Two Rocky Planets Hidden Around Red Stars express
The TESS telescope's data are like a huge archive of old photographs: it already contains images of thousands of stars, but not every detail has been examined. Standard pipelines only look for the most obvious dips in a star's light when a planet passes in front of it. Fainter signals go unnoticed, like a quiet whisper in a noisy room.
The Hidden Gems project team used a special tool called sherlock that can pick out even barely perceptible stellar 'blinks' from the data. That's how they found two planets that had previously slipped under the radar. The first, TOI-237 c, is a rocky sphere with a radius 1.21 times that of Earth. It whips around its red star in just 1.74 days — a year on this planet is shorter than two Earth days. The second, TOI-4336 A c, is slightly smaller at 1.17 Earth radii and takes 7.58 days to orbit its star. That star is part of a triple system: two stars orbit close together, while a third lies far away.
Checks show that the planets' orbits are almost perfectly circular. Computer simulations confirm that both systems are stable: the planets will neither collide nor be ejected. For TOI-237 c, tiny variations in the timing of transits are expected, just a few seconds, but they can be measured with precise instruments.
These two planets now join the list of warm rocky worlds that sit right in the range where atmospheres could have survived. The TESS archive continues to yield its secrets: we just need to look more carefully at the old images.
Original abstract
as written by the authors arXiv:2601.21774
The Hidden Gems project searches the TESS data for additional planets transiting low-mass stars in confirmed systems. Our goal is to identify planet candidates that are below the detection threshold set by the SPOC and QLP pipelines using sherlock, a specialized pipeline for robust detection and vetting of transit signals in TESS data. We present the discovery of two inner rocky planets in the TOI-237 and TOI-4336 A systems, confirmed with ground-based photometry from the TRAPPIST, SPECULOOS, ExTrA, and LCO facilities. TOI-237 c has a radius of 1.21 +/- 0.04Re, orbits its mid-M host star every 1.74 days, and is close to a 3:1 mean-motion resonance with TOI-237 b. TOI-4336 A c has a radius of 1.17 +/- 0.06Re, and orbits with a period of 7.58 days an M3.5 host star which is part of a hierarchical triple system. We performed model comparison to search for non-zero eccentricities, and found that the circular transit models are statistically favored. Dynamical simulations show that both systems are in stable configurations, and the TTVs expected for the TOI-237 system are of the order of seconds. TOI-237 c and TOI-4336 A c join the high-interest population of warm likely super-Earths below the so-called "radius valley". In particular, TOI-237 c is a good candidate for phase curve observations with JWST/MIRI thanks to the small radius of the host star and its short period.
A year on TOI-237 c lasts just 1.74 Earth days — shorter than a weekend.