Editing Caloris Planitia (section)

==Emissions of gas==
Mercury has a very tenuous and transient atmosphere, containing small amounts of [[hydrogen]] and [[helium]] captured from the [[solar wind]], as well as heavier elements such as [[sodium]] and [[potassium]].  These are thought to originate within the planet, being "out-gassed" from beneath its crust.  The Caloris basin has been found to be a significant source of sodium and potassium, indicating that the fractures created by the impact facilitate the release of gases from within the planet.  The unusual terrain is also a source of these gases.<ref>{{cite journal |last=Sprague |first=A. L. |author2=Kozlowski, R. W. H. |author3=Hunten, D. M.  |year=1990 |title=Caloris Basin: An Enhanced Source for Potassium in Mercury's Atmosphere |journal=Science |volume=249 |issue=4973 |pages=1140–1142 |doi=10.1126/science.249.4973.1140 |pmid=17831982 |bibcode = 1990Sci...249.1140S |s2cid=36754700 }}</ref>