TRAPPIST-1
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 23h 06m 29.283s[1] |
| Declination | −05° 02′ 28.59″[1] |
| Characteristics | |
| Evolutionary stage | Main sequence |
| Spectral type | M8V[2] |
| Apparent magnitude (V) | 18.798±0.082[2] |
| Apparent magnitude (R) | 16.466±0.065[2] |
| Apparent magnitude (I) | 14.024±0.115[2] |
| Apparent magnitude (J) | 11.354±0.022[1] |
| Apparent magnitude (H) | 10.718±0.021[1] |
| Apparent magnitude (K) | 10.296±0.023[1] |
| V−R color index | 2.332 |
| R−I color index | 2.442 |
| J−H color index | 0.636 |
| J−K color index | 1.058 |
| Astrometry | |
| Radial velocity (Rv) | −54±2[2] km/s |
| Proper motion (μ) | RA: 922.1±1.8[2] mas/yr Dec.: −471.9±1.8[2] mas/yr |
| Parallax (π) | 80.451 ± 0.12[3][4] mas |
| Distance | 40.54 ± 0.06 ly (12.43 ± 0.02 pc) |
| Absolute magnitude (MV) | 18.4±0.1 |
| Details | |
| Mass | 0.0898±0.0023[3] M☉ |
| Radius | 0.1192±0.0013[5] R☉ |
| Luminosity (bolometric) | 0.000553±0.000018[3] L☉ |
| Luminosity (visual, LV) | 0.00000373[a] L☉ |
| Surface gravity (log g) | 5.2396+0.0056 −0.0073[b][5] cgs |
| Temperature | 2566±26[5] K |
| Metallicity [Fe/H] | 0.04±0.08[6] dex |
| Rotation | 3.295±0.003 d |
| Rotational velocity (v sin i) | 6[7] km/s |
| Age | 7.6±2.2[8] Gyr |
| Other designations | |
| Database references | |
| SIMBAD | data |
| Exoplanet Archive | data |
| Extrasolar Planets Encyclopaedia | data |
TRAPPIST-1, also designated 2MASS J23062928–0502285 or K2-112,[9] is an ultra-cool red dwarf star in the constellation Aquarius. It has a mass of about 9% that of the Sun, a radius slightly larger than the planet Jupiter and a surface temperature of about 2560 K. It is about 39 light years (12 parsecs) from the Sun and is about 7.6±2.2 billion years old, making it older than the Solar System. The star was discovered in 2000.
In 2016 and 2017, observations with numerous space- and ground-based telescopes, including the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) telescope at La Silla Observatory, led to the discovery of initially three, then seven terrestrial planets around the star. The orbital periods - the time it takes for each planet to orbit the star - have precise numerical ratios of 8:5, 5:3, 3:2, 3:2, 4:3, and 3:2. This orbital resonance could have existed since the formation of the planetary system, and is predicted to lead to intense planet-planet interactions that could drive volcanic activity on the planets. The planets are likely to be tidally locked to TRAPPIST-1 and to thus always turn the same side to their host star.
Three to four of the planets (d, e, f, g) are hypothesized to be located within the habitable zone of the star and thus to have temperatures suitable to the presence of liquid water and thus the development of life. Whether they actually contain liquid water is a function of numerous properties of the planets including whether they have an atmosphere. There is no clear evidence that any of the planets has an atmosphere and it is unclear whether planets could hold onto atmospheres around TRAPPIST-1, since its radiation is expected to strip away large amounts of atmospheric gases. The low densities of the planets indicate they may consist of large amounts of volatile material.
