TRAPPIST-1: Do the planets contain water?

TRAPPIST-1: Do the planets contain water?
An artists concept of TRAPPIST-1 © NASA-JPL/Caltech

A new study has found that the seven planets orbiting the nearby ultra-cool dwarf star TRAPPIST-1 are all made mostly of rock, and some could potentially hold more water than Earth.

The planets densities are now known much more precisely than before, suggest that some of them could potentially have up to 5% of their mass in the form of water – around 250 times more than Earth’s oceans.

The hotter planets closest to their parent star are likely to have dense steamy atmospheres and the more distant ones probably have icy surfaces.

The fourth planet is the most similar to Earth, in terms of size, density and the amount of radiation it receives from its star. It seems to be the rockiest planet of the seven, and also has the potential to hold water.

A series of four studies have shed new light on the properties of the TRAPPIST-1 planetary system, currently our most optimal hope for evidence of biological life beyond the Solar System.

What is TRAPPIST-1?

  • TRAPPIST-1 is an ultra-cool dwarf star in the constellation Aquarius, and its seven planets orbit very close to it;
  • Named for the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, which discovered two of the seven planets;
  • Planets around the faint red star TRAPPIST-1 are just 40 light-years from Earth;
  • They were first detected in 2016 by the TRAPPIST-South telescope at the European Southern Observatory’s (ESO) La Silla Observatory; and
  • NASA’s Spitzer Space Telescope, in collaboration with ground-based telescopes, confirmed these planets and uncovered the other five in the system.

What have the new studies have found?

The international team first refined the properties of the star at the centre of the system, and secondly improved the measurements of the planets’ radii. A third study offers better estimates than ever for the planets’ masses, while in the fourth study the team performed reconnaissance observations of the planets’ atmospheres.

A team of scientists lead by Simon Grimm at the University of Bern, Switzerland, have applied complex computer modelling methods to all the available data. They then used the data to determine the planets’ densities. The measurements of the densities, when combined with models of the planets’ compositions, strongly suggest that the seven TRAPPIST-1 planets are not barren rocky worlds.

The four international studies were produced in collaboration with the University of Birmingham, UK. The team found that five of the planets appear devoid of an atmosphere made of hydrogen and helium, like for Neptune or Uranus. This new information reinforces the notion that the seven planets of TRAPPIST-1 are similar to the rocky worlds of our Solar System in many ways.

The next step in exploring TRAPPIST-1 will be NASA’s James Webb Space Telescope, the successor to the Hubble telescope, which will be able to delve into the question of whether these planets have atmospheres and, if so, what those atmospheres are like and whether they allow adequate surface conditions to permit liquid water.

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