claim: Mars is in the Solar System, closer to the sun than Earth.
evidence: A planet is an astronomical body orbiting a star or stellar remnant that. astronomical body. astronomical body. star. star. stellar remnant. Stellar evolution#Stellar remnants. is massive enough to be rounded by its own gravity ,. rounded. Hydrostatic equilibrium. gravity. gravity. is not massive enough to cause thermonuclear fusion , and. thermonuclear fusion. thermonuclear fusion. has cleared its neighbouring region of planetesimals.This definition is drawn from two separate IAU declarations ; a formal definition agreed by the IAU in 2006 , and an informal working definition established by the IAU in 2001 / 2003 for objects outside of the Solar System .. cleared its neighbouring region. Clearing the neighbourhood. definition. Definition of planet. IAU. International Astronomical Union. Solar System. Solar System. The official 2006 definition applies only to the Solar System , whereas the 2003 definition applies to planets around other stars .. definition. Definition of planet. 2006 definition. 2006 definition of planet. Solar System. Solar System. The extrasolar planet issue was deemed too complex to resolve at the 2006 IAU conference .. IAU. International Astronomical Union. extrasolar planet. #Exoplanets. The term planet is ancient , with ties to history , astrology , science , mythology , and religion .. astrology. astrology. mythology. mythology. Several planets in the Solar System can be seen with the naked eye .. Solar System. Solar System. These were regarded by many early cultures as divine , or as emissaries of deities .. deities. deity. As scientific knowledge advanced , human perception of the planets changed , incorporating a number of disparate objects .. In 2006 , the International Astronomical Union -LRB- IAU -RRB- officially adopted a resolution defining planets within the Solar System .. IAU. International Astronomical Union. Solar System. Solar System. International Astronomical Union. International Astronomical Union. defining planets. IAU definition of planet. This definition is controversial because it excludes many objects of planetary mass based on where or what they orbit .. orbit. orbit. definition. Definition of planet. planetary mass. Planemo. Although eight of the planetary bodies discovered before 1950 remain `` planets '' under the modern definition , some celestial bodies , such as Ceres , Pallas , Juno and Vesta -LRB- each an object in the solar asteroid belt -RRB- , and Pluto -LRB- the first trans-Neptunian object discovered -RRB- , that were once considered planets by the scientific community , are no longer viewed as such .. definition. Definition of planet. Ceres. Ceres ( dwarf planet ). Pallas. 2 Pallas. Juno. 3 Juno. Vesta. 4 Vesta. Pluto. Pluto. trans-Neptunian object. trans-Neptunian object. The planets were thought by Ptolemy to orbit Earth in deferent and epicycle motions .. orbit. orbit. Ptolemy. Ptolemy. Earth. Earth. deferent and epicycle. deferent and epicycle. Although the idea that the planets orbited the Sun had been suggested many times , it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations , performed by Galileo Galilei .. planets orbited the Sun. Heliocentrism. telescopic. telescope. astronomical observations. Observational astronomy. Galileo Galilei. Galileo Galilei. Sun. Sun. At about the same time , by careful analysis of pre-telescopic observation data collected by Tycho Brahe , Johannes Kepler found the planets ' orbits were not circular but elliptical .. telescopic. telescope. Tycho Brahe. Tycho Brahe. Johannes Kepler. Johannes Kepler. elliptical. Elliptic orbit. As observational tools improved , astronomers saw that , like Earth , the planets rotated around tilted axes , and some shared such features as ice caps and seasons .. Earth. Earth. Since the dawn of the Space Age , close observation by space probes has found that Earth and the other planets share characteristics such as volcanism , hurricanes , tectonics , and even hydrology .. Earth. Earth. Space Age. Space Age. volcanism. Volcano. tectonics. tectonics. hydrology. hydrology. Planets are generally divided into two main types  : large low-density giant planets , and smaller rocky terrestrials .. terrestrials. terrestrial planet. Under IAU definitions , there are eight planets in the Solar System .. IAU. International Astronomical Union. Solar System. Solar System. In order of increasing distance from the Sun , they are the four terrestrials , Mercury , Venus , Earth , and Mars , then the four giant planets , Jupiter , Saturn , Uranus , and Neptune .. Earth. Earth. terrestrials. terrestrial planet. Sun. Sun. Mercury. Mercury ( planet ). Venus. Venus. Mars. Mars. Jupiter. Jupiter. Saturn. Saturn. Uranus. Uranus. Neptune. Neptune. Six of the planets are orbited by one or more natural satellites .. Several thousands of planets around other stars -LRB- `` extrasolar planets '' or `` exoplanets '' -RRB- have been discovered in the Milky Way .. Milky Way. Milky Way. As of , known extrasolar planets in planetary systems -LRB- including multiple planetary systems -RRB- , ranging in size from just above the size of the Moon to gas giants about twice as large as Jupiter have been discovered , out of which more than 100 planets are the same size as Earth , nine of which are at the same relative distance from their star as Earth from the Sun , i.e. in the habitable zone .. star. star. Earth. Earth. Sun. Sun. Jupiter. Jupiter. planetary systems. planetary systems. multiple planetary systems. List of multiplanetary systems. just above the size of the Moon. Kepler-37b. about twice as large as Jupiter. WASP-17b. On December 20 , 2011 , the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets , Kepler-20e and Kepler-20f , orbiting a Sun-like star , Kepler-20 .. star. star. Earth. Earth. Sun. Sun. Kepler Space Telescope. Kepler ( spacecraft ). Earth-sized. Terrestrial planet. Kepler-20e. Kepler-20e. Kepler-20f. Kepler-20f. Sun-like star. Solar analog. Kepler-20. Kepler-20. A 2012 study , analyzing gravitational microlensing data , estimates an average of at least 1.6 bound planets for every star in the Milky Way .. star. star. Milky Way. Milky Way. gravitational microlensing. gravitational microlensing. Around one in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone .. Earth. Earth. Sun. Sun. Earth-sized. Terrestrial planet