There Are Eight Planets In The Solar System 3w4f4d

There are eight planets in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. The four inner solar system planets (Mercury, Venus, Earth, and Mars) fall under the category of terrestrial planets; Jupiter and Saturn are gas giants (giant plants composed mostly of hydrogen and helium) while Uranus and Neptune are the ice giants (containing mainly elements heavier than hydrogen and helium). Pluto, a dwarf planet, was classified as one of the solar system planets when it was first discovered by Clyde Tombaugh. However, it is now considered to be one of the largest known of the Kuiper Belt—a collection of icy bodies on the outer fringes of the solar system. Pluto was demoted from its planetary status in 2006 when a body of scientists decided a formalized definition for the term “planet.” According to the International Astronomical Union's definition, a 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, and (c) has cleared the neighborhood around its orbit.” Because Pluto is part of the Kuiper Belt, and therefore has not met the third criterion, it is no longer considered a planet. Instead, it is classified as a dwarf planet. Other dwarf planets include Ceres, Haumea, Makemake, and Eris. With an atmosphere, stark surface features, and at least five moons, Pluto is the most complex dwarf planet we know, and one of the most surprising solar system planets. New Horizons flew by our favorite dwarf planet in July 2015 and scientists continue to uncover surprising details about this faraway world. by composition: terrestrial or rocky planets: Mercury, Venus, Earth, and Mars: The terrestrial planets are composed primarily of rock and metal and have relatively high densities, slow rotation, solid surfaces, no rings and few satellites. jovian or gas planets: Jupiter, Saturn, Uranus, and Neptune: The gas planets are composed primarily of hydrogen and helium and generally have low densities, rapid rotation, deep atmospheres, rings and lots of satellites. by size: small planets: Mercury, Venus, Earth, Mars. The small planets have diameters less than 13000 km. giant planets: Jupiter, Saturn, Uranus and Neptune. The giant planets have diameters greater than 48000 km. The giant planets are sometimes also referred to as gas giants. by position relative to the Sun:

inner planets: Mercury, Venus, Earth and Mars. outer planets: Jupiter, Saturn, Uranus, Neptune. The asteroid belt between Mars and Jupiter forms the boundary between the inner solar system and the outer solar system. by position relative to Earth: inferior planets: Mercury and Venus. closer to the Sun than Earth. The inferior planets show phases like the Moon's when viewed from Earth. Earth. superior planets: Mars thru Neptune. farther from the Sun than Earth. The superior planets always appear full or nearly so. by history: classical planets: Mercury, Venus, Mars, Jupiter, and Saturn. known since prehistorical times visible to the unaided eye in ancient times this term also refered to the Sun and the Moon; the order was usually specificied as: Saturn, Jupiter, Mars, Sun, Venus, Mercury and Moon, based on the time for them to go "all the way round" the sphere of the "fixed" stars). modern planets: Uranus, Neptune. discovered in modern times visible only with optical aid Earth. The IAU decided that "classical" should refer to all eight planets (Mercury thru Neptune, including Earth but not Pluto). This is contrary to historical usage but makes some sense from a 21st century perspective.