Editing Planetary core (section)

==Observed types==
The following summarizes known information about the planetary cores of given non-stellar bodies.

===Within the Solar System===

====Mercury====
Mercury has an observed magnetic field, which is believed to be generated within its metallic core.<ref name="Hauck and Van Orman 2011" /> Mercury's core occupies 85% of the planet's radius, making it the largest core relative to the size of the planet in the Solar System; this indicates that much of Mercury's surface may have been lost early in the Solar System's history.<ref name="NASA 2012">{{cite journal |author=NASA |date=2012 |title=MESSENGER Provides New Look at Mercury's Surprising Core and Landscape Curiosities |journal=News Releases |publisher=NASA |location=The Woodlands, Texas |pages=1–2 }}</ref> Mercury has a solid silicate crust and mantle overlying a solid metallic outer core layer, followed by a deeper liquid core layer, and then a possible solid inner core making a third layer.<ref name="NASA 2012" /> 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>

====Venus====
The composition of [[Venus]]' core varies significantly depending on the model used to calculate it, thus constraints are required.<ref name="Fegley 2003">{{cite journal |last=Fegley |first=B. Jr. |title=Venus |journal=Treatise on Geochemistry |publisher=Elsevier |volume=1 |date=2003 |pages=487–507 |doi=10.1016/b0-08-043751-6/01150-6|bibcode = 2003TrGeo...1..487F |isbn=9780080437514 }}</ref>
{|class="wikitable"
|-
!Element
!Chondritic Model
!Equilibrium Condensation Model
!Pyrolitic Model
|-
|Iron
|88.6%
|94.4%
|78.7%
|-
|Nickel
|5.5%
|5.6%
|6.6%
|-
|Cobalt
|0.26%
|Unknown
|Unknown
|-
|Sulfur
|5.1%
|0%
|4.9%
|-
|Oxygen
|0%
|Unknown
|9.8%
|}

====Moon====
The [[Internal structure of the Moon|existence of a lunar core]] is still debated; however, if it does have a core it would have formed synchronously with the Earth's own core at 45 million years post-start of the Solar System based on hafnium-tungsten evidence<ref name="Munker, et al. 2003">{{cite journal |last1=Munker |first1=Carsten |last2=Pfander |first2=Jorg A |last3=Weyer |first3=Stefan |last4=Buchl |first4=Anette |last5=Kleine |first5=Thorsten |last6=Mezger |first6=Klaus |title=Evolution of Planetary Cores and the Earth-Moon System from Nb/Ta Systematics |journal=Science  |volume=301 |date=July 2003 |pages=84–87 |doi=10.1126/science.1084662 |pmid=12843390 |issue=5629|bibcode = 2003Sci...301...84M |s2cid=219712 }}</ref> and the [[giant impact hypothesis]]. Such a core may have hosted a geomagnetic dynamo early on in its history.<ref name="Hauck and Van Orman 2011" />

====Earth====
{{main|Structure of the Earth#Core}}

The Earth has an observed [[magnetic field]] generated within its metallic core.<ref name="Hauck and Van Orman 2011" /> The Earth has a 5–10% mass deficit for the entire core and a density deficit from 4–5% for the inner core.<ref name="McDonough 2003" /> The Fe/Ni value of the core is well constrained by [[chondritic]] meteorites.<ref name="McDonough 2003" /> Sulfur, carbon, and phosphorus only account for ~2.5% of the light element component/mass deficit.<ref name="McDonough 2003"/> No geochemical evidence exists for including any radioactive elements in the core.<ref name="McDonough 2003" />  However, experimental evidence has found that potassium is strongly [[Siderophile elements|siderophile]] when dealing with temperatures associated with core-accretion, and thus [[potassium-40]] could have provided an important source of heat contributing to the early Earth's dynamo, though to a lesser extent than on sulfur rich Mars.<ref name="Murthy, van Westrenen and Fei 2003" /> The core contains half the Earth's vanadium and chromium, and may contain considerable niobium and tantalum.<ref name="McDonough 2003" /> The core is depleted in germanium and gallium.<ref name="McDonough 2003"/> [[Planetary differentiation|Core mantle differentiation]] occurred within the [[Hadean|first 30 million years]] of Earth's history.<ref name="McDonough 2003" /> Inner core crystallization timing is still largely unresolved.<ref name="McDonough 2003" />

