K2-18

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Star
K2-18
Position of K2-18 in the constellation "Leo"
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation lion
Right ascension 11 h 30 m 14.52 s
declination + 07 ° 35 ′ 18.3 ″
Apparent brightness (13.50 ± 0.05) mag
Typing
rel. Brightness
(G-band) 		(12.42 ± 0.01) mag
rel. Brightness
(J-band) 		(9.76 ± 0.03) mag
Known exoplanets 1
B − V color index +1.51 
Spectral class M2.5 V
Astrometry
Radial velocity (0.654 ± 0.001) km / s
parallax (26.27 ± 0.05)  mas
distance (124.1 ± 0.3)  Lj
(38.07 ± 0.08)  pc
Proper movement 
Rec. Share: (−80.38 ± 0.08)  mas / a
Dec. portion: (−133.14 ± 0.06)  mas / a
Physical Properties
Dimensions (0.36 ± 0.05)  M ☉
radius (0.41 ± 0.04)  R ☉
Effective temperature (3460 ± 40)  K.
Metallicity [Fe / H] (+0.12 ± 0.16)
Rotation time 39.63 ± 0.50 d
Other names
and catalog entries
2MASS catalog 2MASS J11301450 + 0735180 [1]
Other names K2-18, EPIC 201912552

Template: Infobox Star / Maintenance / MagGTemplate: Infobox Star / Maintenance / MagJ

K2-18 is a red dwarf at a distance of about 124 light years from Earth.

In the habitable zone of this star, an exoplanet in the format of a so-called super - earth or mini-Neptune was discovered in 2015 with the help of the Kepler space telescope, which was named K2-18b . 2019 based could of measurements of the Hubble Space Telescope , as well as additional data of the Kepler and Spitzer space telescopes , water vapor in the atmosphere are detected on the planet, making it the first Exoplanet with known water sources, which could also be in liquid form.

planet

The planet K2-18 b is about 0.14  AU away from the central star and orbits it in 33 days. Since the star is considerably smaller than the sun, the planet is in the habitable zone with an equilibrium temperature of 284 ± 15 K . Mass and radius could be determined due to the fact that the planet could be detected using the transit method as well as the radial velocity method . It has about 7 to 10 times the mass of the earth and 2.7 times the radius of the earth. This results in a significantly lower density of 2.3 g / cm³ compared to earth . Due to its high mass and low density, it will differ significantly from it in many properties and possibly be more comparable to small gas planets such as Uranus and Neptune. In addition to water vapor, hydrogen and helium were also detected in the exoplanet's atmosphere . The atmosphere should therefore be significantly denser than that of the earth. Correspondingly, it could be assumed that the detected water vapor condenses and falls as rain; however, it probably warms up again in lower atmospheric layers and the drops evaporate . A high pressure is expected on the planet's surface, several million times higher than that on Earth . Because of these extreme pressures, the other conditions on the surface will certainly differ considerably from those on earth. In addition, there is the strong cosmic radiation usually emanating from red dwarfs (see also red dwarf planets ).

Exoplanet K2-18 b (artist's impression)

Web links

Individual evidence

  1. ↑ a b c d e f g K2-18. In: SIMBAD . Center de Données astronomiques de Strasbourg , accessed on September 11, 2019 .
  2. ↑ a b c d e f K2-18. NASA Exoplanet Archives , accessed September 11, 2019 .
  3. ↑ a b Paula Sarkis et al .: The CARMENES Search for Exoplanets around M Dwarfs: A Low-mass Planet in the Temperate Zone of the Nearby K2-18 . In: The Astronomical Journal . 155, No. 6, 2018. arxiv : 1805.00830 . bibcode : 2018AJ .... 155..257S . doi : 10.3847 / 1538-3881 / aac108 .
  4. ↑ Benjamin T. Montet, Timothy D. Morton, Daniel Foreman-Mackey, John Asher Johnson, David W. Hogg, Brendan P. Bowler, David W. Latham: Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation . In: The Astrophysical Journal . 809, No. 1, 2015. arxiv : 1503.07866 . bibcode : 2015ApJ ... 809 ... 25M . doi : 10.1088 / 0004-637X / 809/1/25 .
  5. ↑ a b Angelos Tsiaras, Ingo P. Waldmann, Giovanna Tinetti, Jonathan Tennyson, Sergey N. Yurchenko: Water vapor in the atmosphere of the habitable-zone eight-Earth-mass planet K2-18 b . In: Nature Astronomy . September. arxiv : 1909.05218 . doi : 10.1038 / s41550-019-0878-9 .
  6. ↑ Researchers find water for the first time on K2-18b. Spiegel Online , accessed September 11, 2019 .
  7. ↑ Detected for the first time - In a life-friendly zone: Researchers find water on super-earth. Retrieved September 11, 2019 .
  8. ^ R. Cloutier, N. Astudillo-Defru, R. Doyon, X. Bonfils, J.-M. Almenara: Confirmation of the radial velocity super-Earth K2-18c with HARPS and CARMENES . In: Astronomy & Astrophysics . tape 621 , January 2019, ISSN  0004-6361 , p. A49 , doi : 10.1051 / 0004-6361 / 201833995 , arxiv : 1810.04731 , bibcode : 2019A & A ... 621A..49C ( aanda.org [accessed September 12, 2019]).
  9. ↑ NASA's Hubble Finds Water Vapor on Habitable-Zone Exoplanet for 1st Time. NASA , accessed September 11, 2019 .
  10. ↑ Discovery! Water Vapor - and Likely Clouds, Rain, Too - Found on Strange Alien Planet. Space.com, accessed September 11, 2019 .