Planets

By the current count of astronomers, our solar system includes 8 planets and 5 dwarf planets. The planets were formed during the process of solar system formation, when clumps began to form in the disk of gas and dusk rotating about our young Sun. Eventually, only the planets and other small bodies in the solar system remained. The four rocky planets at the center of the solar system Mercury, Venus, Earth, Mars, are known as the inner planets. Jupiter, Saturn, Uranus, and Neptune are all composed primarily of gas and are known as the outer planets. Find out more about the planets through the links below.

A view of the Earth as seen by the <a href="/space_missions/apollo17.html&edu=high&dev=1">Apollo 17</a> crew while traveling to the <a href="/earth/moons_and_rings.html&edu=high&dev=1">Moon</a> on December 7, 1972. Africa, Madagascar, and the Arabian Peninsula are visible, and you can barely make out the <a href="/earth/polar/antarctica.html&edu=high&dev=1">Antarctic</a>, shrouded in the heavy <a href="/earth/Atmosphere/cloud.html&edu=high&dev=1">cloud</a> cover in the southern hemisphere. Arching cloud patterns show the presence of <a href="/earth/Atmosphere/front.html&edu=high&dev=1">weather fronts</a>.<p><small><em>Image courtesy of NASA/Apollo 17.</em></small></p>Neptune's <a href="/neptune/lower_atmosphere.html&edu=high&dev=1">atmosphere</a> shows a striped pattern of <a href="/neptune/atmosphere/N_clouds_overview.html&edu=high&dev=1">clouds</a>. This cloud pattern is very similar to that of <a href="/jupiter/jupiter.html&edu=high&dev=1">Jupiter</a> and <a href="/saturn/saturn.html&edu=high&dev=1">Saturn</a>. Neptune even has a <a href="/neptune/atmosphere/N_clouds_GDS.html&edu=high&dev=1">Great Dark Spot</a> similar to Jupiter's <a href="/jupiter/atmosphere/J_clouds_GRS.html&edu=high&dev=1">Great Red Spot</a>. The Great Dark Spot of Neptune is thought to be a hole, similar to the hole in the <a href="/earth/Atmosphere/ozone_layer.html&edu=high&dev=1">ozone layer on Earth</a>, in the <a href="/physical_science/chemistry/methane.html&edu=high&dev=1">methane</a> cloud deck of Neptune.<p><small><em>Image courtesy of NASA</em></small></p><a href="/mercury/mercury.html&edu=high&dev=1">Mercury</a>, the innermost planet of the solar system, is a little bigger than the Earth's Moon. The <a href="/mercury/Interior_Surface/Surface/surface_overview.html&edu=high&dev=1">surface</a> of the planet is covered with craters, like the Moon, but temperatures there can reach over 800&deg;F because Mercury is so close to the Sun and rotates so slowly. This picture was taken by the <a href="/space_missions/robotic/messenger/messenger.html&edu=high&dev=1">MESSENGER spacecraft</a> in October 2008.<p><small><em>Image courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.</em></small></p>The uniquely red <a href="/mars/interior/Martian_global_geology.html&edu=high&dev=1">global surface</a> of Mars is marked by many interesting features - some like those on the <a href="/earth/earth.html&edu=high&dev=1">Earth</a> and others strangely different. The reddish color is caused by rust (iron oxide) in the <a href="/mars/exploring/martian_soils.html&edu=high&dev=1">soil</a>. Some of these features are; <a href="/mars/interior/mars_volcanoes.html&edu=high&dev=1">volcanoes</a>, canyon systems, <a href="/mars/interior/Martian_running_water.html&edu=high&dev=1">river beds</a>, <a href="/mars/interior/Mars_cratered_terrain.html&edu=high&dev=1">cratered terrain</a>, and <a href="/mars/interior/Martian_dunefields.html&edu=high&dev=1">dune fields</a>. This image shows a global mosaic of 102 Viking 1 Orbiter images of Mars taken in February, 1980.<p><small><em>Image courtesy of NASA.</em></small></p>This historic image is the first ever taken from a spacecraft in orbit about <a href="/mercury/mercury.html&edu=high&dev=1">Mercury</a>, the innermost planet of the solar system. Taken on 3/29/2011 by <a href="/space_missions/robotic/messenger/messenger.html&edu=high&dev=1">MESSENGER</a>, it shows numerous craters across the <a href="/mercury/Interior_Surface/Surface/surface_overview.html&edu=high&dev=1">surface</a> of the planet. Temperatures there can reach over 800F because Mercury is so close to the Sun and rotates so slowly. MESSENGER entered orbit around Mercury earlier in March 2011.<p><small><em>NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington</em></small></p>New observations by the MESSENGER spacecraft provide support for the hypothesis that Mercury harbors abundant water ice and other frozen volatile materials in its permanently shadowed (shown in red) polar craters. Areas where polar deposits of ice imaged by Earth-based radar are shown in yellow.<p><small><em>Image courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/National Astronomy and Ionosphere Center, Arecibo Observatory</em></small></p>

Explore Planets

What is a Planet?

It may surprise you, but astronomers don't really have a good definition of a "planet". Because ...Read more

Mercury

Mercury, the planet nearest the Sun, is also the smallest planet in the Solar System. Only ...Read more

Venus

Fair but inhospitable Venus, a "Sister" planet to the Earth that is very different from our ...Read more

Earth

Earth, our home planet, is a beautiful blue and white ball when seen from space. ...Read more

Mars

Mars, Earth's outer neighbor, is the fourth planet from the Sun. Mars' bright appearance and ...Read more

Jupiter

   Jupiter is the largest planet in the solar system. When approached from afar, its fantastic ...Read more

Saturn

Saturn, the sixth planet from the Sun, has the most spectacular set of rings in the solar system. ...Read more

Uranus

   Uranus, the seventh planet from the Sun, has its spin axis almost in the plane of its orbit ...Read more

Neptune

Neptune, the eighth and furthest planet from the Sun, is a very cold place. Its bluish color ...Read more

Dwarf Planets

In 2006 the International Astronomical Union (IAU) approved a new classification scheme for ...Read more

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Did you know that Uranus is tilted so that its rotational axis is almost in the plane of the ecliptic?

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Earth and Space Science Concept of the Day

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Sand boil
xSand boil : A sand boil is sand and water that come out onto the ground surface during an earthquake as a result of liquefaction at shallow depth.

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Research Highlights

Geologists Uncover Major Ancient Human Ancestor in South Africa

Researchers working in South Africa have discovered two remarkably well-preserved fossil skeletons of an ancient human ancestor dating to almost two million years ago. The discovery is described in two...Read more


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