Searching for extraterrestrial life might be easier than expected, as one of the most promising locations could be relatively close to us.
A planet discovered in 2024, orbiting the red dwarf star GJ 3378, appears to be more Earth-like than initially thought.
This planet, GJ 3378b, is classified as a super-Earth: larger than Earth but potentially with a rocky surface akin to our planet, the only known life-supporting one in the Universe.
Subsequent observations have confirmed that GJ 3378b is positioned ideally from its star to allow for liquid water on its surface, a key criterion for habitability, and its mass has been refined from 5.3 to just 2.3 Earth masses.
This makes it more likely to be rocky and, at just 25 light-years away, a more attractive candidate for further studies on habitability than previously believed.
According to astronomer Paul Robertson of the University of California, Irvine, who led the team that published their findings in The Astrophysical Journal, GJ 3378b is “among the most potentially Earth-like exoplanets known within the 10-parsec solar neighborhood.”
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“This one’s exciting,” Robertson says 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.”
One of the Universe’s biggest mysteries is whether Earth is unique in its capacity to support life.
Scientists are still deciphering the attributes that might render a planet habitable, ranging from the type of star it orbits to the planetary system’s architecture, and whether it possesses tectonic plates or an atmosphere.
Some characteristics are more challenging to identify than others, but scientists frequently start by looking for an orbital zone termed the habitable zone.
This zone is the distance from the exoplanet to its star, crucial for determining if liquid surface water is possible. Too close and it vaporizes; too far and it freezes.
“Our mantra is ‘follow the water,'” Robertson says. “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.”
Assessing a planet’s composition is the next step. While rocky planets like Earth can support life, it’s uncertain if other types can. Thus, rocky planets are prioritized for investigation, while others remain possible candidates.
GJ 3378b intrigued planetary scientists when initial assessments indicated an orbital period of 24.73 days, placing it firmly in its star’s habitable zone.
Though this period is much shorter than Earth’s year, red dwarfs are cooler and less bright than the Sun, so their habitable zones are much closer.
However, the planet’s mass remained uncertain.
The threshold between two types of planets is around 5 Earth masses. Below this mass, planets are likely rocky super-Earths. Above it, they are more likely to be mini-Neptunes, with thick, gaseous atmospheres.
GJ 3378b’s initial mass estimate of 5.3 Earth masses was on the borderline, and Robertson and his team aimed to clarify this.
They gathered data using various Earth- and space-based instruments, detecting subtle changes in the star’s light caused by the exoplanet’s gravitational pull.
“The name of the game is precision,” says astronomer Michael Endl of the University of Texas at Austin. “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.”
These precise measurements allowed researchers to refine GJ 3378b’s mass and orbit.
Its orbit is slightly closer to the star than initially thought, at 21.45 days, still within the habitable zone.
“This super-Earth receives about 90 percent of the radiation from its star as Earth does from the Sun, so it’s right in the sweet spot,” Robertson says.
And the refined mass of 2.3 Earth masses places it firmly in the super-Earth category.
However, GJ 3378b’s potential habitability remains uncertain. Liquid water exposed to space would sublime, meaning an atmosphere is necessary for surface water, and it’s unclear if GJ 3378b has one.
These smaller stars are more active than the Sun, frequently emitting flares and coronal mass ejections that could strip atmospheres from nearby planets.
Related: The Red Sky Paradox Will Make You Question Our Very Place in The Universe
For now, the research elevates GJ 3378b as a top candidate for habitability investigations.
“The ultimate goal is biosignatures. We really want to know, ‘Are we alone in the universe?'” says 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 research has been published in The Astrophysical Journal.
This article was fact-checked by Jess Cockerill and edited by Fiona MacDonald. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
