Scientists Found an Earth-Sized Planet Hiding in 8-Year-Old Space Data

Eight years ago, a star 45 light-years away briefly dimmed for ten hours. NASA's K2 telescope captured the dip — a faint, 225-parts-per-million drop in brightness — and dutifully logged it. Then the data sat in a public archive, untouched, as the telescope moved on and eventually fell silent. It took a citizen scientist scanning old light curves by eye to flag the anomaly. Now, a team of astronomers has confirmed what that flicker almost certainly was: a planet nearly the size of Earth, orbiting in or near the habitable zone of a bright Sun-like star — the first of its kind ever found.

The Discovery That Was Already Waiting

HD 137010 is a K-type star in the constellation Libra — slightly cooler and smaller than the Sun, but bright enough to see with amateur equipment. In 2017, it fell inside the observing window of K2, NASA's repurposed Kepler telescope. During 88 days of monitoring, a single transit event registered: a smooth, U-shaped dip lasting roughly ten hours. The event was caught not by an algorithm, but by Hans Martin Schwengeler, a volunteer with the Planet Hunters K2 citizen science project, using light-curve inspection software on his own time. The research team at the University of Southern Queensland then took over, spending years ruling out every alternative explanation before publishing in The Astrophysical Journal Letters in early 2026.

Why Finding Earth Analogs Around Sun-Like Stars Is So Hard

The core problem is geometry and patience. A planet needs to orbit at just the right angle to pass between its star and Earth — and for a planet orbiting as far out as Earth does, that transit only happens once a year. K2's observing campaigns lasted just 80 days each, so any planet with an orbital period longer than that could, at best, be caught once. Kepler, the full-power predecessor, stared at one patch of sky for four years and found several small HZ planets — but they orbited stars too faint for detailed study. TESS, the current space telescope, has shorter baselines and lower precision, better suited to closer-in planets around smaller stars. HD 137010 b slipped through all of those gaps and landed in the narrow sweet spot: one transit, high-precision data, a bright host star.

Why Does One Faint Flicker Point to a Habitable World?

The signal-to-noise ratio of the transit event — around 30 under white noise conditions — is remarkably high for a planet this small. The team cross-checked archival photographs of the field going back to 1953, new speckle imaging from the Gemini South Telescope, radial velocity measurements from the HARPS spectrograph, and proper motion data from both Hipparcos and Gaia. Every alternative explanation — background eclipsing binary, bound stellar companion, instrument artifact — was systematically ruled out. The transit's smooth, flat-bottomed profile is inconsistent with a stellar eclipse and consistent with a small, solid body. The ten-hour duration, combined with the host star's known size, points to an orbital period close to one Earth year and a semimajor axis of roughly 0.88 AU. The planet receives about 29% of Earth's solar flux, placing it near the outer edge of the classical habitable zone — potentially cold, but not necessarily frozen if the atmosphere holds enough CO₂.

What Makes HD 137010 Different From Every Other Candidate

The Kepler mission found several small planets orbiting in habitable zones — Kepler-186 f, Kepler-62 f, Kepler-442 b — but all of them circle stars fainter than magnitude 14. That faintness isn't just an inconvenience. It means radial velocity measurements, atmospheric characterization, and transmission spectroscopy are effectively off the table with current technology. HD 137010 shines at magnitude 10.1, roughly 25 times brighter in apparent terms. That brightness gap translates directly into scientific access. It's the difference between a target you can study and a target you can only observe. The team also notes that K-dwarf stars like HD 137010 may be better candidates for habitability than M-dwarfs — the current favorites in exoplanet searches — because K-dwarfs are less prone to the violent UV flares that can strip planetary atmospheres.

What Needs to Happen Before Scientists Can Call This Confirmed

One transit is evidence, not proof. Confirmation requires catching the planet transit again — which means knowing when to look. The team estimated a roughly 7% chance the planet would transit during TESS's first observation window of the southern ecliptic in 2025, and no obvious second transit appeared in that data. The most practical path forward is a coordinated campaign using CHEOPS, a European Space Agency telescope designed precisely for this kind of targeted transit hunting. Meanwhile, radial velocity instruments like ESPRESSO could begin working toward detecting the planet's gravitational tug on its star — a signal expected at just 13 centimeters per second, far below anything confirmed so far. The HARPS archival data also hints at an additional, longer-period companion in the system, possibly a giant planet, which adds both intrigue and complexity to the picture. Confirming HD 137010 b won't be quick. But unlike most candidates of its kind, it's now a target scientists can actually pursue.

• Brightest known HZ candidate — At magnitude 10.1, HD 137010 is the first Earth-sized habitable-zone planet candidate accessible to precision follow-up with current ground-based instruments.
• A citizen science catch — The initial detection came from a volunteer scanning archived light curves, underlining the continuing scientific value of public data and open science programs.
• Cold but not ruled out — With an equilibrium temperature near −68°C assuming no albedo, the planet is cold — but a CO₂-rich atmosphere, as modeled for Kepler-186 f, could still support liquid surface water.

"HD 137010 b is essentially unique as a candidate terrestrial habitable-zone planet transiting a bright Sun-like star. We encourage follow-up observations for the confirmation and characterization of HD 137010 b, and to better understand the architecture of the system." — Venner et al., The Astrophysical Journal Letters, 2026.