KOI-2700b

KOI-2700b
Discovery
Discovered by	Saul Rappaport et al.
Discovery date	March 3, 2014 (candidate); December 3, 2017 (confirmed)
Detection method	Transit method
Designations
Alternative names	KOI 2700.01; KIC 8639908 b; UCAC4 674-076576 b; 2MASS J19480085+4446303 b ;
Orbital characteristics
Semi-major axis	0.0150(4) AU
Orbital period (sidereal)	0.910022(5) d
Inclination	85.1–88.6°
Star	KIC 8639908
Physical characteristics
Mean radius	<1.06 R🜨, ≲0.3 R🜨; ≤0.871 R🜨
Mass	<0.86 ME, ≲0.03 ME
Temperature	1,850 K (1,580 °C; 2,870 °F) (equilibrium)

KOI-2700b is a confirmed^[2] exoplanet that orbits the K-type main-sequence star KIC 8639908, located about 1,608 light-years (493 parsecs)^[a] distant. It orbits the star very rapidly, with an orbital period of 0.91 days (22 hours), at a distance of just 0.0150 AU (2,240,000 km). 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.^[1] 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.^[7] 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.^[5]

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.^[1]^[7]

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 R_☉).^[8]

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 M_E 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 M_E) and radius (1.06 R_🜨) are likely far larger than the actual values, and the planet may be closer to the Moon (0.27 R_🜨^[9]) in size.^[1] Indeed, further research indicates that its true radius likely lies somewhere between 0.1–0.3 R_🜨, smaller than Mercury (0.36 R_🜨).^[8]

The planet is losing mass at a roughly estimated rate of around 2 lunar masses (0.0246 M_E^[9]) per billion years, that is 6,000 metric tons per second,^[1]^[2] and not below 0.007 M_E per 1 Gyr.^[5]

Host star

The planet orbits a faint 15th-magnitude star named KIC 8639908, which is located at right ascension 19^h 00^m 03.14^s and declination 40° 13′ 14.7″ (J2000),^[1] in the northern constellation of Lyra. It is currently in the main sequence^[10] with a spectral type of K5,^[11] a mass of 0.546 M_☉, and a radius of 0.540 R_☉.^[5] At an effective temperature of 4,296 K (4,023 °C; 7,273 °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,^[12] meaning it only has one-fifth the iron content of the Sun.

Similarities have been noted between it and Kepler-1520, a K4V-type^[13] star that hosts another disintegrating exoplanet with a comet-like tail.^[1]

Footnotes

^ Calculated from parallax of 2.0275 mas,^[4] using the formula $d{\text{ (pc)}}\approx 1/p{\text{ (arcsec)}}.$

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Rappaport, Saul; et al. (3 March 2014). "KOI-2700b—A PLANET CANDIDATE WITH DUSTY EFFLUENTS ON A 22 hr ORBIT". The Astrophysical Journal. 784 (1). American Astronomical Society: 40. arXiv:1312.2054. Bibcode:2014ApJ...784...40R. doi:10.1088/0004-637x/784/1/40. ISSN 0004-637X.
^ ^a ^b ^c ^d ^e Garai, Z (2018). "Light-curve analysis of KOI 2700b: the second extrasolar planet with a comet-like tail". Astronomy & Astrophysics. 611. EDP Sciences: A63. arXiv:1712.07461. Bibcode:2018A&A...611A..63G. doi:10.1051/0004-6361/201629676. ISSN 0004-6361.
^ ^a ^b "KIC 8639908 Overview". NASA Exoplanet Archive. Retrieved 13 October 2024.
^ ^a ^b ^c "KOI-2700". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 13 October 2024.
^ ^a ^b ^c ^d ^e van Lieshout, R.; et al. (2014). "Dusty tails of evaporating exoplanets". Astronomy & Astrophysics. 572. EDP Sciences: A76. doi:10.1051/0004-6361/201424876. ISSN 0004-6361.
^ Sanchis-Ojeda, R.; et al. (14 October 2015). "THE K2-ESPRINT PROJECT. I. DISCOVERY OF THE DISINTEGRATING ROCKY PLANET K2-22b WITH A COMETARY HEAD AND LEADING TAIL". The Astrophysical Journal. 812 (2). American Astronomical Society: 112. arXiv:1504.04379. Bibcode:2015ApJ...812..112S. doi:10.1088/0004-637x/812/2/112. ISSN 1538-4357.
^ ^a ^b Booth, Richard A; et al. (31 October 2022). "Dust formation in the outflows of catastrophically evaporating planets". Monthly Notices of the Royal Astronomical Society. 518 (2). Oxford University Press (OUP): 1761–1775. doi:10.1093/mnras/stac3121. ISSN 0035-8711.
^ ^a ^b Gaidos, E; et al. (8 March 2019). "Monitoring of the D doublet of neutral sodium during transits of two 'evaporating' planets". Monthly Notices of the Royal Astronomical Society. 485 (3). Oxford University Press (OUP): 3876–3886. doi:10.1093/mnras/stz693. ISSN 0035-8711.
^ ^a ^b Williams, David R. (2 February 2006). "Moon Fact Sheet". NASA/National Space Science Data Center. Archived from the original on 23 March 2010. Retrieved 31 December 2008.
^ Veras, Dimitri; et al. (7 June 2016). "Dynamical mass and multiplicity constraints on co-orbital bodies around stars". Monthly Notices of the Royal Astronomical Society. 461 (2). Oxford University Press (OUP): 1413–1420. doi:10.1093/mnras/stw1324. ISSN 0035-8711.
^ "KOI-2700 b". ExoKyoto. Kyoto University. Retrieved 14 October 2024.
^ Bodman, Eva H. L.; et al. (1 October 2018). "Inferring the Composition of Disintegrating Planet Interiors from Dust Tails with Future James Webb Space Telescope Observations". The Astronomical Journal. 156 (4). American Astronomical Society: 173. arXiv:1808.07043. Bibcode:2018AJ....156..173B. doi:10.3847/1538-3881/aadc60. ISSN 0004-6256.
^ "Planet Kepler-1520 b". Extrasolar Planets Encyclopaedia. Retrieved 14 October 2024.

