Editing Terrestrial planet (section)

==Structure==
All terrestrial planets in the [[Solar System]] have the same basic structure, such as a central metallic [[planetary core|core]] (mostly [[iron]]) with a surrounding silicate [[Mantle (geology)|mantle]].

The large rocky asteroid [[4 Vesta]] has a similar structure; possibly so does the smaller one [[21 Lutetia]].<ref name=Asphaug-Reufer-2014>
{{cite journal
 |first1=E. |last1=Asphaug
 |first2=A. |last2=Reufer
 |year=2014
 |title=Mercury and other iron-rich planetary bodies as relics of inefficient accretion
 |journal=Nature Geoscience
 |volume=7  |issue=8  |pages=564–568
 |bibcode=2014NatGe...7..564A   |doi=10.1038/NGEO2189
}}
</ref> Another rocky asteroid [[2 Pallas]] is about the same size as Vesta, but is significantly less dense; it appears to have never differentiated a core and a mantle. The Earth's [[Moon]] and Jupiter's moon [[Io (moon)|Io]] have similar structures to terrestrial planets, but Earth's Moon has a much smaller iron core. Another Jovian moon [[Europa (moon)|Europa]] has a similar density but has a significant ice layer on the surface: for this reason, it is sometimes considered an [[icy planet]] instead.

Terrestrial planets can have surface structures such as [[canyon]]s, [[Impact crater|craters]], [[mountain]]s, [[volcano]]es, and others, depending on the presence at any time of an [[erosion|erosive]] liquid or tectonic activity or both.

Terrestrial planets have [[secondary atmosphere]]s, generated by volcanic out-gassing or from comet impact debris. This contrasts with the [[outer planet|outer]], [[giant planet]]s, whose atmospheres are primary; [[primary atmosphere]]s were captured directly from the original [[solar nebula]].<ref name="Schombert-lec14">{{cite web |author=Schombert, James|year=2004 |title=Lecture&nbsp;14 Terrestrial planet atmospheres (primary atmospheres) |series=Astronomy&nbsp;121 Lecture Notes |department=Department of Physics |publisher=University of Oregon |url=http://abyss.uoregon.edu/~js/ast121/lectures/lec14.html |access-date=22 December 2009 |url-status=live |archive-url=http://archive.wikiwix.com/cache/20110713164911/http://abyss.uoregon.edu/~js/ast121/lectures/lec14.html |archive-date=13 July 2011}}</ref>