(All Information From Wikipedia)
TRAPPIST-1 is an ultra-cool red dwarf star in the constellation Aquarius with a planetary system of seven known planets. Its mass is about 9% of the
Sun's, with a radius slightly larger than the planet Jupiter and a surface temperature of about 2,566 K (2,293 °C). The star is 40.7 light-years (12.5 pc) from the Sun and is estimated to be 7.6 billion years old, making it older than the Solar System.
The star was discovered in 2000 and its planets were discovered in 2016 and 2017 based on observations from the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) at La Silla Observatory in Chile and numerous other telescopes. Following the initial discovery of two terrestrial planets in orbit around TRAPPIST-1, a data "anomaly" was found to be caused by five more planets. Their orbital periods – the time each planet takes to orbit the star – range roughly from 1.5 to 19 Earth days. The gravity of TRAPPIST-1's planets holds them in orbital resonance, which could have existed since the formation of the planetary system. The planets are likely to be tidally locked to TRAPPIST-1, which would force them to keep the same side facing their host star at all times.
As many as four of the planets (d, e, f, g) are potentially hospitable to life, having orbits in the star's habitable zone. There is no clear evidence that any of the planets have an atmosphere and it is unclear whether the planets could retain an atmosphere given TRAPPIST-1's radiation emission. Given their low densities, the planets may consist of large amounts of volatile material.
Star
True-color illustration of the Sun (left) next to TRAPPIST-1 (right). Notice that TRAPPIST-1 is darker, redder, and smaller than the Sun. TRAPPIST-1 is in the constellation Aquarius, five degrees south of the celestial equator. The name is a reference to the TRAPPIST project that discovered the first two exoplanets around the star; other designations for the star are 2MUCD 12171, 2MASS J23062928–0502285, EPIC 246199087, K2-112, SPECULOOS-1 and TRAPPIST-1a. TRAPPIST-1 is a very close star, parallax measurements have yielded a distance of 40.662 ± 0.036 light-years (12.467 ± 0.011 pc) from the Solar System, and has a large proper motion. There is no evidence that TRAPPIST-1 has companion stars.
TRAPPIST-1 is a red dwarf, a cold star with a smaller mass than the Sun. Red dwarfs include the spectral types M and K, and TRAPPIST-1 belongs to class M8.0±0.5. Its mass is about 8.98% of the Sun's mass, only barely sufficient mass to allow nuclear fusion to take place. Slightly larger than Jupiter, its radius is 11.9% that of the Sun. While denser than the Sun, TRAPPIST-1 has an unusually low density for its kind of star. Its luminosity is only about 0.055% that of the Sun and is mostly infrared radiation; it is not variable and there is no evidence for a solar cycle. TRAPPIST-1 has an effective temperature of 2,566 K (2,293 °C; 4,159 °F), making it the coldest known star (As of 2022) to host planets. Dwarf stars like TRAPPIST-1 are over ten times more common than Sun-like stars and these stars are more likely to host small planets than Sun-like stars, although systems with multiple planets like TRAPPIST-1 might not be widespread.
Stars like TRAPPIST-1 are so cold that clouds consisting of condensates and dust can form in their photosphere. Patterns of TRAPPIST-1's radiation indicate the existence of dust, which is distributed evenly across the star's surface. The faint radiation at short wavelengths that TRAPPIST-1 emits has been measured with the XMM-Newton satellite and in later surveys, although with low precision.
Rotation period and age
In 2016, TRAPPIST-1's rotational period was first measured as 1.40±0.05 Earth days, a typical period for M dwarfs. Measurements by the Kepler space telescope published in 2017 showed that the star may instead rotate about every 3.295±0.003 Earth days, though that may constitute the rotation period of active regions rather than stellar rotation according to Miles-Páez et al. (2019). As of 2020, discrepancies between rotational data obtained by the Spitzer Space Telescope and Kepler space telescope remain unexplained. The rotation axis of TRAPPIST-1 might be slightly offset from that of its planets.
Based on a combination of techniques, an age of about 7.6±2.2 billion years has been established for TRAPPIST-1, making it older than the Solar System. TRAPPIST-1 is expected to shine for ten trillion years – about 700 times longer than the present age of the Universe – whereas the Sun will leave its main sequence (run out of hydrogen) in a few billion years.
