Earth-size exoplanet is the best candidate for life found to date

Astronomers have discovered an Earth-size planet candidate circling a nearby star on a 355-day orbit. This is a rare case where a single overlooked signal reveals a world strikingly similar to Earth in size and year.

Because the star lies only 146 light-years away and shines brightly enough for close study, the discovery immediately offers astronomers a promising target for future searches for planetary atmospheres.

Finding HD 137010 b

A brief 10-hour dip in the star’s light first revealed the presence of the world now called HD 137010 b.

Analyzing that signal, Alexander Venner of the Max Planck Institute for Astronomy (MPIA) showed that the dimming matches the passage of a planet only slightly larger than Earth.

The faint event had gone unnoticed for years because automated searches expected repeating signals, leaving this lone crossing hidden in plain sight.

With only a single transit recorded so far, the system now stands as a compelling candidate that still requires another observation to confirm the planet’s orbit.

Why this star matters

Around this star, a K-dwarf that is smaller and cooler than the Sun, an Earth-like orbit would be much colder.

Even at roughly Earth’s orbital distance, the candidate receives only about 29 percent of Earth’s sunlight, which pulls its climate estimate downward.

Models placed the world near the habitable zone, the range where liquid water can persist with the right air.

Those same calculations gave it a 40 percent chance of sitting inside the conservative zone, leaving cold conditions as the likelier bet.

HD 137010 b may be too cold

A planet on that edge could be frozen solid, especially if bright surface ice reflected away much of the starlight.

Yet a thicker carbon-dioxide atmosphere could trap heat and keep surface water liquid despite the weak stellar energy.

That tension makes HD 137010 b interesting for a reason beyond size, because climate may hinge on atmospheric makeup rather than orbit alone.

Right now, the data cannot determine which outcome is correct, and that uncertainty keeps the interpretation scientifically cautious.

Scientists rule out false signals

The team had to show the signal was not a trick of hardware or another star.

Archival images, new high-resolution observations, old measurements of the star’s motion, and precision star-tracking all cut away likely impostors.

Those checks mattered because a single dip can come from eclipsing stars, background blends, or detector noise instead of planets.

After ruling out other possibilities, a planet passing in front of the star remained the simplest explanation, though one more observation is still needed to confirm it.

Significance of the signal

Volunteers with the Planet Hunters first flagged the faint signal, offering an early hint that a small planet might be hiding in the data from Kepler Space Telescope.

The brief dip had sat unnoticed for years before astronomers revisited the archive and recognized its significance.

A transit, the slight dimming that occurs when a planet crosses its star, becomes easy for automated searches only when the event repeats.

“The best way to detect it was to actually just look,” said Venner, emphasizing the value of careful human inspection.

Why HD 137010 b stands out

Few comparable worlds are known, and most small planets in temperate orbits circle faint stars that are hard to examine.

The best-known early milestone, Kepler-186f, proved Earth-size planets can exist in the right zone, but its star is far dimmer.

Many other promising small worlds orbit M-dwarfs, small dim stars whose close-in habitable zones can expose nearby atmospheres to radiation.

HD 137010 b stood out because it combined small size, a long orbit, and a host star bright enough for serious follow-up.

Host star brightness matters

Because the host star is bright, future instruments can gather cleaner light and ask sharper questions about the system.

That advantage matters long before anyone can search for life, since even basic checks need enough photons to measure tiny changes.

ESA’s PLATO mission, a planned space telescope designed to search for Earth-size planets around Sun-like stars, is being built to watch these stars for years and hunt terrestrial planets in wider orbits.

“The advantage of this star is that we already know there’s a planet with Earth-like properties,” said Venner.

Planet still needs confirmation

Confirmation will probably come the old-fashioned way, by catching the planet pass in front of its star again.

That job is difficult because a yearlong orbit gives astronomers few chances, and each predicted window still carries uncertainty.

Another approach, radial velocity – the tiny wobble a planet induces in its star – looked even harder to measure in this system.

If the planet is roughly Earth-mass, its pull on the star should be far below today’s easiest detections.

Next steps for HD 137010 b

Separate measurements hinted that something else may tug on the star, perhaps a bigger outer planet or brown dwarf.

That possible companion did not explain away the transit, but it may shape how the system formed and evolved.

A large outer body can dominate a system’s motions and influence where smaller rocky worlds end up.

More monitoring should tell astronomers whether HD 137010 b lives in a quiet system or a much busier one.

HD 137010 b occupies a rare sweet spot – Earth-size, a yearlong orbit, nearby, and unusually accessible for future study.

Whether it proves icy or merely chilly, the candidate already gives planet hunters a concrete target instead of a blind search.

The study is published in The Astrophysical Journal Letters.

Image Credit: NASA/JPL-Caltech; Keith Miller/Caltech/IPAC

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