| Discovery | |
|---|---|
| Discovery site | Kepler Space Observatory |
| Discovery date | 2014 |
| Transit | |
| Orbital characteristics | |
| ~0.136 AU | |
| Eccentricity | null[1] |
| 17.324[1] d | |
| Inclination | null[1] |
| Star | Kepler-277 |
| Physical characteristics | |
Mean radius | 2.92 +0.73 −0.63[1] R🜨 |
| Mass | 87.3 +41.7 −39.9[1][2] MEarth |
Mean density | 19.33+39.9 −13.96 g cm−3 |
| 10.24+14.36 −6.68 g | |
| Temperature | 924 K (651 °C; 1,204 °F)[3] |
Kepler-277b (also known by its Kepler Objects of Interest designation KOI-1215.01) is the second most massive and third-largest rocky planet ever discovered, with a mass close to that of Saturn. Discovered in 2014 by the Kepler Space Telescope, Kepler-277b is a sub-Neptune sized exoplanet with a very high mass and density for an object of its radius, suggesting a composition made mainly of rock and iron. Along with its sister planet, Kepler-277c, the planet's mass was determined using transit-timing variations (TTVs).
Characteristics
Size and temperature
Kepler-277b was detected using the transit method and TTVs, allowing for both its mass and radius to be determined to some level. It is approximately 2.92 R🜨, between the size of Earth and Neptune. At that radius, most planets should be gaseous Mini-Neptunes with no solid surface. However, the mass of Kepler-277b is extremely high for its size. Transit-timing variations indicate a planetary mass of about 87.3 MEarth,[1] comparable to Saturn's mass at 95.16 MEarth. The planet has a density of approximately 19.3 g/cm3 and about 10.4 times the surface gravity of Earth. Such a high density for an object of this size implies that, like its sister planet, Kepler-277b is an enormous rock-based planet.[2] It is currently the second most massive and third largest terrestrial planet ever discovered, behind Kepler-277c in radius[4] and PSR J1719−1438 b in both radius and mass.[5] Due to its proximity to its host star, Kepler-277b is quite hot with an equilibrium temperature of about 924 K (651 °C; 1,204 °F),[3] hot enough to melt certain metals.
Internal structure and composition
Models of Kepler-277b's internal structure suggest that it has a very large iron core with an estimated radius of 2.435 R🜨. The core predominantly consists of an allotrope of iron with a face-centered cubic (FCC) crystalline structure. At the innermost region of Kepler-277b's core where pressures reach as high as 37.52 terapascals, iron exists in a body-centered-tetragonal (BCT) and body-centered cubic (BCC) crystalline structure.[6]
Kepler-277b has a relatively thin silicate mantle in comparison to its core. The mantle of Kepler-277b is thought be predominantly composed of ultrahigh-pressure phases of magnesium silicates (MgSiO3). The uppermost mantle of Kepler-277b is thought to consist of olivine, wadsleyite, and ringwoodite while the lower part of Kepler-277b's upper mantle consists of silicate perovskite and post-perovskite.[6]
Orbit
Kepler-277b orbits close to its host star, with one orbit lasting 17.324 days.[1] Its semi-major axis, or average distance from the parent object, is about 0.136 AU. For comparison, the planet Mercury in the Solar System takes 88 days to orbit at a distance of 0.38 AU. At this distance, Kepler-277b is very hot and most likely tidally locked to its host star. It is close to a 2:1 resonance with Kepler-277c, which orbits at an average distance of about 0.209 AU.
Host star
The parent star Kepler-277 is a large yellow star. It is 1.69 R☉ and 1.12 M☉, with a temperature of 5946 K, a metallicity of -0.315 [Fe/H], and an unknown age.[1] For comparison, the Sun has a temperature of 5778 K, a metallicity of 0.00 [Fe/H], and an age of about 4.5 billion years. The large radius in comparison to its mass and temperature suggest that Kepler-277 could be a Subgiant star.
See also
References
- 1 2 3 4 5 6 7 8 "Kepler-277 b CONFIRMED PLANET OVERVIEW PAGE". NASA Exoplanet Archive. Retrieved 2018-01-20.
- 1 2 Xie, Ji-Wei (7 January 2014). "Transit Timing Variation of Near-Resonance Planetary Pairs. Ii. Confirmation of 30 Planets in 15 Multiple-Planet Systems". The Astrophysical Journal Supplement Series. 210 (2): 25. arXiv:1309.2329. Bibcode:2014ApJS..210...25X. doi:10.1088/0067-0049/210/2/25. S2CID 119105092.
- 1 2 "PHL's calculators". Archived from the original on 2019-06-02. Retrieved 2018-01-21.
- ↑ "Kepler-277".
- ↑ "A planet made of diamond".
- 1 2 Futó, P.; et al. (March 2020). Kepler-277 b: A Supermassive Terrestrial Exoplanet in the Kepler-277 Planetary System (PDF). 51st Lunar and Planetary Science Conference. Lunar and Planetary Institute. Bibcode:2020LPI....51.1055F.