It’s SO COOL that we’ve found seven rocky and (broadly) Earth-sized planets orbiting a red dwarf star just 39 light years away.
How cool? I’m talking leap in the air and shout ‘this is totally fucking uber-cool‘ scale cool. It’s exciting like nothing else astronomical for a long while. It’s – well, figure this: it’s possible that all seven planets – with the right combination of atmosphere – could be similar to Earth. That’s sub-zero cool. Not only that, but if we follow the theme of the TRAPPIST telescope after which the star’s named, every one of them has potential to be named after a style of Belgian beer (Achel, Chimay, Orval, Rochefort, Westmalle, Westvleteren, etc).*
Though – just to temper it a bit – there will be twists. All but the outermost worlds are likely to be tidally locked – just like the Moon is to Earth – which might restrict the habitable zone to a narrow band around the terminator. It’s also likely that the innermost world, TRAPPIST-1a, is wildly volcanic for the same reasons as Io: tidal flexing.
Because red dwarf stars also flare erratically, it’s likely that stellar flares and general irradiation has stripped some or all of these planets of their atmospheres and water, if they had any to begin with. A paper published last year by Julian de Wit and others, when astronomers knew there were planets around this star but hadn’t nailed down the full characteristics of the system, used data from ESA’s XMM-Newton orbiting telescope to show that X-ray flux around the TRAPPIST-1 system was enough to alter planetary atmospheres.
As for life? That’s moot, given the radiation flux. A tech-civilisation? Sure, if its electronics can withstand an 1859 Carrington-level solar storm every hour or two.
And although three of Trappist-1’s planets are directly in the habitable zone, don’t forget that our own solar system also has three rocky planets in the habitable zone. Are they all Earth-like? Uh…no. Venus has an atmosphere with surface pressure 90 times that of Earth, is hot enough to melt lead, and the whole lot is swathed in clouds of boiling sulphuric acid. Mars has almost no atmosphere, no obvious signs of life – and we’re struggling to prove that life ever existed there (I’d be surprised if it hadn’t, but hey – science needs empirical proof).
To have a reasonable facsimile of Earth you need a whole lot of conditions to be true. Just being the right mass and in the right part of the habitable zone isn’t enough – the planet must also have an iron core to generate a magnetic field that protects it from solar wind-driven atmospheric stripping. Our large iron core exists because of early Earth’s collision with a Mars-sized world, which also produced the Moon. And there is evidence that the Moon’s gravitational influence had effect on other ways Earth developed. The final ingredient is water-using carbon-based life, because it’s only through this that an oxygen atmosphere can emerge. Earth didn’t have one for much of its history. What’s more, there is evidence that crustal plate movement may also have played a role in how life developed to enable that.
Just now, we have none of that information about the TRAPPIST-1 worlds. They are known only through transit data: by chance, the plane of the TRAPPIST-1 system matches our sight-line, and the planets were picked up through fluctuations in the star’s brightness while passing across its face. Star systems whose planets are tilted out of our sight-line can’t be discovered that way.
To find out whether any of TRAPPIST-1’s planets is like Earth, or has suffered the same fate as Mars or Venus – or something else – we’ll need more data. And that’ll come, especially after the James Webb Telescope is operational. Because the planets transit, we can discover the compositions of their atmospheres, for instance, through the way they change the spectrum of the star as its light passes through, providing we have sensitive enough instruments.
For all that, the fact that we have to wait doesn’t reduce the excitement. Seven near-Earth mass planets! Who’d have imagined that many around a single star? A star, what’s more, named after the main discovery telescope – the TRAnsiting Planets and PlanetesImals Small Telescope (TRAPPIST) in Chile – which, itself, commemorates the name of a particularly excellent style of Belgian beer. See what I mean about cool?
So – what (for me) are the coolest parts of this discovery? Other than the fact that it’s named after Belgian beer, I mean:
- TRAPPIST-1 is a tiny star – it’s an M8V class red dwarf, physically little bigger than Jupiter, and one of the lowest-mass stars you can have (it’s still a lot more massive than Jupiter, there are some quite neat technical reasons why high-mass planets and low-mass stars end up about Jupiter’s size, which I’ll blog about soon).
- Its planetary system is equally miniscule, more like an enlarged Jupiter system than our own solar system. In fact the innermost two worlds don’t orbit much further away from the primary than Ganymede and Callisto are from Jupiter. And that brings up the coolest thing: most of these worlds, at various times, appear as visible discs – up to twice the size of our Moon – in the skies of the others. And their orbital periods are so short that they’ll visibly grow and shrink as they whirl around the star. How cool is that?
- Despite my caution in absence of more evidence, there IS a chance that at least three of these worlds could resemble Earth and maybe host life ‘as we know it’ (if there is such a thing).
- Jupiter’s major moons are all radically different from each other, even though they formed in the same general area and are subject to exactly the same laws of physics. What’s the bet that the Trappist-1 system kicks up an equally contrasting set of worlds?
- If intelligent, tech-wielding life emerged on one of those worlds, interplanetary travel would be a cinch. Instead of months-long cruise-times demanding large (expensive) hab-modules, along with the medical hurdles posed by long-term radiation and free-fall, Trappist-1’s explorers could get away with transit times of days or – at most – weeks. If our solar system was that dinky, we’d certainly have got to Mars by now.
And, as a final thought, has the phrase ‘looks a bit like the Kerbin system’ occurred to anybody? Just saying…
Copyright © Matthew Wright 2017