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Exoplanetary Scratchpad

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A very old nearby ultra-cool dwarf star (not much larger than Jupiter) 39.13 ly away with seven transiting Earth-sized planets, more than any other system, and the first such planets around such a star. First planets found by the TRAnsiting Planets and PlanetesImals Small Telescope. The planets are very compact and the gravitational interactions are significant, with resonances linking all of them, making it possible to study their mass and densities. They're named in order of distance to star. When the innermost planet b completes 8 orbits, the next planets complete 5, 3, and 2 respectively. The outermost planet (h) was predicted to have a period in a certain resonance with the other outer planets, and this was confirmed. When h orbits twice, g orbits 3 times and f 4 times. Hubble confirmed that non of the HZ planets have extended Hydrogen atmospheres. At first, the innermost two are potentially habitable and represent the easiest to study planets for biosignatures to be detected, and the third was thought to be outside the habitable zone. The first two planets (b, c) are somewhat larger than the earth at the inner edge of the habitable zones (receive the amount of energy half-way between Mercury and Venus and Venus) and orbit at 1.5 and 2.4 days. The atmospheres of the inner planets are thought to have been destroyed by the stars intense solar wind withing millions of years. Planet b and c likely have molten rock mantles due to tidal stresses, while c likely has a rocky surface with Io-like tidally induced volcanoes and a largely rocky interior. The further out planets' atmospheres could have survived for billions of years though. The next two planets (d, e) are somewhat smaller than Earth and are a little more and a little less radiated than it in the middle of the HZ. Planet d (the smallest) likely has a global ocean, while e most likely has a largely rocky interior. Studies have shown that, depending on the composition and strength of the planet's own magnetic field, the star's magnetic field could cause induction heating to occur significantly in the middle planets. This could turn the surface into magma, or at least increase volcanic activity, raising the chances of a greenhouse. The next two planets (f, g) are somewhat larger than Earth and orbit in the outer habitable zone (at Mars like distances and at the outer edge). Planet f was at first thought to be the most habitable, but now next planet out g appears to be the most habitable. The view from the fifth planet would be remarkable, with the star appearing 10 times larger than the sun does in our sky, and the other planets appearing twice the size of the moon. Planet h is the only known planet outside the habitable zone and receives about the same irradiation as Ceres does, and yet still orbits six times closer than mercury does from the sun. There was a race among astronomers using kepler data to determine h's orbit. A study on potential cometary impacts found that the outer 3 planets could have had their original atmosphere's obliterated by the impacts, but that this would also supply new volatiles for a new atmosphere, including enough water for one earth ocean mass, suggesting they would have more massive atmospheres than the other planets.

TRAPPIST-1 System Web Pages[]

TRAPPIST-1 System In the News[]

Three Planets Discovered around Ultra-Cool Dwarf Star (May 2016)[]

Oceans Could Be Retained after HZ Movement (May 2016)[]

Star As X-Ray Bright as Sun, Planets Heavily Irradiated (May 2016)[]

Planets a Good Target for James Webb Space Telescope (May 2016)[]

Planets b and c Have No Extended H Atmosphere (Jun 2016)[]

Difficulty in Detecting TRAPPIST-1 Like Planets by K2 (Jul 2016)[]

Possibility of Determining Axis Tilt of Planets (Aug 2016)[]

Confirmed to be Single Star (Sep 2016)[]

Trapist Used to Calculate How Many Brown Dwarves Would Need to be Monitored to Guarantee One Detection (Sep 2016)[]

Models Show Earth-Sized Planets Naturally Form As Largest Planets around Ultra Cool Dwarves (Oct 2016)[]

Ultra Cool Dwarves Catalog (Dec 2016)[]

Hubble Finds Star Moderately Active (Feb 2017)[]

System Has Seven Earth-Sized Planets (Feb 2017)[]

Panspermia Highly Likely in This System (Mar 2017)[]

Transits and Eclipses (Mar 2017)[]

Formation of TRAPPIST-1 Planets and Other Compact Systems (Mar 2017)[]

Atmosphere Survival Simulated (May 2017)[]

The Race To Trace Planet h's Orbit (May 2017)[]

Star's Magnetic Could Heat Up Planets (Oct 2017)[]

Orbital Evolution and Tidal Dissipation Study (Nov 2017)[]

Stellar Properties Revised (Jan 2018)[]

Parameters Refined with Spitzer (Jan 2018)[]

Cometary Impact Study (Feb 2018)[]

Planets Do Not Have Extended Hydrogen Atmospheres (Feb 2018)[]

Density Studies Suggest a Large Amount of Water (Feb 2018)[]

See Also[]