To hell with our Solar System, with its measly four rocky planets. TRAPPIST-1 40 light-years away has seven, at least three of which might be habitable. Understandably, the discovery of these planets made headline news this past week.
But what might life be like in this system? Well, it might be quite different to here, if it's able to survive the star's intense bursts of radiation. So far, we know very little about the system other than the type of star (an ultra cool red dwarf) and the mass, radius, and orbits of most of the planets. It's enough to make some educated guesses, though.
If there is life there, the views from the surface of the planets might be rather glorious. Above the same point on each planet – as all are tidally locked – the star would appear a salmon-pink color. But as the planets orbit so close to each other, they would also sweep through each other’s skies, sometimes appearing as large as the Moon does in Earth’s sky.
From our planet, we can make out craters, mountains, and more on the surface of the Moon with our naked eyes alone, but we need to send spacecraft on multi-year missions to get a close-up view of other worlds in our Solar System. If an advanced civilization is lucky enough to live on one of the TRAPPIST-1 planets, then they could study their other worlds – some of which might also be habitable – from their own backyards.
From left to right, TRAPPIST-1b, c, d, e, f, g, and h. NASA/JPL-Caltech
Three of the planets in the system – TRAPPIST-1e, f, and g – may have the necessary conditions for water. They’re located in the habitable zone of the star, where temperatures are just right for liquid water, and thus maybe life.
The major unknown at the moment is what sort of atmospheres these planets have to protect against UV radiation from their star. TRAPPIST-1, being 200 times dimmer and 10 times smaller than our Sun, is a type of star that unleashes powerful flares of energy. The planets in the system orbit extremely closely, each no more than a few days, so they are susceptible to these bursts of energy.
“The main barrier to life in a system like this compared to Earth is potentially UV radiation,” Jack O'Malley-James from the Carl Sagan Institute at Cornell University in New York told IFLScience. “It becomes potentially a limiting factor for what life can and can’t do on the surface of the planet.”
An artist's impression of the surface of TRAPPIST-1d. NASA
O'Malley-James recently co-authored a paper on this topic with Lisa Kaltenegger, director of the Carl Sagan Institute, to be published in the Monthly Notices of the Royal Astronomical Society. They looked at the ultraviolet (UV) flux of each world to work out the limits of habitability depending on their atmospheres. The thinner the atmosphere, the more damaging UV radiation makes its way to the surface and the harder it is for life to exist. Having an ozone layer like Earth may be essential.
In a previous paper from the pair, they looked at how biological fluorescence could also be an indicator of life on a world. Consider how, if you looked at Earth from afar, you might notice a lot of green light reflected by vegetation. The same could be true on an alien world with its own plant life.
“If the surface is a really bad UV environment, then maybe life on such a planet could develop biofluorescence,” said Kaltenegger. “That could be something you spot with a telescope on the surface, because when a unique flare hit the planet, it would light up in visible light that wasn’t there before… All of a sudden the planet could become green, red, or so on. It would be super cool to see.”
We’ll need a powerful telescope to see this, though. The upcoming James Webb Space Telescope (JWST), due to launch in October 2018, will be good for studying the planet’s atmosphere in infrared, but it won’t be able to see visible light like this. Instead, we may have to wait for the European Extremely Large Telescope (E-ELT) in 2024.
The type of light hitting these planets may also cause them to look vastly different to Earth. As it's mostly infrared, which is lower energy than visible light, plant life may need to be dark in order to absorb as much light as possible, rather than the bright greens we often get here.
Artist's impression of TRAPPIST-1f. NASA/JPL-Caltech
“If we were to land on one of the planets, don’t expect to see an oasis or green plants,” said Kaltenegger. “You would actually expect plants that basically use all of the light and don’t reflect any. So very dark vegetation that can take up any light it gets, any energy.”
O'Malley-James adds that, if photosynthesis is taking place on any of these worlds, it would likely be at a much slower pace than on Earth. “You could have plants that use redder wavelengths, and photosynthesize using slightly different chemical reactions,” he said. “We don’t really see that on Earth because everything is adapted to use the same kind of light range.”
The one major exception is in deep sea vents on Earth, where microbes have adapted infrared from the heat of the vents to carry out photosynthesis-style reactions. So we do know that, in theory, it’s possible to have life exist in these sorts of conditions.
We know life can exist in harsh radiation environments, too. Experiments on the International Space Station (ISS) have shown that tardigrades can survive unprotected in the vacuum of space; the same might be true for life in the TRAPPIST-1 system.
“Life could be everywhere,” said Kaltenegger. “It’s a completely open question what life can do, if it can evolve in these conditions.”
So what’s next? Well, NASA’s Kepler telescope is currently observing TRAPPIST-1 until March 4 (the data will be released to the public two days later), to further refine the orbits and sizes of the planets, and possibly even see more planets there.
Plenty more telescopes, including Hubble and almost definitely the JWST, will also be training their eyes on this fascinating system. The best is certainly yet to come.
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