Editing Planetary core (section)

==Discovery==

=== Earth's core ===
{{Main|Earth's core}}
In 1797, [[Henry Cavendish]] calculated the average density of the Earth to be 5.48 times the density of water (later refined to 5.53), which led to the accepted belief that the Earth was much denser in its interior.<ref name="Cavendish 1798">{{cite journal |last=Cavendish |first=H. |title=Experiments to determine the density of Earth |journal=Philosophical Transactions of the Royal Society of London |volume=88 |date=1798 |pages=469–479 |doi=10.1098/rstl.1798.0022|doi-access=free }}</ref> Following the discovery of [[iron meteorite]]s, Wiechert in 1898 postulated that the Earth had a similar bulk composition to iron meteorites, but the iron had settled to the interior of the Earth, and later represented this by integrating the bulk density of the Earth with the missing iron and nickel as a core.<ref name="Wiechert 1897">{{cite journal |last=Wiechert |first=E. |title=Uber die Massenverteilung im Inneren der Erde |language=de |trans-title=About the mass distribution inside the Earth |journal=Nachrichten der Königlichen Gesellschaft der Wissenschaften zu Göttingen, Mathematische-physikalische Klasse |volume=1897 |issue=3 |date=1897 |pages=221–243 |url=https://www.digizeitschriften.de/dms/img/?PID=GDZPPN002497891 }}</ref> The first detection of Earth's core occurred in 1906 by Richard Dixon Oldham upon discovery of the [[P-wave]] shadow zone; the liquid outer core.<ref name="Oldham 1906">{{cite journal |last1=Oldham |first1=R. D. |title=The Constitution of the Interior of the Earth, as Revealed by Earthquakes |journal=Quarterly Journal of the Geological Society |date=1 February 1906 |volume=62 |issue=1–4 |pages=456–475 |doi=10.1144/GSL.JGS.1906.062.01-04.21|bibcode=1906QJGS...62..456O |s2cid=129025380 |url=https://zenodo.org/record/1513152 }}</ref> By 1936 seismologists had determined the size of the overall core as well as the boundary between the fluid outer core and the solid inner core.<ref name="Transdyne Corporation">{{Cite web |last=Hemdon |first=J. Marvin |date=2009 |title=Richard D. Oldham's Discovery of the Earth's Core |url=http://nuclearplanet.com/Earth%20Core%20Discovery.html |publisher=Transdyne Corporation}}</ref>

=== Moon's core ===
The [[internal structure of the Moon]] was characterized in 1974 using seismic data collected by the [[List of Apollo missions|Apollo missions]] of [[moonquakes]].<ref>{{Cite journal|last1=Nakamura|first1=Yosio|last2=Latham|first2=Gary|last3=Lammlein|first3=David|last4=Ewing|first4=Maurice|last5=Duennebier|first5=Frederick|last6=Dorman|first6=James|date=July 1974|title=Deep lunar interior inferred from recent seismic data|journal=Geophysical Research Letters|volume=1|issue=3|pages=137–140|doi=10.1029/gl001i003p00137|issn=0094-8276|bibcode=1974GeoRL...1..137N}}</ref> The Moon's core has a radius of 300&nbsp;km.<ref>{{Cite journal|last1=Bussey|first1=Ben|last2=Gillis|first2=Jeffrey J.|last3=Peterson|first3=Chris|last4=Hawke|first4=B. Ray|last5=Tompkins|first5=Stephanie|last6=McCallum|first6=I. Stewart|last7=Shearer|first7=Charles K.|last8=Neal|first8=Clive R.|last9=Righter|first9=Kevin|s2cid=130734866|date=2006-01-01|title=The Constitution and Structure of the Lunar Interior|journal=Reviews in Mineralogy and Geochemistry|volume=60|issue=1|pages=221–364|doi=10.2138/rmg.2006.60.3|issn=1529-6466|bibcode=2006RvMG...60..221W}}</ref> The Moon's iron core has a liquid outer layer that makes up 60% of the volume of the core, with a solid inner core.<ref>{{Cite journal|last1=Weber|first1=R. C.|last2=Lin|first2=P.-Y.|last3=Garnero|first3=E. J.|last4=Williams|first4=Q.|last5=Lognonne|first5=P.|date=2011-01-21|title=Seismic Detection of the Lunar Core|journal=Science|volume=331|issue=6015|pages=309–312|doi=10.1126/science.1199375|pmid=21212323|issn=0036-8075|bibcode=2011Sci...331..309W|s2cid=206530647|url=https://zenodo.org/record/1230912}}</ref>