Star[]
TRAPPIST-1 is in the constellation Aquarius,[10] and very close to the celestial equator.[c][12] The name is a reference to the TRAPPIST[d] project that discovered the star;[18] other names for the star are 2MUCD 12171,[19] 2MASS J23062928–0502285, EPIC 246199087[13] and TRAPPIST-1a.[20] TRAPPIST-1 is a very close star,[21] 39.1 ± 1.3 light-years (12.0 ± 0.4 pc) away from the Solar System as measured by parallax,[e][23] and has a large proper motion.[f][21] Dwarf stars like TRAPPIST-1 are over ten times more common than Sun-like stars[25] and are also more likely to host small planets.[26] There is no evidence that TRAPPIST-1 is a binary star.[27]
TRAPPIST-1 is a late[g] M dwarf[h][30] with 0.0898±0.0023 times the Sun's[i] mass.[3] TRAPPIST-1 is only slightly larger than Jupiter and has a radius of 11.5% that of the Sun,[23] similar to brown dwarfs[j] and other low-mass stars.[34] TRAPPIST-1 has an unusually low density for its kind of star.[35] Its spectral type, which is a scheme to categorize stars by their temperature,[36] is M8.0±0.5.[23] Its luminosity is 0.000553±0.000018 times that of the Sun[3] and is mostly infrared radiation;[37] it is not variable[23] and there is no evidence for a solar cycle.[38] TRAPPIST-1 has an effective temperature[k] of 2,566 ± 26 K (2,292.8 ± 26.0 °C; 4,159.1 ± 46.8 °F).[5]
Stars like TRAPPIST-1 are so cool that clouds consisting of condensates and dust can form in their photosphere.[40] Patterns of TRAPPIST-1's radiation support the existence of dust, which is distributed evenly across the star's surface.[41] The faint radiation at short wavelengths that TRAPPIST-1 emits has been measured with the XMM-Newton satellite[42] and in later surveys, although with low precision.[43]
Rotation period and age[]
In 2016, TRAPPIST-1's rotational period was measured as 1.40±0.05 Earth days,[23] a typical period for M dwarfs.[34] However, 2018 measurements showed that the star actually rotates every 3.295 Earth days[44], though that may constitute the rotation period of active regions rather than stellar rotation.[41] There are disagreements between rotational data obtained by the Spitzer space telescope and Kepler satellite that, as of 2020, remain unexplained.[45]
The ages of stars can be estimated using various techniques, which are not all suitable for every star. Based on a combination of techniques, an age of (7.6±2.2)×109 year has been established for TRAPPIST-1,[46] making it almost twice as old as the Solar System.[47] The life expectancy of a star like TRAPPIST-1 is hundreds to thousands of times longer than that of a Sun-like star[25] and longer than the present age of the Universe.[48]
Activity[]
Numerous photospheric features have been detected on TRAPPIST-1 and may constitute a source of error for measurements of the properties of its planets.[49] Possible faculae[l] have been observed by the Kepler and Spitzer space telescopes.[52] Their effect on the luminosity of TRAPPIST-1 may lead to the planets' densities being misestimated by about −8+7
−20 percent,[53] and to incorrect estimates of their water content.[54] A correlation between bright spots and flare[m] activity has been found.[35] The mean intensity of TRAPPIST-1's magnetic field is about 600 G[56] although many of its properties cannot be directly measured.[57] This intense magnetic field is driven by chromospheric[n] activity[59] and may be capable of trapping coronal mass ejections; these are eruptions of coronal material to the outside of a star.[55][60]
Stars lose mass through the stellar wind.[61] Garraffo et al. 2017 computed the mass loss of TRAPPIST-1 to be about 3×10−14 solar masses per year,[62] which is about 1.5 times that of the Sun,[63] while Dong et al. 2018 simulated a mass loss of 4.1×10−15 solar masses per year.[62] The stellar wind properties of TRAPPIST-1 are not precisely determined.[64]
Planetary system[]
Seven[o] planets orbit TRAPPIST-1, named TRAPPIST-1b, TRAPPIST-1c, TRAPPIST-1d, TRAPPIST-1e, TRAPPIST-1f, TRAPPIST-1g, and TRAPPIST-1h, [31] with each orbit taking a few to about 20 days.[66] They orbit their host star at distances of 1.7×106–8.9×106 kilometres (1.1×106–5.5×106 mi),[67] much closer to TRAPPIST-1 than Mercury is to the Sun,[68] making TRAPPIST-1 a very compact planetary system.[69] They are named in alphabetic order, according to their distance from TRAPPIST-1.[70] As of 2021 there is no evidence of an eighth planet around TRAPPIST-1, but its possible properties have been computed under the assumption that it is part of the resonance.[71] As of 2018 no comets have been detected around TRAPPIST-1.[72] Observations with the Atacama Large Millimeter Array telescope have found no evidence of a circumstellar dust disk,[73] implying that if it does exist it is of low mass. Most of the pre-planetary material was converted into planets.[74]
All orbits are coplanar[p] and highly circular, with minimal eccentricities,[69] and well-aligned with the spin axis ot TRAPPIST-1.[77] The planets all orbit on the same plane and, from the perspective of the Solar System, move past TRAPPIST-1 during their orbit[78] and frequently pass in front of each other.[79]
| Companion (in order from star) |
Mass | Semimajor axis (AU) |
Orbital period (days) |
Eccentricity[81] | Inclination[80] | Radius |
|---|---|---|---|---|---|---|
| b | 1.3771±0.0593 M
|