Kepler-90h

Kepler-90h (also known by its Kepler Object of Interest designation KOI-351.01) is an exoplanet orbiting within the habitable zone of the early G-type main sequence star Kepler-90, the outermost of eight such planets discovered by NASA's Kepler spacecraft. It is located about 2,840 light-years (870 parsecs), from Earth in the constellation Draco. The exoplanet was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured.

Kepler-90h
Illustration of the Kepler-90 system compared to the inner solar system. Kepler-90h is the outermost planet of the Kepler-90 system.
Discovery
Discovered byKepler spacecraft
Discovery dateNovember 12, 2013[1]
Transit[2]
Orbital characteristics
1.01 ± 0.11 AU (151,000,000 ± 16,000,000 km)[1]
Eccentricity0.0 ≤ 0.001[1]
331.60 ± 0.00037[1] d
Inclination89.6 ± 1.3[2]
StarKepler-90
Physical characteristics
Mean radius
1.01 (± 0.09)[3] RJ
Mass0.639±0.016[4] MJ
Temperature292 K (19 °C; 66 °F)[2]

    Characteristics

    Physical characteristics

    Kepler-90h is a gas giant with no solid surface. Its equilibrium temperature is 292 K (19 °C; 66 °F).[3] It is around 1.2 times as massive and around 1.01 times as large as Jupiter.[3] This makes it very similar to Jupiter, in terms of mass and radius.[3]

    Orbit

    Kepler-90h orbits its host star about every 331.6 days at a distance of 1.01 astronomical units, very similar to Earth's orbital distance from the Sun (which is 1 AU).[3]

    Habitability
    See also: Habitability of natural satellites

    Kepler-90h resides in the circumstellar habitable zone of the parent star. The exoplanet, with a radius of 1.01 RJ, is too large to be rocky, and because of this the planet itself may not be habitable. Hypothetically, large enough moons, with a sufficient atmosphere and pressure, may be able to support liquid water and potentially life.

    For a stable orbit the ratio between the moon's orbital period Ps around its primary and that of the primary around its star Pp must be < 1/9, e.g. if a planet takes 90 days to orbit its star, the maximum stable orbit for a moon of that planet is less than 10 days.[5][6] Simulations suggest that a moon with an orbital period less than about 45 to 60 days will remain safely bound to a massive giant planet or brown dwarf that orbits 1 AU from a Sun-like star.[7] In the case of Kepler-90h, this would be practically the same to have a stable orbit.

    Tidal effects could also allow the moon to sustain plate tectonics, which would cause volcanic activity to regulate the moon's temperature[8][9] and create a geodynamo effect which would give the satellite a strong magnetic field.[10]

    To support an Earth-like atmosphere for about 4.6 billion years (the age of the Earth), the moon would have to have a Mars-like density and at least a mass of 0.07 M⊕.[11] One way to decrease loss from sputtering is for the moon to have a strong magnetic field that can deflect stellar wind and radiation belts. NASA's Galileo's measurements hints large moons can have magnetic fields; it found that Jupiter's moon Ganymede has its own magnetosphere, even though its mass is only 0.025 M⊕.[7]

    Host star

    The planet orbits a (G-type) Kepler-90, its host star. The star is 1.2 times as massive as the Sun and is 1.2 times as large as the Sun. It is estimated to be 2 billion years old, with a surface temperature of 6080 K. In comparison, the Sun is about 4.6 billion years old[12] and has a surface temperature of 5778 K.[13]

    The star's apparent magnitude, or how bright it appears from Earth's perspective, is 14.[14] It is too dim to be seen with the naked eye, which typically can only see objects with a magnitude around 6 or less.[15]

    Discovery

    In 2009, NASA's Kepler spacecraft was completing observing stars on its photometer, the instrument it uses to detect transit events, in which a planet crosses in front of and dims its host star for a brief and roughly regular period of time. In this last test, Kepler observed 50000 stars in the Kepler Input Catalog, including Kepler-90; the preliminary light curves were sent to the Kepler science team for analysis, who chose obvious planetary companions from the bunch for follow-up at observatories. Observations for the potential exoplanet candidates took place between 13 May 2009 and 17 March 2012. After observing the respective transits, which for Kepler-90h occurred roughly every 331 days (its orbital period), it was eventually concluded that a planetary body was responsible for the periodic 331-day transits. The discovery, was announced on November 12, 2013.[16]

    Artist's impression of the planets of Kepler-90 exoplanetary system compared to the eight planets of the Solar System. Kepler-90h is depicted on the far right, being the largest and outermost planet of the Kepler-90 system.

    See also

    References
    1. "TEPcat: Kepler-90h". www.astro.keele.ac.uk. 31 December 2013. Retrieved 3 January 2013.
    2. "Planet Kepler-90 h". exoplanet.eu. Retrieved 3 January 2014.
    3. "Kepler-90 h". NASA Exoplanet Archive. Retrieved 15 July 2016.
    4. Kepler-90: Giant transit-timing variations reveal a super-puff, 2020, arXiv:2011.08515
    5. Kipping, David (2009). "Transit timing effects due to an exomoon". Monthly Notices of the Royal Astronomical Society. 392: 181–189. arXiv:0810.2243. Bibcode:2009MNRAS.392..181K. doi:10.1111/j.1365-2966.2008.13999.x.
    6. Heller, R. (2012). "Exomoon habitability constrained by energy flux and orbital stability". Astronomy & Astrophysics. 545: L8. arXiv:1209.0050. Bibcode:2012A&A...545L...8H. doi:10.1051/0004-6361/201220003. ISSN 0004-6361.
    7. Andrew J. LePage. "Habitable Moons:What does it take for a moon — or any world — to support life?". SkyandTelescope.com. Retrieved 11 July 2011.
    8. Glatzmaier, Gary A. "How Volcanoes Work – Volcano Climate Effects". Retrieved 29 February 2012.
    9. "Solar System Exploration: Io". Solar System Exploration. NASA. Retrieved 29 February 2012.
    10. Nave, R. "Magnetic Field of the Earth". Retrieved 29 February 2012.
    11. "In Search Of Habitable Moons". Pennsylvania State University. Retrieved 11 July 2011.
    12. Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
    13. Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
    14. "Planet Kepler-90 b". Extrasolar Planets Encyclopaedia. Retrieved 26 April 2018.
    15. Sinnott, Roger W. (19 July 2006). "What's my naked-eye magnitude limit?". Sky and Telescope. Retrieved 17 April 2019.
    16. Schmitt, Joseph R.; Wang, Ji; Fischer, Debra A.; Jek, Kian J.; Moriarty, John C.; Boyajian, Tabetha S.; Schwamb, Megan E.; Lintott, Chris; Smith, Arfon M.; Parrish, Michael; Schawinski, Kevin; Lynn, Stuart; Simpson, Robert; Omohundro, Mark; Winarski, Troy; Goodman, Samuel J.; Jebson, Tony; Lacourse, Daryll (2013). "Planet The First Kepler Eight Planet Candidate System from the Kepler Archival Data", Astrophysical Journal, p. 23.

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