Editing Ethane (section)

===Atmospheric and extraterrestrial===
[[File:Titan North Pole Lakes PIA08630.jpg|right|thumb|250px|A photograph of [[Titan (moon)|Titan]]'s northern latitudes. The dark features are hydrocarbon lakes containing ethane]]

Ethane occurs as a trace gas in the [[Earth's atmosphere]], currently having a concentration at [[sea level]] of 0.5 [[parts per billion|ppb]].<ref>{{cite web|url=http://www.atmosphere.mpg.de/enid/3tg.html|title=Trace gases (archived)|website=Atmosphere.mpg.de|archive-url=https://web.archive.org/web/20081222061502/http://www.atmosphere.mpg.de/enid/3tg.html |access-date=2011-12-08|archive-date=2008-12-22 }}</ref> Global ethane quantities have varied over time, likely due to [[Gas flare|flaring]] at [[natural gas field]]s.<ref name="SimpsonSulbaek Andersen2012">{{cite journal|last1=Simpson|first1=Isobel J.|last2=Sulbaek Andersen|first2=Mads P.|last3=Meinardi|first3=Simone|last4=Bruhwiler|first4=Lori|last5=Blake|first5=Nicola J.|last6=Helmig|first6=Detlev|last7=Rowland|first7=F. Sherwood|last8=Blake|first8=Donald R.|title=Long-term decline of global atmospheric ethane concentrations and implications for methane|journal=Nature|volume=488|issue=7412|year=2012|pages=490–494|doi=10.1038/nature11342|pmid=22914166|url=https://zenodo.org/record/898122|bibcode=2012Natur.488..490S|s2cid=4373714}}</ref> Global ethane emission rates declined from 1984 to 2010,<ref name="SimpsonSulbaek Andersen2012"/> though increased [[shale gas]] production at the [[Bakken Formation]] in the U.S. has arrested the decline by half.<ref name="KortSmith2016">{{cite journal|last1=Kort|first1=E. A.|last2=Smith|first2=M. L.|last3=Murray|first3=L. T.|last4=Gvakharia|first4=A.|last5=Brandt|first5=A. R.|last6=Peischl|first6=J.|last7=Ryerson|first7=T. B.|last8=Sweeney|first8=C.|last9=Travis|first9=K.|title=Fugitive emissions from the Bakken shale illustrate role of shale production in global ethane shift|journal=Geophysical Research Letters|year=2016|doi=10.1002/2016GL068703|volume=43|issue=9|pages=4617–4623|bibcode=2016GeoRL..43.4617K|doi-access=free|hdl=2027.42/142509|hdl-access=free}}</ref><ref>{{cite web|url=http://ns.umich.edu/new/multimedia/videos/23735-one-oil-field-a-key-culprit-in-global-ethane-gas-increase|title=One oil field a key culprit in global ethane gas increase|date=April 26, 2016|publisher=University of Michigan}}</ref>

Although ethane is a [[greenhouse gas]], it is much less abundant than methane, has a lifetime of only a few months compared to over a decade,<ref name="Feasibility">{{cite journal|last1=Aydin|first1=Kamil Murat|last2=Williams|first2=M.B.|last3=Saltzman|first3=E.S.|title=Feasibility of reconstructing paleoatmospheric records of selected alkanes, methyl halides, and sulfur gases from Greenland ice cores|journal=Journal of Geophysical Research|volume=112|date=April 2007|issue=D7 |doi=10.1029/2006JD008027 |bibcode=2007JGRD..112.7312A }}</ref> and is also less efficient at absorbing radiation relative to mass. In fact, ethane's [[global warming potential]] largely results from its conversion in the atmosphere to methane.<ref>{{cite journal|last1=Hodnebrog|first1=Øivind|last2=Dalsøren|first2=Stig B.|last3=Myrhe|first3=Gunnar|title=Lifetimes, direct and indirect radiative forcing, and global warming potentials of ethane (C<sub>2</sub>H<sub>6</sub>), propane (C<sub>3</sub>H<sub>8</sub>), and butane (C<sub>4</sub>H<sub>10</sub>)|journal=Atmospheric Science Letters|year=2018|volume=19 |issue=2 |doi=10.1002/asl.804|doi-access=free|bibcode=2018AtScL..19E.804H }}</ref> It has been detected as a trace component in the atmospheres of all four [[giant planet]]s, and in the atmosphere of [[Saturn]]'s moon [[Titan (moon)|Titan]].<ref>{{cite web|first = Bob|last = Brown|year = 2008|url = http://www.jpl.nasa.gov/news/news.cfm?release=2008-152|title = NASA Confirms Liquid Lake on Saturn Moon|display-authors = et al|publisher = NASA Jet Propulsion Laboratory|access-date = 2008-07-30|archive-date = 2011-06-05|archive-url = https://web.archive.org/web/20110605031218/http://www.jpl.nasa.gov/news/news.cfm?release=2008-152|url-status = dead}}</ref>

