View source for KOI-2700b

{{use dmy dates|date=October 2024}}
{{Short description|Disintegrating exoplanet}}
{{Infobox planet
| name                     = KOI-2700b
<!-- DISCOVERY           -->
| discovery_ref            = <ref name=Rappaport2014/>
| discoverer               = [[Saul Rappaport]] ''et al.''
| discovered               = March 3, 2014 (candidate)<br>December 3, 2017 (confirmed)<ref name=Garai2018/>
| discovery_method         = [[Transit method]]
<!-- DESIGNATIONS        -->
| alt_names                = 
* [[Kepler object of interest|KOI]] 2700.01<ref name=archive/>
* [[Kepler Input Catalog|KIC]] 8639908 b<ref name=archive/>
* [[USNO CCD Astrograph Catalog|UCAC4]] 674-076576 b<ref name="SIMBAD"/>
* [[2MASS]] J19480085+4446303 b <ref name="SIMBAD"/>
<!-- ORBITAL             -->
| orbit_ref                = 
| apsis                    = astron
| semimajor                = {{val|0.0150|(4)|ul=AU}}<ref name=vanLieshout2014/>
| eccentricity             = 
| period                   = {{val|0.910022|(5)|ul=d}}<ref name=vanLieshout2014/>
| inclination              = 85.1&ndash;88.6°<ref name=Garai2018/>
| semi-amplitude           = 
| star                     = KIC 8639908
<!-- PHYS CHARS          -->
| physical_ref             = 
| mean_radius              = <1.06 {{Earth radius|link=y}}, ≲0.3 {{Earth radius}};<ref name=Rappaport2014/> ≤0.871 {{Earth radius}}<ref name=Garai2018/>
| mass                     = <0.86 {{Earth mass|link=y}}, ≲0.03 {{Earth mass}}<ref name=Rappaport2014/>
| density                  = 
| single_temperature       = {{convert|1850|K|C F}}<ref name=Sanchis-Ojeda2015/> ([[equilibrium temperature|equilibrium]])
<!-- ATMOSPHERE          -->
<!-- NOTES               -->
}}
'''KOI-2700b''' is a confirmed<ref name=Garai2018/> [[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 [[evaporation|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.<ref name=Rappaport2014/> 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.<ref name=Booth2022/> In the case of KOI-2700b, the tail most likely consists of [[fayalite]] (Fe<sub>2</sub>SiO<sub>4</sub>) and/or [[corundum]] (Al<sub>2</sub>O<sub>3</sub>). A composition of pure [[iron]], [[graphite]], or [[silicon carbide]] has been ruled out.<ref name=vanLieshout2014/> 

The tail leaves a distinct print on the [[light curve]]s of the star. Specifically, the dips caused by the [[astronomical transit|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]].<ref name=Rappaport2014/><ref name=Booth2022/>

In addition to the dust tail, a cloud of partially [[ionization|ionized]] [[sodium]] vapor may surround the planet, extending to a size comparable to that of the host star (~0.54 {{Solar radius}}).<ref name=Gajdos2019/>

===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}} is required for the release of detectable amounts of dust, and in all likelihood, planets larger than roughly half the [[Earth radius|radius of Earth]] do not emit a dust tail whatsoever. Thus, the discovery paper points out that the [[Scientific modelling|modelled]] upper limits for the mass (0.86 {{Earth mass}}) 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}}<ref name=Moon/>) in size.<ref name=Rappaport2014/> Indeed, further research indicates that its true radius likely lies somewhere between 0.1&ndash;0.3 {{Earth radius}}, smaller than [[Mercury (planet)|Mercury]] (0.36 {{Earth radius}}).<ref name=Gajdos2019/>

The planet is losing mass at a roughly estimated rate of around 2 [[Moon#Size and mass|lunar mass]]es (0.0246 {{Earth mass}}<ref name=Moon/>) per [[billion years]], that is 6,000 [[metric ton]]s per [[second]],<ref name=Rappaport2014/><ref name=Garai2018/> and not below 0.007 {{Earth mass}} per 1 Gyr.<ref name=vanLieshout2014/>

