Planets were assembled out of small "building bodies" called planetesimals, which themselves aggregated from the dust in the solar nebula. Planets with low eccentricities have more circular orbits, while planets with a high eccentricities have more elliptical orbits. Planets and satellites are "built-in", and the program comes with some 7500 asteroids and comets. Planets around M stars receive much less visible light but much more infrared light. Planets, as we noted, move relative to the stars, and they do so, generally, moving from west to east in the sky.

Jupiter

Jupiter's axial tilt is very small, so its seasonal variation is minimal; Uranus, on the other hand, has an axial tilt so extreme it is virtually on its side, which means that its hemispheres are either perpetually in sunlight or perpetually in darkness around the time of its solstices. Jupiter is the most massive planet in our solar system and is 320 times heavier than the Earth. Jupiter and Saturn are believed to possess cores of rock and metal surrounded by mantles of metallic hydrogen. Jupiter is so big that all the other planets could fit inside it.

Extra solar

Extra solar planets are telling astronomers how planetary systems form and evolve. Since 1992, and the discovery of hundreds of extra solar planets, scientists are beginning to observe similar features across the galaxy. Several projects have also been proposed to create an array of space telescopes to search for extrasolar planets with masses comparable to the Earth. In 2003, The International Astronomical Union (IAU) Working Group on Extrasolar Planets made a position statement on the definition of a planet that incorporated a working definition:[2]Objects with true masses below the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 times the mass of Jupiter for objects with the same isotopic abundance as the Sun)[20] that orbit stars or stellar remnants are "planets" (no matter how they formed). These two monographs, although concentrating on the possibilities of intelligent life, needed to make a strong statement regarding the probability of the existence of extrasolar planets. Schneider, used in the search for extrasolar worlds are astrometric detection , direct imaging , radial velocity, ground based photometry, and occultation. This method is used in order to determine reflected light from anextrasolar planet. As an extrasolar planet revolves about its star, it will pass between its star and the line of sight as seen from the Earth. Another issue that needs to be examined for future extrasolar planetary discoveries is the type of methodology and instrumentation that needs to be used.

Planets are found much more commonly around stars like our sun that are rich in iron and other metals, hinting that such elements played an important role in planet formation. Planets are much smaller with core temperatures and pressures too low for nuclear fusion to occur. Mars has some of the most highly varied and interesting terrain of any of the terrestrial planets, some of it quite spectacular: Olympus Mons: the largest mountain in the Solar System rising 24 km (78,000 ft.)