Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune are the eight planets in our solar system. Mercury, Venus, Earth, and Mars are the four terrestrial planets in the inner solar system; Jupiter and Saturn are gas giants (giant plants primarily made of hydrogen and helium), while Uranus and Neptune are ice giants (containing mainly elements heavier than hydrogen and helium). Pluto, a dwarf planet, was initially discovered by Clyde Tombaugh, it was categorized as one of the solar system's planets. The Kuiper Belt, a group of frozen bodies at the edge of the solar system, is presently thought to include some of the largest known members. When a group of experts settled on a formal meaning for the word "planet," Pluto was downgraded from its planetary status in 2006.
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, according to the International Astronomical Union's definition. Due to its association with the Kuiper Belt and failure to satisfy the third requirement, Pluto is no longer regarded as a planet. It is categorized as a dwarf planet instead. The dwarf planets Ceres, Hume, Make, and Eris are among the others. Pluto is the most complex dwarf planet we are aware of, with an atmosphere, angular surface features, and at least five moons. It is also one of the most unexpected planets in the solar system. Our favorite dwarf planet was visited by New Horizons in July 2015, and researchers are still learning new things about this remote planet. Why is the Solar System Called That? The universe is full of planetary systems with planets orbiting hosts stars, much like our own. Because we refer to anything connected to our star by the adjective "solar," which comes from the Latin word "solid" our planetary system is known as "the solar system." Where is the solar system? The Milky Way Galaxy's Orion-Cygnus Arm contains the solar system. The closest star system to our solar system is Alpha Centauri, which consists of the stars Proxima Centauri, Alpha Centauri A, and Alpha Centauri B. The Sun, our star, and everything gravitationally connected to it, including the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune, dwarf planets like Pluto, dozens of moons, and millions of asteroids, comets, and meteoroids, make up our solar system. We have found thousands of planetary systems orbiting other stars in the Milky Way, in addition to our own solar system. There are an unknown number of smaller dwarf planets and innumerable small bodies orbiting the Sun. Six of the major planets, the six largest possible dwarf planets, and many of the smaller bodies are orbited by natural satellites, commonly called "moons" after Earth's Moon. Two natural satellites, Jupiter's moon Ganymede and Saturn's moon Titan, are larger but not more massive than Mercury, the smallest terrestrial planet, and Jupiter's moon Callisto is nearly as large. Each of the giant planets and some smaller bodies are encircled by planetary rings of ice, dust, and moon lets. The asteroid belt, which lies between the orbits of Mars and Jupiter, contains objects composed of rock, metal, and ice. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of objects composed mostly of ice and rock.
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