TESS survey shows the radius valley vanishes for planets around mid-to-late M dwarfs

Star system: LTT 3780 A | Distance from the Sun: 71.8 light years

Researchers conducted the most comprehensive search for planets around mid-to-late M dwarf stars using data from the TESS mission. Surveying over 8,000 such stars, they identified 77 transiting planet candidates and measured how often planets occur as a function of their size, orbital period, and the amount of starlight they receive. The study found that each mid-to-late M dwarf hosts on average about 1.1 planets larger than Earth within 30 days of orbit, a rate similar to that of early M dwarfs. This confirms that M dwarfs are prolific hosts of small, close-in planets.
Unlike the planet populations around larger stars, which show a 'radius valley'—a gap in the distribution of planet sizes—the planets around mid-to-late M dwarfs show a single peak in size at about 1.25 times Earth's radius. The study also found that super-Earths are much more common than sub-Neptunes around these stars, with a ratio of 5.5 to 1. This supports theories that predict the radius valley fades for lower-mass stars and that sub-Neptunes around M dwarfs are likely water-rich worlds. No hot Jupiters were found in the survey, and the researchers set a strict upper limit on their occurrence.
Key findings
The radius valley, a gap in planet sizes, disappears for planets around mid-to-late M dwarfs.
Super-Earths are much more common than sub-Neptunes around these stars.
M dwarfs are confirmed as abundant hosts of small, close-in planets, with no hot Jupiters detected in this survey.

Scientific study

TESS Planet Occurrence Rates Reveal the Disappearance of the Radius Valley Around Mid-to-Late M Dwarfs (external link)