Editing Mercury (planet) (section)

=== Internal structure ===
[[File:Mercury with magnetic field.svg|left|thumb|upright=1.0|Mercury's internal structure and magnetic field]]
Mercury appears to have a solid silicate [[Crust (geology)|crust]] and mantle overlying a solid, metallic outer core layer, a deeper liquid core layer, and a solid inner core.<ref>{{cite web |url=https://www.nasa.gov/mission_pages/messenger/media/PressConf20120321.html |title=MESSENGER Provides New Look at Mercury's Surprising Core and Landscape Curiosities |publisher=NASA |editor-first=Tricia |editor-last=Talbert |date=March 21, 2012 |access-date=April 20, 2018 |archive-date=January 12, 2019 |archive-url=https://web.archive.org/web/20190112170032/https://www.nasa.gov/mission_pages/messenger/media/PressConf20120321.html |url-status=dead }}</ref><ref>{{Cite web |url=https://news.agu.org/press-release/scientists-find-evidence-mercury-has-a-solid-inner-core/ |title=Scientists find evidence Mercury has a solid inner core |format=Press release |date=April 17, 2023 |last1=Genova |first1=Antonio |display-authors=et al |website=AGU Newsroom |language=en-US |access-date=April 17, 2019 |archive-date=April 17, 2019 |archive-url=https://web.archive.org/web/20190417162031/https://news.agu.org/press-release/scientists-find-evidence-mercury-has-a-solid-inner-core/ |url-status=live }}</ref> The composition of the iron-rich core remains uncertain, but it likely contains nickel, silicon and perhaps sulfur and carbon, plus trace amounts of other elements.<ref>{{cite book | chapter=The Chemical Composition of Mercury | last1=Nittler | first1=Larry R. | last2=Chabot | first2=Nancy L. | last3=Grove | first3=Timothy L. | last4=Peplowski | first4=Patrick N. | title=Mercury: The View after MESSENGER | editor1-first=Sean C. | editor1-last=Solomon | editor2-first=Larry R. | editor2-last=Nittler | editor3-first=Brian J. | editor3-last=Anderson | isbn=9781316650684 | series=Cambridge Planetary Science Book Series | publication-place=Cambridge, UK | publisher=Cambridge University Press | year=2018 | pages=30–51 | doi=10.1017/9781316650684.003 | arxiv=1712.02187 | bibcode=2018mvam.book...30N | s2cid=119021137 }}</ref> The planet's density is the second highest in the Solar System at 5.427&nbsp;g/cm<sup>3</sup>, only slightly less than Earth's density of 5.515&nbsp;g/cm<sup>3</sup>.<ref name="fact" /> If the effect of [[gravitational compression]] were to be factored out from both planets, the materials of which Mercury is made would be denser than those of Earth, with an uncompressed density of 5.3&nbsp;g/cm<sup>3</sup> versus Earth's 4.4&nbsp;g/cm<sup>3</sup>.<ref>{{cite web |date=May 8, 2003 |url=https://astrogeology.usgs.gov/Projects/BrowseTheGeologicSolarSystem/MercuryBack.html |title=Mercury |publisher=US Geological Survey |access-date=November 26, 2006 |archive-url=https://web.archive.org/web/20060929091534/http://astrogeology.usgs.gov/Projects/BrowseTheGeologicSolarSystem/MercuryBack.html |archive-date=September 29, 2006 |url-status=dead }}</ref> Mercury's density can be used to infer details of its inner structure. Although Earth's high density results appreciably from gravitational compression, particularly at the [[planetary core|core]], Mercury is much smaller and its inner regions are not as compressed. Therefore, for it to have such a high density, its core must be large and rich in iron.<ref>{{cite journal |title=On the Internal Structures of Mercury and Venus |last=Lyttleton |first=Raymond A. |author-link=Raymond Lyttleton |journal=Astrophysics and Space Science |volume=5 |issue=1 |pages=18–35 |year=1969 |doi=10.1007/BF00653933 |bibcode=1969Ap&SS...5...18L |s2cid=122572625 }}</ref>

