TRAPPIST-1 instance of ultra-cool dwarf
TRAPPIST-1 is a cold dwarf star, with a surface temperature of about 2,566 K (2,293 °C; 4,159 °F), in the constellation Aquarius. It has a planetary system of seven known planets. TRAPPIST-1 is slightly larger than Jupiter and has a mass of about 9% of that of the Sun. Located 40.7 light-years (12.47 parsecs) (pc) away it is estimated to be 7.6 billion years old, making it older than the Solar System.
It was discovered in 1999. Observations in 2016 from the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) at La Silla Observatory in Chile and numerous other telescopes led to the discovery of two terrestrial planets in orbit around TRAPPIST-1. In 2017, further analysis of the original observations identified five more planets. The seven planets orbit around the star in about 1.5 days to 19 days. The planets are likely tidally locked to TRAPPIST-1, meaning one side of each planet may permanently face the star, leading to permanent day on one side and permanent night on the other.
As many as four of the planets – designated d, e, f, g –  orbit at distances where temperatures are suitable for the existence of liquid water, and thus potentially hospitable to life. There is no evidence any of the planets have an atmosphere and it is unclear whether they could retain such due to radiation emission from TRAPPIST-1. The planets have low densities; they may consist of large amounts of volatile materials.Description
TRAPPIST-1 is in the constellation Aquarius, five degrees south of the celestial equator. The star was discovered in 1999 by astronomer John Gizis and colleagues; the name is a reference to the TRansiting Planets and PlanetesImals Small Telescope (TRAPPIST) project that discovered the first two exoplanets around the star. TRAPPIST-1 is a very close star located at 40.66±0.04 light-years from Earth, with a large proper motion. It has no companion stars.It is a red dwarf of spectral class M8.0±0.5, meaning it is small and cold. Its radius and mass are about 12% and 9%, respectively, that of the Sun; it is barely larger than Jupiter this size being just sufficient to allow nuclear fusion to take place. Because of its smallness the star has a low effective temperature of 2,566 K (2,293 °C) making it, as of 2022, the coldest-known star to host planets. TRAPPIST-1's density is unusually low for a red dwarf, and its luminosity, emitted mostly as infrared radiation, is about 0.055% that of the Sun. There is no evidence it has a stellar cycle.TRAPPIST-1 is cold enough for condensates to form in its photosphere; these have been detected through the polarization they induce in its radiation during transits of its planets. The star emits faint radiation at short wavelengths such as x-rays and UV radiation, as measured with the XMM-Newton satellite and other facilities with low precision.Research history and reception
TRAPPIST-1 was discovered in 2000 during a survey of Two Micron All-Sky Survey data for the identification of close-by ultra-cool dwarf stars. Its planetary system was discovered by a team led by Michaël Gillon, a Belgian astronomer of the University of Liege, in 2016 during observations made at La Silla Observatory, Chile, using the TRAPPIST telescope; the system's discovery was based on anomalies in the light curves measured by the telescope in 2015. These anomalies were initially interpreted as indicating the existence of three planets – TRAPPIST-1b, TRAPPIST-1c and a third planet. In 2016, Spitzer Space Telescope; the ground-based TRAPPIST and TRAPPIST-North in Oukaïmeden Observatory, Morocco; the South African Astronomical Observatory; and the Liverpool Telescopes and William Herschel Telescopes in Spain revealed this third planet was in fact multiple planets. The observations of TRAPPIST-1 are considered among the most-important research findings of Spitzer Space Telescope. Observations by the Himalayan Chandra Telescope, the United Kingdom Infrared Telescope and the Very Large Telescope complemented the findings by the TRAPPIST telescope. Since then, research has confirmed the existence of at least seven planets in the system, and their orbits have been constrained by measurements from the Spitzer and Kepler telescopes. Some news reports incorrectly attributed the discovery of the TRAPPIST-1 planets to NASA; the TRAPPIST project that led to their discovery received funding from both NASA and the European Research Council of the European Union (EU).
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