McMaster University Astronomers Discover Sub-Neptune Planets Effectively Vanish Around Smallest Milky Way Stars

McMaster astronomers find sub-Neptune planets vanish around M dwarf stars, challenging theories on how most worlds in the Milky Way are formed.

By: AXL Media

Published: Apr 30, 2026, 6:25 AM EDT

Source: Information for this report was sourced from EurekAlert!

Challenging the Standard Model of Galactic Planet Distribution

The long-held assumption that planetary patterns around Sun-like stars represent the galactic norm has been upended by new research from McMaster University. While sub-Neptunes and super-Earths are the most frequent celestial bodies found orbiting stars similar to our Sun, these common worlds are not distributed equally across the Milky Way. Lead author Erik Gillis and his team have identified a significant gap in the planetary census, discovering that the most common type of star in the galaxy does not host the most common type of planet.

The Unseen Majority of the Milky Way Solar Neighborhood

Mid-to-late M dwarfs represent the vast majority of stars in our galaxy, measuring between eight and 40 percent of the size of the Sun. Despite their prevalence, these small stars have historically remained difficult to observe due to their inherent faintness. However, the McMaster team leveraged the Transiting Exoplanet Survey Satellite (TESS), which monitors the entire sky in 28-day intervals, to gather an unprecedented dataset. This shift in observational focus has allowed astronomers to move beyond the minority of Sun-like stars to understand the environments where most galactic planets actually reside.

The Great Disappearance of Sub-Neptune Worlds

The most striking revelation from the TESS data is the near-total absence of sub-Neptune planets around these small M dwarf stars. While super-Earths, which are rocky planets up to ten times the mass of our own, remain plentiful, the gas-shrouded sub-Neptunes effectively vanish in these systems. According to Erik Gillis, this discovery does not just refine our current understanding but fundamentally changes it, suggesting that the physical mechanisms shaping planetary systems around small stars differ significantly from those in our own solar neighborhood.