EDIT: if we are looking for a name for the system, I think we should call it ...
Quote from: Bynaus on 02/22/2017 07:35 pmEDIT: if we are looking for a name for the system, I think we should call it ... [In the spirit of the suggestion. ]Presumably you mean a name for the star? (TRAPPIST-1 is a catalog designation.) The system would then be called 'the [name of star] system'!The IAU Working Group on Star Names might go for Axanar. The only two catalog designations I can find are 2MASS J23062928-0502285 and the later TRAPPIST-1 suggesting the star was discovered in the Two Micron All-Sky Survey of 1997-2001. So, there's unlikely to be any of the traditional or historical names for which the WGSN has a preference. The WGSN might object though if they consider a name from the title of a fan-made Star Trek movie to be a name of a principally commercial nature. Also, the film concerns the 'Battle of Axanar' and the WGSN also prohibit names related to military activities!
XRays won't penetrate far into the water - as long as you've got water oceans, you can have underwater life. Of course if you have that, then you probably have an atmosphere above it.
Arxiv preprint on UV / XUV and habitability in the Trappist-1 system. Long story short, if there is an Earth-like moderately dense atmosphere with an ozone layer - all good. That failing, not even UV-resistant bacteria can make it.https://arxiv.org/abs/1702.06936
The system is only about 500 Ma old, so biogenic O2-rich atmospheres/ozone layers seem not very likely anyway.
That number is only a very rough minimum. The age of extremely long lived M dwarfs is notoriously hard to pin down because they evolve so slowly. The star could be billions of years old, especially because it seems to be a quiet star flare-wise.
Quote from: the_roche_lobe on 02/23/2017 08:13 amThat number is only a very rough minimum. The age of extremely long lived M dwarfs is notoriously hard to pin down because they evolve so slowly. The star could be billions of years old, especially because it seems to be a quiet star flare-wise.On the other hand, it has a high metallicity ([Fe/H] = +0.04), which suggests it can be *too* old. Similarly, it has a fast rotation rate. But as you say, 0.5 billion is a minimum. It could easily be a few billion.
Yes, I think the runaway greenhouse limit for the smallest red dwarfs is around 0.9 S_Earth. So if scaled properly, the HZ is slightly further out for a smaller star. The paper preprint linked above says that they did climate models on all of them, and b, c, d ran into the runaway greenhouse state, while e, f, g remained temperate (h is likely too cold).
I was thinking to myself that this solar system model may be giving us a glimpse of what planetary systems look like in the absence of a gas giant that cleans smaller rocky bodies out of the inner orbital space.
Greg Laughlin is always worth reading. Here’s the relevant paragraph from his post today:“2MASS J20362926-0502285, now much better known as TRAPPIST-1, straddles the boundary between the lowest mass main sequence stars and the highest mass brown dwarfs. Depending on precisely what its mass and metallicity turn out to be, it could either be arriving at self-sustaining core hydrogen fusion, which would make it a main sequence star (about a 60% chance) or it could be currently achieving its peak brown dwarf luminosity and bracing for a near-eternity of cooling into obscurity (about a 40% chance).”Also quite interesting here is his take on the future of this system, assuming TRAPPIST-1 is indeed a main sequence star:“An object with solar composition and 0.08 solar masses never turns into a red giant. As time goes on, it maintains a near-constant radius, and slowly burns nearly all of its hydrogen into helium. In roughly 10 trillion years, TRAPPIST-1 will reach a maximum temperature of ~4000K, pushing it briefly toward K-dwarf status for a few tens of billions of years, before eventually running out of fuel and fading out as a degenerate helium dwarf.”
An interesting thought has occurred to me. ...
Quote from: JasonAW3 on 02/23/2017 06:24 pmAn interesting thought has occurred to me. ...That's not quite how it works. The star is, by far, the dominant tidal influence on the planet's rotation states.Test your idea though: The mass ratio of TRAPPIST-1 to its planets is about the same as that of Jupiter to its moons, Saturn to its moons, and Uranus to its moons, with rather similar levels of compactness (Jupiter being somewhat less of course). What are the rotation states are the moons of Jupiter, Saturn, and Uranus?(Also, I suspect the torque on a planet's rotation by a passing planet would probably average to zero, given circular orbits)
By the way there's a special Google Doodle today celebrating this discovery.IAU really need to give this star a proper name.
[W]ater vapor in the upper atmosphere could photo-dissociate and sustain an outflow of escaping hydrogen. The stellar Ly-α line is bright enough to perform transit spectroscopy, and we detect marginal flux decreases in localized, high-velocity ranges during the transit of planet b, and shortly after thetransit of planet c. This could hint at the presence of extended hydrogen exospheres around the two inner planets, and suggest that atmospheric escape might play an active role in the evolution of all TRAPPIST-1 planets.
What impact could larger planets such as gas and ice giants further out in the system have on the habitability of these rocky worlds?