Activity
Numerous photospheric features have been detected on TRAPPIST-1. Possible faculae (bright spots) have been observed by the Kepler space telescope and Spitzer Space Telescope, but some of TRAPPIST-1's bright spots may be too large to count as faculae. A correlation between bright spots and flare activity has been found. The photospheric features may introduce inaccuracies in measurements of its planets. The effect of bright spots on the luminosity of TRAPPIST-1 may lead to the planets' densities being underestimated by 8+20
−7 percent, and to incorrect estimates of their water content. The mean intensity of TRAPPIST-1's magnetic field is about 600 G although many of its properties cannot be directly measured. This intense magnetic field is driven by chromospheric activity and may be capable of trapping coronal mass ejections.
Stars lose mass through the stellar wind. Garraffo et al. (2017) computed the mass loss of TRAPPIST-1 to be about 3×10−14 solar masses per year, about 1.5 times that of the Sun, while Dong et al. (2018) simulated the observed properties of TRAPPIST-1 with a mass loss of 4.1×10−15 solar masses per year. The stellar wind properties of TRAPPIST-1 are not precisely determined.
Planetary system
TRAPPIST-1's seven planets – TRAPPIST-1b, 1c, 1d, 1e, 1f, 1g, and 1h – are named in alphabetic order according to their discovery and distance from TRAPPIST-1 Each takes between 1.5 to 19 Earth days to orbit the star, and orbits at distances of about 0.011 astronomical units (1,700,000 km) to 0.059 astronomical units (8,900,000 km). All of them are much closer to TRAPPIST-1 than Mercury is to the Sun, making TRAPPIST-1 a very compact planetary system. No evidence of additional planets around TRAPPIST-1 has been found, and the existence of gas planets more than 4.6 times as massive as Jupiter at an orbital period of 1 year, and of a planet more massive than 1.6 Jupiter masses at 5 years can be ruled out. A hypothetical eighth planet would be designated TRAPPIST-1i, and its orbital properties have been predicted under the assumption that it orbits exterior to planet h and is part of the planetary resonance. Kral et al. (2018) did not detect any comets around TRAPPIST-1, and Marino et al. (2020) found no evidence of a Kuiper belt although it is questionable that a Solar System-like belt around TRAPPIST-1 would be visible from Earth. Observations with the Atacama Large Millimeter Array telescope have found no evidence of a circumstellar dust disk, implying that if it does exist it is of low mass. It is thought that most of the solid material around TRAPPIST-1 was converted into planets.
The inclinations of the orbits relative to the system's ecliptic are less than 1°, making TRAPPIST-1 the flattest planetary system in the NASA Exoplanet Archive. They are highly circular, with minimal eccentricities, and well-aligned with the spin axis of TRAPPIST-1. The planets all orbit in the same plane and, from the perspective of the Solar System, move past ("transit") TRAPPIST-1 during their orbit and frequently pass in front of each other.
TRAPPIST-1b, also designated as 2MASS J23062928-0502285 b, is a mainly rocky, Venus-like exoplanet orbiting around the ultra-cool dwarf star
TRAPPIST-1, located approximately 40 light-years (12 parsecs) away from Earth in the constellation of Aquarius. The planet was detected using the transit method, where a planet dims the host star's light as it passes in front of it. It was first announced on May 2, 2016, and between 2017 and 2018, more studies were able to refine its physical parameters.
The planet is about the same mass as Earth but about 12% larger. Its relatively low density, along with spectroscopic observations, has confirmed an extremely thick and hot atmosphere. Observations published in 2018 showed that the atmosphere of TRAPPIST-1b was much larger than that of Earth or Venus, as well as being very hot and potentially rich in CO2. More recent modeling studies have suggested the planet is too hot to allow the formation of sulfuric acid clouds, such as are found on Venus, the hottest planet in the Solar System.
