TRAPPIST 1 planets found to be rich with water, boosting chances for life

ALIEN life could be a stone-throw away. The Hubble Space Telescope has confirmed four extraordinary planets — all within the ‘Goldilocks zone’ of a nearby star — are rich with water.


IT caused a sensation when the discovery was first announced a year ago. Seven roughly Earth-sized worlds were found in orbit around just one star — TRAPPIST 1.

And that dim red dwarf star is relatively close in astronomical terms: just 39 light years away.

This means it and its clutch of rocky worlds are potentially within the reach of current technology to observe their composition.

Four of the planets sit neatly within the star’s ‘Goldilocks zone’, a distance where it was neither too hot nor too cold to sustain liquid water.

Now the Hubble Space Telescope and European Southern Observatory have revealed that at least five of the planets consist of up to 5 percent water. In comparison, Earth’s oceans account for just 0.02 per cent of our planet’s mass, despite covering about 71 per cent of its surface.

The potential the existence of so many water worlds in one place has for the emergence of life has left astronomers sitting on the edge of their seats.

Astronomers used the Hubble Space Telescope to learn more about the Trappist system by studying the planets’
atmospheres as they passed in front of their star, appearing as a dark, travelling dot from the observer’s point of view.

The findings were published overnight in two papers in the journals Nature Astronomy, and Astronomy and Astrophysics.

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This infographic lists the main properties of the seven TRAPPIST-1 planets, along with the four innermost planets in the Solar System at the same scale.


The Trappist-1 system is considered the current best hope for finding evidence of alien life.

Though much remains unknown about the planets’ surfaces and atmospheres, the new measurements have not ruled out the possibility that they may harbour even rudimentary life, the scientists reported.

“So far, no sign allows us to say that they are not habitable,” said University of Birmingham astronomer Amaury Triaud, the co-author of a study on the subject.

“All the traffic lights we have passed so far are green.”

As for the odds of the planets hosting organic life forms, “we cannot say at this stage, as they are vastly different from the only planet we know to harbour life (Earth),” Triaud told AFP.

“But they have suitable characteristics and are to date the best place beyond the edge of our (Solar) system to search.”
But the presence of liquid water is considered essential for life to exist anywhere.

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The TRAPPIST-1 system contains a total of seven known Earth-sized planets. Three of them — TRAPPIST-1e, f and g — are located in the habitable zone of the star (shown in green in this artist’s impression).


Research teams have gleaned more information about the dwarf star at the centre of the Trappist-1 system, as well as improved measurements of the size and mass of each planet, and the composition of their atmospheres.

All seven planets were considered potential candidates for harbouring water, but the chances of finding it in liquid form are highest in the temperate “Goldilocks” zone.

At least five of the TRAPPIST-1 planets are now believed to have a covering of “volatile substances” ... such as an atmosphere, ocean or sheets of ice.

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This diagram compares the sizes, masses and estimated temperatures of the TRAPPIST-1 planets with Solar System planets. The colours indicate temperatures and the black line matches the densities and composition of the terrestrial planets in the Solar System. Planets above the line are less dense and planets below are more dense.

The water may be in the form of gas or ice, or trapped deep inside the rocky orbs, the researchers said. But four of these planets are warm enough for that water to be liquid if protected by an atmosphere from boiling off into space.

“When we combine our new masses with our improved radii measurements, and our improved knowledge of the star, we obtain precise densities for each of the seven worlds, and reach information on their internal composition,” said Triaud.

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This artist’s impression compares the seven planets orbiting the ultra-cool red dwarf star TRAPPIST-1 to the Earth at the
same scale. They are shown to the same scale but not in the correct relative positions.


Compared to our Solar System, the Trappist-1 family is very tightly knit. With orbits ranging from 1.5 to 12 days, the planets would have fit comfortably in the distance between the Sun and its closest planet, Mercury.

Trappist-1 has a mass less than 10 per cent the mass of our Sun and is much cooler, which explains why its planets can orbit so nearby.

“All seven planets remarkably resemble Mercury, Venus, our Earth, its Moon, and Mars.” According to study co-author Simon Grimm from the University of Bern, the third and fourth planets from the star are “the most likely” to host some form of life.

“The more we learn about these planets, the more habitable they seem to be,” Grimm told AFP by email.

Brice-Olivier Demory, Professor at CSH and co-author of the study published in the journal Astronomy and Astrophysics, said: “We were able to measure precisely the density of exoplanets that are similar to Earth in terms of their size, mass and irradiation, with an uncertainty of less than 10 per cent, which is a first and a decisive step in the characterisation of potential habitability.”

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This diagram compares the masses and energy input of the seven TRAPPIST-1 planets, along with the properties of the four innermost Solar System planets.


Astrophysicists believe the two innermost planets, TRAPPIST-1b and c have dense atmospheres, potentially giving them a runaway greenhouse effect such as found on Venus.

TRAPPIST-1e is likely to be rocky with a thin atmosphere.

TRAPPIST-1d, roughly only one third the mass of Earth, is however ‘surrounded by volatile substances such as water’. It’s not known if it is its gas, ice or liquid state.

The three outer planets — TRAPPIST 1f, g and h — are believed to be too far from their weak red dwarf star for it to melt water ice.

Hubble has so far failed to detect the presence of a hydrogen-rich atmosphere around any of the TRAPPIST worlds. It’s hoped the new James Webb Space Telescope, due to begin operations in 2019, will be powerful enough to do so.