Kepler-70b

Kepler-70b
Exoplanet List of exoplanets

Artist's impression of Kepler-70b (top left) orbiting very close to its star (center). The small bright point to the right is planet "c".
Parent star
Star Kepler-70
Constellation Cygnus
Right ascension (α) 19h 45m 25s
Declination (δ) +41° 5′ 34″
Apparent magnitude (mV) 14.87 [1]
Distance3849 ± 310 ly
(1180 ± 95 [2] pc)
Spectral type sdB
Mass (m) 0.496 ± 0.002 M☉
Radius (r) 0.203 ± 0.007 R☉
Temperature (T) 27730 ± 270 K
Orbital elements
Semi-major axis(a) 0.006 AU
(0.897 Gm)
Orbital period(P) 0.2401 ± 0.000004 d
Inclination (i) ~65°
Physical characteristics
Minimum mass(m sin i)0.440 M⊕
Radius(r)0.759 [note 1][2] R⊕
Density(ρ)5500 kg m−3
Stellar flux(F⊙)6.4x105 ⊕
Temperature (T) >6000 K
Discovery information
Discovery date 12/22/2011 (announced) [3]
Discoverer(s) Charpinet et al.[3]
Discovery method Reflection/emission modulations
Discovery site Kepler telescope
Discovery status Published
Other designations
Database references
Extrasolar Planets
Encyclopaedia		data
SIMBADdata
Exoplanet Archivedata
Open Exoplanet Cataloguedata

Kepler-70b (formerly known as its Kepler Object of Interest designation KOI-55.01;[3] sometimes listed as KOI-55 b) is an exoplanet discovered orbiting the subdwarf B star (sdB) Kepler-70. It orbits its host along with another planet, Kepler-70c, both of which orbit very close to their host star. Kepler-70b completes one orbit around its star in just 5.76 hours, one of the shortest orbital periods of any exoplanetary system yet discovered, only second to the exoplanet PSR 1719-14 b with a period of 2.2 hours. It is also the hottest known exoplanet as of mid-2017, with a surface temperature of several thousand Kelvin.[4] Its density is 5500 kg/m3 which is not much different from Earth.[5]

Characteristics

Mass, radius and temperature

Kepler-70b is likely a rocky exoplanet with a mass of 0.44 M⊕ and a radius of 0.76 R⊕. It has a surface temperature of several thousand Kelvin, one of the hottest known surface temperatures on any exoplanet. While the precise temperature is not known, is expected to be hotter then the surface of the Sun.[4]

Orbit

The exoplanet has an orbit period shorter than any exoplanet known to date, with an orbital period of 5.76 hours (345 minutes). This comes in second to the exoplanet PSR 1719-14 b, which, coincidentally, orbits a stellar remnant, much like the planets of Kepler-70.

Host star

The host star, Kepler-70 (also formally known as KOI-55, 2MASS J19452546+4105339 or KIC 5807616), is a subdwarf B-type star that has left its red giant stage of its lifetime – according to the Extrasolar Planets Encyclopedia – about 18.4 million years ago.[2] It has a surface temperature of 27730 ± 270 K, nearly 6 times as hot as the surface temperature of the Sun, which has a surface temperature of 5778 K.[6] The star has a mass of 0.496 M☉ and a radius of 0.203 R☉[note 2] It is expected to become a white dwarf in the future, after fusing the remaining helium in its core, and shrink in size to around the size of the Earth.

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14.87. Therefore, Kepler-70 is too dim to be seen with the naked eye.

Encounters

Kepler-70c passes 240,000 kilometres (150,000 mi) away from Kepler-70b during their closest approach, possibly causing tidal forces against each other. This is currently the closest recorded approach between planets.

Cultural impact

According to the main author of the paper in Nature which announced the discovery of the two planets, Stephane Charpinet, the two planets "probably plunged deep into the star’s envelope during the red giant phase, but survived.”[7] However, this is not the first sighting of planets orbiting a post-red giant star - numerous pulsar planets have been observed, but no planet has been found with such a short period around any star, whether or not on the main sequence.

Origins

The two planets were most likely gas giants which spiraled inward toward their host star, which subsequently became a red giant, vaporizing much of the planets except for parts of their solid cores, which are now orbiting the Subdwarf B star.[7]

See also

Notes

  1. ↑ Assuming an albedo of 0.1.
  2. ↑ These statistics were very likely higher then what they were today when it was a red giant, the estimated mass of Kepler-70 before it became a subdwarf, would probably have been around 0.89–0.95 M☉.

References

  1. ↑ "SIMBAD query result". SIMBAD. Retrieved 1 January 2012.
  2. 1 2 3 "Notes for Planet KOI-55 b". Extrasolar Planet Database. Archived from the original on 19 January 2012. Retrieved 1 January 2012.
  3. 1 2 3 Charpinet, S.; et al. (December 21, 2011), "A compact system of small planets around a former red-giant star", Nature, 480 (7378): 496–499, Bibcode:2011Natur.480..496C, PMID 22193103, doi:10.1038/nature10631
  4. 1 2 S. Charpinet et al.: A compact system of small planets around a former red-giant star, Nature 480, 496–499, supplementary material (online)
  5. ↑ "Kepler mission discoveries". Retrieved 23 May 2013.
  6. ↑ Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
  7. 1 2 "Two More Earth-Sized Planets Discovered by Kepler, Orbiting Former Red Giant Star". Universe Today. Retrieved 1 January 2012.

Coordinates: 19h 45m 25s, +41° 5′ 34″

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