Physical characteristics
Mass, radius, and temperature
TRAPPIST-1b is very similar in both mass, radius, and gravity to Earth. It has a radius of 1.121 REarth, a mass of 1.02 MEarth, and about 81% Earth's surface gravity. However, the density of the planet indicates that it is not entirely rocky. With a density of 3.98 g/cm3, about ≤5% of its mass must be volatiles, likely in the form of a thick Venus-like atmosphere due to it receiving nearly four times more energy than Earth does. The planet's surface temperature is estimated to be between 750 K (477 °C; 890 °F) and 1,500 K (1,230 °C; 2,240 °F), potentially as high as 2,000 K (1,730 °C; 3,140 °F). This is much hotter than the surface of Venus and may be hot enough that the surface is molten lava. In addition, the planet should be very geologically active due to tidal squeezing similar to Jupiter's moon Io, which happens to have a similar orbital period and eccentricity (see TRAPPIST-1#Resonance for references).
Orbit
TRAPPIST-1b orbits very close to its parent star. One orbit requires only 36 hours, or about 1.51 Earth days. It orbits about 0.0115 AU (1.72 million km; 1.07 million mi) from its star, just 1.2% the distance between Earth and the Sun. The close proximity to its host star means that TRAPPIST-1b is likely tidally locked. It also has a very circular orbit, with an eccentricity of 0.00622, significantly more circular than Earth's orbit.
Host star
TRAPPIST-1b orbits the ultracool dwarf star TRAPPIST-1. It has a mass of 0.089 M☉ and is only 0.121 R☉, with a surface temperature of 2,511 K (2,238 °C; 4,060 °F) and an age between 3 and 8 billion years. The Sun, in comparison, has a surface temperature of 5,778 K (5,505 °C; 9,941 °F) and is about 4.5 billion years old. TRAPPIST-1 is also very dim, with a luminosity about 0.0005 times that of the Sun. It is too faint to be seen with the naked eye, having an apparent magnitude of 18.80.
Atmosphere
The combined transmission spectra of TRAPPIST-1 b and c rule out cloud-free hydrogen-dominated atmospheres for both planets, so they are unlikely to harbor extended gas envelopes. Also, no helium emission from TRAPPIST-1b has been detected. Other atmospheres, from a cloud-free water-vapor atmosphere to a Venus-like atmosphere, remain consistent with the featureless spectra.
In 2018, the planet's atmosphere was better examined by the Spitzer Space Telescope and found to be quite large and hot. The planet's transmission spectrum and refined density estimate suggest two main possibilities for the atmosphere: one rich in carbon dioxide, and one rich in water vapor. The more likely CO2 atmosphere would have a scale height of approximately 52 kilometers (32 miles) (Earth's being 8 km (5.0 mi), and Venus' at 15.9 km (9.9 mi)) and an average temperature in excess of 1,400 K (1,130 °C; 2,060 °F), far greater than its equilibrium temperature of 391.8 K (118.7 °C; 245.6 °F). A water vapor atmosphere would need to have a scale height of >100 km (62 mi) and a temperature >1,800 K (1,530 °C; 2,780 °F) to produce the variations seen in the planet's transit depths and its transmission spectrum, and would be vulnerable to photodissociation where CO2 would not be. Other sources for the effects seen, such as hazes and thick clouds, would require an even larger atmosphere. TRAPPIST-1b will have to be studied further to confirm its potential large atmosphere.
TRAPPIST-1c, also designated as 2MASS J23062928-0502285 c, is a mainly rocky, Venus-like exoplanet orbiting around the ultracool dwarf star TRAPPIST-1 approximately 40 light-years away from Earth in the constellation Aquarius. It is the most massive and third largest planet of the system, with about 116% the mass and 110% the radius of Earth. Its density indicates a primarily rocky composition with a very thick Venus-like atmosphere, although it is expected to be thinner than that of TRAPPIST-1b.
Physical characteristics
Mass, radius, and temperature
TRAPPIST-1c was observed with the transit method, which enabled scientists to calculate its radius. Transit-timing variations and computer simulations were able to determine the mass, density, and gravity of the planet. TRAPPIST-1c is the third-largest planet of the TRAPPIST-1 system, with a radius of 1.095 REarth. It is also the most massive of the system as well, with a mass of 1.156 MEarth, slightly higher than that of the next most massive, TRAPPIST-1g. Despite its Earth-like mass and radius, TRAPPIST-1c has a lower density (4.89 g/cm3) and gravity (0.966g) than Earth.[dubious – discuss] This is consistent with a rock-based composition and a thick, Venus-like atmosphere, similar to TRAPPIST-1b.[citation needed] TRAPPIST-1c's atmosphere is expected to be thinner than that of its inner sibling, but still large enough to raise its surface temperature far above the calculated 334.8 K (61.7 °C; 143.0 °F) equilibrium temperature. In addition, the planet should be very geologically active due to tidal squeezing similar to Jupiter's moon Io, which happens to have a similar orbital period and eccentricity (see TRAPPIST-1#Resonance for references).
