Lead
A team of astronomers led by Alexander Venner (Max Planck Institute for Astronomy) has identified an Earth-size planet candidate, HD 137010 b, after spotting a single 10-hour dip in archival Kepler data. The signal implies a 355-day orbit around a K-type star about 146 light-years away, making it unusually close and bright for follow-up. Initial modeling places the candidate near the habitable zone but receiving roughly 29 percent of Earth’s sunlight, so surface conditions could be cold unless a dense atmosphere warms the world. Confirmation requires observing another transit or alternative detection, but the object already ranks among the most promising targets for atmospheric study.
Key takeaways
- HD 137010 b was revealed by a single 10-hour transit in Kepler archival data and is a candidate for an Earth-size planet on a 355-day orbit.
- The host is a K-dwarf located about 146 light-years from Earth, bright enough to enable higher-quality follow-up than is possible for many temperate small planets.
- Models estimate the planet receives roughly 29% of Earth’s insolation, lowering its equilibrium temperature compared with Earth.
- Climate modeling places HD 137010 b near the habitable zone, with a ~40% probability of lying inside the conservative habitable range under standard assumptions.
- Automated searches missed the event because it is a lone transit; human inspection by Planet Hunters volunteers and targeted reanalysis revealed the signal.
- False-positive scenarios (background eclipsing binaries, blends, detector artifacts) were examined and largely excluded by archival images, high-resolution follow-up, radial-velocity history, and precise astrometry.
- Confirming the orbital period will likely require catching a second transit, a challenging task for a ~1-year orbit; radial-velocity confirmation would be difficult if the planet is near Earth mass.
Background
Searches for temperate, Earth-size planets have intensified since Kepler showed small worlds are common. Most confirmed small planets in temperate orbits orbit faint M-dwarf stars, which complicates atmospheric characterization because those stars are dim and active. Kepler data remain a rich resource: single or non-repeating events can hide real planets when automatic pipelines require periodic signals, so citizen scientists and careful reanalyses continue to add discoveries.
HD 137010 is a K-type dwarf—smaller and cooler than the Sun—so an Earth-like orbital distance yields lower stellar flux than Earth receives from the Sun. That difference makes the system scientifically interesting: whether a planet at that distance is habitable depends strongly on atmosphere rather than orbital radius alone. The discovery team combined archival imaging, high-resolution observations, and stellar motion records to rule out many non-planet explanations for the transit-like dip.
Main event
The discovery began with a brief, ~10-hour decline in the star’s brightness recorded by the Kepler Space Telescope archive. That faint event went unnoticed for years because automated routines typically search for repeated transits; when Venner and collaborators reexamined the light curves with guidance from Planet Hunters volunteers they identified the single dip as consistent with a planet just slightly larger than Earth.
After the transit was recognized, the team worked through a standard false-positive checklist. They inspected archival images to search for background eclipsing binaries, obtained high-resolution imaging to look for nearby stellar companions, checked historic radial-velocity measurements for large unseen companions, and used precise astrometric data to ensure the dip was linked to the K-dwarf rather than another source. These lines of evidence made a transiting planet the simplest remaining explanation.
The inferred orbital period from the single transit is 355 days, placing HD 137010 b in a long-period regime where opportunities to observe repeats are rare. Predicting the next transit window carries uncertainty because one event provides only limited orbital-phase information. Radial-velocity detection would be a complementary route but appears challenging: if the planet has Earth-like mass, the induced stellar wobble would be below the sensitivity of most current instruments.
Additional measurements have hinted at another gravitational influence in the system—possible evidence for a more massive outer planet or brown dwarf—but those hints do not explain the transit itself. If present, a large outer companion could have influenced the inner planet’s formation and orbital evolution, so characterizing the full architecture will be important for interpreting HD 137010 b.