[n1-7] Calculated from parallax of 2.0275 mas,^[4] using the formula $d{\text{ (pc)}}\approx 1/p{\text{ (arcsec)}}.$

[Rappaport2014-1] ^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ Rappaport, Saul; et al. (3 March 2014). "KOI-2700b—A PLANET CANDIDATE WITH DUSTY EFFLUENTS ON A 22 hr ORBIT". The Astrophysical Journal. 784 (1). American Astronomical Society: 40. arXiv:1312.2054. Bibcode:2014ApJ...784...40R. doi:10.1088/0004-637x/784/1/40. ISSN 0004-637X.

[Garai2018-2] Garai, Z (2018). "Light-curve analysis of KOI 2700b: the second extrasolar planet with a comet-like tail". Astronomy & Astrophysics. 611. EDP Sciences: A63. arXiv:1712.07461. Bibcode:2018A&A...611A..63G. doi:10.1051/0004-6361/201629676. ISSN 0004-6361.

[archive-3] "KIC 8639908 Overview". NASA Exoplanet Archive. Retrieved 13 October 2024.

[SIMBAD-4] "KOI-2700". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 13 October 2024.

[vanLieshout2014-5] van Lieshout, R.; et al. (2014). "Dusty tails of evaporating exoplanets". Astronomy & Astrophysics. 572. EDP Sciences: A76. doi:10.1051/0004-6361/201424876. ISSN 0004-6361.

[Sanchis-Ojeda2015-6] Sanchis-Ojeda, R.; et al. (14 October 2015). "THE K2-ESPRINT PROJECT. I. DISCOVERY OF THE DISINTEGRATING ROCKY PLANET K2-22b WITH A COMETARY HEAD AND LEADING TAIL". The Astrophysical Journal. 812 (2). American Astronomical Society: 112. arXiv:1504.04379. Bibcode:2015ApJ...812..112S. doi:10.1088/0004-637x/812/2/112. ISSN 1538-4357.

[Booth2022-8] Booth, Richard A; et al. (31 October 2022). "Dust formation in the outflows of catastrophically evaporating planets". Monthly Notices of the Royal Astronomical Society. 518 (2). Oxford University Press (OUP): 1761–1775. doi:10.1093/mnras/stac3121. ISSN 0035-8711.

[Gajdos2019-9] Gaidos, E; et al. (8 March 2019). "Monitoring of the D doublet of neutral sodium during transits of two 'evaporating' planets". Monthly Notices of the Royal Astronomical Society. 485 (3). Oxford University Press (OUP): 3876–3886. doi:10.1093/mnras/stz693. ISSN 0035-8711.

[Moon-10] Williams, David R. (2 February 2006). "Moon Fact Sheet". NASA/National Space Science Data Center. Archived from the original on 23 March 2010. Retrieved 31 December 2008.

[Veras2016-11] Veras, Dimitri; et al. (7 June 2016). "Dynamical mass and multiplicity constraints on co-orbital bodies around stars". Monthly Notices of the Royal Astronomical Society. 461 (2). Oxford University Press (OUP): 1413–1420. doi:10.1093/mnras/stw1324. ISSN 0035-8711.

[Kyoto-12] "KOI-2700 b". ExoKyoto. Kyoto University. Retrieved 14 October 2024.

[Bodman2018-13] Bodman, Eva H. L.; et al. (1 October 2018). "Inferring the Composition of Disintegrating Planet Interiors from Dust Tails with Future James Webb Space Telescope Observations". The Astronomical Journal. 156 (4). American Astronomical Society: 173. arXiv:1808.07043. Bibcode:2018AJ....156..173B. doi:10.3847/1538-3881/aadc60. ISSN 0004-6256.

[EPE1520-14] "Planet Kepler-1520 b". Extrasolar Planets Encyclopaedia. Retrieved 14 October 2024.

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