Orbit
The orbit of TRAPPIST-1c is very close to its host star. One year on this planet lasts a mere 2.42 days (58 hours), a fraction as long as that of our Solar System's innermost planet, Mercury. The planet orbits at a distance of 0.0158 AU, which is about 1.6% the distance between Earth and the Sun. At this proximity, TRAPPIST-1c is most likely tidally locked. However, due to the small size of its host star, the planet only receives about 2.1 times the sunlight as Earth (similar to Venus, at 1.9 times). Its orbital eccentricity is very low at 0.00654, similar to that of TRAPPIST-1b.
Host star
TRAPPIST-1c orbits the ultracool dwarf star TRAPPIST-1. It is 0.121 R☉ and 0.089 M☉, with a temperature of 2511 K and an age between 3 and 8 billion years. For comparison, the Sun has a temperature of 5778 K and is about 4.5 billion years old. TRAPPIST-1 is also very dim, with about 0.0005 times (0.05%) the luminosity of the Sun. It is too faint to be see with the naked eye, having an apparent magnitude of 18.80.
Atmosphere
The combined transmission spectrum of TRAPPIST-1 b and c rules out a cloud-free hydrogen-dominated atmosphere for each planet, so they are unlikely to harbor an extended gas envelope. Other atmospheres, from a cloud-free water-vapor atmosphere to a Venus-like atmosphere, remain consistent with the featureless spectrum.
In 2018, the composition of TRAPPIST-1c was determined, and has been found to be rock-based with a very thick, Venus-like atmosphere. The atmosphere of TRAPPIST-1c is likely thinner than that of TRAPPIST-1b.
TRAPPIST-1d, also designated as 2MASS J23062928-0502285 d, is a small exoplanet (about 30% the mass of the Earth), which orbits on the inner edge of the habitable zone of 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. The first signs of the planet were announced in 2016, but it wasn't until the following years that more information concerning the probable nature of the planet was obtained. TRAPPIST-1d is the least massive planet of the system and is likely to have a compact hydrogen-poor atmosphere similar to Venus, Earth, or Mars. It receives just 4.3% more sunlight than Earth, placing it on the inner edge of the habitable zone. It has about <5% of its mass as a volatile layer, which could consist of atmosphere, oceans, and/or ice layers. Recent studies by the University of Washington have concluded that TRAPPIST-1d might be a Venus-like exoplanet with an uninhabitable atmosphere. The planet is an eyeball planet candidate.
Physical characteristics
Radius, mass, and temperature
TRAPPIST-1d was detected with the transit method, allowing scientists to accurately determine its radius. The planet is about 0.784 REarth with a small error margin of about 147 km. Transit timing variations and complex computer simulations helped accurately determine the mass of the planet, which led to scientists being able to calculate its density, surface gravity, and composition. TRAPPIST-1d is a mere 0.297 MEarth, making it one of the least massive exoplanets yet found. It has 61.6% the density of Earth (3.39 g/cm3) and just under half the gravity. Both its mass, density, and surface gravity are the lowest in the entire TRAPPIST-1 system. Compared to Mars, it has nearly three times that planet's mass but is still significantly less dense, which would indicate the presence of a significant atmosphere; models of the low density of TRAPPIST-1d indicates a mainly rocky composition, but with about ≤5% of its mass in the form of a volatile layer. The volatile layer of TRAPPIST-1d may consist of atmosphere, ocean, and/or ice layers. TRAPPIST-1d has an equilibrium temperature of 282.1 K (9.0 °C; 48.1 °F), assuming an albedo of 0. For an Earth-like albedo of 0.3, the planet's equilibrium temperature is around 258 K (−15 °C; 5 °F), very similar to Earth's at 255 K (−18 °C; −1 °F).
