Astronomers stumble upon the formation of a massive exoplanet which ‘should not’ have existed

Astronomers are now grappling with the reconsideration of planetary formation theories after chancing upon an exoplanet that defies conventional expectations of existence.

This newly discovered planet, named LHS 3154b, possesses a mass akin to Neptune and dwarfs Earth by over 13 times. Intriguingly, it orbits an ultracool M-dwarf star named LHS 3154, which is remarkably nine times smaller than our Sun. M-dwarf stars represent the coolest and smallest star type in the galaxy.

LHS 3154b maintains a close orbit around its diminutive star, completing one orbit every 3.7 Earth days. This configuration establishes it as one of the largest planets identified in proximity to one of the universe’s most low-mass and coldest stars, as detailed in a recent study published in the journal Science.

The discovery of this planet challenges established notions regarding the formation of planetary systems. Study co-author Suvrath Mahadevan, a professor of astronomy and astrophysics at Penn State Verne M. Willaman, emphasized the surprise of finding such a heavy planet around a low-mass star, underscoring the limited understanding of the universe.

Traditional planetary system formation involves stars emerging from vast clouds of dust and gas, generating disks of leftover material where planets eventually form. The size of the planets is influenced by the quantity of material within these disks, a factor closely tied to the star’s mass.

M dwarf stars, prevalent throughout the Milky Way, typically host small rocky planets rather than larger gas giants. LHS 3154’s planetary disk wasn’t anticipated to contain enough solid mass to produce a planet of LHS 3154b’s magnitude, prompting a reevaluation of current understandings of planet and star formation.

Situated approximately 51 light-years from the sun, LHS 3154b was identified using the Habitable Zone Planet Finder (HPF) on the Hobby-Eberly Telescope at the McDonald Observatory in Texas. The HPF, designed by Mahadevan’s team, specializes in detecting planets within the habitable zone of cool, small stars—regions conducive to supporting liquid water and potentially sustaining life.