Planetary core
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planetary core
The central part of a planet, large moon, or large asteroid that is denser than, and compositionally distinct from, the layers that surround it. Earth has a solid inner core with a radius of about 1,300 km below a fluid outer core some 2,300 km thick. Both regions of the core consist largely of iron and nickel that sank to the center of the planet while it was still molten. Circulating currents in the core give rise to Earth's magnetic field.
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Planetary core
The planetary core consists of the innermost layer(s) of a planet.
The core may be composed of solid and liquid layers.[1] The cores of Mars and Venus are thought to be completely solid as they lack an internally generated magnetic field.[2] In our solar system, core size can range from about 20% (the Moon) to 85% of a planet's radius (Mercury).
Gas giants also have iron-rich cores.[citation needed] Although these cores are proportionately much smaller than those of terrestrial planets, gas giants are so large that their cores can actually be larger than Earth. Jupiter's core is thought to be approximately 12 times the mass of Earth (3% of Jupiter's total mass), and the exoplanet HD 149026 b is thought to have a core approximately 70 times the mass of Earth.
It is thought that some gas giants orbiting very close to their primaries may have their atmospheres stripped away, leaving only their core behind. This as-yet hypothetical class of planets are called "Chthonian planets".
Some moons, asteroids and other minor planets may also have well-differentiated cores depending on their size and history. Jupiter's moons Io and Europa are in many ways sisters of the terrestrial planets and have very substantial cores comprising about a third of their radii. The large asteroid 4 Vesta is likewise believed to have a differentiated structure with a distinct core.
References
- ^ Solomon, S C (2007). "Hot News on Mercury's Core". Science 316 (5825): 702–3. doi:10.1126/science.1142328. PMID 17478710.(Subscription required)
- ^ Luhmann, J. G; Russell, C. T (1997). "Mars: Magnetic Field and Magnetosphere". In Shirley, J. H; Fainbridge, R. W. Encyclopedia of Planetary Sciences. New York: Chapman and Hall. pp. 454–456. http://www-spc.igpp.ucla.edu/personnel/russell/papers/mars_mag/. Retrieved 2012-05-06.
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