Editing Exoplanet (section)

== Surface ==

=== Surface composition ===
Surface features can be distinguished from atmospheric features by comparing emission and reflection spectroscopy with [[transmission spectroscopy]]. Mid-infrared spectroscopy of exoplanets may detect rocky surfaces, and near-infrared may identify magma oceans or high-temperature lavas, hydrated silicate surfaces and water ice, giving an unambiguous method to distinguish between rocky and gaseous exoplanets.<ref>{{cite journal| arxiv=1204.1544|bibcode = 2012ApJ...752....7H |doi = 10.1088/0004-637X/752/1/7 | volume=752|issue = 1 | title=Theoretical Spectra of Terrestrial Exoplanet Surfaces| journal=The Astrophysical Journal| page=7|year = 2012 |last1 = Hu |first1 = Renyu |last2 = Ehlmann |first2 = Bethany L. |last3 = Seager |first3 = Sara |s2cid = 15219541 }}</ref>

=== Surface temperature ===
[[File:WASP-33b.jpg|thumb|upright=1.6|alt=Artist's illustration of temperature inversion in an exoplanet's atmosphere, with and without a stratosphere|Artist's illustration of temperature inversion in exoplanet's atmosphere.<ref>{{cite web |title=NASA, ESA, and K. Haynes and A. Mandell (Goddard Space Flight Center)|url=http://www.spacetelescope.org/images/opo1525a/|access-date=15 June 2015}}</ref>]]
Measuring the intensity of the light it receives from its parent star can estimate the temperature of an exoplanet. For example, the planet [[OGLE-2005-BLG-390Lb]] is estimated to have a surface temperature of roughly −220&nbsp;°C (50 K). However, such estimates may be substantially in error because they depend on the planet's usually unknown [[albedo]], and because factors such as the [[greenhouse effect]] may introduce unknown complications. A few planets have had their temperature measured by observing the variation in infrared radiation as the planet moves around in its orbit and is eclipsed by its parent star. For example, the planet [[HD 189733b]] has been estimated to have an average temperature of 1,205 K (932&nbsp;°C) on its dayside and 973 K (700&nbsp;°C) on its nightside.<ref name="knutson_charbonneau07">{{Cite journal | doi = 10.1038/nature05782 | url=http://www.ucolick.org/~jfortney/papers/Knutson07.pdf|arxiv=0705.0993 | pmid=17495920 | bibcode = 2007Natur.447..183K  | title = A map of the day–night contrast of the extrasolar planet HD 189733b | journal = Nature | volume = 447 | issue = 7141 | pages = 183–186 | year = 2007 | last1 = Knutson | first1 = H. A.  | last2 = Charbonneau | first2 = D.  | last3 = Allen | first3 = L. E. |author3-link=Lori Allen (astronomer) | last4 = Fortney | first4 = J. J.  | last5 = Agol | first5 = E.  | last6 = Cowan | first6 = N. B.  | last7 = Showman | first7 = A. P.  | last8 = Cooper | first8 = C. S.  | last9 = Megeath | first9 = S. T. | s2cid=4402268}}</ref>