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Astronomers have observed enough planetary transits to confirm the existence of seven "Earth-sized" exoplanets orbiting TRAPPIST-1, an ultra-cool (~2550 K) red dwarf star about 39.5 light years away. Three of the exoplanets are located inside the "habitable zone" of their parent star. These three orbit from 0.028 to 0.045 AU away from the star:
Astronomers using the TRAPPIST–South telescope at ESO's La Silla Observatory, the Very Large Telescope (VLT) at Paranal and the NASA Spitzer Space Telescope, as well as other telescopes around the world, have now confirmed the existence of at least seven small planets orbiting the cool red dwarf star TRAPPIST-1. All the planets, labelled TRAPPIST-1b, c, d, e, f, g and h in order of increasing distance from their parent star, have sizes similar to Earth.
The exoplanets are presumed to be tidally locked. The six closest to TRAPPIST-1 have been determined to be rocky, while the seventh, TRAPPIST-1h, requires additional observations to determine its characteristics due to its longer orbital period.
Mass estimates for the planets range from 0.41 Earth masses (M⊕) to 1.38 M⊕. Radii range from 0.76 Earth radii (R⊕) to 1.13 R⊕.
Spitzer, Hubble, and other telescopes will continue to make observations of the TRAPPIST-1 planetary system, but the best data will likely come from the James Webb Space Telescope (JWST), which is scheduled to launch in late 2018. JWST will allow the atmospheres and temperatures of many exoplanets to be characterized, which will help to settle whether the "habitable zones" of red dwarf stars are actually hospitable.
Artist illustrations and data for the TRAPPIST-1 system compared to Mercury, Venus, Mars, and Earth.
Here's a website dedicated to the star.
Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1 (DOI: 10.1038/nature21360) (DX)
(Score: 4, Interesting) by takyon on Thursday February 23 2017, @09:39PM
The implications of the low orbital period, or more precisely, being close to a red dwarf star which could flare up and cause ion escape, are not too good:
https://soylentnews.org/article.pl?sid=17/02/10/0547243 [soylentnews.org]
http://iopscience.iop.org/article/10.3847/2041-8213/836/1/L3 [iop.org]
The good news is that the James Webb Space Telescope should shed some light on habitability because it will be able to give us a lot of information about the atmospheres. As opposed to Hubble which has only ruled out that 2 of the exoplanets in this system have atmospheres that are not dominated by hydrogen and helium.
Note: TRAPPIST-1's age is supposed to be "at least 500 million years". That means that if ion escape is happening over hundreds of millions of years like that paper suggests, the process might not be finished yet.
You mention seasons but that has to do with the rotation/tilt of the planet. These exoplanets are presumed to be tidally locked. The consensus seems to be that tidal locking is not a big issue for habitability. The atmosphere can circulate heat around the entirety of the planet, and there may be a temperate zone where day meets night (although even full daylight on some of these planets is estimated to look like dusk/dawn on Earth). Maybe tidal locking will actually improve habitability for those planets closest to the star (my speculation).
One thing I was interested in but didn't note in the summary: these planets seem to be less dense than Earth. TRAPPIST-1e and f have radii comparable to Earth but with significantly lower mass. This could be an indication that they are very water rich... perhaps "water worlds" with no land?
[SIG] 10/28/2017: Soylent Upgrade v14 [soylentnews.org]