====Mars====
Mars possibly hosted a core-generated magnetic field in the past.<ref name="Hauck and Van Orman 2011"/> The dynamo ceased within 0.5 billion years of the planet's formation.<ref name="Williams and Nimmo 2004"/> Hf/W isotopes derived from the martian meteorite [[Zagami]], indicate rapid accretion and core differentiation of Mars; i.e. under 10 million years.<ref name="Halliday and N. 2000"/> Potassium-40 could have been a major source of heat powering the early Martian dynamo.<ref name="Murthy, van Westrenen and Fei 2003" />
  
Core merging between proto-Mars and another differentiated planetoid could have been as fast as 1000 years or as slow as 300,000 years (depending on the viscosity of both cores and mantles).<ref name="Monteaux and Arkani-Hamed 2013" /> Impact-heating of the Martian core would have resulted in stratification of the core and kill the Martian dynamo for a duration between 150 and 200 million years.<ref name="Monteaux and Arkani-Hamed 2013" /> Modelling done by Williams, et al. 2004 suggests that in order for [[Mars]] to have had a functional dynamo, the Martian core was initially hotter by 150&nbsp;[[Kelvin|K]] than the mantle (agreeing with the differentiation history of the planet, as well as the impact hypothesis), and with a liquid core potassium-40 would have had opportunity to partition into the core providing an additional source of heat. The model further concludes that the core of mars is entirely liquid, as the latent heat of crystallization would have driven a longer-lasting (greater than one billion years) dynamo.<ref name="Williams and Nimmo 2004"/> If the core of Mars is liquid, the lower bound for sulfur would be five weight&nbsp;%.<ref name="Williams and Nimmo 2004" />

====Ganymede====
[[Ganymede (moon)|Ganymede]] has an observed magnetic field generated within its metallic core.<ref name="Hauck and Van Orman 2011" />

====Jupiter====
Jupiter has an observed magnetic field generated [[Jupiter#Internal structure|within its core]], indicating some metallic substance is present.<ref name="Pollack, et al. 1977" /> Its magnetic field is the strongest in the Solar System after the Sun's.

Jupiter has a rock and/or ice core 10–30 times the mass of the Earth, and this core is likely soluble in the gas envelope above, and so primordial in composition. Since the core still exists, the outer envelope must have originally accreted onto a previously existing planetary core.<ref name="Stevenson 1982" /> Thermal contraction/evolution models support the presence of [[metallic hydrogen]] within the core in large abundances (greater than Saturn).<ref name="Pollack, et al. 1977" />

====Saturn====
[[Saturn]] has an observed magnetic field generated [[Saturn#Internal structure|within its metallic core]].<ref name="Pollack, et al. 1977"/> Metallic hydrogen is present within the core (in lower abundances than Jupiter).<ref name="Pollack, et al. 1977" />
Saturn has a rock and or ice core 10–30 times the mass of the Earth, and this core is likely soluble in the gas envelope above, and therefore it is primordial in composition. Since the core still exists, the envelope must have originally accreted onto previously existing planetary cores.<ref name="Stevenson 1982" /> Thermal contraction/evolution models support the presence of [[metallic hydrogen]] within the core in large abundances (but still less than Jupiter).<ref name="Pollack, et al. 1977" />

