By Amit Malewar Published: April 29, 2026
Collected at: https://www.techexplorist.com/galaxy-common-planets-missing-common-stars/102853/
Around stars like our Sun, the most common planets aren’t giant Jupiters but smaller cousins: sub‑Neptunes, which resemble Neptune but on a reduced scale, and super‑Earths, rocky worlds up to ten times Earth’s mass. For nearly a decade, astronomers have known these two planet types are everywhere around Sun‑like stars.
But here’s the catch: Sun‑like stars are only a minority in our galaxy. That leaves a big gap in our picture of planet formation, because most stars are different, and we still don’t fully know what kinds of worlds they host.
Astronomers now believe our galaxy is teeming with planets, at least one for every star. These worlds, called exoplanets, orbit stars beyond our solar system.
But here’s the twist: new research from McMaster University shows that the most common planets in the galaxy don’t actually orbit the most common stars.
For this study, researchers examined planets orbiting mid‑to‑late M dwarfs, tiny stars that are 8–40% the size of our Sun. These stars make up the majority of the Milky Way, but because they’re so faint, they’ve been tough to study.
NASA’s TESS satellite changed that. By scanning a new patch of sky every 28 days, TESS built a sweeping map of these dim stars and their planets.
The surprise? Around mid‑to‑late M dwarfs, sub‑Neptunes vanish almost entirely. Instead, these stars host many super‑Earths but virtually no Neptune‑like worlds. This unexpected pattern challenges long‑standing theories of planet formation.
Erik Gillis, a PhD student in the Department of Physics and Astronomy, said, “We didn’t just refine the picture, we changed it. Around these stars, sub-Neptunes effectively vanish, which means the mechanisms shaping planets here are different.”
The difference between super-Earths and sub-Neptunes lies in photoevaporation, a process in which intense starlight blasts away a planet’s atmosphere. The scarcity of sub‑Neptunes around these small stars hints at something profound: planet formation here may lean toward water‑rich worlds rather than gas‑wrapped giants.
“If we want to understand the origins of planets and the origins of life, we need a complete picture of how planets form and what they’re made of. This research brings us closer to that,” says Gillis.
The new findings, published in The Astronomical Journal, arrive at a thrilling moment for exoplanet science. The first worlds beyond our solar system were discovered only 30 years ago, a blink compared to other branches of astronomy.
Since then, we’ve studied just a small slice of the universe, piecing together patterns of planetary systems and assuming they hold everywhere. Missions like TESS are now changing that, giving us thousands of examples to compare.
“Our solar system was once the only model we had,” says Cloutier. “Now we can uncover patterns that rewrite our assumptions.”
It was already astonishing to learn that the most common type of planet in the galaxy doesn’t exist in our own solar system. With this new work, astronomers are sketching a clearer picture of where super‑Earths and sub‑Neptunes come from, and reshaping our understanding of how worlds are born.
Journal Reference:
- Erik Diego Gillis, Ryan Cloutier, and Emily K. Pass. TESS Planet Occurrence Rates Reveal the Disappearance of the Radius Valley around Mid-to-late M Dwarfs. The Astronomical Journal. DOI: 10.3847/1538-3881/ae5810
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