==Host star==
The planet orbits a faint 15th-[[apparent magnitude|magnitude]] star named KIC 8639908, which is located at [[right ascension]] {{RA|19|00|03.14}} and [[declination]] {{DEC|40|13|14.7}} ([[J2000]]),<ref name=Rappaport2014/> in the northern [[constellation]] of [[Lyra]]. It is currently in the [[main sequence]]<ref name=Veras2016/> with a [[Stellar classification|spectral type]] of K5,<ref name=Kyoto/> a mass of 0.546 {{Solar mass|link=y}}, and a radius of 0.540 {{Solar radius|link=y}}.<ref name=vanLieshout2014/> At an [[effective temperature]] of {{convert|4296|K|C F}}, it radiates 8.9% the [[Solar luminosity|luminosity of the Sun]] from its [[photosphere]]. The star is very metal-poor, possessing a [[metallicity]] of −0.7,<ref name=Bodman2018/> meaning it only has one-fifth the iron content of the [[Sun]].

Similarities have been noted between it and [[Kepler-1520]], a K4V-type<ref name=EPE1520/> star that hosts another disintegrating exoplanet with a comet-like tail.<ref name=Rappaport2014/>

==See also==
* [[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==
{{noteslist|notes=
{{efn|name=n1|Calculated from [[Stellar parallax|parallax]] of 2.0275 [[milliarcsecond|mas]],<ref name=SIMBAD/> using the formula <math>d \text{ (pc)} \approx 1 / p \text{ (arcsec)}.</math>}}
}}
==References==
{{reflist|refs=
<ref name=archive>{{Cite Exoplanet Archive|KIC 8639908|access-date=2024-10-13}}</ref>

<ref name=SIMBAD>{{Cite simbad|title=KOI-2700|access-date=2024-10-13}}</ref>

<ref name=Rappaport2014>{{cite journal | display-authors=1 | last1=Rappaport | first1=Saul | last2=Barclay | first2=Thomas | last3=DeVore | first3=John | last4=Rowe | first4=Jason | last5=Sanchis-Ojeda | first5=Roberto | last6=Still | first6=Martin | title=KOI-2700b—A PLANET CANDIDATE WITH DUSTY EFFLUENTS ON A 22 hr ORBIT | journal=The Astrophysical Journal | publisher=American Astronomical Society | volume=784 | issue=1 | date=2014-03-03 | issn=0004-637X | doi=10.1088/0004-637x/784/1/40 | doi-access=free | page=40| arxiv=1312.2054 | bibcode=2014ApJ...784...40R }}</ref>

<ref name=Gajdos2019>{{cite journal | display-authors=1 | last1=Gaidos | first1=E | last2=Hirano | first2=T | last3=Ansdell | first3=M | title=Monitoring of the D doublet of neutral sodium during transits of two 'evaporating' planets | journal=Monthly Notices of the Royal Astronomical Society | publisher=Oxford University Press (OUP) | volume=485 | issue=3 | date=2019-03-08 | issn=0035-8711 | doi=10.1093/mnras/stz693 | doi-access=free | pages=3876–3886| arxiv=1903.06217 }}</ref>

<ref name=Sanchis-Ojeda2015>{{cite journal | display-authors=1 | last1=Sanchis-Ojeda | first1=R. | last2=Rappaport | first2=S. | last3=Pallè | first3=E. | last4=Delrez | first4=L. | last5=DeVore | first5=J. | last6=Gandolfi | first6=D. | last7=Fukui | first7=A. | last8=Ribas | first8=I. | last9=Stassun | first9=K. G. | last10=Albrecht | first10=S. | last11=Dai | first11=F. | last12=Gaidos | first12=E. | last13=Gillon | first13=M. | last14=Hirano | first14=T. | last15=Holman | first15=M. | last16=Howard | first16=A. W. | last17=Isaacson | first17=H. | last18=Jehin | first18=E. | last19=Kuzuhara | first19=M. | last20=Mann | first20=A. W. | last21=Marcy | first21=G. W. | last22=Miles-Páez | first22=P. A. | last23=Montañés-Rodríguez | first23=P. | last24=Murgas | first24=F. | last25=Narita | first25=N. | last26=Nowak | first26=G. | last27=Onitsuka | first27=M. | last28=Paegert | first28=M. | last29=Eylen | first29=V. Van | last30=Winn | first30=J. N. | last31=Yu | first31=L. | title=THE K2-ESPRINT PROJECT. I. DISCOVERY OF THE DISINTEGRATING ROCKY PLANET K2-22b WITH A COMETARY HEAD AND LEADING TAIL | journal=The Astrophysical Journal | publisher=American Astronomical Society | volume=812 | issue=2 | date=2015-10-14 | issn=1538-4357 | doi=10.1088/0004-637x/812/2/112 | doi-access=free | page=112| arxiv=1504.04379 | bibcode=2015ApJ...812..112S }}</ref>

