TRAPPIST-1d

TRAPPIST-1d
Exoplanet List of exoplanets

Artist's impression of the rocky planet TRAPPIST-1d (foreground) orbiting its host star (upper right).
Parent star
Star TRAPPIST-1
Constellation Aquarius
Right ascension (α) 23h 06m 29.283s
Declination (δ) –05° 02′ 28.59″
Apparent magnitude (mV) 18.8[1]
Distance39.5 ± 1.3 ly
(12.1 ±0.4[1] pc)
Spectral type M8V[1][2]
Mass (m) 0.08 (± 0.009)[1] M☉
Radius (r) 0.117 (± 0.004)[1] R☉
Temperature (T) 2550.0 (± 55.0)[1] K
Metallicity [Fe/H] 0.04 (± 0.08)[3]
Age >0.5[1] Gyr
Physical characteristics
Mass(m)~1.7 M⊕
Radius(r)1.163 (± 0.065)[1] R⊕
Stellar flux(F⊙)0.02+0.98
−0.0 ⊕
Temperature (T) 200 K (−73 °C; −100 °F)
Orbital elements
Semi-major axis(a) 0.08 (± 0.06)[1] AU
Eccentricity (e) 0.0[1]
Orbital period(P) 18.202+54
−14[1] d
Inclination (i) 89.87 (± 0.1)[1]°
Other designations
2MASS J23062928-0502285 d, 2MASSI J2306292-050227 d, 2MASSW J2306292-050227 d, 2MUDC 12171 d
Discovery information
Discovery date May 2, 2016
Discoverer(s)
Discovery method Transit
Discovery status Published
Database references
Extrasolar Planets
Encyclopaedia		data
SIMBADdata
Exoplanet Archivedata
Open Exoplanet Cataloguedata

TRAPPIST-1d (also known as 2MASS J23062928-0502285 d) is an exoplanet, likely rocky, orbiting within or slightly outside the habitable zone around the ultracool dwarf star TRAPPIST-1 approximately 40 light-years (12.1 parsecs, or nearly 3.7336×1014 km) away from Earth in the constellation of Aquarius. 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.

Characteristics

Mass, radius, and temperature

TRAPPIST-1d is an Earth-sized exoplanet, meaning it has a mass and radius close to that of Earth. It has an equilibrium temperature of 200 K (−73 °C; −100 °F).[4] It has a radius of 1.16 R⊕. The mass has not yet been estimated, but based on its size, a mass of around 1.7 M⊕ is possible.

Host star

The planet orbits an (M-type) ultracool dwarf star named TRAPPIST-1. The star has a mass of 0.08 M☉ and a radius of 0.11 R☉. It has a temperature of 2550 K and is at least 500 million years old. In comparison, the Sun is 4.6 billion years old[5] and has a temperature of 5778 K.[6] The star is metal-rich, with a metallicity ([Fe/H]) of 0.04, or 109% the solar amount. This is particularly odd as such low-mass stars near the boundary between brown dwarfs and hydrogen-fusing stars should be expected to have considerly less metals then the Sun. Its luminosity (L☉) is 0.04% of that of the Sun.

The star's apparent magnitude, or how bright it appears from Earth's perspective, is 18.8. Therefore, it is too dim to be seen with the naked eye.

Orbit

TRAPPIST-1d orbits its host star with an orbital period of around 18 days (with a large margin of error) and an orbital radius of about 0.08 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU).

Habitability

Artist's impression of the TRAPPIST-1 system, viewed from near the surface of planet "d".

The exoplanet was announced to be either orbiting within or slightly outside of the habitable zone of its parent star, the region where, with the correct conditions and atmospheric properties, liquid water may exist on the surface of the planet. TRAPPIST-1d has a radius of around 1.16 R⊕, so it is likely rocky. Its host star is a red ultracool dwarf, with only about 8% of the mass of the Sun (close to the boundary between brown dwarfs and hydrogen-fusing stars). As a result, stars like TRAPPIST-1 have the ability to live up to 4–5 trillion years, 400–500 times longer than the Sun will live.[7] Because of this ability to live for long periods of time, it is likely TRAPPIST-1 will be one of the last remaining stars when the Universe is much older than it is now, when the gas needed to form new stars will be exhausted, and the remaining ones begin to die off.