The radius of Mercury's core is estimated to be {{convert|2020|±|30|km|mi|abbr=on}}, based on interior models constrained to be consistent with a [[moment of inertia factor]] of {{val|0.346|0.014}}.<ref name="Margot2012" /><ref name="Hauck_etal_2013" /> Hence, Mercury's core occupies about 57% of its volume; for Earth this proportion is 17%. Research published in 2007 suggests that Mercury has a molten core.<ref name="cornell">{{cite news |first=Lauren |last=Gold |title=Mercury has molten core, Cornell researcher shows |date=May 3, 2007 |work=Chronicle |publisher=Cornell University |url=http://www.news.cornell.edu/stories/May07/margot.mercury.html |access-date=May 12, 2008 |archive-date=June 17, 2012 |archive-url=https://web.archive.org/web/20120617123129/http://www.news.cornell.edu/stories/May07/margot.mercury.html |url-status=live }}</ref><ref name="nrao">{{cite news |last=Finley |first=Dave |date=May 3, 2007 |title=Mercury's Core Molten, Radar Study Shows |publisher=National Radio Astronomy Observatory |url=http://www.nrao.edu/pr/2007/mercury/ |access-date=May 12, 2008 |archive-date=May 3, 2012 |archive-url=https://web.archive.org/web/20120503202505/http://www.nrao.edu/pr/2007/mercury/ |url-status=live }}</ref> The mantle-crust layer is in total {{convert|420|km|mi|abbr=on}} thick.<ref>{{cite journal |last1=Hauck |first1=Steven A. |display-authors=etal |title=The curious case of Mercury's internal structure |journal=Journal of Geophysical Research: Planets |date=May 6, 2013 |volume=118 |issue=6 |pages=1204–1220 |doi=10.1002/jgre.20091 |bibcode=2013JGRE..118.1204H |s2cid=17668886 |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/jgre.20091 |access-date=June 5, 2023 |hdl=1721.1/85633 |hdl-access=free |archive-date=June 5, 2023 |archive-url=https://web.archive.org/web/20230605175115/https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/jgre.20091 |url-status=live }}</ref> Projections differ as to the size of the crust specifically; data from the {{nowrap|''Mariner 10''}} and ''MESSENGER'' probes suggests a thickness of {{convert|35|km|mi|abbr=on}}, whereas an [[Airy isostacy]] model suggests a thickness of {{convert|26|±|11|km|mi|abbr=on}}.<ref name="Padovan2015" /><ref>{{Cite book |last1=Solomon |first1=Sean C. |url=https://books.google.com/books?id=4o92DwAAQBAJ |title=Mercury: The View after MESSENGER |last2=Nittler |first2=Larry R. |last3=Anderson |first3=Brian J. |date=December 20, 2018 |publisher=Cambridge University Press |isbn=978-1-107-15445-2 |pages=534 |language=en |access-date=November 19, 2022 |archive-date=March 1, 2024 |archive-url=https://web.archive.org/web/20240301162217/https://books.google.com/books?id=4o92DwAAQBAJ |url-status=live }}</ref><ref>{{cite journal | title=A thin, dense crust for Mercury | last=Sori | first=Michael M. | journal=Earth and Planetary Science Letters | volume=489 | pages=92–99 | date=May 2018 | doi=10.1016/j.epsl.2018.02.033 | bibcode=2018E&PSL.489...92S | doi-access=free }}</ref> One distinctive feature of Mercury's surface is the presence of numerous narrow ridges, extending up to several hundred kilometers in length. It is thought that these were formed as Mercury's core and mantle cooled and contracted at a time when the crust had already solidified.<ref>{{cite journal |title=Lobate Thrust Scarps and the Thickness of Mercury's Lithosphere |last1=Schenk |first1=Paul M. |last2=Melosh |first2=H. Jay |author-link2=H. Jay Melosh |journal=Abstracts of the 25th Lunar and Planetary Science Conference |volume=1994 |pages=1994LPI....25.1203S |bibcode=1994LPI....25.1203S |date=March 1994 }}</ref><ref>{{cite conference | last1=Watters | first1=T. R. | first2=F. | last2=Nimmo | first3=M. S. | last3=Robinson | title=Chronology of Lobate Scarp Thrust Faults and the Mechanical Structure of Mercury's Lithosphere | conference=Lunar and Planetary Science Conference | page=1886 | year=2004 | bibcode= 2004LPI....35.1886W }}</ref><ref>{{cite journal | journal=Geology | date=November 1998 | volume=26 | issue=11 | pages=991–994 | title=Topography of lobate scarps on Mercury; new constraints on the planet's contraction | first1=Thomas R. | last1=Watters | first2=Mark S. | last2=Robinson | first3=Anthony C. | last3=Cook | doi=10.1130/0091-7613(1998)026<0991:TOLSOM>2.3.CO;2 | bibcode=1998Geo....26..991W }}</ref>

