Iron planet

Short description: Type of terrestrial planet

Comparison of sizes of planets with different compositions

An iron planet is a type of planet that consists primarily of an iron-rich core with little or no mantle. Mercury is the largest celestial body of this type in the Solar System (as the other terrestrial planets are silicate planets), but larger iron-rich exoplanets are called super-Mercuries.

Iron is the sixth most abundant element in the universe by mass after hydrogen, helium, oxygen, carbon, and neon.

## Contents

* 1 Origin
* 2 Characteristics
* 3 Candidates
* 4 See also
* 5 References

## Origin

Iron-rich planets may be the remnants of normal metal/silicate rocky planets whose rocky mantles were stripped away by giant impacts. Some are thought to consist of diamond fields. Current planet formation models predict iron-rich planets will form in close-in orbits or orbiting massive stars where the protoplanetary disk presumably consists of iron-rich material.[1]

## Characteristics

Iron-rich planets are smaller and denser than other types of planets of comparable mass.[2] Such planets would have no plate tectonics or strong magnetic field as they cool rapidly after formation. These planets are not like Earth.[1] Since water and iron are unstable over geological timescales, wet iron planets in the goldilocks zone may be covered by lakes of iron carbonyl and other exotic volatiles rather than water.[3]

In science fiction, such a planet has been called a "Cannonball".[4]

## Candidates

An extrasolar planet candidate that may be composed mainly of iron is Kepler-974b.[5]

A super-Mercury candidate is GJ 367b.[6]

The star HD 23472 is orbited by two super-Mercuries.[7]

HD 137496 b is a dense hot super-Mercury.[8]

LHS 3844 b is potentially an Fe-rich super-Mercury.[9]

## See also

* Dwarf planet
* Extrasolar planet
* Terrestrial planet

## References

1. ↑ 1.0 1.1 "Characteristics of Terrestrial Planets" by John Chambers, from "The Great Planet Debate: Science as Process", August 14–16, 2008, The Johns Hopkins University Applied Physics Laboratory Kossiakoff Center, Laurel, MD. http://gpd.jhuapl.edu/abstracts/abstractFiles/chambers_abstract.pdf
2. ↑ "All Planets Possible - Astrobiology Magazine". 30 September 2007. http://www.astrobio.net/pressrelease/2476/all-planets-possible.
3. ↑ "Big Planets: Super-Earths in Science Fiction" by Stephen Baxter, JBIS Vol 67, No 03 (March 2014), p.108
4. ↑ Gillett, Stephen L. (1996). Ben Bova. ed. World-Building. Cincinnati, Ohio: Writer's Digest Books. p. 173. ISBN 158297134X. https://archive.org/details/worldbuildingsci00gill.
5. ↑ Rappaport, Saul; Sanchis-Ojeda, Roberto; Rogers, Leslie A.; Levine, Alan; Winn, Joshua N. (19 April 2018). "The Roche Limit for Close-orbiting Planets: Minimum Density, Composition Constraints, and Application to the 4.2 hr Planet KOI 1843.03". The Astrophysical Journal Letters 773 (1): L15. doi:10.1088/2041-8205/773/1/L15. Bibcode: 2013ApJ...773L..15R. http://stacks.iop.org/2041-8205/773/i=1/a=L15. Retrieved 19 April 2018.
6. ↑ Goffo, Elisa et al. (2023). "Company for the Ultra-high Density, Ultra-short Period Sub-Earth GJ 367 b: Discovery of Two Additional Low-mass Planets at 11.5 and 34 Days". The Astrophysical Journal Letters 955 (1): L3. doi:10.3847/2041-8213/ace0c7. Bibcode: 2023ApJ...955L...3G.
7. ↑ Barros, S. C. C. et al. (2022). "HD 23472: A multi-planetary system with three super-Earths and two potential super-Mercuries". Astronomy & Astrophysics 665: A154. doi:10.1051/0004-6361/202244293. Bibcode: 2022A&A...665A.154B.
8. ↑ Azevedo Silva, T. et al. (2022). "The HD 137496 system: A dense, hot super-Mercury and a cold Jupiter". Astronomy & Astrophysics 657: A68. doi:10.1051/0004-6361/202141520. Bibcode: 2022A&A...657A..68A.
9. ↑ Kane, Stephen R.; Roettenbacher, Rachael M.; Unterborn, Cayman T.; Foley, Bradford J.; Hill, Michelle L. (2020). "A Volatile-poor Formation of LHS 3844b Based on Its Lack of Significant Atmosphere". The Planetary Science Journal 1 (2): 36. doi:10.3847/PSJ/abaab5. Bibcode: 2020PSJ.....1...36K.

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Exoplanetology

* Planet
* Definition
* IAU
* Planetary science

Main topics|

* Exoplanet
* Methods of detecting exoplanets
* Planetary system

Sizes
and types|

| Terrestrial|

* Carbon planet
* Coreless planet
* Desert planet
* Dwarf planet
* Ice planet
* Iron planet
* Lava planet
* Mega-Earth
* Ocean planet
* Sub-Earth
* Super-Earth

|

Gaseous|

* Eccentric Jupiter
* Gas dwarf
* Helium planet
* Hot Jupiter
* Hot Neptune
* Ice giant
* Mini-Neptune
* Super-Neptune
* Super-Jupiter

Other types|

* Brown dwarf
* Chthonian planet
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* Planetesimal
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Formation
and evolution|

* Accretion
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Systems|

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Host stars|

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Detection|

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Habitability|

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Catalogues|

* Catalog of Nearby Habitable Systems
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Lists|

* Exoplanetary systems
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Other|

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* Planets in science fiction
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Exoplanet search projects

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Ground-based|

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Space missions|

| Past|

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* detected exoplanets

|

Current|

* Gaia (2013–present)
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* TESS (2018–present)

Planned|

* CHEOPS (2019)
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* ARIEL (2028)
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Proposed|

* ATLAST
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* HabEx
* HDST
* LUVOIR
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* New Worlds Mission
* OST
* PEGASE

Cancelled|

* Darwin
* EChO
* Eddington
* Space Interferometry Mission
* Terrestrial Planet Finder

* Detection methods
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* Lists of exoplanets
* nearest

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