Orbit
TRAPPIST-1d is a closely orbiting planet, with one full orbit taking just 4.05 days (about 97 hours) to complete. It orbits at a distance of just 0.02228 AU from the host star, or about 2.2% the distance between Earth and the Sun. For comparison, Mercury, the Solar System's innermost planet, takes 88 days to orbit at a distance of about 0.38 AU. The size of TRAPPIST-1 and the close orbit of TRAPPIST-1d around it means that the star as seen from the planet appears 5.5 times as large as the Sun from the Earth. While a planet at TRAPPIST-1d's distance from the Sun would be a scorched world, the low luminosity of TRAPPIST-1 means that the planet gets only 1.043 times the sunlight that Earth receives, placing it within the inner part of the conservative habitable zone.
Host star
The planet orbits an (M-type) ultracool dwarf star named TRAPPIST-1. The star has a mass of 0.089 M☉ (close to the boundary between brown dwarfs and hydrogen-fusing stars) and a radius of 0.121 R☉. It has a temperature of 2,516 K (2,243 °C; 4,069 °F), and is between 3 and 8 billion years old. In comparison, the Sun is 4.6 billion years old and has a temperature of 5778 K (5504.85 °C, 9940.73 °F). 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 metals than the Sun. Its luminosity (L☉) is 0.05% of that of the Sun.
Stars like TRAPPIST-1 have the ability to live up to 4–5 trillion years, 400–500 times longer than the Sun will live (the Sun only has about 8 billion years of lifespan left, slightly more than half of its lifetime). 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 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 (the limit for that is 6.5).
The star is not just very small and far away, it also emits comparatively little visible light, mainly shining in the invisible infrared. Even from the close in proximity of TRAPPIST-1d, about 50 times closer than Earth is from the Sun, the planet receives less than 1% the visible light Earth sees from our Sun. This would probably make the days on TRAPPIST-1d never brighter than twilight is on Earth. However, that still means that TRAPPIST-1 could easily shine at least 3000 times brighter in the sky of TRAPPIST-1d than the full moon does in Earth's night sky.
Habitability
Models and scientists are divided on whether their convergent solutions from the data for TRAPPIST-1d indicates Earth-like habitability or a severe greenhouse effect.
In some respects, this exoplanet is one of the most Earth-like found. It does not have a hydrogen or helium-based atmosphere, which makes larger planets uninhabitable (the planet is not massive enough to retain light gases).
The planet is located at the inner edge of the expected habitable zone of its parent star (where liquid water can reasonably be expected to exist on its surface). The planet may also have liquid and atmospheric water, up to many times more than Earth. However, some three-dimensional modeling solutions have a little water surviving beyond the early hot phase in the planet's history. Most models by the University of Washington for TRAPPIST-1d strongly converge on a Venus-like planet (runaway greenhouse effect) with an uninhabitable atmosphere.
Because TRAPPIST-1d is only ~30% the Earth's mass, it, like Venus and Mars, may have no magnetic field, which would allow the parent star's solar wind to strip away the more volatile components of its atmosphere (including water), leaving it hydrogen-poor like those planets. However, due to its close orbit, TRAPPIST-1d is likely tidally locked and it may be very geologically active due to tidal squeezing as happens to Jupiter's moon Io and the volcanic gases could replenish the atmosphere lost to the solar wind. TRAPPIST-1d may resist this the tidal heating, especially if it has an Earth-like albedo of ≥0.3, according to other analyses. The same researchers point out that such proximity to the host star tends to increase geothermal activity, and tidally heat the bottom of any seas. If the planet has suffered a runaway greenhouse, its atmosphere should be thinner and cooler than Venus', due to its smaller mass and the fact it only receives about as much radiation as the Earth (while Venus receives about twice as much).
The lack of a magnetic field will also result in the surface receiving more charged particles than the Earth does. And if the planet is tidally locked, a dense atmosphere could be enough to transfer heat from the illuminated side to the much colder dark side.
Discovery
A team of astronomers headed by Michaël Gillon of the Institut d’Astrophysique et Géophysique at the University of Liège in Belgium used the TRAPPIST (Transiting Planets and Planetesimals Small Telescope) telescope at the La Silla Observatory in the Atacama desert, Chile, 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. The team made their observations from September to December 2015 and published its findings in the May 2016 issue of the journal Nature.
