Massive exoplanet orbiting tiny star challenges planet formation theory

An artist's impression of the gas giant planet GJ 3512b orbiting its red dwarf host star released on Sept 26 2019

The most commonly accepted explanation for how the gas giant planets formed is that rocky icy cores were created by the accumulation of smaller bodies in the outer regions of the disc.

The planet, known as GJ 3512 b, completes one orbit around the star every seven months.

But a new discovery of a large planet orbiting the small star GJ3512 is worth noting.

The planet orbiting this particularly small and cool red dwarf star, officially known as GJ 3512, is at least half the mass of Jupiter. For comparison, the Sun is about 1,050 times more massive than Jupiter.

Co-author Hubert Klahr from the Max Planck Institute for Astronomy in Heidelberg, Germany, said: "Until now, the only planets whose formation was compatible with disc instabilities were a handful of young, hot and very massive planets far away from their host stars".

Planets are born from the same disk of interstellar gas and dust that produces the star around which they orbit. "In any case, here, we show the opposite - that is, we have discovered a gas mammoth planet circling an extremely low-mass star".

There is evidence of a second planet now orbiting the star, while a third planet might have been ejected from the star system in the past, explaining the elliptical orbit of the Jupiter-like planet, Morales said. This process would have ejected a third planet from the system. But it's hard to see how planets could form in this way around a low mass star - the disc would not be massive enough.

How is this possible?

An global team of astronomers has reported its findings in the journal Science.

Multiple approaches to researching this phenomenon led them to one conclusion: gravitational disk collapse.

Astronomers use computer simulations to inform their theories of how planets form out of the clouds, or "discs", of gas and dust orbiting young stars. At this point, they were able to gather a hydrogen and helium envelope before the planets migrated to the inner edge of the disc, or the disc dispersed. Several of the other planets that have been discovered orbiting red dwarf stars have instead been found by the transit method - looking at how a star's light dims as a planet passes in front of it.

As per specialists, who distributed their work on Thursday in the diary Science, finding such a huge planet nearly a little star could drive space experts to reexamine how planets structure.

"It's exciting because we've wondered for long a time whether giant planets like Jupiter and Saturn can form around such small stars", said Prof Peter Wheatley, from the University of Warwick, UK, who was not involved with the latest study. "This find prompts us to review our models". The radial velocity method is based on gravity and the Doppler effect, in which light increases or decreases in frequency as a source and observed object move toward or away from each other.

The planet composition comprises Jupiter's structure, being mainly gas. This relies on detecting how the wavelength of the starlight gets periodically shifted (to blue or red) by a tiny amount as the unseen planet orbits, tugging the star to and fro.



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