The planet is very likely tidally locked, with one side of its hemisphere permanently facing towards the star, while the opposite side shrouded in eternal darkness. However, between these two intense areas, there would be a sliver of habitability – called the terminator line, where the temperatures may be suitable (about 273 K (0 °C; 32 °F)) for liquid water to exist. Additionally, a much larger portion of the planet may be habitable if it supports a thick enough atmosphere to transfer heat to the side facing away from the star.

During formation of the system, it is possible that water loss during its first few million years of existence occurred.[8] This was likely due to photoevaporation.

TRAPPIST-1d may be the only exoplanet in the system to have kept enough water to remain habitable depending on its initial content. The two innermost planets, b and c, probably lost up to four times the amount of Earth's oceans, depending on their composition.[8]

Discovery

A team of astronomers headed by Michaël Gillon of the Institut d’Astrophysique et Géophysique at the University of Liège[9] in Belgium used the TRAPPIST (Transiting Planets and Planetesimals Small Telescope) telescope at the La Silla Observatory in the Atacama desert, Chile,[10] to observe TRAPPIST-1 and search for orbiting planets. By utilising transit photometry, they discovered three Earth-sized planets orbiting the dwarf star; the innermost two are tidally locked to their host star while the outermost appears to lie either within the system's habitable zone or just outside of it.[11][12] The team made their observations from September to December 2015 and published its findings in the May 2016 issue of the journal Nature.[10][13]

See also

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 "Planet TRAPPIST-1 d". Exoplanet.eu. Retrieved 2016-05-06.
  2. ↑ Costa, E.; Mendez, R.A.; Jao, W.-C.; Henry, T.J.; Subasavage, J.P.; Ianna, P.A. (August 4, 2006). "The Solar Neighborhood. XVI. Parallaxes from CTIOPI: Final Results from the 1.5 m Telescope Program" (PDF). The Astronomical Journal. The American Astronomical Society. 132 (3): 1234. Bibcode:2006AJ....132.1234C. doi:10.1086/505706.
  3. ↑ https://www.eso.org/public/archives/releases/sciencepapers/eso1615/eso1615a.pdf
  4. ↑ http://www.openexoplanetcatalogue.com/planet/TRAPPIST-1d/
  5. ↑ Fraser Cain (16 September 2008). "How Old is the Sun?". Universe Today. Retrieved 19 February 2011.
  6. ↑ Fraser Cain (15 September 2008). "Temperature of the Sun". Universe Today. Retrieved 19 February 2011.
  7. ↑ Adams, Fred C.; Laughlin, Gregory; Graves, Genevieve J. M. "Red Dwarfs and the End of the Main Sequence". Gravitational Collapse: From Massive Stars to Planets. Revista Mexicana de Astronomía y Astrofísica. pp. 46–49. Bibcode:2004RMxAC..22...46A.
  8. 1 2 Bolmont, Emeline; Selsis, Franck; Owen, James E.; Ribas, Ignasi; Raymond, Sean N.; Leconte, Jérémy; Gillon, Michael (2016). "Water loss from Earth-sized planets in the habitable zones of ultracool dwarfs: Implications for the planets of TRAPPIST-1". arXiv:1605.00616Freely accessible [astro-ph.EP].
  9. ↑ "AGO - Department of Astrophysics, Geophysics and Oceanography".
  10. 1 2 "Could these newly-discovered planets orbiting an ultracool dwarf host life?". The Guardian. 2 May 2016.
  11. ↑ "Three Potentially Habitable Worlds Found Around Nearby Ultracool Dwarf Star - Currently the best place to search for life beyond the Solar System". eso.org. Retrieved 2016-05-02.
  12. ↑ "Three New Planets Are the Best Bets for Life". Popular Mechanics. 2016-05-02. Retrieved 2016-05-02.
  13. ↑ Gillon, Michaël; Jehin, Emmanuël; et al. (2016). "Temperate Earth-sized planets transiting a nearby ultracool dwarf star". Nature. 533 (7602): 221–224. doi:10.1038/nature17448.

Coordinates: 23h 06m 29.283s, −05° 02′ 28.59″

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