Astronomy:Eyeball planet

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Short description: Hypothetical type of tidally locked planet
Example of a "hot" eyeball planet's spatial features, with a scalded side facing the star and water on the other side
Example of a "cold" eyeball planet's spatial features, with an ice shell pierced by an ocean on the side facing the star
Both images are artist's impressions of exoplanets in the TRAPPIST-1 system (TRAPPIST-1d and TRAPPIST-1f).

An eyeball planet[1] is a hypothetical type of tidally locked planet (one side of the planet faces permanently its star), and such tidal locking induces spatial features (for example in the geography or composition of the planet) resembling an eyeball in the case to contain enough liquids.[2] They are terrestrial planets where liquids may be present, in which tidal locking will induce a spatially dependent temperature gradient (the planet will be hotter on the side facing the star and colder on the other side). If this temperature gradient includes temperatures over the freezing point, it could avoid a snowball state or becoming an ice planet,[3] so that there could be areas in which liquid may exist on the surface of the planet to ring- or disk-shaped areas (then the circular liquid or terrestrial region present under the substellar point, would be like the iris of a human eye, being the frozen part like its white or sclera part).

Such planets are further divided into "hot" and "cold" types, depending on which side of the planet the liquid is present. A "hot" eyeball planet is usually closer to its host star, and the centre of the "eye", facing the star (day side), is made of rock while liquid is present on the opposite side (night side). A "cold" eyeball planet, usually farther from the star, will have liquid on the side facing the host star while the rest of its surface is made of ice and rocks by a cold trap effect.[4][5][6]

Because most planetary bodies have a natural tendency to become tidally locked to their host body after enough time has passed, eyeball planets may be common and could host life, particularly in planetary systems orbiting red and brown dwarfs which have lifespans much longer than other main-sequence stars.[7]

Search for life on an eyeball planet in the habitable zone around M dwarf star, a habitable planet with day and night terminator.[8][9][10]

Potential candidates

Kepler-1652b is potentially an eyeball planet.[11] The TRAPPIST-1 system may contain several such planets.[12] According to the observations of the James Webb Space Telescope in 2024, the super-Earth[lower-alpha 1] planet LHS 1140b might either have a thin ice shell with a subsurface ocean or an icy surface covered partially in liquid water, the latter of which is an attribute of "cold" eyeball planet.[13]

See also

References

  1. ↑ Pierrehumbert, Raymond; Gaidos, Eric (2011-05-19). "Hydrogen Greenhouse Planets Beyond the Habitable Zone". The Astrophysical Journal 734 (1): L13. doi:10.1088/2041-8205/734/1/l13. ISSN 2041-8205. Bibcode: 2011ApJ...734L..13P. https://doi.org/10.1088/2041-8205/734/1/l13. 
  2. ↑ Starr, Michelle (5 January 2020). "Eyeball Planets Might Exist, And They're as Creepy as They Sound". ScienceAlert.com. https://www.sciencealert.com/eyeball-planets-might-exist-yep-they-re-exactly-as-creepy-as-they-sound. 
  3. ↑ Bisesi, Erica; Murante, Giuseppe; von Hardenberg, Jost; Caballero, José A.; Maris, Michele; Billi, Daniela; La Rocca, Nicoletta; Silva, Laura (22 August 2026). "Assessing the Climate and Habitability of Tidally Locked Rocky Exoplanets". Astrobiology. doi:10.1177/15311074261479167. PMID 42631591. 
  4. ↑ Pierrehumbert, Raymond; Gaidos, Eric (2011). "Hydrogen Greenhouse Planets Beyond the Habitable Zone". The Astrophysical Journal Letters 734 (1): L13. doi:10.1088/2041-8205/734/1/L13. Bibcode: 2011ApJ...734L..13P. https://doi.org/10.1088/2041-8205/734/1/L13. 
  5. ↑ Raymond, Sean (2020). "Forget Earthlike—We'll First Find Aliens on Eyeball Planets". https://nautil.us/forget-earthlike-well-first-find-aliens-on-eyeball-planets-234567/. 
  6. ↑ "Water Trapped Worlds". 7 June 2023. https://exoplanets.nasa.gov/news/112/water-trapped-worlds/. 
  7. ↑ Raymond, Sean (20 February 2015). "Forget 'Earth-Like'—We'll First Find Aliens on Eyeball Planets". Nautilus. https://nautil.us/forget-earth_likewell-first-find-aliens-on-eyeball-planets-235308/. 
  8. ↑ "Exoplanetary 'Terminator Zones' Have Potential to Suppert Alien Life, Study Suggests". 2023-03-20. https://www.sci.news/astronomy/exoplanetary-terminator-zones-11756.html. 
  9. ↑ "Terminator Zones on Harsh Planets May Sustain Life in an Endless Twilight". 2023-03-17. https://www.sciencealert.com/terminator-zones-on-harsh-planets-may-sustain-life-in-an-endless-twilight. 
  10. ↑ Terminator Habitability: The Case for Limited Water Haitability on M-Dwarf Planets. March 2023.
  11. ↑ Tasker, Elizabeth (7 September 2017). The Planet Factory: Exoplanets and the Search for a Second Earth. Bloomsbury Publishing. ISBN 978-1-4729-1775-1. https://books.google.com/books?id=nflQDQAAQBAJ. 
  12. ↑ Anders, Charlie Jane (13 February 2019). "The Bizarre Planets That Could Be Humanity's New Homes" (in en). https://www.theatlantic.com/science/archive/2019/02/space-colonies-on-tidally-locked-planets/582661/. 
  13. ↑ "Habitable Zone Exoplanet LHS 1140b is Probably Snowball or Water World" (in en-US). 9 July 2024. https://www.sci.news/astronomy/habitable-zone-explanet-lhs-1140b-13083.html. 

Notes

  1. ↑ The mass range of super-Earths is disputed.



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