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Rubidium_71
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Neil deGrasse Tyson offered an opinion...
http://www.inquisitr.com/4021299/th...-trappist-1-neil-degrasse-tyson-has-bad-news/
http://www.inquisitr.com/4021299/th...-trappist-1-neil-degrasse-tyson-has-bad-news/
Trigonometric parallax by CTIOPI:jordankonisky said:Can anyone described how this distance was determined?
I come up with 0.9 light years. Close enough for wiki inspired government work.mfb said:At that distance, the parallax method is very precise - the current uncertainty is 1.3 light years
According to my always questionable maths, GAIA will yield an accuracy of ±0.0005 ly for Trappist 1. [based on the numbers provided by Bandersnatch's second reference], and Gaia will reduce this uncertainty to less than 0.1 light years in 2-3 years.
Thanks. What about possible deviations of their orbits? It doesn't seem they come closest always in the same point, if I'm correct.mfb said:See post 13. Strong, but similar to the Moon's effect on Earth for the interesting planets.
Thanks, mfb.mfb said:According to an orbital stability calculator posted earlier, the orbits are long-term stable for reasonable values of their eccentricity.
Using thousands of numerical simulations to identify the planets stable for millions of years, Quarles concluded that six of the seven planets are consistent with an Earth-like composition. The exception is TRAPPIST-1f, which has a mass of 25 percent water, suggesting that TRAPPIST-1e may be the best candidate for future habitability studies.
It's in arxiv as [1704.02261] Plausible Compositions of the Seven TRAPPIST-1 Planets Using Long-term Dynamical Simulationsmfb said:
Small iron cores would work, yes. In fact, that likely explains the densities of Mars and the Moon -- they are less dense than what one would expect from the Earth's composition.DrStupid said:How reliable is the relationship between mean density and water content? Are there alternative explanations for low densities (e.g. small metal cores)?
Planets b, c, and possibly d are all in runaway greenhouse state, so their low densities are likely the result of massive and thick steam atmospheres not a layer of ocean or ice. Little water building up bars of water vapor envelope can already explain the radius and masses of the inner three planets without involving large quantity of water in the condensed form.lpetrich said:[1802.01377] The nature of the TRAPPIST-1 exoplanets -- the most recent paper on them at arxiv.
Not So Strange New Worlds - NASA Spitzer Space Telescope, Imagining the Planets of TRAPPIST-1 - NASA Spitzer Space Telescope
These planets likely have a few percent of water by mass, and this translates into something like
b: 400, c: 200, d: 250, e: ~0, f: 250, g: 400, h: 150, all km of depth
with error bars around 100 km of depth. The Earth has 0.023% water by mass, with average depth 3.7 km and planetwide average 2.6 km.