Astronomers have discovered a new exoplanet orbiting the nearby K-dwarf star HD 137010 after detecting a single, shallow transit in the archival data from NASA’s Kepler extended K2 mission.
HD 137010b is estimated to be only 6% larger than Earth, with a surface temperature more similar to Mars — potentially below minus 70 degrees Celsius. Image credit: NASA / JPL-Caltech / Keith Miller, Caltech & IPAC.
HD 137010 is a K3.5V dwarf star located about 146 light-years away in the constellation of Libra.
Its age is estimated to lie between about 4.8 and 10 billion years, and its low level of magnetic activity is consistent with an old, relatively quiet star.
Also known as BD-19 4097, HIC 75398, 2MASS J15242123-1944215 or TYC 6179-1111-1, the star has a visual magnitude of 10.1, making it one of the brightest stars known to host an Earth-sized planet with temperate orbital properties.
Designated HD 137010b, the newly-discovered planet was detected during K2 Campaign 15, when NASA’s Kepler space telescope observed the parent star for nearly three months in 2017.
“Previous discoveries of Earth-sized planets in habitable zones are mostly around so-called red dwarfs, which are much smaller and dimmer than our Sun,” said University of Southern Queensland astronomer Alexander Venner, first author of the study.
“Scientists have concerns that these planets might lose their entire atmospheres due to high-energy radiation from their host stars, leaving them uninhabitable to known life.”
“In contrast, the host star of HD 137010b has properties much closer to our Sun, which makes it more likely that the planet could sustain an atmosphere based on current theoretical models.”
In the study, Dr. Venner and colleagues examined K2 data, nearby stellar light curves, archival imaging, radial velocity measurements, and astrometric data to assess the nature of the signal, which lasted about 10 hours.
The checks strongly indicate that the transit occurred on the target star and is astrophysical in origin, rather than being caused by background contamination, a nearby eclipsing binary, or a solar system object.
From the transit depth, the astronomers derived a planetary radius of about 1.06 times that of Earth.
Based on the transit duration and stellar properties, they estimate an orbital period of roughly 355 days.
At this distance from the host star, HD 137010b is estimated to receive roughly 29% of the stellar flux received by Earth from the Sun, placing it near the outer edge of the star’s habitable zone.
“If HD 137010b has an atmosphere like that of Earth or Mars, it is likely to be colder than Antarctica,” Dr. Venner said.
“But a thicker atmosphere could warm the planet enough to allow liquid water, which might be a good environment for life.”
“While current generations of astronomical instruments cannot fully characterize this newly-discovered planet, it could become a prime target for future radial velocity instruments aiming to detect Earth analogues.”
“Future space missions designed to directly image Earth-like planets, like the NASA Habitable Worlds Observatory, may also be capable of capturing images of HD 137010b.”
The discovery is reported in a paper in the Astrophysical Journal Letters.
_____
Alexander Venner et al. 2026. A Cool Earth-sized Planet Candidate Transiting a Tenth Magnitude K-dwarf from K2. ApJL 997, L38; doi: 10.3847/2041-8213/adf06f