Mercury's core has a higher iron content than that of any other planet in the Solar System, and several theories have been proposed to explain this. The most widely accepted theory is that Mercury originally had a metal–silicate ratio similar to common [[chondrite]] meteorites, thought to be typical of the Solar System's rocky matter, and a mass approximately 2.25 times its current mass.<ref name="Benz" /> Early in the Solar System's history, Mercury may have been struck by a [[planetesimal]] of approximately {{frac|1|6}} Mercury's mass and several thousand kilometers across.<ref name="Benz" /> The impact would have stripped away much of the original crust and mantle, leaving the core behind as a relatively major component.<ref name="Benz" /> A similar process, known as the [[giant impact hypothesis]], has been proposed to explain the formation of Earth's Moon.<ref name="Benz" />

Alternatively, Mercury may have formed from the [[solar nebula]] before the Sun's energy output had stabilized. It would initially have had twice its present mass, but as the [[protostar|protosun]] contracted, temperatures near Mercury could have been between 2,500 and 3,500&nbsp;K and possibly even as high as 10,000&nbsp;K.<ref name="CameronAGW1">{{cite journal |title=The partial volatilization of Mercury |last=Cameron |first=Alastair G. W. |author-link=Alastair G. W. Cameron |journal=Icarus |volume=64 |issue=2 |pages=285–294 |year=1985 |doi=10.1016/0019-1035(85)90091-0 |bibcode=1985Icar...64..285C}}</ref> Much of Mercury's surface rock could have been vaporized at such temperatures, forming an atmosphere of "rock vapor" that could have been carried away by the [[solar wind]].<ref name="CameronAGW1" /> A third hypothesis proposes that the solar nebula caused [[drag (physics)|drag]] on the particles from which Mercury was [[Accretion (astrophysics)|accreting]], which meant that lighter particles were lost from the accreting material and not gathered by Mercury.<ref>{{cite journal |title=Iron/silicate fractionation and the origin of Mercury |last=Weidenschilling |first=Stuart J. |journal=Icarus |volume=35 |issue=1 |pages=99–111 |year=1987 |doi=10.1016/0019-1035(78)90064-7 |bibcode=1978Icar...35...99W}}</ref>

Each hypothesis predicts a different surface composition, and two space missions have been tasked with making observations of this composition. The first ''[[MESSENGER]]'', which ended in 2015, found higher-than-expected potassium and sulfur levels on the surface, suggesting that the giant impact hypothesis and vaporization of the crust and mantle did not occur because said potassium and sulfur would have been driven off by the extreme heat of these events.<ref name="csmon20110929">{{cite news |url=https://www.csmonitor.com/Science/2011/0929/Messenger-s-message-from-Mercury-Time-to-rewrite-the-textbooks |title=Messenger's message from Mercury: Time to rewrite the textbooks |work=The Christian Science Monitor |first=Mark |last=Sappenfield |date=September 29, 2011 |access-date=August 21, 2017 |archive-date=August 21, 2017 |archive-url=https://web.archive.org/web/20170821214604/https://www.csmonitor.com/Science/2011/0929/Messenger-s-message-from-Mercury-Time-to-rewrite-the-textbooks |url-status=live }}</ref> ''[[BepiColombo]]'', which will arrive at Mercury in 2025, will make observations to test these hypotheses.<ref name="ESA-Bepi">{{cite web |url=http://sci.esa.int/bepicolombo/ |title=BepiColombo |series=Science & Technology |publisher=European Space Agency |access-date=April 7, 2008 |archive-date=March 6, 2018 |archive-url=https://web.archive.org/web/20180306193632/http://sci.esa.int/bepicolombo/ |url-status=live }}</ref> The findings so far would seem to favor the third hypothesis; however, further analysis of the data is needed.<ref name="intra">{{cite news |url=https://www.chemistryworld.com/news/messenger-sheds-light-on-mercurys-formation/3002463.article |title=Messenger sheds light on Mercury's formation |work=Chemistry World |first=Jon |last=Cartwright |date=September 30, 2011 |access-date=August 21, 2017 |archive-date=August 6, 2017 |archive-url=https://web.archive.org/web/20170806063258/https://www.chemistryworld.com/news/messenger-sheds-light-on-mercurys-formation/3002463.article |url-status=live }}</ref>