Analysis & implications
HD 137010 b occupies a rare parameter space: small radius, long orbital period, and a comparatively bright host star. That combination matters for future atmospheric characterization because brightness provides the photon counts needed for precise follow-up spectroscopy and photometry. Planets of similar size around faint stars remain harder to study, which is why a nearby, bright K-dwarf with a yearlike orbit is notable even if the planet is cooler than Earth.
The estimated stellar flux—about 29% of Earth’s—pushes the candidate toward cold surface conditions under Earth-like atmospheric assumptions. Surface water could freeze if the planet lacks a strong greenhouse atmosphere, especially if high-albedo ice increases cooling. Conversely, a dense CO2-rich atmosphere or other greenhouse contributors could trap enough heat to allow liquid water at the surface despite low insolation; distinguishing between these scenarios requires atmospheric detection or tighter mass constraints.
Confirmation and characterization carry observational challenges but also clear payoffs. A second transit would nail the period and allow planning for targeted atmospheric observations. If radial-velocity instruments improve or if the planet turns out to be more massive than Earth, mass and bulk composition could be measured, constraining habitability models. Even without immediate detection of biosignatures, HD 137010 b would serve as a benchmark for how small planets behave in lower-irradiation environments around K-dwarfs.
Comparison & data
| Object | Orbital period | Host type | Insolation (Earth = 100%) | Distance |
|---|---|---|---|---|
| Earth | 365 days | G-type (Sun) | 100% | — |
| HD 137010 b (candidate) | 355 days | K-dwarf | ~29% | ~146 light-years |
The simple comparison highlights why HD 137010 b is interesting: its orbital period is close to a terrestrial year but the cooler K-dwarf host reduces stellar flux to roughly 29% of Earth’s. That flux difference is central to climate expectations and makes atmospheric properties the key determinant of surface conditions. Compared with many temperate candidates orbiting M-dwarfs, HD 137010 b’s brighter host improves prospects for high-quality spectroscopy if observational opportunities can be scheduled.
Reactions & quotes
Researchers emphasized the role of human review in finding the event and the value of a bright host for future study. The discovery team credited volunteer classifiers for drawing attention to the faint dip and noted the detection illustrates how archives can still yield major finds.
“The best way to detect it was to actually just look.”
Alexander Venner / Max Planck Institute for Astronomy
Venner made that point in the context of explaining why automated pipelines can miss single, non-repeating transits. He and colleagues also highlighted that a bright host star makes follow-up more feasible and that the discovery gives observers a concrete target rather than a statistical candidate.
“The advantage of this star is that we already know there’s a planet with Earth-like properties.”
Alexander Venner / Max Planck Institute for Astronomy
That second remark frames the immediate scientific value: knowing a candidate exists around a bright nearby star lets planned missions and observatories prioritize monitoring and spectroscopic campaigns. Observers cautioned, however, that confirmation remains required before declaring the object a bona fide planet.
Unconfirmed
- The planet interpretation rests on a single recorded transit; a second observed transit is needed to confirm the 355-day period and rule out rare alternatives.
- Hints of an outer companion come from separate measurements but remain tentative and uncharacterized; its mass and orbit are unconfirmed.
- The planet’s mass and atmospheric composition are unknown; whether a dense greenhouse atmosphere exists is speculative until spectroscopic or mass measurements are obtained.
Bottom line
HD 137010 b represents one of the most accessible Earth-size, yearlike candidates discovered to date because it combines small size, a long orbital period, and a relatively bright nearby host. Those properties make it a high-priority target for planning follow-up observations, especially spectroscopy aimed at constraining atmospheric composition. Confirming the planet will be observationally demanding: a single-transit detection leaves timing uncertainty and a long orbital period provides few opportunities to catch repeats.
If confirmed, HD 137010 b will offer a crucial test case for how planets with Earth-like size behave when stellar energy is substantially lower than Earth’s—whether they freeze, remain marginally habitable, or sustain warm conditions via thick atmospheres. For now the discovery showcases the continuing scientific value of archival data, citizen-science review, and careful vetting in finding promising worlds beyond our solar system.