Kleine ster met een reusachtige exoplaneet

Het bestaan van een grote exoplaneet bij een kleine ster valt niet te rijmen met gangbare theorieën over planeetvorming.

Stars generally are much bigger than even the largest planets that orbit them. But in this case, the star and the planet are not much different in size, the researchers said on Thursday. The star, called GJ 3512, is about 12% the size of our sun, while the planet that orbits it has a mass of at least about half of Jupiter, our solar system’s largest planet.

“Yes, an absolute surprise,” said astrophysicist Juan Carlos Morales of the Institute of Space Studies of Catalonia at the Institute of Space Sciences in Spain, who led the research published in the journal Science. “The discovery was surprising because theoretical formation models suggest that low-mass stars typically host small planets, similar to Earth or small Neptunes. In this case, we have found a gas giant planet similar to Jupiter around a very small star,” Morales added.

The planet, which like Jupiter is composed mainly of gas, was discovered using a telescope at the Calar Alto Observatory in Spain. It travels around its star in a very elliptical orbit lasting 204 days. 

Red dwarfs are small, with relatively low surface temperatures. GJ 3512 is not only much smaller than our sun, it is somewhat comparable in size to a very large planet, being only about 35% bigger than Jupiter. “They emit less energy, so they are fainter than the sun, and their surface temperature is rather cool, below 3800 (degrees) Kelvin (6,380 degrees Fahrenheit/3,527 Celsius) approximately. This is why the have a reddish color,” Morales said.

There is evidence of a second planet currently 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.

Planets are born from the same disk of interstellar gas and dust that produces the star around which they orbit. Under the leading model for planetary formation, called the “core accretion” model, an object initially forms from solid particles in the disk and the gravitational tug of this embryonic planet allows for an atmosphere to arise from the surrounding gas.

A competing model, called the gravitational instability model, may explain this unusual system. “In this case, the protoplanetary disk around the young star may be slightly more massive than expected and cold,” Morales said. “This makes the disk become unstable so some dense regions can appear. These clumps can grow until they collapse, forming a planet.”

Bron: reuters.com

ENG 1/ Astronomers from the #CARMENES consortium, led by Juan Carlos Morales, researcher from @IEEC_space at @iSpaceSci (CSIC) have discovered one, possibly even two, gas giant planets orbiting the nearby red dwarf star #GJ3512. https://t.co/dxFvLkV3tl pic.twitter.com/RCrOca3MCt

— IEEC (@IEEC_space) September 26, 2019

Giant planet found circling tiny red dwarf star GJ 3512. Unexpectedly, around that red dwarf, the scientists discovered a gas-giant planet, called GJ 3512b, whose mass was nearly half that of Jupiter. 1/#Exoplanets #Astrophysics #Cosmology

???? https://t.co/2437dZL2vj pic.twitter.com/MqIjPCMLXU

— Beyond Galaxies ???? (@_beyondgalaxies) September 27, 2019

The world that came in from the cold | Science https://t.co/r6KPvs3MGi

GJ 3512 pic.twitter.com/tJLIkB9vua

— matiere* (@matiere) September 27, 2019