Using the Hobby-Eberly Telescope at McDonald Observatory, astronomers have taken a closer look at a nearby exoplanet and discovered it may be more Earth-like than previously thought. The planet, known as GJ 3378b, orbits a small, cool star called a red dwarf. Just 25 light-years from Earth in the direction of the northern constellation Camelopardalis, it lies in its star’s “habitable zone”—the region where temperatures could allow liquid water to exist—making it a candidate to host life.
“Our mantra is ‘follow the water,'” explained Paul Robertson, an astronomer at the University of California, Irvine, and lead author on the new study of GJ 3378b published in The Astrophysical Journal. “It’s the one thing every known living thing on Earth needs, so that’s the first thing we look for when trying to find environments that could sustain life.”
Reddwarfs are the coolest group of stars in existence. They are much smaller and dimmer than our sun and often appear reddish, hence their name. They are the most common stars in our galaxy, making them an important target in the search for life outside our solar system.
“About 70% of stars in our galaxy are red dwarfs, so they represent the standard,” explained Michael Endl, an astronomer at UT Austin, member of its Center for Planetary Systems Habitability, and co-author on the paper. “It’s really important that we understand the planet population around these stars.”
How the planet was measured
However, because these stars are so dim, and Earth-like planets are so small, they can be very difficult to detect and require specialized instrumentation. To learn about GJ 3378b, the team used the Habitable-zone Planet Finder instrument on the Hobby-Eberly Telescope to observe its host star. As a planet orbits, its gravitational force tugs on the star. This creates a subtle wobble in the host star that can be used to calculate the planet’s mass and orbit.
“The Habitable-zone Planet Finder is optimized to use infrared light,” Robertson explained. “As stars get smaller, they get cooler, and most of their energy comes out in infrared wavelengths. So, we put an infrared spectrometer on a 10-meter telescope (33 feet), and that gives us more raw light-collecting power to observe these faint stars.”
“The name of the game is precision,” Endl added. “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.”
A lighter world than expected
GJ 3378b is what astronomers refer to as a “super-Earth.” These planets are rocky and larger than our own, but not so large as to hold onto a thick atmosphere that would crush all life on the surface. When the planet was first discovered in 2024, it was thought to be about five times the mass of Earth. But the new analysis shows it is closer to 2.3 times Earth’s mass. That change increases the likelihood that the planet is indeed rocky and doesn’t hold a smothering atmosphere.
The team also refined the planet’s orbit from 25 days to 21 days. Even though either is a tiny orbit—for comparison, Earth’s is 365 days—with a host star roughly a third the size of our sun, that proximity is necessary to place the planet within the habitable zone. That said, its smaller orbit may also subject the planet to intense radiation that could evaporate any atmosphere present. More observations are needed to be sure.
Preparing for a closer look
Since 2018, the Habitable-zone Planet Finder has helped astronomers search for planets outside our solar system and catalog those that might host life, like GJ 3378b. This list will be available for the next generation of telescopes—the Giant Magellan Telescope, Extremely Large Telescope and Habitable Worlds Observatory—when they start observations in the coming years. With massive light-collecting mirrors (for example, the Giant Magellan’s will be 24 meters, or 80 feet, across), they will be able to directly observe these planets and, hopefully, find the signatures of life.
“The ultimate goal is biosignatures. We really want to know, ‘Are we alone in the universe?'” Endl said. “We are still in the reconnaissance phase of our solar neighborhood, trying to find the planets around the nearest stars because those will be the easiest ones to detect a biosignature on. This planet brings us one step closer to knowing all of our neighbors and, ultimately, which might be hospitable for life.” https://mcdonaldobservatory.org/2026/06/nearby-super-earth-may-be-a-better-candidate-for-life-than-previously-thought
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