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Space.com's Guide to the Solar System
posted: 01:30 pm ET
11 November 1999
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Mars reference pagePlanets are just part of our solar system. Comets, asteroids and the planets' moons are part of the solar system, too, all orbiting around a star we call the Sun. And it's all held together by gravity. The planets are often divided into two groups: the four inner planets (Mercury, Venus, Earth and Mars) and the five outer planets (Jupiter, Saturn, Uranus, Neptune and Pluto). Click for more detail: Asteroids | Comets | Eclipses | Meteors | The Moon | The Sun
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PLANET | DISTANCE FROM
SUN IN MILES | DIAMETER
IN MILES | ROTATION
IN EARTH TIME | ORBIT
IN EARTH TIME | | Mercury | 36 million | 3,031 | 58.6 days | 88 days | | Venus | 67 million | 7,521 | 243 days | 225 days | | Earth | 93 million | 7,926 | 23 hrs, 56 min | 365.24 days | | Mars | 142 million | 4,217 | 24.6 hrs | 687 days | | Jupiter | 483 million | 88,730 | 9.9 hrs | 11.9 years | | Saturn | 886 million | 74,900 | 10.2 hrs | 29.5 years | | Uranus | 1.78 billion | 31,763 | 17.2 hrs | 84 years | | Neptune | 2.79 billion | 30,755 | 16.1 hrs | 165 years | | Pluto | 3.67 billion | 1,430 | 6.4 days | 248 years | How the solar system formedScientists believe the solar system began forming 10 to 12 billion years ago as swirling gas and dust formed a dense core. The core, with most of the mass, collapsed around 5 or 6 billion years ago and later became the Sun. The small amount of remaining material swirled into a disk. Some of it crashed together and formed planets. That's the main theory, at least, and though most scientists think that's how it happens, there are a handful of other explanations. Final factMost scientists suspect there are oodles of other solar systems like ours. And as of late, they had found nearly two dozen other planets orbiting faraway stars. None of them appear to have the right conditions to support life, though.
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