Some planets in the TRAPPIST-1 system might have magma oceans

Jupiter and its big moons, the TRAPPIST-1 system and the solar system (Image NASA/JPL-Caltech)
Jupiter and its big moons, the TRAPPIST-1 system and the solar system (Image NASA/JPL-Caltech)

An article published in the journal “Nature Astronomy” describes a research on the magnetic field of the star TRAPPIST-1 and its possible consequences on its inner planets. According to a team of researchers led by the Space Research Institute (IWF) of the Austrian Academy of Sciences (Öaw) at least two of those planets could be heated by the effects of that magnetic field to the point of having a surface composed of a magma ocean.

The announcement arrived in February 2017 of the existence of 7 rock planets that orbit the ultra-cool dwarf TRAPPIST-1 was really sensational. This tiny star system was already considered interesting because it was already confirmed that it hosted a few planets and the attention on it increased dramatically when the number went up to 7.

The positions of the planets’ orbits suggested the theoretical possibility that there was liquid water at least in some areas of ​​all those planets. However, the data available on the characteristics of the star TRAPPIST-1 and the possible atmospheres of the planets were still limited. Now a research on the star’s magnetic field could once again question the chances that on such planets the conditions are favorable to hosting life forms.

The star TRAPPIST-1 is really tinly, with a size similar to Jupiter, yet the magnitude of its magnetic field is estimated at a hundred times the Sun’s. This is due to the different structure of the two stars and the fact that the magnetic field is generated by its convection. The Sun has a radiative area inside it and a convective area in its outer layers. TRAPPIST-1 is a purely convective star, which makes its magnetic field very powerful.

Kristina Kislyakova of the University of Vienna explained that her team was interested in investigating the induction heating effects generated by stellar magnetic fields on their planets. Electric currents form within a planet that passes through a variable magnetic field with the consequence that the planet heats up. A very powerful magnetic field can heat up a planet so much as to melt its mantle.

TRAPPIST-1 is an ideal object for this type of study for its powerful magnetic field and the presence of 7 planets. The researchers estimated the energy released into the planets due to induction heating. The result is that the inner planets of that solar system may have a liquid surface or at least enough magma to have a remarkable volcanic activity.

Once again a comparison can be made between TRAPPIST-1 and Jupiter’s system with its moons. Io is the closest to the planet among the great moons and has a strong volcanic activity but it doesn’t have a stable atmosphere. There may be a strong volcanic activity on some planets of TRAPPIST-1 with the consequent creation of clouds.

Luca Fossati, one of the article’s authors, explained that the effects of those clouds depend on their density and composition. They could generate a greenhouse effect or reflect the star’s light lowering the planet’s temperature. In essence, more information on the characteristics of the planets are needed to better understand what’s happening on their surface.

The researchers plan to extend this type of study to other star systems such as Proxima Centauri b and some with planets orbiting white dwarfs. Right now, the results may be disappointing for the people who hoped that all TRAPPIST-1 planets could be at least partially favorable to life but it certainly confirms that it’s very interesting for astronomical and astrobiological research.

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