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Kepler-277c (also known by its Kepler Objects of Interest designation KOI-1215.02) is the third most massive and second-largest rocky planet ever discovered, with a mass about 64 times that of Earth. Discovered in 2014 by the Kepler Space Telescope, Kepler-277c is a Neptune-sized exoplanet with a very high mass and density for an object of its radius, suggesting a composition made mainly of rock with some amounts of water. Along with its sister planet, Kepler-277b, the planet's mass was determined using transit-timing variations (TTVs).

Characteristics

Size and temperature

Kepler-277c was detected using the transit method and TTVs, allowing for both its mass and radius to be determined to some level. It is approximately 3.36 R_🜨, close to the size of Neptune. At that radius, most planets should be gaseous Mini-Neptunes with no solid surface. However, the mass of Kepler-277c is extremely high for its size. Transit-timing variations indicate a planetary mass of about 64.2 M_E, close to Saturn's mass at 95.16 M_E. The planet has a density of approximately 9.33 g/cm and about 5.7 times the surface gravity of Earth. Such a high density for an object of this size implies that, like its sister planet, Kepler-277c is an enormous rock-based planet with a small portion of its mass as water. It is currently the third most massive and second largest terrestrial planet ever discovered, behind Kepler-277b in mass and PSR J1719-1438 b in both radius and mass. Due to its proximity to its host star, Kepler-277c is quite hot with an equilibrium temperature of about 745 K (472 °C; 881 °F), hot enough to melt certain metals.

Orbit

Kepler-277c orbits close to its host star, with one orbit lasting 33.006 days. Its semi-major axis, or average distance from the parent object, is about 0.209 AU. For comparison, the planet Mercury takes 88 days to orbit the Sun at a distance of 0.38 AU. At this distance, Kepler-277c is very hot and most likely tidally locked to its host star. It is close to a 1:2 resonance with Kepler-277b, which orbits at an average distance of about 0.136 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 , and an unknown age. For comparison, the Sun has a temperature of 5778 K, a metallicity of 0.00 , 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

• Mega-Earth
• Kepler-277b

References

1. ^ "Kepler-277 c CONFIRMED PLANET OVERVIEW PAGE". NASA Exoplanet Archive. Retrieved 2018-01-20.
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.
3. ^ "PHL's calculators". Archived from the original on 2019-06-02. Retrieved 2018-01-21.
4. "Kepler-277".
5. "A planet made of diamond".

• Exoplanets discovered in 2014
• Transiting exoplanets
• Exoplanets discovered by the Kepler space telescope
• Lyra
• Mega-Earths