The exoplanet known as GJ 3378b sits roughly 25 light-years away from us in the constellation Camelopardalis, making it one of our closest cosmic neighbors.
Robertson called the location ideal: “This super-Earth gets about 90% of the radiation from its host star that Earth gets from its sun, so it’s right in the sweet spot,” he noted.
Red dwarfs like GJ 3378b’s host blast out stellar winds and radiation that can strip a planet’s atmosphere clean off.
Whether GJ 3378b managed to hold onto one remains unknown.
Adding to the challenge is the fact that the planet does not transit its host star as seen from Earth, the technique astronomers normally rely on to characterize atmospheres.
A rocky world orbiting inside the habitable zone of a nearby red dwarf has drawn interest from astronomers. The exoplanet known as GJ 3378b sits roughly 25 light-years away from us in the constellation Camelopardalis, making it one of our closest cosmic neighbors.
Paul Robertson of the University of California, Irvine, who led the team that refined the planet’s mass and orbit, put the discovery in perspective in a statement: “It’s one of our closest cosmic neighbors. Twenty-five light years sounds like a long way, but the Milky Way is about 100,000 light years across, so in that respect it’s our next-door neighbor.”
Correcting the cosmic math
Astronomers first reported a candidate signal for the planet in 2024 using the SPIRou instrument on the Canada-France-Hawaii Telescope (CFHT) on Mauna Kea.
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Their initial analysis pegged it as a mini-Neptune, with about 5.26 Earth masses. A follow-up investigation by Robertson’s team, drawing on higher-resolution data from two additional telescopes, came back with different numbers. The actual mass is closer to 2.3 Earth masses, which puts it firmly in rocky super-Earth territory.
The findings were published recently in a peer-reviewed scientific journal, the Astrophysical Journal (ApJ).
The team also revised the orbital period downward from about 25 days to 21 days. This places the exoplanet closer to its star and squarely inside the habitable zone, where liquid water could exist on the surface provided it retains a protective atmosphere that’s holding things together.
Robertson called the location ideal: “This super-Earth gets about 90% of the radiation from its host star that Earth gets from its sun, so it’s right in the sweet spot,” he noted.
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The catch, however, is the star itself. Red dwarfs like GJ 3378b’s host blast out stellar winds and radiation that can strip a planet’s atmosphere clean off. Whether GJ 3378b managed to hold onto one remains unknown.
Adding to the challenge is the fact that the planet does not transit its host star as seen from Earth, the technique astronomers normally rely on to characterize atmospheres. Without transits, even the James Webb Space Telescope can’t do much here, and confirmation will likely have to wait for NASA’s Habitable Worlds Observatory, which isn’t slated for launch until the 2040s.
All the information we have about the exoplanet GJ 3378b comes from radial velocity observations, essentially the wobble its gravity causes in the host star, detected as a Doppler shift in the star’s light.
“The ultimate goal is biosignatures,” said Michael Endl, a University of Texas at Austin astronomer and co-author on the study.
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“We really want to know, are we alone in the universe? 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,” he noted.
Sources: UC Irvine, ApJ, NASA Exoplanet Archive Entry, Space
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