Revised measurements for planet Gliese 367 b show it is not pure iron

Star system: Gliese 367 | Distance from the Sun: 30.7 light years

Gliese 367 b is an ultra-short-period planet that orbits its host, a Red dwarf star, in just 7.7 hours. Because it is located only about 9 parsecs (roughly 29 light-years) from Earth, it has been a target for intense study. Previous research suggested the planet possessed an extremely high density, implying it might be composed almost entirely of solid iron, a finding that challenged standard models of how planets form. New, high-precision measurements have now updated the understanding of this object's physical nature.

The updated study used photometry—the measurement of light—from the TESS satellite to constrain the planet's radius to 0.736 Earth radii. By accounting for effects like tidal distortion, where the gravity of the host star stretches the planet, researchers gained a clearer picture of its size and shape.

Radial velocity analysis, which tracks the tiny wobbles of a star caused by the gravitational pull of an orbiting planet, was conducted using the ESPRESSO instrument. This data provided a revised mass for the planet of 0.503 Earth masses and a bulk density of 6.9 grams per cubic centimeter.

These updated figures indicate that Gliese 367 b contains an iron mass fraction of approximately 50 to 70 percent. This composition is much more consistent with the planet Mercury in our own solar system than the previously proposed iron-dominated models, suggesting the planet is less unusual than once believed.

Key findings
- Gliese 367 b has a radius of 0.736 Earth radii and a mass of 0.503 Earth masses.
- The bulk density of the planet is measured at 6.9 grams per cubic centimeter.
- Interior composition modeling shows an iron fraction of 50 to 70 percent.
- The findings align the composition of Gliese 367 b with that of Mercury.
- Previous claims that the planet was an iron-rich anomaly are now considered unlikely.

Scientific study

Revisiting the Exo-Mercury Candidate GJ 367 b with ESPRESSO and a Self-Consistent Tidal Distortion Model (external link)