Query: Mars is in the Solar System, closer to the sun than Earth.

Relevant passages:
Mars <=SEP=> Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System , after Mercury . Named after the Roman god of war , it is often referred to as the `` Red Planet '' because the iron oxide prevalent on its surface gives it a reddish appearance . Mars is a terrestrial planet with a thin atmosphere , having surface features reminiscent both of the impact craters of the Moon and the valleys , deserts , and polar ice caps of Earth .   The rotational period and seasonal cycles of Mars are likewise similar to those of Earth , as is the tilt that produces the seasons . Mars is the site of Olympus Mons , the largest volcano and second-highest known mountain in the Solar System , and of Valles Marineris , one of the largest canyons in the Solar System . The smooth Borealis basin in the northern hemisphere covers 40 % of the planet and may be a giant impact feature . Mars has two moons , Phobos and Deimos , which are small and irregularly shaped . These may be captured asteroids , similar to 5261 Eureka , a Mars trojan .   There are ongoing investigations assessing the past habitability potential of Mars , as well as the possibility of extant life . Future astrobiology missions are planned , including the Mars 2020 and ExoMars rovers . Liquid water can not exist on the surface of Mars due to low atmospheric pressure , which is about that of the Earth 's , except at the lowest elevations for short periods . The two polar ice caps appear to be made largely of water . The volume of water ice in the south polar ice cap , if melted , would be sufficient to cover the entire planetary surface to a depth of 11 m . In November 2016 , NASA reported finding a large amount of underground ice in the Utopia Planitia region of Mars . The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior .   Mars can easily be seen from Earth with the naked eye , as can its reddish coloring . Its apparent magnitude reaches − 2.91 , which is surpassed only by Jupiter , Venus , the Moon , and the Sun . Optical ground-based telescopes are typically limited to resolving features about 300 km across when Earth and Mars are closest because of Earth 's atmosphere .

Planet <=SEP=> A planet is an astronomical body orbiting a star or stellar remnant that  is massive enough to be rounded by its own gravity ,  is not massive enough to cause thermonuclear fusion , and  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 . The official 2006 definition applies only to the Solar System , whereas the 2003 definition applies to planets around other stars . The extrasolar planet issue was deemed too complex to resolve at the 2006 IAU conference .  The term planet is ancient , with ties to history , astrology , science , mythology , and religion . Several planets in the Solar System can be seen with the naked eye . These were regarded by many early cultures as divine , or as emissaries of deities . As scientific knowledge advanced , human perception of the planets changed , incorporating a number of disparate objects . In 2006 , the International Astronomical Union ( IAU ) officially adopted a resolution defining planets within the Solar System . This definition is controversial because it excludes many objects of planetary mass based on where or what they orbit . 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 ( each an object in the solar asteroid belt ) , and Pluto ( the first trans-Neptunian object discovered ) , that were once considered planets by the scientific community , are no longer viewed as such .   The planets were thought by Ptolemy to orbit Earth in deferent and epicycle motions . 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 . 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 . 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 . 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 .   Planets are generally divided into two main types : large low-density giant planets , and smaller rocky terrestrials . Under IAU definitions , there are eight planets in the 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 . Six of the planets are orbited by one or more natural satellites .   Several thousands of planets around other stars ( `` extrasolar planets '' or `` exoplanets '' ) have been discovered in the Milky Way . As of , known extrasolar planets in planetary systems ( including multiple planetary systems ) , 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 . 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 . A 2012 study , analyzing gravitational microlensing data , estimates an average of at least 1.6 bound planets for every star in the Milky Way .  Around one in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone .