TOI-1752’s Two Worlds: A Lava-Hot Super-Earth and a Temperate Sub-Neptune

The TOI-1752 system is now described as a confirmed two-planet system around an M1V red dwarf roughly 337 light-years from Earth. Its inner planet, TOI-1752 b, is a small world on an ultra-short orbit that makes it a candidate “lava world.” Its outer companion, TOI-1752 c, is a larger sub-Neptune with a 32.7-day orbit and an orbit associated with the optimistic habitable zone. 9111213

The key caveat is that “habitable zone” describes a range of stellar heating under particular atmospheric assumptions. It does not show that a planet has liquid water, a suitable surface, or life.

How the planets were confirmed

NASA’s Transiting Exoplanet Survey Satellite, or TESS, searches for recurring dips in a star’s brightness as a planet passes across—or transits—the star’s visible disk. Those signals identify candidates, but additional observations are needed to distinguish planets from false positives such as eclipsing binary stars. Multicolour transit photometry is one method used to test whether a signal behaves consistently with a planet transiting the target star. 1

The IAA-CSIC-led research combined TESS data with observations from the ground. The Instituto de Astrofísica de Andalucía says the study used space-based TESS measurements and multicolour observations from Earth, while reporting from the Canary Islands identifies MuSCAT2 on the Telescopio Carlos Sánchez at Teide Observatory as part of the follow-up effort. 1112

The resulting study validates both objects as planets. The published research describes TOI-1752 b and TOI-1752 c as two small planets transiting the nearby red-dwarf host and reports their measured radii and orbital periods. 13

TOI-1752 b: the ultra-short-period “lava world” candidate

TOI-1752 b has a radius of about 1.69 times Earth’s and completes an orbit in approximately 0.94 days. NASA’s exoplanet archive lists it as a confirmed transiting planet. 5

That orbit places the planet extremely close to its red-dwarf star. The resulting intense irradiation is why the study and accompanying coverage use the “lava world” description. It is best understood as a model-based description of an exceptionally hot environment—not as a direct observation of molten rock on the surface. 513

Its small size makes TOI-1752 b a super-Earth by radius, but the label does not mean that it resembles Earth in surface conditions. In this context, it mainly distinguishes the planet from larger Neptune-like worlds.

TOI-1752 c: a roughly 2.29-Earth-radius sub-Neptune

TOI-1752 c is the system’s outer planet. NASA lists it as a Neptune-like exoplanet with a mass of 5.86 Earth masses, a radius of about 0.204 Jupiter radii—roughly 2.29 Earth radii—and a 32.7-day orbital period at a distance of 0.1614 astronomical units from its star. 2

The study reports a more precise orbital period of 32.7144 days and a radius of 2.29 Earth radii, consistent with the NASA catalogue values. 213 That places TOI-1752 c between Earth and Neptune in size, but its measured radius alone cannot reveal whether it has a rocky surface, a deep hydrogen-rich envelope, high-pressure water layers, or another internal structure.

News reports have described the planet as receiving approximately Earth-like irradiation and as having an estimated equilibrium temperature near 18–20°C. Those figures should be treated as reported estimates rather than proof of a temperate, Earth-like surface. 10

Why the habitable-zone label needs caution

A planet is placed in a habitable-zone category when its distance from its star could, under suitable atmospheric conditions, allow surface liquid water. The classification does not establish that those conditions exist.

For a sub-Neptune such as TOI-1752 c, the atmosphere and interior are especially important. A thick volatile envelope could produce pressures and temperatures very different from Earth’s surface, even if the planet receives a similar amount of stellar energy. Conversely, clouds, atmospheric composition, circulation, and the absence or presence of a solid surface can all affect what “habitable” means in practice.

No biosignature or evidence of life has been established for TOI-1752 c in the supplied research record. Determining whether the planet has an atmosphere—and what that atmosphere contains—would require further observations, including the kind of transit spectroscopy that can separate a planet’s atmospheric signal from the much brighter light of its host star.

Comparison with K2-18 b

TOI-1752 c invites comparison with K2-18 b because both are transiting sub-Neptunes orbiting red dwarfs on similar roughly 33-day periods. The NASA Exoplanet Archive lists K2-18 b with a 32.94-day orbit and a radius of about 2.37 Earth radii. 3

The comparison is useful, but the two planets should not be treated as identical. Similar orbital periods and sizes do not guarantee similar masses, atmospheres, cloud properties, or internal compositions. TOI-1752’s value is that its inner and outer planets also provide a contrasting pair around the same star.

What the system can teach scientists

The two planets occupy dramatically different orbital environments: TOI-1752 b circles its star in less than a day, while TOI-1752 c takes nearly 33 days. Studying both planets together could help researchers investigate how planets form and migrate, how intense stellar irradiation removes or alters atmospheres, and how radius relates to a planet’s internal composition.

The published work is identified as appearing in Monthly Notices of the Royal Astronomical Society. 1213 Follow-up measurements of TOI-1752 c’s atmosphere and mass would be particularly valuable. They could help determine whether the planet is a gas-rich sub-Neptune, a water-rich world, or another type of intermediate-size planet—and clarify how much can really be inferred from a habitable-zone orbit alone.