premise: Mars is in the Solar System, closer to the sun than Earth.
hypothesis: Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System , after Mercury . 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 . Solar System . The four smaller inner planets , Mercury , Venus , Earth and Mars , are terrestrial planets , being primarily composed of rock and metal .