A Nearby “Super-Earth” May Be More Habitable Than Astronomers Thought

Planet GJ 3378b got a lot less massive, putting it on the short list for potentially habitable worlds.

06 Jul 2026, 13:33 by Jordan Strickler · ZME Science

Planet GJ 3378b is 25 light-years from Earth and orbits its star at a blistering 21 days. Credit: NASA

Twenty-five light-years away, in the constellation Camelopardalis, a small red star hosts a rocky world that just became one of the more compelling addresses in our cosmic neighborhood. Astronomers have re-measured the planet GJ 3378b and found it’s roughly half as massive as they thought — a seemingly small correction that has outsized implications for whether the place could actually support life.

The planet was first flagged back in 2024, when researchers estimated its mass at around five times that of Earth. That’s a problematic number if you’re hoping for a habitable world, since planets that bulky tend to hang onto thick, crushing atmospheres more reminiscent of Venus than anywhere you’d want to visit.

But the new study, published in the Astrophysical Journal and led by Paul Robertson of UC Irvine, revises that estimate significantly. The revised figure is approximately 2.3 Earth masses. That’s squarely in “Super-Earth” territory, big enough to be geologically interesting, small enough to plausibly support a rocky surface rather than a suffocating gas envelope.

“Our mantra is ‘follow the water,’” Robertson said, explaining the guiding logic behind the hunt. Water is the one non-negotiable ingredient every organism on Earth depends on, which makes it the first thing astronomers look for when scanning other worlds for potential habitability.

Catching a Star’s Wobble

Nobody has photographed GJ 3378b directly — it’s far too small and too close to its glaring host star for that. Instead, the team relied on a technique astronomers have used for decades: watching the star wobble. As a planet orbits, its gravity gives the star a tiny, rhythmic tug, nudging it back and forth. Measure that motion precisely enough, and you can back out the planet’s mass and orbital period.

The trouble is that GJ 3378b orbits a red dwarf — a class of star so dim and cool that most of its light comes out in the infrared rather than visible wavelengths. That’s where the Habitable-zone Planet Finder comes in, an infrared spectrograph mounted on the 10-meter Hobby-Eberly Telescope at McDonald Observatory in West Texas, purpose-built to tease out these faint signals.

“As stars get smaller, they get cooler, and most of their energy comes out in infrared wavelengths,” Robertson said, explaining why the instrument was designed as it was. “So, we put an infrared spectrometer on a 10-meter telescope, and that gives us more raw light-collecting power to observe these faint stars.”

Co-author Michael Endl of UT Austin adds that without enough precision, the planetary signal simply doesn’t show up. There’s no partial credit in this business — either your instrument is sharp enough to catch the wobble, or the planet stays invisible.

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“The name of the game is precision,” said Endl. “In order to find those low mass planets, you’re always looking for tiny signals. If your instruments aren’t precise enough, you won’t find them. You can’t find them.”

Red dwarfs matter enormously to this search, if only because there are so many of them. They make up roughly seven out of every ten stars in the Milky Way, which means understanding what kinds of planets tend to form around them isn’t a niche pursuit — it’s close to the default case for planet-hunting in general.

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A Tighter Orbit

Along with slimming down the planet’s mass, the new analysis also tightened up its orbit, shortening the year from 25 days to 21. That might sound uncomfortably close for a habitable planet, but red dwarfs are so much dimmer than the Sun that their habitable zones sit much closer in. GJ 3378b’s star is only about a third the size of ours, so a 21-day lap still puts the planet in the zone where liquid water could theoretically persist on its surface.

There’s a catch, though. Orbiting that close to any star, even a mild-mannered red dwarf, exposes a planet to a heavier dose of radiation, the kind that can strip away an atmosphere over time. Whether GJ 3378b still has one left to lose is something nobody currently knows. That question will likely require the next generation of observatories to answer.

That generation is already under construction. The Giant Magellan Telescope, the Extremely Large Telescope, and NASA’s proposed Habitable Worlds Observatory are all designed with mirrors large enough — the Giant Magellan’s spans roughly 80 feet — to eventually image planets like GJ 3378b directly and search their atmospheres for the chemical fingerprints of life.