KOI-2700b

Template:Use dmy dates Template:Short description Template:Infobox planet KOI-2700b is a confirmed exoplanet that orbits the K-type main-sequence star KIC 8639908, located about Template:ConvertTemplate:Efn distant. It orbits the star very rapidly, with an orbital period of Template:Convert, at a distance of just Template:Convert. 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 Template: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 Template:Earth mass 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 Template:Earth mass) and radius (1.06 Template:Earth radius) are likely far larger than the actual values, and the planet may be closer to the Moon (0.27 Template:Earth radius) in size. Indeed, further research indicates that its true radius likely lies somewhere between 0.1–0.3 Template:Earth radius, smaller than Mercury (0.36 Template:Earth radius).

The planet is losing mass at a roughly estimated rate of around 2 lunar masses (0.0246 Template:Earth mass) per billion years, that is 6,000 metric tons per second, and not below 0.007 Template:Earth mass per 1 Gyr.

Host star

The planet orbits a faint 15th-magnitude star named KIC 8639908, which is located at right ascension Template:RA and declination Template:DEC (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 Template:Solar mass, and a radius of 0.540 Template:Solar radius. At an effective temperature of Template:Convert, 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

• 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)