The newly discovered Earth-like exoplanet TOI-4552 b has a year that lasts only 8 hours

Star system: UPM J1738-4738 | Distance from the Sun: 89.2 light years

Ultra-short period (USP) rocky planets, which orbit their stars in less than a day, are rare, especially around red dwarfs. TOI-4552 b (also UPM J1738-4738 b) is a newly validated Earth-sized planet with a 0.3-day orbit around a quiet M4.5V red dwarf just 90 light years away. It was first found in TESS transit data and later confirmed using TESS photometry, ground-based transit observations, and high-resolution imaging, which ruled out false positives from background stars or eclipsing binaries.

Spectroscopic data from NIRPS and HARPS instruments provided the planet’s mass and the star’s chemical makeup. TOI-4552 b has a mass of 1.83 times Earth’s and a radius of 1.11 Earth radii, placing it between Earth-like and iron-rich compositions. Its high density suggests a large iron core, but the exact interior structure still remains uncertain. 

Because the planet orbits its host star at an incredibly close distance (0.006 AU, or 1 % of distance between Mercury and the Sun), it completes a full revolution in just 8 hours, moving at staggering orbital velocities. This proximity means the planet is likely tidally locked, with one side perpetually scorched by its sun. The surface is almost certainly a global ocean of molten lava rather than solid rock, as the intense stellar radiation keeps temperatures high enough to melt stone. 

Furthermore, the massive gravitational forces exerted by the nearby star create powerful tidal heating within the planet’s interior, potentially triggering constant volcanic eruptions and warping the very shape of this nearby world.

The planet’s short period, high emission metric, and low stellar activity make it an excellent target for future studies of its atmosphere and surface with JWST.

Key findings
- TOI-4552 b is an Earth-sized planet with a 0.3-day orbit around a nearby red dwarf
- The planet’s mass and radius suggest a dense, possibly iron-rich composition
- High-resolution imaging and spectroscopy confirm its planetary nature and rule out false positives
- The host star is quiet, with no signs of activity that could affect measurements
- TOI-4552 b is a prime candidate for atmospheric and surface studies with JWST

Scientific study

TOI-4552 b: A new ultra-short period rocky world revealed by NIRPS and TESS (external link)