Gliese 3378b’s new mass and orbit place it near the cosmic shoreline

Star system: Gliese 3378 | Distance from the Sun: 25.2 light years

Gliese 3378 (GJ 3378) is a red dwarf star located just 7.7 parsecs from the Sun. It hosts a planet, Gliese 3378b, which was previously thought to be a super-Earth with a mass of about five Earth masses and an orbital period of nearly twenty-five days. New observations using several high-precision spectrographs, including HPF, NEID, CARMENES, and SPIRou, have led to a revised understanding of this planet’s properties. The updated analysis finds that Gliese 3378b is lighter than previously believed, with a minimum mass of about 2.3 Earth masses, and it orbits its star every 21.45 days.

Despite the shorter orbital period, Gliese 3378b remains within the star’s habitable zone, where liquid water could exist on its surface. The lower mass increases the chance that the planet is rocky, rather than a mini-Neptune with a thick atmosphere. Its new position in the so-called “cosmic shoreline” region means it may be at risk of losing its atmosphere due to the star’s radiation, a process that can strip away gases from planets in this part of the habitable zone.

This study highlights the importance of combining data from multiple instruments to refine our understanding of exoplanets. The findings suggest that Gliese 3378b is a promising target for future studies of planetary atmospheres and habitability around red dwarfs.

Key findings
- Gliese 3378b’s mass revised to about 2.3 Earth masses, lower than previous estimates.
- The planet’s orbital period is now measured at 21.45 days.
- Gliese 3378b remains in the habitable zone, increasing its potential for liquid water.
- The planet is near the “cosmic shoreline,” where atmospheric loss is likely.
- Combined data from several spectrographs improved the accuracy of the planet’s properties.

Scientific study

A Revised Mass and Period for the Habitable Zone super-Earth GJ 3378b: A Planet Straddling the Cosmic Shoreline (external link)