Tuesday, 20 February, 2018

TRAPPIST-1 worlds likely terrestrial and water-rich

This artist's concept shows what the TRAPPIST-1 planetary system may look like based on available data about the planets diameters masses and distances from the host star as of February 2018 TRAPPIST 1 planets found to be rich with water, boosting chances for life
Theresa Hayes | 06 February, 2018, 19:04

"The discovery of TRAPPIST-1 and the capabilities of ESO's facilities in Chile and the NASA Spitzer Space Telescope in orbit have made this possible - giving us our first glimpse of what Earth-sized exoplanets are made of!"

In September 2017, scientists with the help of NASA's Hubble Space Telescope found that the outer Earth-sized planets orbiting the nearby dwarf star TRAPPIST-1 might still harbour substantial amounts of water.

TRAPPIST 1 planets entail life supporting atmosphere according to a recent study carried out by scientists. This discovery is an important step towards determining if the planets might harbor liquid water on their surfaces, which could enable them to support living organisms.

Dr Amaury Triaud, from the University of Birmingham, a leading member of the worldwide team, said: "Of the seven planets, and of all the exoplanets that have been identified so far, Trappist-1e is the most resembling Earth, when we consider the amount of energy a planet receives from its star, and its density, which reflects its internal composition".

Altogether, the densities suggest that water could account for up to five percent of the mass of some of the planets - by comparison, water only makes up about 0.02 percent of the Earth's mass.

One, Trappist-1e, stands out as being the most Earth-like in terms of its size, density and the amount of light energy received from its star. By measuring the power of these tugs, and putting that data into a sophisticated computer-modeling algorithm, the researchers were able to get an idea of how dense each planet was.

The planets, which scientists say are the best-studied worlds outside our solar system, "remarkably resemble Mercury, Venus, our Earth, its moon and Mars", said Amaury Triaud, a University of Birmingham astronomer who co-authored one of the studies.

The study suggested the hotter planets closest to their parent star are likely to have dense steamy atmospheres, and the more distant ones probably have icy surfaces. Study co-author Brice-Olivier Demory, at the University of Bern, said as much: "Densities, while important clues to the planets' compositions, do not say anything about habitability". It may have a denser iron core than Earth.

TRAPPIST-1f, g and h are far enough from the star, water could be frozen across their surfaces. If they have thin atmospheres, they would be unlikely to contain the heavy molecules of Earth, such as carbon dioxide, the study said. Focusing on the mass, radii, and first atmospheric constraints of the exoplanets, the latest findings confirm the terrestrial and globally rocky nature of the TRAPPIST-1 planets.

"It is interesting that the densest planets are not the ones that are the closest to the star, and that the colder planets can not harbor thick atmospheres", said Caroline Dorn, study co-author based at the University of Zurich, Switzerland. A recent study using NASA's Hubble Space Telescope found no detection of hydrogen-dominated atmospheres on planets TRAPPIST-1d, e and f - another piece of evidence for rocky composition - although the hydrogen-dominated atmosphere can not be ruled out for g. The amount by which the starlight dims is related to the radius of the planet.

"It's interesting because we have four planets that are at different distances from the star". Because the TRAPPIST-1 planets are all squashed in so closely, their gravitational pulls can mess with each other's orbits. Those variations in orbital timing are used to estimate the planets' masses. They used the telescope observations to calculate the densities more precisely than ever, then used those numbers in complex simulations. These will be able to narrow down the possibility that the planet is habitable. "And still, TRAPPIST-1 does exist!" At present, the Hubble Space Telescope is integral to this kind of work, but the James Webb Telescope will provide even greater capacity for observation when it's ready to be employed.

"Our conceptions of what these planets look like today may change dramatically over time", said Robert Hurt, senior visualization scientist at the Spitzer Science Center.