For many years, astronomers believed they understood the types of planets that dominate our galaxy. The consensus was that around stars similar to our Sun, two primary planet types emerged: sub-Neptunes, which are smaller, gas-rich worlds, and super-Earths, rocky planets that can be up to ten times the mass of Earth. However, new research from McMaster University has significantly altered this perspective.
The earlier assumptions were based on studies of stars that do not represent the vast diversity of stellar types in the Milky Way. While Sun-like stars are familiar, they are actually a minority. The most prevalent stars in our galaxy are mid-to-late M dwarfs (red dwarfs), which are small, dim, and cool, measuring between eight to forty percent the size of our Sun. Their faintness has historically made them difficult to study, leading to gaps in our understanding of planetary formation.
The Role of TESS
The Transiting Exoplanet Survey Satellite (TESS), launched in 2018, has transformed our ability to observe these elusive stars. By scanning a new section of the sky every 28 days and completing a comprehensive survey over 26 months, TESS has provided unprecedented data on the planets orbiting M dwarfs.
PhD student Erik Gillis and his supervisor, Ryan Cloutier, utilized TESS data to investigate the types of planets surrounding these stars. Their findings revealed a striking absence of sub-Neptunes around mid-to-late M dwarfs. Instead, these stars appear to produce super-Earths in large quantities, while gas-rich sub-Neptunes are nearly non-existent.
Understanding Planet Formation
Traditionally, the phenomenon of photoevaporation—where intense radiation from a young star strips away a planet’s atmosphere—was thought to explain the distinct populations of super-Earths and sub-Neptunes. M dwarfs, particularly in their early stages, are known to be energetically violent and should theoretically be capable of this atmospheric stripping. However, the near-total absence of sub-Neptunes suggests that photoevaporation alone cannot account for the observed planetary distributions.
The McMaster team proposes that the formation of planets around M dwarfs inherently favors water-rich worlds over gas-shrouded ones. This shift in understanding emphasizes the need for a more nuanced view of planetary formation in our galaxy.
A New Perspective on Planetary Systems
These findings, published in the Astronomical Journal, arrive at a pivotal moment in exoplanet research. Since the first exoplanets were confirmed just thirty years ago, the field has rapidly evolved, with missions like TESS enabling researchers to analyze thousands of planetary systems simultaneously. As Gillis noted, a comprehensive understanding of planetary origins and the potential for life requires a complete picture of how planets form and their compositions—an aspect that has been largely overlooked regarding the most common stars in the galaxy.
This article was produced by NeonPulse.today using human and AI-assisted editorial processes, based on publicly available information. Content may be edited for clarity and style.
