TRAPPIST-1g
{{short description|Earth-size exoplanet orbiting TRAPPIST-1}}
{{Use dmy dates|date=February 2017}}
{{Infobox planet
| name = TRAPPIST-1g
| image = TRAPPIST-1g artist impression 2018.png
| caption = Artist's impression of TRAPPIST-1g. (February 2018)
| discoverer = Michaël Gillon et al.
| discovery_site = Spitzer Space Telescope
| discovered = 22 February 2017
| discovery_method = Transit
| apsis = astron
| aphelion =
| perihelion =
| semimajor = {{val|0.04683|0.00040|ul=AU}}
| eccentricity = {{val|0.00208|0.00058}}
| period = {{val|12.352446|0.000054|ul=d}}
| inclination = {{val|89.742|0.012|u=deg}}
| arg_peri = {{val|191.34|13.83|u=deg}}
| star = TRAPPIST-1
| mean_radius = {{val|1.129|0.015|0.013|ul=Earth radius}}
| mass = {{val|1.321|0.038|ul=Earth mass}}
| density = {{val|5.042|0.136|0.158|ul=g/cm3}}
| surface_grav = {{val|1.035|0.026}} g
{{val|10.15|0.25|ul=m/s2}}
| single_temperature = Teq: {{val|197.3|1.9|ul=K}} ({{cvt|197.3|K|C F|disp=out}})
}}
TRAPPIST-1g, also designated as 2MASS J23062928-0502285 g and K2-112 g, is an exoplanet orbiting around the ultra-cool dwarf star TRAPPIST-1, located {{convert|40.7|ly|pc|lk=on|abbr=off}} away from Earth in the constellation Aquarius. It was one of four new exoplanets to be discovered orbiting the star in 2017 using observations from the Spitzer Space Telescope.{{cite web |url=http://spaceref.com/astronomy/temperate-earth-sized-planets-found-in-extraordinarily-rich-planetary-system-trappist-1.html |title=Temperate Earth-Sized Planets Found in Extraordinarily Rich Planetary System TRAPPIST-1 |date=22 February 2017 |publisher=SpaceRef |access-date=11 February 2017 }}{{Dead link|date=November 2024 |bot=InternetArchiveBot |fix-attempted=yes }} The exoplanet is within the optimistic habitable zone of its host star.{{Cite press release |title=NASA telescope reveals largest batch of Earth-size, habitable-zone planets around single star |date=21 February 2017 |url=https://exoplanets.nasa.gov/news/1419/nasa-telescope-reveals-largest-batch-of-earth-size-habitable-zone-planets-around-single-star/ |access-date=22 February 2017 |newspaper=Exoplanet Exploration: Planets Beyond our Solar System}} It 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.
The second-most-distant-known planet in its system, TRAPPIST-1g is a planet somewhat larger than Earth and with a similar density, meaning it is likely a rocky planet.
Physical characteristics
= Mass, radius, and temperature =
TRAPPIST-1g has a radius of {{val|1.129|ul=Earth radius}} and a mass of {{val|1.321|ul=Earth mass}}, with a density only slightly less than Earth's, though initial estimates suggested its density was only 4.186 g/cm3, about 76% of Earth's. Based on mass-radius calculations and its distant location relative to its host star (0.047 AU) and the fact that the planet only receives 25.2% of the stellar flux that Earth does, the planet is likely covered by a thick ice envelope if an atmosphere does not exist.{{Cite journal |last1=Quick |first1=Lynnae C. |last2=Roberge |first2=Aki |last3=Tovar Mendoza |first3=Guadalupe |last4=Quintana |first4=Elisa V. |last5=Youngblood |first5=Allison A. |name-list-style=and |date=2023-10-04 |title=Prospects for Cryovolcanic Activity on Cold Ocean Planets |journal=The Astrophysical Journal |volume=956 |issue=29 |page=29 |bibcode=2023ApJ...956...29Q |doi=10.3847/1538-4357/ace9b6 |doi-access=free}}
=Atmosphere=
TRAPPIST-1g could have a global water ocean or an exceptionally thick steam atmosphere. According to a simulation of magma ocean-atmosphere interaction, TRAPPIST-1g is likely to retain a large fraction of primordial steam atmosphere during the initial stages of evolution, and therefore today is likely to possess a thick ocean covered by atmosphere containing hundreds of bars of abiotic oxygen.{{citation|arxiv=2008.09599|title=Magma Ocean Evolution of the TRAPPIST-1 Planets|year=2021|last1=Barth|first1=Patrick|last2=Carone|first2=Ludmila|last3=Barnes|first3=Rory|last4=Noack|first4=Lena|last5=Mollière|first5=Paul|last6=Henning|first6=Thomas|journal=Astrobiology|volume=21|issue=11|pages=1325–1349|doi=10.1089/ast.2020.2277|pmid=34314604|bibcode=2021AsBio..21.1325B|s2cid=221246323}}
On 31 August 2017, astronomers at the Hubble Space Telescope reported the first evidence of possible water content on the TRAPPIST-1 exoplanets.
= 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 2,550 K. The age of the star is about {{val|7.6|2.2}} billion years old.{{cite journal |last1=Burgasser |first1=Adam J. |last2=Mamajek |first2=Eric E. |name-list-style=and |date=17 August 2017 |title=On the Age of the TRAPPIST-1 System |journal=The Astrophysical Journal |language=en |volume=845 |issue=2 |pages=110 |arxiv=1706.02018 |bibcode=2017ApJ...845..110B |doi=10.3847/1538-4357/aa7fea |s2cid=119464994 |doi-access=free}} In comparison, the Sun is 4.6 billion years old and has a temperature of 5,778 K. 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 considerably less metal content than the Sun. Its luminosity (L☉) is 0.05% of that of the Sun.
The star's apparent magnitude, or how bright it appears from Earth's perspective, is 18.8, too dim to be seen with the naked eye.
= Orbit =
TRAPPIST-1g orbits its host star with an orbital period of about 12.354 days and an orbital radius of about 0.0451 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU). This is in the outer limit of TRAPPIST-1's theoretical habitable zone. The orbit of TRAPPIST-1g has an eccentricity of 0.00208, much lower than that of Earth and the lowest in its system. Its orbit varies by only about 41,000 kilometers (compared to about 5 million km for Earth), meaning the planet's climate is likely very stable. It is in a 3:2 orbital resonance with TRAPPIST-1h and a 3:4 resonance with TRAPPIST-1f.
See also
References
{{reflist|refs=
{{cite news |author=PTI |title=First evidence of water found on TRAPPIST-1 planets - The results suggest that the outer planets of the system might still harbour substantial amounts of water. This includes the three planets within the habitable zone of the star, lending further weight to the possibility that they may indeed be habitable. |url=http://indianexpress.com/article/technology/science/first-evidence-of-water-found-on-trappist-1-planets-4827977/ |date=4 September 2017 |work=The Indian Express |access-date=4 September 2017 }}
}}
{{TRAPPIST-1}}
{{Exoplanet}}
{{2017 in space}}
{{Aquarius (constellation)}}
{{Portal bar|Astronomy|Biology|Space}}
{{DEFAULTSORT:TRAPPIST-1g}}
Category:Exoplanets discovered in 2017
Category:Near-Earth-sized exoplanets
Category:Near-Earth-sized exoplanets in the habitable zone
Category:Transiting exoplanets