In February 2017, a team of European astronomers announced the discovery of a system of seven planets orbiting the star TRAPPIST-1. Since then, multiple studies have been carried out to determine whether or not any of these planets could be habitable.
Now, a team of researchers at Columbia University’s Cool Worlds Laboratory (USA) have determined that one of the TRAPPIST-1 planets (TRAPPIST-1e) has a large iron core, a finding that could have implications for the habitability of this planet.
The experts used mass and radius measurements of the TRAPPIST-1 planets to infer the minimum and maximum fraction of the core radius (CRF) for each planet. “If the mass and radius are known very precisely, as in the TRAPPIST-1 system, they can be compared with the expected theoretical models of interior structure,” explains David Kipping.
They determined that the minimum core size of six of the TRAPPIST-1 planets was essentially zero. This means that their compositions could be explained without necessarily having an iron core, for example a pure silicate mantle.
But in the case of TRAPPIST-1e, they found that its core must comprise at least 50% of the planet by radius, and at most 78%.
Compared to our planet, the core is composed of an inner layer of solid iron and nickel, and a liquid outer core of molten iron and nickel, which comprise 55% of the Earth’s radius.
After doing their calculations, the astronomers concluded that there must be a dense core, comparable to Earth in TRAPPIST-1e. This finding could mean that of all the planets in this system, this is the most “Earth-like” and likely has a protective magnetosphere. Furthermore, it is only 39 light years distant from Earth.
As Kipping pointed out, this could have huge implications when it comes to searching for habitable exoplanets, and it could put TRAPPIST-1e at the top of the list.
“This is what excites me most about TRAPPIST-1e. This planet is a little smaller than Earth , it is right in the habitable zone and now we know that it has a large iron core like Earth. We also know that it does not it has a slight volatile envelope thanks to other measurements. Also, TRAPPIST-1 appears to be a quieter star than Proxima, so I’m much more optimistic about TRAPPIST-1e as a potential biosphere than Proxima b at this point, “says Kipping.
While the discovery of Proximab was made by astronomers at ESO using the Radial Velocity Method, this campaign was significant in drawing attention to the probability of finding potentially habitable terrestrial planets around nearby M-type (red dwarf) stars. .
In the future, Kipping and his team also hope to conduct studies of Proxima b to determine if it has an atmosphere and to determine what its Minimum and Maximum Core Radius Fraction might be.
Reference: TRAPPIST-1e Has a Large Iron Core Gabrielle Suissa, David Kipping arXiv: 1804.10618 [astro-ph.EP] 2018
Image credit: NASA / JPL-Caltech
