How Many Planets Are There in Solar System? Overview of the Solar System

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The solar system comprises the Sun and everything that orbits it, including eight planets and their moons, as well as asteroids, comets, and other small bodies. Our solar system lies in the Milky Way’s Orion Arm and contains many smaller objects like moons, asteroids, and comets. Planet names come from Greek and Roman mythology.

Astronomers estimate there are over 100 billion planets in our galaxy and an even greater number when the entire observable universe is considered. Extrapolating from our solar system suggests the universe has billions, if not trillions, of rocky planets.

Planetary Composition and Characteristics

The four inner planets – Mercury, Venus, Earth, and Mars – are terrestrial, meaning they are rocky. The four outer planets – Jupiter, Saturn, Uranus, and Neptune – are gas giants with no definite surface. Jupiter, the largest planet, harbors a famous storm called the Great Red Spot. Its magnetic field shields inner planets from asteroids, though sometimes debris is sent inwards.

Jupiter and Saturn combined account for over 90% of the mass in the solar system apart from the Sun. Among the major planets, Mercury is the smallest and orbits the Sun fastest at 29 miles per second. Saturn is the least dense planet and is actually less dense than water, meaning it would float.

Discovery and Classification

The number of official planets has changed over history as our understanding has evolved. In 2006, Pluto was reclassified as a "dwarf planet," reducing the number of true planets to eight. Some astronomers predict there may be a ninth planet orbiting the Sun that has yet to be directly observed.

The Quest for Exoplanets

A system 35 light-years away mirrors our own. It has at least four rocky planets closest to their star which may sustain life. The third planet appears to have oceans. Strict criteria limit livable planets. Reaching this system would take 700,000 years.

Frequently Asked Questions

  • Is there 8 or 9 planets in the solar system?
    Currently, there are eight recognized planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. In 2016, some mathematical evidence was presented for a hypothetical massive Planet Nine beyond Neptune, but it has yet to be visually confirmed.

  • What are the 9 planets in order?
    The solar system has eight planets orbiting the Sun. They are, in order from the Sun:

    1. Mercury
    2. Venus
    3. Earth
    4. Mars
    5. Jupiter
    6. Saturn
    7. Uranus
    8. Neptune

Pluto was once considered a planet but is now classified as a dwarf planet.

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