TRAPPIST-1e, also designated as 2MASS J23062928-0502285 e, is a rocky, close-to-Earth-sized exoplanet orbiting within the habitable zone around the ultracool dwarf star TRAPPIST-1 approximately 40 light-years (12 parsecs; 380 trillion kilometers; 240 trillion miles) away from Earth in the constellation of Aquarius. Astronomers found the exoplanet 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 exoplanet was one of seven new exoplanets discovered orbiting the star using observations from the Spitzer Space Telescope. Three of the seven (e, f, and g) are in the habitable zone. TRAPPIST-1e is similar to Earth's mass, radius, density, gravity, temperature, and stellar flux. It is also confirmed to not have a cloud-free hydrogen-dominated atmosphere, meaning it is more likely to have a compact atmosphere like the terrestrial planets in the Solar System.
In November 2018, researchers determined that of the seven exoplanets in the multi-planetary system, TRAPPIST-1e has the best chance of being an Earth-like ocean planet, and the one most worthy of further study regarding habitability. Furthermore, according to the Habitable Exoplanets Catalog, TRAPPIST-1e is one of the most potentially habitable exoplanets discovered.
Physical characteristics
Mass, radius, composition and temperature
TRAPPIST-1e was detected with the transit method, where the planet blocked a small percentage of its host star's light when passing between it and Earth. This allowed scientists to accurately determine the planet's radius at 0.910 REarth, with a small uncertainty of about 166–172 km (103–107 mi). Transit-timing variations and advanced computer simulations helped constrain the planet's mass, which turned out to be 0.772 MEarth, or about 5% less massive than Venus. With both the radius and mass of TRAPPIST-1e determined with low error margins, scientists could accurately calculate the planet's density, surface gravity, and composition. TRAPPIST-1e is unusual in its system as it is the only planet with a pure rock-iron composition, and the only one with a higher density than Earth (TRAPPIST-1c also appears to be entirely rock, but it has a thick atmosphere that makes it less dense than TRAPPIST-1e). It has a density of 5.65 g/cm3, about 1.024 times Earth's density of 5.51 g/cm3. The higher density of TRAPPIST-1e implies an Earth-like composition and a solid rocky surface. This is also unusual among the TRAPPIST-1 planets, as most are completely covered in either a thick steam/hot CO2 atmosphere, a global liquid ocean, or an ice shell. TRAPPIST-1e has 93% the surface gravity of Earth, the second highest in the system. Its radius and mass are also the third least among the TRAPPIST-1 planets.
The planet has a calculated equilibrium temperature of 246.1 K (−27.1 °C; −16.7 °F) given an albedo of 0, also known as its "blackbody" temperature. For a more realistic Earth-like albedo however, this provides an unrealistic picture of the surface temperature of the planet. Earth's equilibrium temperature is 255 K;[better source needed] it is Earth's greenhouse gases that raise its surface temperatures to the levels we experience. If TRAPPIST-1e has a thick atmosphere, its surface could be much warmer than its equilibrium temperature.
Host star
The planet orbits an (late M-type) ultracool dwarf star named TRAPPIST-1. The star has a mass of 0.089 M☉ – near the boundary between a brown dwarf and low-mass star – and a radius of 0.121 R☉. It has a temperature of 2,516 K (2,243 °C; 4,069 °F) and is 7.6 billion years old. In comparison, the Sun is 4.6 billion years old and has a temperature of 5,778 K (5,505 °C; 9,941 °F). 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 0.0522% 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 far too dim to be seen with the naked eye.
Orbit
TRAPPIST-1e orbits its host star quite closely. One full revolution around TRAPPIST-1 takes only 6.099 Earth days (~146 hours) to complete. It orbits at a distance of 0.02928285 AU (4.4 million km; 2.7 million mi), or just under 3% the separation between Earth and the Sun. For comparison, the closest planet in the Solar System, Mercury, takes 88 days to orbit the Sun at a distance of 0.38 AU (57 million km; 35 million mi). Despite its close proximity to its host star, TRAPPIST-1e gets only about 60% the starlight that Earth gets from the Sun due to the low luminosity of its star. The star would cover an angular diameter of about 2.17 degrees from the surface of the planet, and would appear about four times larger than the Sun does from Earth.
