spaceSpace and Physics

Some Of The Exciting TRAPPIST-1 Planets Could Contain More Water Than Earth


Jonathan O'Callaghan

Senior Staff Writer

An updated graphic of the TRAPPIST-1 system based on these new findings. NASA/JPL-Caltech

Astronomers say they now know more about the TRAPPIST-1 system, 40 light-years away, than any other besides our own – and it looks like there’s a lot of water on its planets.

Four studies have been published, including in Nature Astronomy and Astronomy and Astrophysics, that give us a fascinating glimpse at these seven worlds. Perhaps most excitingly, astronomers report that up to 5 percent of some of the planets’ mass may be water – 250 times that on Earth.


“The form that water would take on TRAPPIST-1 planets would depend on the amount of heat they receive from their star, which is a mere 9 percent as massive as our Sun,” NASA noted in a statement.

The three outermost planets – f, g, and h – are thought to be far enough from the star that their water is frozen as ice. However, three of the planets (e, f, and g) orbit in the star’s habitable zone. TRAPPIST-1e in particular looks like it could host water, while the innermost planets may contain water in the form of atmospheric vapor, like Venus in our Solar System.

All of the planets appear rocky, and they may have vast quantities of water. NASA/R. Hurt/T. Pyle

Scientists probed the planets using data from NASA’s Hubble, Kepler, and Spitzer space telescopes. They found that all seven planets were likely made of rock, and they all had the potential to be temperate, bearing a striking similarity to the rocky worlds in our Solar System.

One of the planets in particular, TRAPPIST-1e, which is the fourth from the star, appears to be the most Earth-like in the system in terms of its size and density. Of the seven planets, it is the only one to be slightly more dense than our own, suggesting its iron core – if it has one – is denser than ours.


Scientists were also able to conduct preliminary atmospheric studies on the atmospheres of the four most Earth-sized planets (d, e, f, and g) by studying the light of their star as it passes through them. At least three of them (d, e, and f) appear to have an atmosphere unlike those of Neptune and Uranus – rich in hydrogen and helium – suggesting they are more similar to our own terrestrial worlds.

At least three of the planets (e, f, and g) appear to be in the star's habitable zone. NASA/JPL-Caltech

“One of these four could be a water world,” said Hannah Wakeford of the Space Telescope Science Institute in a statement. “One could be an exo-Venus, and another could be an exo-Mars.”

These studies re-iterate just how exciting this planetary system is. There is a possibility that one or more of these worlds could be habitable. And being on our cosmic doorstep, they are close enough for us to study them in detail. There will be plenty more exciting findings to come from this system in the future.

“No one ever would have expected to find a system like this,” said Wakeford. “It’s a goldmine for the characterization of Earth-sized worlds.”


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