Astronomers have discovered a massive exoplanet orbiting Gliese 3512 (GJ 3512), an M-dwarf star (red dwarf) located 31 light-years away. Dubbed Gliese 3512b, the planet has a mass of 0.46 Jupiter masses, very high for such a small host star, and an eccentric 204-day orbit. Using simulations, the researchers have also demonstrated that the Gliese 3512 planetary system challenges generally accepted theories of planet formation.
An artist’s impression of a Jupiter-like exoplanet and a cool red dwarf. Image credit: CARMENES / RenderArea / J. Bollain / C. Gallego.
M-dwarf stars are low-mass stars that emit most of their faint light in the near-infrared. They the most common type of star in the Milky Way. However, despite their ubiquity, only about 10% of nearly 4,000 exoplanets discovered to date orbit these stars.
“Around such stars there should only be planets the size of the Earth or somewhat more massive super-Earths,” said University of Bern’s Professor Christoph Mordasini, co-author of a paper published in the journal Science.
“Gliese 3512b, however, is a giant planet with a mass about half as big as the one of Jupiter, and thus at least one order of magnitude more massive than the planets predicted by theoretical models for such small stars.”
“Although we know about 4,000 planets outside the Solar System, there are still discoveries which bring new surprises. The planet around Gliese 3512 is one of those,” said Georg-August-Universität’s Professor Stefan Dreizler.
To discover Gliese 3512b, Professor Mordasini, Professor Dreizler and their colleagues used the Doppler technique, which monitors the back-and-forth motion of a star when it is orbited by one or more exoplanets.
They also found evidence suggesting the presence of another candidate planet in the system.
“Gliese 3512 was so faint that it almost did not make it into the list of targets,” they said.
“However, once the data had been analyzed, it was clear that its behavior suggested something very interesting.”
“The star’s velocity was changing very rapidly and consistently, indicating the presence of at least one massive companion, an unusual feature for a red dwarf.”
“In addition, the irregular orbit of Gliese 3512b suggests the possibility of an earlier collision with another planet meaning there could be a wandering world in the galactic void.”
According to the team, the widely utilized core accretion models of planet formation fail to explain how this particular system was able to form. Alternative disk instability theories may be more relevant in some cases than previously thought, when it comes to explaining planet formation.
“One possible explanation for the failure of current theory could be the mechanism underlying the model, known as core accretion. Planets are formed by the gradual growth of small bodies into ever larger masses. We call this a bottom-up process,” the scientists said.
“Maybe Gliese 3512b was formed by a fundamentally different mechanism, a so-called gravitational collapse,” they added.
“A part of the gas disk in which the planets are formed collapses directly under its own gravitational force — a top-down process,” Professor Mordasini said.
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J.C. Morales et al. 2019. A giant exoplanet orbiting a very-low-mass star challenges planet formation models. Science 365 (6460): 1441-1445; doi: 10.1126/science.aax3198
