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 . "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."
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 . "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."
Red dwarfs 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 star 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."
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 visible in the host star, which can be used to calculate the planet's mass and orbit.
Red dwarfs 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 star 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."
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 visible in the host star, which can be used to calculate the planet's mass and orbit.
"The Habitable-zone Planet Finder is optimized to use infrared light," explained Robertson. "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, and that gives us more raw light-collecting power to observe these faint stars."
"The name of the game is precision," added 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."
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 down from 25 days to 21. Even though either of these is a tiny orbit – for comparison Earths' is 365 days – with a host star roughly a third the size of our Sun, that proximity is necessary to place that 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.
Since 2018 the Habitable-zone Planet Finder has helped astronomers search for planets outside our solar system and catalogue 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 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?'" said Endl. "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."
The Habitable-zone Planet Finder was built by Penn State University , with participation from UT Austin. Supplemental data from Kitt Peak National Observatory , the Transiting Exoplanet Survey Satellite (TESS), and the Gaia space telescope helped confirm observations. Analysis was made possible by the Texas Advanced Computing Center . This research received funding from the National Science Foundation , NASA , and the Heising-Simons Foundation .
"The Habitable-zone Planet Finder is optimized to use infrared light," explained Robertson. "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, and that gives us more raw light-collecting power to observe these faint stars."
"The name of the game is precision," added 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."
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 down from 25 days to 21. Even though either of these is a tiny orbit – for comparison Earths' is 365 days – with a host star roughly a third the size of our Sun, that proximity is necessary to place that 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.
Since 2018 the Habitable-zone Planet Finder has helped astronomers search for planets outside our solar system and catalogue 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 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?'" said Endl. "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."
The Habitable-zone Planet Finder was built by Penn State University , with participation from UT Austin. Supplemental data from Kitt Peak National Observatory , the Transiting Exoplanet Survey Satellite (TESS), and the Gaia space telescope helped confirm observations. Analysis was made possible by the Texas Advanced Computing Center . This research received funding from the National Science Foundation , NASA , and the Heising-Simons Foundation .