==== Remnant planetary cores ====
Missions to bodies in the [[asteroid belt]] will provide more insight to planetary core formation. It was previously understood that collisions in the solar system fully merged, but recent work on planetary bodies argues that remnants of collisions have their outer layers stripped, leaving behind a body that would eventually become a planetary core.<ref>{{Cite journal|last1=Williams|first1=Quentin|last2=Agnor|first2=Craig B.|last3=Asphaug|first3=Erik|date=January 2006|title=Hit-and-run planetary collisions|journal=Nature|volume=439|issue=7073|pages=155–160|doi=10.1038/nature04311|pmid=16407944|issn=1476-4687|bibcode=2006Natur.439..155A|s2cid=4406814}}</ref> The [[Psyche mission]], titled “Journey to a Metal World,” is aiming to studying [[16 Psyche|a body]] that could possibly be a remnant planetary core.<ref>{{Cite book|last1=Lord|first1=Peter|last2=Tilley|first2=Scott|last3=Oh|first3=David Y.|last4=Goebel|first4=Dan|last5=Polanskey|first5=Carol|last6=Snyder|first6=Steve|last7=Carr|first7=Greg|last8=Collins|first8=Steven M.|last9=Lantoine|first9=Gregory|title=2017 IEEE Aerospace Conference |chapter=Psyche: Journey to a metal world |date=March 2017|pages=1–11|publisher=IEEE|doi=10.1109/aero.2017.7943771|isbn=9781509016136|s2cid=45190228}}</ref>

===Extrasolar===
As the field of exoplanets grows as new techniques allow for the discovery of both diverse exoplanets, the cores of exoplanets are being modeled. These depend on initial compositions of the exoplanets, which is inferred using the absorption spectra of individual exoplanets in combination with the emission spectra of their star.

====Chthonian planets====
A [[chthonian planet]] results when a gas giant has its outer atmosphere stripped away by its parent star, likely due to the planet's inward migration. All that remains from the encounter is the original core.

====Planets derived from stellar cores and diamond planets====
[[Carbon planet]]s, previously stars, are formed alongside the formation of a [[millisecond pulsar]]. The first such planet discovered was 18 times the density of water, and five times the size of Earth. Thus the planet cannot be gaseous, and must be composed of heavier elements that are also cosmically abundant like carbon and oxygen; making it likely crystalline like a diamond.<ref name="National Geographic Society 2011">{{cite journal |publisher=National Geographic Society |title="Diamond" Planet Found; May be Stripped Star |journal=National Geographic |date=2011-08-25 |url=http://news.nationalgeographic.com/news/2011/08/110825-new-planet-diamond-pulsar-dwarf-star-space-science/ |archive-url=https://web.archive.org/web/20111016203105/http://news.nationalgeographic.com/news/2011/08/110825-new-planet-diamond-pulsar-dwarf-star-space-science |url-status=dead |archive-date=October 16, 2011 }}</ref>

[[PSR J1719-1438]] is a 5.7 millisecond pulsar found to have a companion with a mass similar to Jupiter but a density of 23&nbsp;g/cm<sup>3</sup>, suggesting that the companion is an ultralow mass carbon [[white dwarf]], likely the core of an ancient star.<ref name="Bailes, et al. 2011">{{cite journal |last=Bailes |first=M. |display-authors=etal |title=Transformation of a Star into a Planet in a Millisecond Pulsar Binary |journal=Science |volume=333 |date=September 2011 |pages=1717–1720 |doi=10.1126/science.1208890 |pmid=21868629 |issue=6050|arxiv = 1108.5201 |bibcode = 2011Sci...333.1717B |s2cid=206535504 }}</ref>

====Hot ice planets====
Exoplanets with moderate densities (more dense than Jovian planets, but less dense than terrestrial planets) suggests that such planets like [[GJ1214b]] and [[GJ436]] are composed of primarily water. Internal pressures of such water-worlds would result in exotic phases of [[water]] forming on the surface and within their cores.<ref name="MessageToEagle.com 2012">{{cite web |publisher=MessageToEagle |title=Hot Ice Planets |date=2012-04-09 |url=http://www.messagetoeagle.com/hoticeplanets.php |access-date=2014-04-13 |archive-date=2016-03-04 |archive-url=https://web.archive.org/web/20160304233856/http://www.messagetoeagle.com/hoticeplanets.php |url-status=dead }}</ref>