Astronomers have flagged a tantalizing candidate for a frozen twin of Earth, a world known as HD 137010 b that appears to circle a Sun-like star about 146 light-years away. The planet seems to be roughly Earth-sized and parked near the outer edge of its star’s habitable zone, where liquid water is possible in principle but far from guaranteed. The early data point to a place that is more deep freeze than blue marble, forcing scientists to rethink what “habitable” really means when a planet spends most of its time below minus 70 degrees Celsius.
The discovery is also a reminder of how fragile the evidence for distant worlds can be. HD 137010 b currently rests on a single, 10-hour blip in starlight recorded by NASA’s Kepler telescope in 2017, a hint strong enough to excite researchers but not yet solid enough to count as a confirmed planet. That tension between promise and uncertainty is exactly why this icy candidate matters: it shows how the frontier of exoplanet science is shifting from simply finding other Earths to understanding the many ways a planet can be almost, but not quite, like our own.
What we actually know about HD 137010 b
The basic outline of HD 137010 b is deceptively simple. The candidate appears to be similar in size to Earth and orbits a star that is broadly comparable to our Sun, making it an obvious target in the search for familiar worlds. One reason the planet has drawn attention is its relative proximity, at about 146 light-years away and orbiting a star bright enough that future telescopes can study it in detail. That combination of size, distance and stellar brightness is rare, which is why HD 137010 b has quickly become a favorite in exoplanet circles despite its frigid reputation.
The initial signal came from a single transit, when the planet crossed in front of its star and dimmed the light for roughly 10 hours. In the case of HD 137010, In the Kepler recorded only that single event, even though, normally, several transits are necessary to detect a planet beyond doubt. Further analysis revealed a planet transiting across its star’s face for approximately 10 hours, while an Earth transit seen by an outside observer would take around 13 hours, which is one reason scientists think HD 137010 b is close to our planet in size.
A “cold Earth” on the edge of habitability
Where HD 137010 b diverges sharply from our world is temperature. Climate models suggest the planet sits near the outer boundary of its star’s habitable zone, where sunlight is weak and any surface water would be prone to freezing solid. Estimates put typical conditions around minus 70 degrees Celsius, cold enough to turn an entire globe into a “super snowball” locked under thick ice. That is why some researchers describe it as a cold Earth, a planet that matches our size but not our climate.
Webb also cautioned that HD 137010 b could turn out to be what scientists call a “super snowball,” a large, frozen world where most of the surface is buried under ice and effectively unreachable with today’s technology. That description, reported in coverage of the discovery, underscores how far this candidate sits from the cozy middle of the habitable zone. In that sense, HD 137010 b is less a second Earth and more a distant cousin, closer in spirit to the icy moons of the outer Solar System than to the Pale Blue Dot we know.
The confirmation problem: one lonely transit
For all the excitement, the most awkward fact about HD 137010 b is that astronomers have only seen it once. There is only one transit detected, and typically in planetary science we are talking a gold standard of three detections before calling a world confirmed. As one researcher put it, There is only one transit detected, and typically in planetary science we are talking a gold standard of three detections. That means HD 137010 b currently sits in a limbo category: more compelling than a random noise spike, but not yet elevated to the status of a fully verified planet.
That ambiguity has real scientific consequences. With only a single dip in brightness, astronomers cannot yet pin down the planet’s orbital period, eccentricity or exact distance from its star, all of which feed directly into temperature estimates and habitability models. Learn about HD 137010 b as a cold Earth-sized planet candidate that sits near the outer edge of its star’s habitable zone, as one analysis urged readers to Learn, and it becomes clear how much of the story still rests on probabilities rather than repeated measurements. Until a second or third transit is captured, either by ground-based observatories or future space missions, every conclusion about HD 137010 b will carry a large asterisk.
Frozen does not mean lifeless
Even if the planet is as cold as current models suggest, that does not automatically rule out interesting chemistry or even life. In our own Solar System, Europa and Enceladus are encased in ice yet host subsurface oceans warmed by tidal flexing, and those hidden seas are among the prime astrobiology targets for the coming decades. A similar configuration on HD 137010 b, with a thick ice shell insulating liquid water below, would fit the “super snowball” label while still allowing habitable niches out of direct starlight. That is why some researchers argue that a frozen Earth-sized world could be more biologically promising than a scorched super-Earth much closer to its star.
At the same time, the odds are stacked against a surface that looks anything like Earth’s. While it is the same size as Earth, it is anything like our Earth, with models suggesting a planet that is locked in ice-cold conditions rather than cycling through oceans and continents. That contrast is a useful corrective to the popular assumption that “Earth-sized” automatically means “Earth-like.” HD 137010 b shows that radius alone tells us very little about what it would feel like to stand on a planet’s surface, or whether there is any surface to stand on at all.
How JWST and future telescopes could settle the debate
The next phase of the story will be written not by Kepler, which has already retired, but by a new generation of observatories. The James Webb Space Telescope, or JWST, was designed in part to take spectra of planets in the habitable zone and search for life, and HD 137010 b is exactly the kind of target that could benefit from that capability. If astronomers can predict its orbit well enough to catch another transit, JWST could dissect the starlight filtering through any atmosphere, looking for signatures of water vapor, carbon dioxide or methane that would reveal whether the planet is wrapped in ice, gas or something in between.
Other teams are already sketching out how to use both space-based and ground-based instruments to refine the planet’s orbit and temperature. A cold Earth 146 lightyears away could be habitable, as one detailed overview of the system argued readers should Earth, but only if factors like atmospheric composition and orbital eccentricity conspire to keep parts of the surface above freezing for at least part of the year. My own expectation is that JWST will not deliver a cinematic “yes or no” on habitability, but rather a more nuanced picture: perhaps a thin, dry atmosphere that confirms the deep-freeze scenario, or a surprisingly thick blanket of greenhouse gases that nudges the planet closer to the liquid-water threshold.
More from Morning Overview
*This article was researched with the help of AI, with human editors creating the final content.
