Frozen Earth Twin Discovered Orbiting Nearby Star

A Distant Mirror of Our World

Astronomers have announced the discovery of what appears to be an "ice cold Earth," a chilly but potentially habitable rocky world similar to our own located less than 150 light-years away. As described in a recent study, this excitingly Earth-like exoplanet candidate, named HD-137010 b, may be slightly larger and about 1.2 times as massive as our planet. The length of its year may also be equal to ours, since it appears to swing around its mellow, orange star every 355 days.

HD 137010 b was first flagged as a potential planet candidate by citizen scientists participating in the Planet Hunters project, which sifts through data from NASA's Kepler Space Telescope. HD 137010 is a K-type dwarf with a visual magnitude of 10.1, making it observable with amateur telescopes. They teased out its existence using data from NASA's now-retired Kepler space telescope, astronomy's first devoted planet-hunter, via a technique called the transit method. The transit method involves using an observatory like Kepler to 'stare' at a star and wait for its light to dim as a potential exoplanet transits, or passes in front of it. The resultant stellar silhouette causes a dip in starlight that can reveal the exoplanet's radius and orbital details.

Astronomers have only seen HD-137010 b transit once. And since they must view multiple transits to confirm a candidate exoplanet, worlds with Earth-like orbits "require several years of observations." Yet this single detection stands out for its exceptional quality, giving researchers confidence in their findings despite the limited data.

A World of Extremes

HD 137010 is a K-type orange dwarf, which is slightly smaller and cooler. That means the candidate exoplanet potentially receives less than a third of the light and heat that the Earth does, with estimated temperatures lower than minus 90 degrees Fahrenheit. Mars, for comparison, is around minus 85 degrees Fahrenheit. Judging by the length of its year, researchers suggest that there is a 51 percent chance that HD-137010 b resides just inside its star's habitable zone, skirting the solar boundary where liquid water may form on its surface.

Although it may be frostier than Mars, HD-137010 b could still exhibit fortuitous atmospheric conditions to allow water to exist on its surface. Given what researchers know about other Earth-sized exoplanets in their stars' habitable zones, they say "it appears eminently plausible that a moderately CO2-rich" atmosphere could trap enough heat to support liquid water. This greenhouse effect could transform what appears to be a frozen wasteland into something more hospitable.

A frozen world may not seem conducive to life as we know it, but Earth itself was a snowball multiple times throughout its 4.5-billion-year geologic evolution. The discovery challenges our assumptions about where life might emerge, suggesting that even seemingly hostile environments could harbor surprises.

The Hunt for Confirmation

Confirmation seems unlikely, for now. No other exoplanet-hunting telescope currently plans to even look at the star, let alone scrutinize it long enough to bag more transits. Sara Webb, an astrophysicist at Swinburne University, called the discovery "exciting" but told The Guardian that three transits, not just one, are considered the "gold standard" for planetary science. Still, Huang says the detection was a "textbook example" of a planetary transit, thanks to the closeness and brightness of the star.

The transit had a depth of 225 ppm, which means that the planet blocks about 0.0225% of the star's light when it transits. That means that it has a high signal-to-noise ratio (SNR), which is critical in exoplanet detections, and surprising for a shallow detection. With an SNR of about 30, that means the signal is about 30 times stronger than noise. That represents exceptional photometric precision.

Opening New Frontiers

According to researchers, "This is the first planet candidate with Earth-like radius and orbital properties transiting a Sun-like star bright enough for substantial follow-up observations." Future observations may need to wait for next-generation observatories, like the ESA's PLATO, as such worlds are at the observational limit of today's facilities.

The discovery of HD 137010 b represents more than just another exoplanet find. It demonstrates that Earth-like worlds might be hiding in plain sight, waiting to be discovered in archived data from missions that ended years ago. As our detection methods improve and new telescopes come online, we may find that the universe is far more populated with potentially habitable worlds than we ever imagined. Even in the frozen reaches of space, the building blocks for life might be quietly waiting to be understood.