Atmosphere
TRAPPIST-1e is confirmed to not have a cloud-free hydrogen-dominated atmosphere, meaning it is more likely to have a compact, hydrogen-free atmosphere like those of the Solar System's rocky planets, further raising the chances of habitability. Hydrogen is a powerful greenhouse gas, so if there was enough to be easily detected, it would mean that the surface of TRAPPIST-1e would be inhospitable. Since such an atmosphere is not present, it raises the chances for the planet to have a more Earth-like atmosphere instead. However, no atmosphere has been detected, and it is still possible that the planet has no atmosphere at all. Additionally, no helium emission from TRAPPIST-1e was detected as of 2021.
Habitability
The exoplanet was announced to be orbiting within 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-1e has a radius of around 0.91 REarth, so it is likely a rocky planet. 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 potential to remain stable for up to 12 trillion years, which is over 1,000 times longer than the Sun. Because of this ability to live for such a long period of time, it is likely TRAPPIST-1 will be one of the last remaining stars in the Universe, when the gas needed to form new stars will be exhausted, and the existing stars begin to die off.
Other factors and 2018 studies
Despite being likely tidally locked – meaning one hemisphere permanently faces the star while the other does not – which may reduce the habitability of the planet, more detailed studies of TRAPPIST-1e and the other TRAPPIST-1 planets released in 2018 determined that the planet is one of the most Earth-sized worlds found, with 91% the radius, 77% the mass, 102.4% the density (5.65 g/cm3), and 93% the surface gravity. TRAPPIST-1e is confirmed to be a terrestrial planet with a solid, rocky surface. It is cool enough for liquid water to pool on the surface, but not too cold for it to freeze like on TRAPPIST-1f, g, and h.
The planet receives a stellar flux 60.4% that of Earth, about a third lower than that of Earth but significantly more than that of Mars. Its equilibrium temperature ranges from 225 K (−48 °C; −55 °F) to 246.1 K (−27.1 °C; −16.7 °F), depending on how much light the planet reflects into space. Both of these are between those of Earth and Mars as well. In addition, its atmosphere is confirmed to not be dense or thick enough to harm the habitability potential as well, according to models by the University of Washington. The atmosphere, if it is dense enough, may also help to transfer additional heat to the dark side of the planet.
Future observations
As it is one of the most promising potentially habitable exoplanets known, TRAPPIST-1e will be an early target of the James Webb Space Telescope in a research program led by Nikole Lewis. Launched on 25 December 2021, the telescope will allow more extensive analysis of the planet's atmosphere, facilitating the search for any chemical signs of life, or biosignatures.
Discovery
A team of astronomers headed by Michaël Gillon used the TRAPPIST (Transiting Planets and Planetesimals Small Telescope) telescope at the La Silla Observatory in the Atacama desert, Chile, 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. The team made their observations from September–December 2015 and published its findings in the May 2016 issue of the journal Nature.
TRAPPIST-1f, also designated as 2MASS J23062928-0502285 f, is an exoplanet, likely rocky but under a massive water-steam gaseous envelope at very high pressure and temperature, orbiting within the habitable zone around the ultracool dwarf star TRAPPIST-1 40 light-years (12 parsecs) 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.
It was one of four new exoplanets to be discovered orbiting the star using observations from the Spitzer Space Telescope.
The planet is an eyeball planet candidate.
Physical characteristics
TRAPPIST-1f is an Earth-sized exoplanet, meaning it has a radius close to that of Earth. It has an equilibrium temperature of 219 K (−54 °C; −65 °F), which increases to above 1,400 K (1,130 °C; 2,060 °F) if the warming of its likely very dense atmosphere is taken into account. It has a radius of 1.045 ± 0.038 REarth and a mass of 0.68 ± 0.18 MEarth, giving it a density of 3.3±0.9 g/cm3. These values suggest surface gravity around 6.1 m/s2 (62% of Earth value).
Atmosphere
According to simulation of magma ocean-atmosphere interaction, TRAPPIST-1f is likely to retain a fraction of primordial steam atmosphere during the initial stages of evolution, and therefore today is likely to possess a thick ocean covered by atmosphere rich in abiotic oxygen. Helium emission from TRAPPIST-1f (and planets b and e) has not been detected as of 2022.
