The Strange Case Of The Planet That Shouldn't Be There

 Historically, the quest to find the holy grail of planets in orbit around stars beyond our Sun, proved to be a difficult endeavor. The discovery of the first exoplanet, circling a Sun-like star, happened a generation ago, and it certainly stands as one of humanity's greatest accomplishments. Discovering a giant exoplanet can be likened to observing light bouncing off the wings of a flying moth fluttering near the 1,000-watt light-bulb of a glowing street lamp--when the observer is 10 miles away. One half of the Nobel Prize in Physics 2019 was awarded jointly to Michel Mayor and Didier Queloz "for the discovery of an exoplanet orbiting a solar-type star."

Some of the exoplanets discovered since then resemble the planets inhabiting our own Solar System, while others have been proven to be genuine oddballs--so different from our Sun's family of planets that they defied the wildest dreams of planet-hunting astronomers before their discovery. In September 2019, Spanish and German astronomers of the Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-Infrared and optical Echelle Spectrographs (CARMENES) consortium announced their discovery of yet another exoplanet oddball that should not exist according to current knowledge. The group of scientists who discovered the planet that shouldn't be there detected a behemoth of a gaseous planet whose mass is unusually hefty compared to its puny parent-star GJ 3512. The astronomers conclude that this weird world likely originated from a gravitationally unstable protoplanetary accretion disk composed of gas and dust that circled around its then still-youthful dwarf parent-star. This contradicts the currently most widely accepted model of planet formation, which requires a solid protoplanetary core to gather surrounding gas.

Indeed, planet-hunting astronomers are certain that baby planets are born as a by-product of the process of star formation. According to this viewpoint, planets are born in what is left of the accretion disk from which their parent-star emerged. The most widely accepted model for the formation of baby planets is based on the idea that an object first emerges from the aggregation of naturally sticky solid dust particles within the accretion disk. The gravitational tugs of these planetary embryos (protoplanets) cause an atmosphere to form from the ambient gas. The scientists of the CARMENES consortium, led by Dr. Juan Carlos Morales, a researcher from the Institute of Space Sciences (ICE, CSIC) in Spain, with contributions from Dr. Diana Kossakowski and Dr. Hubert Klahr from the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, discovered this gas-giant planet, that is similar to our own Solar System's banded behemoth Jupiter. The distant world contradicts the most widely accepted model of planet formation because it seems to have formed directly out of the accretion disk, without a solid nucleus of condensation to collect the surrounding gas.

The distant world, dubbed GJ 3512 b, along with its dwarf parent-star GJ 3512, are only approximately 30 light-years from our Sun. The planet sports a mass of at least 50% that of Jupiter, and it takes 204 days to complete a single orbit around its star.

On its own, GJ3512 b isn't an oddball. However, because it is in orbit around a small red dwarf star it joins the ranks of the most unusual and special exoplanets. Tiny red dwarf stars are the smallest, as well as the most abundant, of all true nuclear-fusing stars in our Milky Way Galaxy. GJ 3512 has only about 12% of our Sun's mass. This means that the maximum gas ratio between the parent-star and its planet is 270. In comparison, our Sun is approximately 1050 times heftier than Jupiter. This observation of a planet that has no right to be where it is--if the most widely accepted model is true--gives theoretical physicists a headache. The gas and dust protoplanetary accretion disks from which low-mass stars, like the red dwarf GJ 3512 emerge, contain comparatively little material. Indeed, too little, as the models show, to be able to even form planetary embryos that could be born and then grow up to become gas giants like GJ 3512.

"One way out would be a very massive disk that has the necessary building blocks in sufficient quantity," commented Dr. Klahr in a September 26, 2019 MPIA Press Release. Dr. Klahr leads a working group on the theory of planet formation at the MPIA. However, if the protoplanetary accretion disk swirling around a star has more than approximately 1/10 of the stellar mass, the gravitational effect of the parent-star is no longer enough to keep the disk stable. The gravity of the disk material itself becomes a major performer in the play, and its influence grows both noticeable and significant. The upshot is a gravitational collapse similar to what occurs during the birth of a baby star. However, this has not yet been observed to occur around young dwarf stars.

The Quest

On January 9, 1992, the radio astronomers Dr. Aleksander Wolszczan and Dr. Dale Frail announced their important discovery of a duo of indisputably bizarre planets orbiting a form of stellar corpse called a pulsar. Pulsars are rapidly and regularly spinning newborn neutron stars, and they are the relics left by a doomed massive star that has collapsed in a Type II (core-collapse) supernova event. These objects are very dense. A teaspoon full of neutron star material can weigh as much as a fleet of limos.