<ref name=vanLieshout2014>{{cite journal | display-authors=1 | last1=van Lieshout | first1=R. | last2=Min | first2=M. | last3=Dominik | first3=C. | title=Dusty tails of evaporating exoplanets | journal=Astronomy & Astrophysics | publisher=EDP Sciences | volume=572 | year=2014 | issn=0004-6361 | doi=10.1051/0004-6361/201424876 | doi-access=free | page=A76| arxiv=1410.3494 }}</ref>

<ref name=Garai2018>{{cite journal | last=Garai | first=Z | title=Light-curve analysis of KOI 2700b: the second extrasolar planet with a comet-like tail | journal=Astronomy & Astrophysics | publisher=EDP Sciences | volume=611 | year=2018 | issn=0004-6361 | doi=10.1051/0004-6361/201629676 | doi-access=free | page=A63| arxiv=1712.07461 | bibcode=2018A&A...611A..63G }}</ref>

<ref name=EPE1520>{{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}}</ref>

<ref name=Kyoto>{{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}}</ref>

<ref name=Bodman2018>{{cite journal | display-authors=1 | last1=Bodman | first1=Eva H. L. | last2=Wright | first2=Jason T. | last3=Desch | first3=Steven J. | last4=Lisse | first4=Carey M. | title=Inferring the Composition of Disintegrating Planet Interiors from Dust Tails with Future James Webb Space Telescope Observations | journal=The Astronomical Journal | publisher=American Astronomical Society | volume=156 | issue=4 | date=2018-10-01 | issn=0004-6256 | doi=10.3847/1538-3881/aadc60 | doi-access=free | page=173| arxiv=1808.07043 | bibcode=2018AJ....156..173B }}</ref>

<ref name=Veras2016>{{cite journal | display-authors=1 | last1=Veras | first1=Dimitri | last2=Marsh | first2=Thomas R. | last3=Gänsicke | first3=Boris T. | title=Dynamical mass and multiplicity constraints on co-orbital bodies around stars | journal=Monthly Notices of the Royal Astronomical Society | publisher=Oxford University Press (OUP) | volume=461 | issue=2 | date=2016-06-07 | issn=0035-8711 | doi=10.1093/mnras/stw1324 | doi-access=free | pages=1413–1420| arxiv=1606.00440 }}</ref>

<ref name="Moon">{{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}}</ref>

<ref name=Booth2022>{{cite journal | display-authors=1 | last1=Booth | first1=Richard A | last2=Owen | first2=James E | last3=Schulik | first3=Matthäus | title=Dust formation in the outflows of catastrophically evaporating planets | journal=Monthly Notices of the Royal Astronomical Society | publisher=Oxford University Press (OUP) | volume=518 | issue=2 | date=2022-10-31 | issn=0035-8711 | doi=10.1093/mnras/stac3121 | doi-access=free | pages=1761–1775| arxiv=2204.13117 }}</ref>
}}
[[Category:Exoplanets discovered in 2014]]
[[Category:Transiting exoplanets]]
[[Category:Lyra]]
[[Category:Kepler objects of interest]]
[[Category:Exoplanets discovered by the Kepler space telescope]]
[[Category:Sub-Earth exoplanets]]