Atmospheric ethane results from the Sun's [[photochemistry|photochemical]] action on methane gas, also present in these atmospheres: [[ultraviolet]] photons of shorter [[wavelength]]s than 160 [[nanometer|nm]] can photo-dissociate the methane molecule into a [[methyl]] radical and a [[hydrogen]] atom. When two methyl radicals recombine, the result is ethane:

: CH<sub>4</sub> &nbsp;→&nbsp; CH<sub>3</sub>• + •H
: CH<sub>3</sub>• + •CH<sub>3</sub> &nbsp;→&nbsp; C<sub>2</sub>H<sub>6</sub>

In Earth's atmosphere, [[hydroxyl radical]]s convert ethane to [[methanol]] vapor with a half-life of around three months.<ref name="Feasibility"/>

It is suspected that ethane produced in this fashion on Titan rains back onto the moon's surface, and over time has accumulated into hydrocarbon seas covering much of the moon's polar regions. In mid-2005, the ''[[Cassini-Huygens|Cassini]]'' orbiter discovered [[Ontario Lacus]] in Titan's south polar regions. Further analysis of infrared spectroscopic data presented in July 2008<ref>{{cite journal|doi=10.1038/nature07100|title=The identification of liquid ethane in Titan's Ontario Lacus|year=2008|last1=Brown|first1=R. H.|last2=Soderblom|first2=L. A.|last3=Soderblom|first3=J. M.|last4=Clark|first4=R. N.|last5=Jaumann|first5=R.|last6=Barnes|first6=J. W.|last7=Sotin|first7=C.|last8=Buratti|first8=B.|last9=Baines|first9=K. H.|last10=Nicholson|first10=P. D.|journal=Nature|volume=454|issue=7204|pages=607–10|pmid=18668101|bibcode = 2008Natur.454..607B |s2cid=4398324|display-authors=8}}</ref> provided additional evidence for the presence of liquid ethane in Ontario Lacus. Several significantly larger hydrocarbon lakes, [[Ligeia Mare]] and [[Kraken Mare]] being the two largest, were discovered near Titan's north pole using radar data gathered by Cassini. These lakes are believed to be filled primarily by a mixture of liquid ethane and methane.

In 1996, ethane was detected in [[Comet Hyakutake]],<ref name= Mumma/> and it has since been detected in some other [[comets]]. The existence of ethane in these distant solar system bodies may implicate ethane as a primordial component of the [[solar nebula]] from which the sun and planets are believed to have formed.

In 2006, Dale Cruikshank of NASA/Ames Research Center (a ''[[New Horizons]]'' co-investigator) and his colleagues announced the spectroscopic discovery of ethane on [[Pluto]]'s surface.<ref>{{Cite web |last=Stern |first= A. |author-link=Alan Stern |date=November 1, 2006 |title=Making Old Horizons New |url=http://pluto.jhuapl.edu/overview/piPerspectives/piPerspective_11_1_2006.php |url-status=dead |archive-url=https://web.archive.org/web/20080828012339/http://pluto.jhuapl.edu/overview/piPerspectives/piPerspective_11_1_2006.php |archive-date=August 28, 2008 |access-date=2007-02-12 |website=The PI's Perspective |publisher=Johns Hopkins University Applied Physics Laboratory}}</ref>