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=elem&dev=">Apollo 17</a> crew while traveling to the <a href="/earth/moons_and_rings.html&edu=elem&dev=">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=elem&dev=">Antarctic</a>, shrouded in the heavy <a href="/earth/Atmosphere/cloud.html&edu=elem&dev=">cloud</a> cover in the southern hemisphere. Arching cloud patterns show the presence of <a href="/earth/Atmosphere/front.html&edu=elem&dev=">weather fronts</a>.<p><small><em>Image courtesy of NASA/Apollo 17.</em></small></p>Neptune's <a href="/neptune/lower_atmosphere.html&edu=elem&dev=">atmosphere</a> shows a striped pattern of <a href="/neptune/atmosphere/N_clouds_overview.html&edu=elem&dev=">clouds</a>. This cloud pattern is very similar to that of <a href="/jupiter/jupiter.html&edu=elem&dev=">Jupiter</a> and <a href="/saturn/saturn.html&edu=elem&dev=">Saturn</a>. Neptune even has a <a href="/neptune/atmosphere/N_clouds_GDS.html&edu=elem&dev=">Great Dark Spot</a> similar to Jupiter's <a href="/jupiter/atmosphere/J_clouds_GRS.html&edu=elem&dev=">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=elem&dev=">ozone layer on Earth</a>, in the <a href="/physical_science/chemistry/methane.html&edu=elem&dev=">methane</a> cloud deck of Neptune.<p><small><em>Image courtesy of NASA</em></small></p><a href="/mercury/mercury.html&edu=elem&dev=">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=elem&dev=">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=elem&dev=">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=elem&dev=">global surface</a> of Mars is marked by many interesting features - some like those on the <a href="/earth/earth.html&edu=elem&dev=">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=elem&dev=">soil</a>. Some of these features are; <a href="/mars/interior/mars_volcanoes.html&edu=elem&dev=">volcanoes</a>, canyon systems, <a href="/mars/interior/Martian_running_water.html&edu=elem&dev=">river beds</a>, <a href="/mars/interior/Mars_cratered_terrain.html&edu=elem&dev=">cratered terrain</a>, and <a href="/mars/interior/Martian_dunefields.html&edu=elem&dev=">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=elem&dev=">Mercury</a>, the innermost planet of the solar system. Taken on 3/29/2011 by <a href="/space_missions/robotic/messenger/messenger.html&edu=elem&dev=">MESSENGER</a>, it shows numerous craters across the <a href="/mercury/Interior_Surface/Surface/surface_overview.html&edu=elem&dev=">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?

Do you know what a planet is? Guess what... astronomers are not quite sure what a planet is! ...Read more

Mercury

Mercury, the planet nearest the Sun, is the second 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

More about Planets

Historical Events

Full Earth and Space Science    History Calendar (Members only)

Teacher Opportunities

Full Teacher Events Calendar (Educator Members only)

Did you know?

Did you know that the Maya and the Aztecs were early observers of Venus?

Did you know that Pluto is not always outside the orbit of Neptune?

 

Earth and Space Science Concept of the Day

Do you know what this word or phrase means?

Loess
xLoess : An aeolian sediment formed by the accumulation of wind-blown silt and lesser and variable amounts of sand and clay that are loosely cemented by calcium carbonate. Loess is usually homogeneous, highly porous, and is traversed by vertical capillaries t

Click on the word to find out!

Research Highlights

Pollution from Asia Circles Globe at Stratospheric Heights

Air pollution can get high in the atmosphere – high above most of the clouds you see in the sky. Scientists are finding air pollution more than 20 miles above the surface of the Earth. That’s in the stratosphere...Read more


Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA