Planets orbiting ultra-cool TRAPPIST-1 are rocky and rich in water, new research shows

An artist’s impression of the seven planets of the TRAPPIST-1 system. Most are rich in volatile substances such as water.

(M. Kornmesser/ESO)

The seven planets in orbit around the ultra cool dwarf stars TRAPPIST-1 are mostly rocky, with a potential to hold more water than the Earth.

New research shows that the density of the world in this busy system to a greater precision than ever before. The results of this study show that some of the planets could have up to 5 percent of their mass in liquid water form, about 250 times as much water as in earth’s oceans.

“The TRAPPIST-1 planets are very Earth — they have a solid core, surrounded by an atmosphere,” Simon Grimm, an exoplanet scientist at the University of Bern in Switzerland, told by e-mail. Working with a team of researchers, Grimm accurately modeled, the densities of the seven worlds. [Meet the 7 Earth-Size Exoplanets TRAPPIST-1]

In addition to reducing the size of the composition of the exoplanets, the researchers also found that one of the worlds can boast some well-known characteristics.

More Of

  • 250 times as much water

  • TRAPPIST-1 planets

  • Meet the 7 Earth-Size Exoplanets TRAPPIST-1

  • TRAPPIST-1: How Long Would It Take to Fly to the 7-Planet System?

“TRAPPIST-1st is the exoplanet, which is the most similar to Earth in terms of mass, radius and energy received from the stars,” Grimm said.

A special system

In 2016, astronomers of The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile identified three planets around the dim stars TRAPPIST-1. Less than a year later, NASA announces the discovery of yet more worlds, for a total of seven. All of the exoplanets orbit in the habitable zone of their stars, the region where water can remain liquid on the surface. The TRAPPIST-1 system has the largest number of rocky worlds ever found in a habitable zone of a star located only 40 light-years from Earth. [TRAPPIST-1: How Long Would It Take to Fly to the 7-Planet System?]

Intrigued by the system, Grimm and his colleagues decided to measure the system using a technique known as transit timing variations (TTVs). By observing small variations in the amount of time it takes a world to pass between the star and our point of view, a so-called transit, TTVs to the researchers, a number of the most sensitive observations of planetary mass and density.

“With the help of TTVs is currently the only method for determining the masses and so the density of the planets such as the TRAPPIST-1 system,” Grimm said.

Other methods do not work, because the planets are too light or the star is too faint, ” he said. The method allows astronomers to determine the mass of the planets relative to the stellar masses. In combination with the rays as measured by transits of the planet around its star, the technique appears to be the density of each world.

The researchers relied on data captured by NASA’s Spitzer Space Telescope and a number of the European Southern Observatory instruments in Chile for the making of further comments that could reveal the variations in the orbits of the planets.

If a planet has traveled around its star only, then the only attraction would feel like, would come up from the stars. But if a system contains two or more worlds, and the planets interaction, gravity, attract each other with a force related to their masses. These shifts are dependent on the planets’ mass, distance and other orbital parameters.

At the same time, busy systems, such as TRAPPIST-1 make it more difficult to tease out the effects of individual planets, as each world draws a little on his neighbours. The TRAPPIST-1 planets are easier to measure, because they orbit in sync; together, the seven exoplanets form of resonance chain connecting them all together and suggests a slow, peaceful evolution.

“The TRAPPIST-1 system is special because all the planets are in a resonance state,” Grimm said.

Grimm found a simulation that he had previously used for the calculation of the orbits of the planets and adapted to the TTV analysis. With the help of more than 200 transits are team modeled the mass and density of the worlds, the simulation of the orbits of the planets to their modeled transits matched what was observed.

The researchers found in the density of the worlds, ranging from 0.6 to 1.0 times the Earth density. The seven worlds are rich in water, with the water level at some reach as high as 5 percent of the total mass. In comparison, only 0.02 percent of earth’s mass is contained in water.

TRAPPIST-1b and c, of the inner worlds, probably rocky cores and are surrounded by a dense atmosphere thicker than that of the Earth. Located close to their star, the hottest worlds probably thick, steamy atmosphere, while most are located can be covered with ice.

TRAPPIST-1d is the lightest of the seven planets, with a weight of about 30 percent of the mass of earth. The low mass can be caused by a large atmosphere, an ocean, or a frozen icy layer.

TRAPPIST-1f, g and h are located at a sufficient distance from their parent star that water could be frozen in ice on their surfaces. The thin atmosphere would probably be the lack of the heavier molecules found on Earth.

Then there is the TRAPPIST beer-1st, the most Earth-like of the group. If any planet is slightly heavier than the Earth, TRAPPIST-1st probably has a denser iron core, and the lack of a thick atmosphere, the ocean or the ice.

The researchers have warned that the new results, which were published in the journal Astronomy & Astrophysics, not directly say anything about the quality of life. However, by helping researchers to better understand the conditions involved in the busy system, the new research can help to make strides in the understanding of all of the worlds to life.

Originally published on

Follow us

Don't be shy, get in touch. We love meeting interesting people and making new friends.

Most popular