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Sun: Our Sun is a star, a hot ball of glowing gases at the heart of our solar system. Its influence extensd far beyond the orbits of distant Neptune and Pluto. Mercury: Sun-scorched Mercury's dayside is super heated, but at night temperatures drop hundreds of degrees below freezing. Ice may even survive in a few craters. Venus: A dim world of intense heat and volcanic activity, Venus' thick, toxic atmosphere traps heat in a runaway greenhouse effect. Earth: Air, water, land and life - including humans - combine forces on Earth to create a constantly changing world that we are still striving to understand. Moon: The Moon's presence stabilizes Earth's wobble. This has led to a more stable climate - and may have helped life flourish on our home planet. Mars: Today Mars is a dry desert world, despite some signs that water may have once flowed freely across its surface. Where did the water go? Asteroids: These rocky fragments have been left over from the beginnings of our solar system. Studying them should reveal more about the formation of planets. Ceres: Dwarf planet and asteroid? Discovered in 1801, this most massive known body in the asteroid belt has had its classificiation changed several times. Meteoroids: Scientists estimate that thousands of tons of meteoritic material fall on Earth each day. Large pieces that don't vaporize are called meteorites. Jupiter: Understanding Jupiter's intense magnetic field, swirling atmosphere and diverse moons will reveal much about how planets forms and interact. Saturn: All four giant gas planets have rings - made of chunks of ice and rock - but none are as spectacular or as complicated as Saturn's. Uranus: A collision with an Earth-sized object millions of years ago may explain why Uranus is the only planet tipped on its side. Neptune: Understanding the rapidly changing storms in Neptune's clouds and the source of its unique partial rings will improve our knowledge of the evolution of planets. Comets: Cosmic snowballs of frozen gases, rock and dust, Comets may hold clues to the origin of our Solar System about 4.6 billion years ago. Pluto: Discovered in 1930, Pluto remains an unexplored celestial snowball orbiting billions of kilometers from our Sun. It is about 30% smaller than Earth's Moon. Eris: The most distant object ever seen orbiting the Sun, this new dwarf planet is the largest solar system body discovered since Neptune and its moon Triton in 1846. Kuiper Belt Objects: This vast reservoir of icy bodies beyond the orbit of Neptune may hold important keys to the formation of our solar system. Beyond Our Solar System: The discovery of planets orbiting stars other than the SUn confirms our solar system is not unique. Extrasolar planets seem to be common in our galaxy. Solar System: Our Solar System is a natural laboratory - on a grand scale - in which we seek to unravel the mysteries of the universe. Solar System: Our Solar System is a natural laboratory - on a grand scale - in which we seek to unravel the mysteries of the universe.
Planet Selector Map
From our small world we have gazed upon the cosmic ocean for thousands of years. Ancient astronomers observed points of light that appeared to move among the stars.
Moons and Planets of the Solar System

What is a planet? The International Astronomical Union (IAU) said that the definition for a planet is now officially known as "a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape and (c) has cleared the neighborhood around its orbit." At the same time, new moons are also being discovered, both around existing planets and within these mysterious new worlds. Once the existence of a moon is confirmed and its orbit determined, the moon is given a final name by the International Astronomical Union (IAU), the organization that assumed this task since 1919.

A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.

Plutoids

Almost two years after the International Astronomical Union (IAU) General Assembly introduced the category of dwarf planets, the IAU, as promised, has decided on a name for trans-neptunian dwarf planets similar to Pluto. The name "plutoid" was proposed by the members of the IAU Committee on Small Body Nomenclature (CSBN), accepted by the Board of Division III, by the IAU Working Group for Planetary System Nomenclature (WGPSN) and approved by the IAU Executive Committee at its recent meeting in Oslo, Norway.

Plutoids are celestial bodies in orbit around the Sun at a semi-major axis greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit. Satellites of plutoids are not plutoids themselves, even if they are massive enough that their shape is dictated by self-gravity. The three known and named plutoids are Pluto, Eris and as of July 2008, MakeMake. It is expected that more plutoids will be named as science progresses and new discoveries are made. For more information about the IAU and plutoids, click here.

Planet Named by the IAU Provisionally Named
Mercury 0 0
Venus 0 0
Earth 1 0
Mars 2 0
Jupiter 49 14
Saturn 52 8
Uranus 27 0
Neptune 13 0
Total Moons Named: 144  
Body Type Named by the IAU Provisionally Named
Known Dwarf Planets 4 0
Known Plutoids 3 0
Dwarf Planet Watch List 5 6

References:

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Click the image on the left to discover some of the most extreme organisms on our planet, and find out what they are telling astrobiologists about the search for life beyond Earth.
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