Editing Exosphere (section)

==Surface boundary exosphere==
[[Mercury (planet)|Mercury]], [[Ceres (dwarf planet)|Ceres]] and several large natural satellites, such as the [[Moon]], [[Europa (moon)|Europa]], and [[Ganymede (moon)|Ganymede]], have exospheres without a denser atmosphere underneath,<ref name="NASA-20150306">{{cite web |last=Day |first=Brian |title=Why LADEE Matters |url=https://www.nasa.gov/mission_pages/LADEE/news/why-ladee-matters.html |date=20 August 2013 |publisher=NASA Ames Research Center |access-date=19 April 2015 |archive-date=18 April 2015 |archive-url=https://web.archive.org/web/20150418060132/http://www.nasa.gov/mission_pages/LADEE/news/why-ladee-matters.html |url-status=dead }}</ref> referred to as a '''surface boundary exosphere'''.<ref>{{cite web |title=Is There an Atmosphere on the Moon? |url=https://www.nasa.gov/mission_pages/LADEE/news/lunar-atmosphere.html#.VX6V-d9PbGI |date=30 January 2014 |publisher=NASA |access-date=4 August 2016 |archive-date=2 November 2019 |archive-url=https://web.archive.org/web/20191102182404/https://www.nasa.gov/mission_pages/LADEE/news/lunar-atmosphere.html#.VX6V-d9PbGI |url-status=dead }}</ref>  Here, molecules are ejected on [[parabolic trajectory|elliptic trajectories]] until they collide with the surface. Smaller bodies such as asteroids, in which the molecules emitted from the surface escape to space, are not considered to have exospheres.