Changes

Since the dawn of the [[space age]], probes have been sent to every planet in the [[Solar System]], and the discoveries they have made have shifted [[planetary science]] from the realm of astronomy to the realms of [[geography]] and [[geology]]. The planets have been found to share many characteristics, such as volcanism, hurricanes, tectonics and even hydrology, previously only known on Earth. Since 1992, and the discovery of hundreds of [[extrasolar planets]], scientists are beginning to observe similar features across the galaxy.  

Since the dawn of the [[space age]], probes have been sent to every planet in the [[Solar System]], and the discoveries they have made have shifted [[planetary science]] from the realm of astronomy to the realms of [[geography]] and [[geology]]. The planets have been found to share many characteristics, such as volcanism, hurricanes, tectonics and even hydrology, previously only known on Earth. Since 1992, and the discovery of hundreds of [[extrasolar planets]], scientists are beginning to observe similar features across the galaxy.  

Under IAU definitions, there are eight planets in the Solar System ([[Mercury (planet)|Mercury]], [[Venus]], [[Earth]], [[Mars]], [[Jupiter]], [[Saturn]], [[Uranus]], and [[Neptune]]) and also at least three [[dwarf planets]] ([[Ceres (dwarf planet)|Ceres]], [[Pluto]], and [[Eris (dwarf planet)|Eris]]). Many of these planets are orbited by one or more [[natural satellite|moons]], which can be larger than small planets. There have also been more than two hundred planets discovered [[extrasolar planet|orbiting other stars]].<ref name="Encyclopaedia">{{cite web |title=Interactive Extra-solar Planets Catalog |work=The Extrasolar Planets Encyclopaedia |url=http://exoplanet.eu/catalog.php |last=Schneider |first=Jean |date=[[October 30]], [[2006]] |accessdate=2006-10-31}}</ref> Planets are generally divided into two main types: large, low-density [[gas giant]]s and smaller, rocky [[terrestrial planet|terrestrials]]. Dwarf planets, a separate category, can either be terrestrials or frozen [[ice dwarf]]s.

Under IAU definitions, there are eight planets in the Solar System ([[Mercury (planet)|Mercury]], [[Venus]], [[Earth]], [[Mars]], [[Jupiter]], [[Saturn]], [[Uranus]], and [[Neptune]]) and also at least three [[dwarf planets]] ([[Ceres (dwarf planet)|Ceres]], [[Pluto]], and [[Eris (dwarf planet)|Eris]]). Many of these planets are orbited by one or more [[natural satellite|moons]], which can be larger than small planets. There have also been more than two hundred planets discovered [[extrasolar planet|orbiting other stars]]."Encyclopaedia"> Interactive Extra-solar Planets Catalog, The Extrasolar Planets Encyclopaedia, http://exoplanet.eu/catalog.php Planets are generally d. ivided into two main types: large, low-density [[gas giant]]s and smaller, rocky [[terrestrial planet|terrestrials]]. Dwarf planets, a separate category, can either be terrestrials or frozen [[ice dwarf]]s.

==Etymology==

==Etymology==

In ancient times, astronomers noted how certain lights moved across the sky in relation to the other stars.  These objects were believed to orbit the [[Earth]], which was considered to be stationary. The lights were first called "πλανήται" (''planētai''),<ref>See [[romanization of Greek]] for the transcription scheme meaning "wanderers", by the ancient Greeks, and it is from this that the word "planet" was derived. http://www.m-w.com/dictionary/planet|title=Definition of planet|publisher=Merriam-Webster OnLine|accessdate=2007-07-23}} http://www.wordsources.info/words-mod-planets.html|title=Words For Our Modern Age: Especially words derived from Latin and Greek sources|publisher=Wordsources.

In ancient times, astronomers noted how certain lights moved across the sky in relation to the other stars.  These objects were believed to orbit the [[Earth]], which was considered to be stationary. The lights were first called "πλανήται" (''planētai''),<ref>See [[romanization of Greek]] for the transcription scheme meaning "wanderers", by the ancient Greeks, and it is from this that the word "planet" was derived. http://www.m-w.com/dictionary/planet|title=Definition of planet|publisher=Merriam-Webster OnLine|accessdate=2007-07-23}} http://www.wordsources.info/words-mod-planets.html|title=Words For Our Modern Age: Especially words derived from Latin and Greek sources|publisher=Wordsources.