=== Cores of the rocky planets ===
The cores of the [[Terrestrial planet|rocky planets]] were initially characterized by analyzing data from spacecraft, such as NASA's [[Mariner 10]] that flew by Mercury and Venus to observe their surface characteristics.<ref>{{Citation|title=Mariner 10 mission highlights : Venus mosaic P-14461 |date=1987|publisher=National Aeronautics and Space Administration, Jet Propulsion Laboratory, California Institute of Technology|oclc=18035258}}</ref> The cores of other planets cannot be measured using seismometers on their surface, so instead they have to be inferred based on calculations from these fly-by observation. Mass and size can provide a first-order calculation of the components that make up the interior of a planetary body. The structure of rocky planets is constrained by the average density of a planet and its [[Moment of inertia factor|moment of inertia]].<ref name="solomon 1979">{{Cite journal |last=Solomon |first=Sean C. |date=June 1979 |title=Formation, history and energetics of cores in the terrestrial planets |journal=Physics of the Earth and Planetary Interiors |language=en |volume=19 |issue=2 |pages=168–182 |bibcode=1979PEPI...19..168S |doi=10.1016/0031-9201(79)90081-5 |issn=0031-9201}}</ref> The moment of inertia for a differentiated planet is less than 0.4, because the density of the planet is concentrated in the center.<ref>{{Cite book|title=Planetary interiors|author=Hubbard, William B.|date=1992|publisher=Krieger Pub. Co|isbn=089464565X|oclc=123053051}}</ref> Mercury has a moment of inertia of 0.346, which is evidence for a core.<ref>{{Cite journal|last1=Margot|first1=Jean-Luc|last2=Peale|first2=Stanton J.|last3=Solomon|first3=Sean C.|last4=Hauck|first4=Steven A.|last5=Ghigo|first5=Frank D.|last6=Jurgens|first6=Raymond F.|last7=Yseboodt|first7=Marie|last8=Giorgini|first8=Jon D.|last9=Padovan|first9=Sebastiano|date=December 2012|title=Mercury's moment of inertia from spin and gravity data: MERCURY'S MOMENT OF INERTIA|journal=Journal of Geophysical Research: Planets|volume=117|issue=E12|pages=n/a|doi=10.1029/2012JE004161|bibcode=2012JGRE..117.0L09M|doi-access=free}}</ref> Conservation of energy calculations as well as magnetic field measurements can also constrain composition, and surface geology of the planets can characterize differentiation of the body since its accretion.<ref>{{Cite journal|last=Solomon|first=Sean C.|date=August 1976|title=Some aspects of core formation in Mercury|journal=Icarus|volume=28|issue=4|pages=509–521|doi=10.1016/0019-1035(76)90124-X|bibcode=1976Icar...28..509S|hdl=2060/19750022908|s2cid=120492617 |hdl-access=free}}</ref> Mercury, Venus, and Mars’ cores are about 75%, 50%, and 40% of their radius respectively.<ref name="de pater 2015">{{Cite book |last1=De Pater |first1=Imke |title=Planetary sciences |last2=Lissauer |first2=Jack Jonathan |date=2015 |publisher=Cambridge University Press |isbn=978-1-107-09161-0 |edition=2nd |location=Cambridge |doi=10.1017/cbo9781316165270.023}}</ref><ref name="stevenson 2001">{{Cite journal |last=Stevenson |first=David J. |date=July 2001 |title=Mars' core and magnetism |journal=Nature |language=en |volume=412 |issue=6843 |pages=214–219 |bibcode=2001Natur.412..214S |doi=10.1038/35084155 |issn=0028-0836 |pmid=11449282 |s2cid=4391025}}</ref>