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HD 219134 b (or HR 8832 b) is one of at least five exoplanets orbiting HD 219134, a main-sequence star in the constellation of Cassiopeia.[3][1][4][5] HD 219134 b has a size of about 1.6 REarth, and a density of 6.4 g/cm3 and orbits at 21.25 light-years away.[3] The exoplanet was initially detected by the instrument HARPS-N of the Italian Telescopio Nazionale Galileo via the radial velocity method and subsequently observed by the Spitzer telescope as transiting in front of its star.[3][4] The exoplanet has a mass of about 4.5 times that of Earth and orbits its host star every three days.[3] In 2017, it was found that the planet likely hosts an atmosphere.

HD 219134 b
An artist's impression of the hot rocky exoplanet HD 219134 b.
Discovery
Discovery siteHARPS-N of the Telescopio Nazionale Galileo
Discovery date30 July 2015
Detection method
radial velocity method (HARPS-N)
Orbital characteristics
Semi-major axis
0.038764 (± 0.0047)[1] AU
Eccentricity0 (fixed)[1]
Orbital period (sidereal)
3.092926 (± 0.0004)[1] d
Inclination85.058 ± 0.08[1]
StarHD 219134
Physical characteristics
Mean radius
1.602±0.055[2] REarth
Mass4.74 (± 0.19)[1] MEarth
Mean density
6.36 (± 0.72)[1] g cm−3
Surface gravity
1.847 +0.213
−0.19 g
Temperature1,015 K (742 °C; 1,367 °F)

    Characteristics



    Mass, radius and temperature


    HD 219134 b is a super-Earth, an exoplanet with a radius and mass bigger than Earth, but smaller than that of the ice giants Neptune and Uranus. Using both the radial velocity and transit method, both its mass and radius have been well determined, allowing for accurate modelling of the planet's composition. HD 219134 b has a radius of 1.602 REarth and a mass of 4.74 MEarth, giving it a density of about 6.4 g/cm3 and 1.85 times the gravity of Earth. This is consistent with a rocky, Earth-like composition. This is relatively unusual, as most planets of ≥1.6 REarth are expected to be rich in volatile materials, such as water and gas. Despite its Earth-like composition, the planet's equilibrium temperature is around 1,015 K (742 °C; 1,367 °F), far too hot for liquid water or life. Depending on the amount of cloud cover in the atmosphere of HD 219134 b, the actual temperature may be somewhat lower, but nowhere near the range for liquid water.

    Zooming in on the exoplanet HD 219134 b
    (00:53; animation; 30 July 2015).

    Host star


    The planet orbits a (K-type) star named HD 219134, orbited by a total of five to seven planets. The star has a mass of 0.81 M☉ and a radius of 0.778 R☉. It has a temperature of 4699 K and is about 11.0 billion years old, making it one of the oldest stars. In comparison, the Sun is 4.6 billion years old[6] and has a temperature of 5778 K.[7]

    The star's apparent magnitude, or how bright it appears from Earth's perspective, is 5. It can be seen with the naked eye.


    Orbit


    HD 219134 b orbits its host star with about 28% of the Sun's luminosity with an orbital period of 3 days and an orbital radius of about 0.03 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU).


    Atmosphere


    In 2017, it was predicted that HD 219134 b and HD 219134 c likely have atmospheres that are secondary in nature, based on the compositions of the planets and the potential for atmospheric escape. For HD 219134 b, the predicted atmosphere was calculated to reach a height of about 0.18 REarth (~1,150 km), below the predicted height of a primordial hydrogen atmosphere (0.28 REarth). This would indicate a secondary atmosphere produced by processes like volcanic activity and evaporation of volatile materials. However, the composition of volatile materials on HD 219134 b and c could not be accurately determined, yet it is believed that the former has a very thin gaseous envelope, far thinner than those of Uranus and Neptune.[8]


    See also



    References


    1. Motalebi, F.; et al. (2015). "The HARPS-N Rocky Planet Search, I. HD 219134b: A transiting rocky planet in a multi-planet system at 6.5 pc from the Sun" (PDF). Astronomy & Astrophysics. 584: A72. arXiv:1507.08532. Bibcode:2015A&A...584A..72M. doi:10.1051/0004-6361/201526822.
    2. Gillon, Michaël; et al. (2017). "Two massive rocky planets transiting a K-dwarf 6.5 parsecs away". Nature Astronomy. 1 (3). 0056. arXiv:1703.01430. Bibcode:2017NatAs...1E..56G. doi:10.1038/s41550-017-0056.
    3. Chou, Felicia; Clavin, Whitney (30 July 2015). "NASA's Spitzer Confirms Closest Rocky Exoplanet". NASA. Retrieved 31 July 2015.
    4. "PIA19832: Location of Nearest Rocky Exoplanet Known". NASA. 30 July 2015. Retrieved 30 July 2015.
    5. "HD 219134". exoplanetarchive.ipac.caltech.edu.
    6. Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
    7. Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
    8. Dorn, Caroline; Heng, Kevin; Gillon, M.; Lovis, C.; Segransan, D.; Buchhave, L. A.; Demory, B. O.; Malavolta, L.; Dressing, C. D.; Sasselov, D.; Rice, K.; Charbonneau, D.; Collier Cameron, A.; Latham, D.; Molinari, E.; Pepe, F.; Affer, L.; Bonomo, A. S.; Cosentino, R.; Dumusque, X.; Figueira, P.; Fiorenzano, A. F. M.; Gettel, S.; Harutyunyan, A.; Haywood, R. D.; Johnson, J.; Lopez, E.; Lopez-Morales, M.; Mayor, M.; et al. (2018). "Secondary Atmospheres on HD 219134 b and C". The Astrophysical Journal. 853 (1): 64. arXiv:1711.07745. Bibcode:2018ApJ...853...64D. doi:10.3847/1538-4357/aa9c80.



    На других языках

    [de] HD 219134 b

    HD 219134 b ist ein Exoplanet, der den rund 21 Lichtjahre von der Sonne entfernten Hauptreihenstern HR 8832 (auch HD 219134) im Sternbild Kassiopeia umkreist. Er ist der innerste von bis zu sechs[5]  – bekannten Planeten im Planetensystem des Sterns.
    - [en] HD 219134 b

    [es] HD 219134 b

    HD 219134 b (o HR 8832 b) es uno de los siete exoplanetas orbitando a HR 8832, una estrella de secuencia principal en la constelación de Casiopea en julio de 2015, es una super Tierra HD 219134 b, con una medida de aproximadamente 1.6 Radios de la Tierra, y una densidad de 6g/cm3, fue reportado como el planeta rocoso más cercano a la Tierra, a 21.25 años luz de distancia.1 El exoplaneta fue inicialmente detectado por el instrumento HARPS-N en Italia con el Telescopio Nazionale Galileo vía el método de velocidad radial y posteriormente observado por el telescopio Spitzer transitando delante de su estrella.1 2 El exoplaneta tiene una masa de aproximadamente 4.5 veces la de la Tierra y órbita su estrella madre cada tres días.1

    [ru] HD 219134 b

    HD 219134 b (Глизе 892 b, HR 8832 b) — одна из семи экзопланет у звезды Глизе 892 в созвездии Кассиопеи.


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