Exoplanets like Neptune near red dwarfs don’t fit any theory of planet formation.

Astronomers have discovered an exoplanet whose existence doesn’t fit the standard model of planet formation. LHS 3154b is unusually massive for a very low-mass star and has a short orbit around it. This paper was published in the journal Science. Models of planet formation based on the accretion of material from protoplanetary disks to solid cores predict that large planets (with a mass greater than Neptune) should not be born from low-mass stars, which is supported by numerous observational data. confirmed by. This idea also applies to planetary systems consisting of small exoplanets around red dwarf stars near the Sun. Therefore, in the Standard Model, the outcome of the planet formation process depends largely on the total mass of the small solid particles in the disk, which in turn depends on and is proportional to the mass of the parent star.

However, there are currently several candidates for massive planets that do not fit the model. This is believed to be due to model uncertainties, and in such cases a gravitational instability mechanism may exist within the giant gaseous outer disk. A team of astronomers led by Princeton University’s Guðmundur Stefansson has discovered an exoplanet that does not conform to both of the standard theories of exoplanet formation. Observations of the red dwarf star LHS 3154 were conducted from January 23, 2020 to April 13, 2022 using the HPF spectrometer installed on the 10-meter Hobby-Eberly Telescope at McDonald Observatory. Exoplanets were discovered using the radial velocity method.

LHS 3154 has a spectral type of M6.5, is located nearly 52 light-years from the Sun, has a mass of 0.111 solar masses, and is characterized by an age of 5 billion years. Exoplanet LHS 3154b has an orbital period of 3.71 days and a minimum mass of 13.2 Earth masses. The semi-major axis of the exoplanet’s orbit has a length of 0.022 astronomical units and an eccentricity of 0.076.

The origin of such systems is difficult to explain using nuclear accretion or gravitational instability models because they involve very large planet-to-stellar mass ratios in the short term. In the latter case, the possibility of planetary migration requires a protoplanetary disk of even greater mass than accretion onto the core model. Researchers he identifies three possible explanations. First, much of the dust in protoplanetary disks around low-mass stars may be centimeter-sized or larger objects that evade detection on the millimeter scale, leading to an underestimation of the total mass of dust in the disk. may be. Second, the disk can absorb large amounts of additional material from the surrounding molecular cloud. Third, and finally, if the mass of the protoplanetary disk is greater, the core of the protoplanet may form within a million years of the formation of the protostar.

source: https://www.science.org/doi/10.1126/science.abo0233