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 7-8 billion years old. In comparison, the Sun is 4.6 billion years old and has a temperature of 5778 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; on the other hand, metal-rich stars are also more likely to have planets than metal-poor ones. 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. Therefore, it is too dim to be seen with the naked eye.
Orbit
TRAPPIST-1f orbits its host star with an orbital period of about 9.206 days and an orbital radius of about 0.037 times that of Earth's (compared to the distance of Mercury from the Sun, which is about 0.38 AU).
Habitability
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. On 31 August 2017, astronomers at the Hubble Space Telescope reported the first evidence of possible water content on the TRAPPIST-1 exoplanets.
TRAPPIST-1f has a radius about the same as Earth, at around 1.045 REarth, but only about two thirds of Earth's mass, at around 0.68 MEarth. So, it is considered somewhat unlikely to be a fully rocky planet, and extremely unlikely to be an Earth-like one, that is rocky with a large iron core but without a thick hydrogen-helium atmosphere enveloping the planet. Simulations strongly suggest the planet is approximately 20% water by composition, much higher than that of Earth. With such a massive water envelope, the pressure and temperature will be high enough to keep the water in a gaseous state and any liquid water will only exist as clouds near the top of TRAPPIST-1f's atmosphere. TRAPPIST-1f is therefore likely to be no more habitable than any other gas or ice-giant with water clouds in its atmosphere.
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. 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 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 moderate temperature – called the terminator line, where the temperatures may be suitable (about 273 K or 0 °C or 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.
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 39 light-years (12 parsecs) away from Earth in the constellation Aquarius. It was one of four new exoplanets to be discovered orbiting the star using observations from the Spitzer Space Telescope. The exoplanet is within the optimistic habitable zone of its host star. 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 larger than Earth yet less dense, meaning it likely hosts some form of water.
Physical characteristics
Mass, radius, and temperature
TRAPPIST-1g has roughly 115% the mass and radius of Earth, though its density is 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.
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.
Water
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 2550 K. The age of the star is about 7.6±2.2 billion years old. In comparison, the Sun is 4.6 billion years old and has a temperature of 5778 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.
TRAPPIST-1h, also designated as 2MASS J23062928-0502285 h, is an exoplanet orbiting around the ultra-cool dwarf star TRAPPIST-1 39 light-years (12 parsecs) away from Earth in the constellation Aquarius. It was one of four new exoplanets to be discovered orbiting the star using observations from the Spitzer Space Telescope. Throughout 2017 and 2018, more studies were able to refine its physical parameters.
The outermost known planet in its system, it is roughly one third the mass of Earth, and about 77% as large. Its relatively low density indicates that it is likely water-rich, like several other planets in the system.
Physical characteristics
Mass, radius, and temperature
TRAPPIST-1h has a radius of 0.773 REarth, a mass of 0.331 MEarth, and about 56% Earth's surface gravity. It has a density of 3.97 g/cm3, extremely similar to that of Mars. Given this density, about ≤5% of its mass must be water, likely in the form of a thick ice shell, seeing as it only receives about 13% of the stellar flux that Earth does. It has an equilibrium temperature of 169 K (−104 °C; −155 °F), similar to that of Earth's south pole.
Host star
TRAPPIST-1h orbits the ultracool dwarf star TRAPPIST-1. It is 0.121 R☉ and 0.089 M☉, with a temperature of 2511 K and an age between 3 and 8 billion years. For comparison, the Sun has a temperature of 5778 K and is about 4.5 billion years old. TRAPPIST-1 is also very dim, with about 0.0005 times the luminosity 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
Despite it being the most distant known planet in its system, TRAPPIST-1h orbits its host star with an orbital period of 18.868 days and an orbital radius of about 0.0619 AU. This is even smaller than Mercury's orbit around the Sun (which is about 0.38 AU).
Stable liquid water
Although TRAPPIST-1h's orbit falls near its star's frost line, it could harbor liquid water under an H2-rich atmosphere, either primordial or resulting from continuous outgassing combined with internal heating, although existence of such atmosphere was strongly disfavored by observations in 2021 and 2022. It could also potentially harbor a subsurface ocean by way of tidal heating, which could lead to cryovolcanism in the form of erupting geysers.
DONE