Discovery Alert: An Ice-Cold Earth?
A candidate planet that could be remarkably similar to Earth, HD 137010 b, has one potentially important difference: It could be colder than the perpetually frozen Mars.
Scientists continue to mine data collected by NASA’s Kepler space telescope, retired in 2018, and continue to create surprises. A new paper reveals the latest: a possible rocky planet slightly larger than Earth, orbiting a Sun-like star about 146 light-years away.
The planet’s orbital period – listed as a “candidate” pending further confirmation – is likely to be similar to Earth’s, around a year. The planet HD 137010 b could also lie just outside its star’s “habitable zone,” the orbital distance that could allow liquid water to form on the planet’s surface under a suitable atmosphere.
Planets orbiting other stars are called exoplanets. And it may turn out to be the first exoplanet with Earth-like properties that, from our vantage point, passes across the face of a Sun-like star, close enough and bright enough for meaningful follow-up observations.
Now the bad news. The amount of heat and light such a planet would receive from its star is less than a third of that Earth receives from the Sun. Although of a similar stellar type to our Sun, the star HD 137010 is cooler and dimmer. This could mean a planet surface temperature of no more than minus 90 degrees Fahrenheit (minus 68 degrees Celsius). For comparison, the average surface temperature of Mars is about minus 85 degrees Fahrenheit (minus 65 degrees Celsius).
The planet HD 137010 b will also need follow-up observations to move from “candidate” to “confirmed”. Exoplanet scientists use a variety of techniques to identify planets, and this discovery comes from a single “transit” – a single example of a planet crossing the face of its star in a sort of miniature eclipse – detected during Kepler’s second mission, known as K2. Even with just one transit, the study authors were able to estimate the orbital period of the candidate planet. They tracked how long it took for the planet’s shadow to move across the face of the star — in this case, 10 hours, while Earth takes about 13 — then compared it to orbital models of the system itself. Yet although the accuracy of this single detection is much higher than that of most transits captured by space telescopes, astronomers need to see these transits repeat regularly in order to confirm that they are caused by a real planet.
And capturing more transits is going to be tricky. The planet’s orbital distance, so similar to that of Earth, means that such transits occur much less often than for planets in closer orbits around their stars (this is one of the main reasons why exoplanets with Earth-like orbits are so difficult to detect in the first place). With luck, confirmation could come from more in-depth observations from Kepler/K2’s successor, NASA’s Transiting Exoplanet Survey Satellite (TESS), the still-functional workhorse for planetary detection, or from the European Space Agency’s CHEOPS (CHAracterising ExOPlanets Satellite). Otherwise, collecting additional data on the planet HD 137010 b may have to wait for the next generation of space telescopes.
Despite the possibility of a frigid climate, HD 137010 b could also turn out to be a temperate or even aquatic world, say the authors of the article on this exoplanet. It would simply require an atmosphere richer in carbon dioxide than ours. The science team, based on modeling of the planet’s possible atmospheres, gives it a 40% chance of falling in the “conservative” habitable zone around the star, and a 51% chance of falling in the broader “optimistic” habitable zone. On the other hand, the study authors say the planet has about a 50-50 chance of falling completely beyond the habitable zone.
An international scientific team published a paper on the discovery, “A Cool Earth-sized Planet Candidate Transiting a Tenth Magnitude K-dwarf From K2,” in The Astrophysical Journal Letters on January 27, 2026. The team was led by a Ph.D. in astrophysics. Alexander Venner, a student at the University of Southern Queensland, Toowoomba, Australia, is now a postdoctoral researcher at the Max Planck Institute for Astronomy, Heidelberg, Germany.
