Dwarf star TRAPPIST-1’s habitable zone found to be packed with seven rocky exoplanets
It started with just three planets. Astronomers using The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) discovered three exoplanets orbiting a redish, ultra-cool dwarf star some 40 light years away. That star, hence dubbed TRAPPIST-1, became the focus for a number of different telescopes around the Earth, the Hubble space telescope and now NASA’s Spitzer Space Telescope, all of which as revealed that there’s a lot more to see orbiting this star. In addition to confirming the first three rocky planets, four more have been found to be tucked into a tight orbit around TRAPPIST-1, and anywhere from three to all seven may be home to liquid water.
Locations for liquid water?
Distant planets in other solar systems, called exoplanets, are turning out to be more and more numerous the more we look. Many are large gas giants, like Jupiter and Saturn, that probably don’t sustain any life on their own, at least not in a way we currently recognize. Rocky planets with more modest atmospheres, on the other hand, are more likely to be analogs to Earth, particularly if they’re in the Habitable Zone of their solar system. These planets would be in orbits that are close enough to their respective stars to be warm, but not so close to be blazing, dried up crisps, so that things like water and possibly biology can function in a way similar to what you find on our own planet.
In the case of the new TRAPPIST-1 exoplanets, this habitable zone is unusually close to the star. All seven planets orbit closer to their star than Mercury does in our own solar system, but because TRAPPIST-1 is a smaller, cooler star, that’s not a problem as far as temperatures are concerned. The orbits are actually so tight, that if you were to stand on the surface of one planet, you’d be able to see it’s neighbor in the sky with more detail than we can see in a full moon on Earth. It also means that some of the planets complete a full orbit around their star in as little as 1.5 days on Earth.
Strange surface conditions
Beyond the tight orbits, there are a few other idiosyncrasies of these new exoplanets that might be harder for an Earthling to cope with if they could ever make the 40-light-year trip. All seven planets in the system are what’s known as tidally-locked in their orbits, which means that they keep the same side of the planet facing their star at all times, in the same way our Moon always has the same side facing Earth. This would mean that there is no day and night cycle on these planets, as one side is always dark, and the other is always light.
The quality of that daylight is a bit different from what we’re used to also. As you might expect from a small, reddish-brown star, the light is mostly red, and probably doesn’t get much brighter than the light reflected from a full moon on Earth. A lot of the light emitted by the star is actually in the infrared portion of the electromagnetic spectrum, meaning we can’t really see it with our eyes, although it was helpful for the Spitzer Space Telescope’s instruments to pick up.
At this point, the big questions to tackle aren’t so much about the views, but about how wet any of these planets may be. The Spitzer and Hubble telescopes will follow up with more observations of the distant planets for signs of their atmospheric composition. When the James Webb Space Telescope launches next year, it will be able to assist with these observations, detecting things like water, methane or oxygen, but also signs of the planets’ temperatures and surface pressures. Even if life-sustaining water isn’t found, the fact that these planets exist in the small habitable zone of an ultra-cool dwarf star in the first place suggests that there is a lot of exoplanet real estate to look for in the universe, and that these types of rocky worlds are much more common than once thought.
My second grader said: If you wanted to visit these planets, you’d probably want to have your base where the daylight meets the dark, so that you could just cross over to the ‘night’ side of the planet whenever you wanted to sleep.
This might make sense, although the low-light conditions and lack of blue-spectrum light would probably wreak havoc on your circadian rhythm either way. There’s also a chance that the temperature differentials between the two sides of these planets might lead to some rough, windy weather, making a good night’s sleep a tricky thing to come by.