User:Dadofme/sandbox

TRAPPIST-1, also known as 2MASS J23062928-0502285, is an ultra-cool dwarf star located 39.5 ly away from Earth in the constellation Aquarius.

In 2015, astronomers discovered three Earth-sized planets orbiting the dwarf star. The team, led by Michaël Gillon at the University of Liège in Belgium, detected the planets using transit photometry with the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) at the La Silla Observatory in Chile. On 22 February 2017, astronomers announced four additional exoplanets around TRAPPIST-1. Besides TRAPPIST, this work utilized the Very Large Telescope at Paranal and the NASA Spitzer Space Telescope, among others, and brought the total number of planets orbiting the star to seven, of which at least three, and possibly all, are in its habitable zone.

Discovery and nomenclature
The star at the centre of the system now known as TRAPPIST-1 was first catalogued in the late 1990s during the 2MASS astronomical survey. At that time it was known as "2MASS J23062928-0502285".

The system was later studied by a team at the University of Liège, who made their initial observations using the Transiting Planets and Planetesimals Small Telescope–South (TRAPPIST) from September to December 2015 and published their findings in the May 2016 issue of the journal Nature. The star's current name, TRAPPIST-1, pays homage to the telescope, which itself acknowledges the Catholic Christian religious order of Trappists and to the Trappist beer it produces, primarily in Belgium.

The planets are designated in the order of their discovery, beginning with b for the first planet discovered, c for the second and so on. Three planets around TRAPPIST-1 were first discovered and designated b, c and d in order of increasing orbital periods, and the second batch of discoveries was similarly designated e to h.

Stellar characteristics
TRAPPIST-1 is an ultracool dwarf star, of spectral class M8.0 ± 0.5, that is approximately 8% the mass of and 11% the radius of the Sun. It has a temperature of 2550 K and is at least 500 million years old. In comparison, the Sun is about 4.6 billion years old and has a temperature of 5778 K.

Owing to its low luminosity, the star has the ability to live for up to 4–5 trillion years, meaning that TRAPPIST-1 should remain a main sequence star when the Universe is much older than it is now, when the gas needed to make stars will have been used up. The star is metal-rich, with a metallicity ([Fe/H]) of 0.04, or 109% the solar amount. Its luminosity is 0.05% of that of the Sun, most of which is emitted in the infrared spectrum.

Planetary system
In February 2017, astronomers announced that the planetary system of this star is composed of seven Earth-like planets, three of which (e, f, g) orbit in the habitable zone.



All seven of TRAPPIST-1's planets orbit much closer than Mercury orbits the Sun. The distance between the orbits of TRAPPIST-1b and TRAPPIST 1c is only 1.6 times the distance between the Earth and the moon. The planets should appear prominently in each other's skies, and in some cases, appearing several times larger than the moon appears from Earth. A year on the closest planet passes in only 1.5 Earth days, while the sixth planet's year passes in only 12.3 days. The seventh planet's year is much less certain at $20$ days, because only a single transit has been observed. It is probable that the rotation of each of these planets around its axis is synchronized with its translation around the star (one day = one year). Tidally locked planets likely have very large differences in temperature between their permanently lit day sides and their permanently dark night sides, which could produce very strong winds circling the planets. The best places for life may be close to the mild twilight regions between the two sides. Another important consideration is that red dwarf stars are subject to frequent, intense flares that are likely to have stripped away the atmospheres of any planets in such close orbits.

The orbits of planets b-g are nearly in resonance, having relative periods of approximately 24/24, 24/15, 24/9, 24/6, 24/4 and 24/3, respectively, or nearest-neighbor period ratios (proceeding outward) of about 8/5, 5/3, 3/2, 3/2 and 4/3 (1.603, 1.672, 1.506, 1.509 and 1.342). This represents the longest known chain of near-resonant exoplanets, and is thought to have resulted from interactions between the planets as they migrated inward within the residual protoplanetary disk after forming at greater initial distances. Due to the poorly-known orbital period of h, it is unknown if it is in an orbital resonance with the other six planets, although it is probably in a 2:24 resonance with the other planets.

Strong extreme-ultraviolet irradiation of the planetary system
An XMM-Newton X-ray study shows that the Earth-sized planets in the habitable zone of the star are subject to sufficient X-ray and extreme ultraviolet (EUV/XUV) irradiation to significantly alter their primary and perhaps secondary atmospheres.

Spectrum of TRAPPIST-1 b and c
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.

Tidal locking
All seven planets are likely to be tidally synchronized (or possibly but less likely trapped in a higher-order spin-orbit resonance), making the development of life there "much more challenging".

In popular culture
On 23 February 2017, the discovery was celebrated with an animated Google Doodle made by Nate Swinehart.