In 2017, NASA announced the discovery of seven Earth-sized planets orbiting the nearby star TRAPPIST-1. But what’s so special about them?
TRAPPIST-1 is a tiny star about the size of Jupiter but 80 times as heavy as Jupiter. If it were a bit smaller, it would not even be considered a star, because it would not be big enough to produce its own light by fusing hydrogen into helium in its core.
The red dwarf lies less than 40 light-years away in the constellation Aquarius. Most of the planets orbiting it are rocky.
What makes this system interesting, however, is that some planets could potentially hold more liquid water than Earth.
Some of the planets might have up to 5 percent of their mass in liquid water form. That’s about 250 times as much water as found in Earth’s oceans.
It’s the first time we have ever found so many Earth-size planets orbiting around a single star. And because the star is so tiny, finding seven planets orbiting around it was quite shocking. No one understands how such a small star managed to form so many planets.
What’s more interesting is that three of the TRAPPIST-1 planets are firmly within the star’s habitable zone – aka the Goldilocks’ Zone – in which liquid water can exist on a planet’s surface.
The form that water would take on TRAPPIST-1 planets would depend on the amount of heat they receive from their star. Water on planets closest to their star could exist in the form of atmospheric water vapor. On others, water could be liquid and on those farthest away, it could exist as ice.
TRAPPIST-1 is the most thoroughly known planetary system apart from our own.
In 2018, researchers from the University of Washington simulated environmental states for each planet of the TRAPPIST-1 system, using terrestrial climate and photochemistry models. The models show that the evolution of all seven exoplanets was likely similar to that of Venus. That means water would have evaporated early on in the system’s formation.
These models also suggest the planets would have dense, uninhabitable atmospheres. However, TRAPPIST-1e planet may host liquid water on its surface and, as a result, be able to support Earth-like life.
TRAPPIST-1e, which orbits in the goldilocks zone, may also have a lot of oxygen.
TRAPPIST-1b is too hot to be hospitable.
TRAPPIST-1c and d receive slightly more energy from their star than Venus and Earth do from the sun and, as a result, might have dense, uninhabitable atmospheres.
Meanwhile, the outer planets — TRAPPIST-1f, g, and h — may be frozen worlds, depending on how much water formed on the planets during their evolution.
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The star we today call TRAPPIST-1 was first discovered in 1999 by astronomer John Gizis and colleagues, using the Two Micron All-Sky Survey (2MASS).
TRAPPIST-1 is named for the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, which discovered two of the seven planets we know of today – announced in 2016. NASA’s Spitzer Space Telescope, in collaboration with ground-based telescopes, confirmed these planets and uncovered the other five in the system.
Each of these planets passes in front of the star when viewed from Earth, causing transit events. By measuring how much light goes missing when the planet passes in front of the star, we can figure out how large each planet is.
The TRAPPIST-1 planets orbit their host star much more closely than planets in our solar system orbit the Sun. The closest planet, TRAPPIST-1 b, orbits around its star once every 1.5 days. For comparison, Earth takes a year to complete one orbit around the Sun. The most distant planet, TRAPPIST-1 h, completes an orbit every 18 days. If you were to put all of the TRAPPIST-1 planets into our solar system, their orbits would all fit within the orbit of Mercury, the solar system’s innermost planet.
However, it is too early to conclude whether there is life on any of the TRAPPIST-1 planets. Scientists surely need further studies and James Webb Space Telescope will be able to clear out some doubts. The telescope is slated to launch at the end of October 2021.
Bottom Line: There is a high possibility that future studies of this unique planetary system could reveal conditions suitable for life.