from the Sun — Jupiter, Saturn, Uranus, and Neptune.

The Gas Giants are much larger than the rocky planets and are made mostly of hydrogen, helium, frozen water, ammonia, methane and carbon monoxide. They all have rings and moons.

Jupiter and Saturn contain the largest percentages of hydrogen and helium. Uranus and Neptune contain largest shares of ices — frozen water, ammonia, methane, and carbon monoxide.

Venus
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Astronomical symbol for the planet Venus
Venus' hand mirror

Venus

Venus is the hottest planet and the brightest object in the sky after the Sun and the Moon.

The Soviet space program landed 10 probes on Venus. Pictures taken by these landers can be seen here.

Check out this gallery of Venus images.

Learn more about Venus at NinePlanets.org, Windows to the Universe, and NASA.

Mars
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Astronomical symbol for the planet Mars
Mars' shield and spear

Mars

Mars has enormous volcanoes, valleys and dust storms. Olympus Mons might be the largest volcano in the solar system.

We've been sending spacecraft to Mars since 1960. Explore the many missions humans have sent to the Red Planet.

NASA has been landing rovers on Mars since 1997. As of 2015, the rover Opportunity remains active on the planet. Learn about the rover missions and what they have discovered.

Check out this gallery of Mars images.

Learn more about Mars at NinePlanets.org, Windows to the Universe, and NASA.

Saturn
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Astronomical symbol for the planet Saturn
Saturn's scythe

Saturn

Saturn has the most spectacular and complex set of rings in the solar system. The rings are made of chunks of ice and rock, are very thin sheets, and there are lots of them!

The Cassini-Huygens Mission to Saturn launched in 1997 and is still (as of 2015) orbiting the planet and sending back spectacular images and data!

Check out this gallery of Saturn images.

Learn more about Saturn at NinePlanets.org, Windows to the Universe, and NASA.

Beyond Neptune

Past Neptune there are a class of objects known as the trans-Neptunians. The most well-known of these is the dwarf planet, Pluto. But there are at least two more dwarf planets, Eris and Makemake, and a possible third, Sedna. This NASA site will show some of the objects we know about.

Pluto
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Astronomical symbol for the dwarf planet Pluto
PL monogram for Pluto and the astronomer Percival Lowell

Pluto

Pluto is so small that some moons in the solar system are bigger than this dwarf planet. Pluto is usually farther away from the sun than Neptune, but its unique orbit sometimes brings it closer than the eighth planet. Pluto's surface is covered by ice made from frozen nitrogen.

Pluto has five moons — Charon, Nix, Hydra, Kerberos, and Styx.

In July, 2015, the New Horizons spacecraft visited Pluto, the first human spacecraft to do so.

Pluto was changed from a planet to a dwarf planet on August 24, 2006.

Check out this gallery of Pluto images.

Learn more about Pluto at NinePlanets.org, Windows to the Universe, and NASA.

Kuiper Belt and Beyond

Kuiper Belt

Pluto is just one of the many thousands of objects that make up the Kuiper Belt. These are the icy remnants of the solar system's formation 4.5 billion years ago.

Astronomers believe that past the Kuiper Belt is the Oort Cloud, a collection of icy debris that surrounds the solar system at almost a light-year away. This marks the edge of our solar system.

Did You Know . . . ?

“When the Cassini-Huygens spacecraft arrived at Saturn on July 4, 2004 it was traveling so fast that engineers had to burn the spacecraft's engines for 97 minutes to slow it down. If mission engineers didn't do this, the spacecraft would have kept on going instead of entering the orbit around Saturn.”

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