KOI-2700b
{{use dmy dates|date=October 2024}}
{{Short description|Disintegrating exoplanet}}
{{Infobox planet
| name = KOI-2700b
| discoverer = Saul Rappaport et al.
| discovered = March 3, 2014 (candidate)
December 3, 2017 (confirmed)
| discovery_method = Transit method
| alt_names =
| orbit_ref =
| apsis = astron
| semimajor = {{val|0.0150|(4)|ul=AU}}
| eccentricity =
| period = {{val|0.910022|(5)|ul=d}}
| semi-amplitude =
| star = KIC 8639908
| physical_ref =
| mean_radius = <1.06 {{Earth radius|link=y}}, ≲0.3 {{Earth radius}}; ≤0.871 {{Earth radius}}
| mass = <0.86 {{Earth mass|sym=y|link=y}}, ≲0.03 {{Earth mass|sym=y}}
| density =
| single_temperature = {{convert|1850|K|C F}} (equilibrium)
}}
KOI-2700b is a confirmed exoplanet that orbits the K-type main-sequence star KIC 8639908, located about {{convert|1608|ly|pc|abbr=off}}{{efn|name=n1}} distant. It orbits the star very rapidly, with an orbital period of {{convert|0.91|d|h|abbr=off}}, at a distance of just {{convert|0.0150|AU|km|abbr=on}}. This, along with its small mass, is causing it to evaporate and lose material, which leaves a comet-like tail of dust stretching from the planet.
Physical properties
=Dust tail=
The most noteworthy characteristic of the planet is a tail of dust that follows it, spanning about a quarter of its orbit. The tail is formed from escaped material from the surface, much like that of a comet, providing a rare insight into the composition and formation of exoplanets. In the case of KOI-2700b, the tail most likely consists of fayalite (Fe2SiO4) and/or corundum (Al2O3). A composition of pure iron, graphite, or silicon carbide has been ruled out.
The tail leaves a distinct print on the light curves of the star. Specifically, the dips caused by the transiting planet change in depth from transit to transit, and are asymmetrical, first falling sharply and then recovering more gradually. In addition, the star appears to brighten slightly before transit, which can be explained by the dust grains causing forward scatter.
In addition to the dust tail, a cloud of partially ionized sodium vapor may surround the planet, extending to a size comparable to that of the host star (~0.54 {{Solar radius}}).
=Mass and radius=
The precise mass and radius of the planet are unknown, but it is expected to be very small and rocky, as a mass of ≲0.03 {{Earth mass|sym=y}} is required for the release of detectable amounts of dust, and in all likelihood, planets larger than roughly half the radius of Earth do not emit a dust tail whatsoever. Thus, the discovery paper points out that the modelled upper limits for the mass (0.86 {{Earth mass|sym=y}}) and radius (1.06 {{Earth radius}}) are likely far larger than the actual values, and the planet may be closer to the Moon (0.27 {{Earth radius}}) in size. Indeed, further research indicates that its true radius likely lies somewhere between 0.1–0.3 {{Earth radius}}, smaller than Mercury (0.36 {{Earth radius}}).
The planet is losing mass at a roughly estimated rate of around 2 lunar masses (0.0246 {{Earth mass|sym=y}}) per billion years, that is 6,000 metric tons per second, and not below 0.007 {{Earth mass|sym=y}} per 1 Gyr.
Host star
The planet orbits a faint 15th-magnitude star named KIC 8639908, which is located at right ascension {{RA|19|00|03.14}} and declination {{DEC|40|13|14.7}} (J2000), in the northern constellation of Lyra. It is currently in the main sequence with a spectral type of K5, a mass of 0.546 {{Solar mass|link=y}}, and a radius of 0.540 {{Solar radius|link=y}}. At an effective temperature of {{convert|4296|K|C F}}, it radiates 8.9% the luminosity of the Sun from its photosphere. The star is very metal-poor, possessing a metallicity of −0.7, meaning it only has one-fifth the iron content of the Sun.
Similarities have been noted between it and Kepler-1520, a K4V-type star that hosts another disintegrating exoplanet with a comet-like tail.
See also
- Catastrophically evaporating planet
- List of smallest exoplanets
- Ultra-short period planets
- Other disintegrating rocky planets with comet-like tails:
- Kepler-1520b (KIC 12557548 b)
- K2-22b (EPIC 201637175 b)
- BD+05 4868 (TIC 466376085 b)
Footnotes
References
{{reflist|refs=
{{Cite Exoplanet Archive|KIC 8639908|access-date=2024-10-13}}
{{Cite simbad|title=KOI-2700|access-date=2024-10-13}}
{{cite encyclopedia|title=Planet Kepler-1520 b|encyclopedia=Extrasolar Planets Encyclopaedia|url=https://exoplanet.eu/catalog/kepler_1520_b--1179/|access-date=2024-10-14}}
{{cite web|title=KOI-2700 b|work=ExoKyoto|publisher=Kyoto University|url=https://www.exoplanetkyoto.org/exohtml/KOI-2700_b.html|access-date=2024-10-14}}
{{cite web |last=Williams |first=David R. |title=Moon Fact Sheet |publisher=NASA/National Space Science Data Center |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html |date=February 2, 2006 |access-date=December 31, 2008 |url-status=live |archive-url=https://web.archive.org/web/20100323165650/http://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html |archive-date=March 23, 2010}}
}}
Category:Exoplanets discovered in 2014
Category:Transiting exoplanets
Category:Kepler objects of interest
Category:Exoplanets discovered by the Kepler space telescope