An international team of researchers led by scientists from Penn State University has announced the detection of a ‘super Earth’ rocky exoplanet orbiting within its star’s habitable zone, where liquid water could exist on the surface, less than 20 light-years from Earth.
The research team behind the discovery said the new planet, dubbed GJ 251 c, has a habitable-zone orbit, a rocky composition, and a relatively close proximity to Earth, making it a prime target for searching for signs of life.
Dr. Suvrath Mahadevan, the Verne M. Willaman Professor of Astronomy at Penn State and co-author of the paper detailing the potentially historic discovery, told The Debrief in an email how finding a potentially habitable, rocky exoplanet in our cosmological backyard offers an unprecedented opportunity to search for life beyond Earth.
“We have a new, potentially rocky planet in the Habitable Zone of a quite nearby star!” the professor said. “One that is close enough that we have a chance of actually seeing the planet light separate from the starlight in the coming decade.”
For comparison, the Trappist-1 multi-planet system, which contains several rocky exoplanets that may lie within the star’s habitable zone and is considered a prime target for astrobiologists to search for signs of life, is just over 40 light-years from Earth. GJ 251 c is only half the distance.
Funding from the U.S. National Science Foundation, NASA, and the Heising-Simons Foundation helped the researchers analyze over 20 years of observational data from the Habitable Zone Planet Finder (HZPF). The observatory was custom-designed by Penn State researchers to search for planets that might host life.
Unlike planets found when they pass between Earth and their host star, causing the light to dim, called the transit method, GJ 251 c was found by the HZPF by detecting a subtle “wobble in the host star GJ 251. This wobble is caused by the gravitational pull of an orbiting planet.
“We call it the Habitable Zone Planet Finder, because we are looking for worlds that are at the right distance from their star that liquid water could exist on their surface. This has been the central goal of that survey,” Mahadevan said in a statement announcing the team’s research. “This discovery represents one of the best candidates in the search for atmospheric signature of life elsewhere in the next five to ten years.”
Approximately four times Earth’s size, GJ 251 c is close enough for the research team to say that several planned observatories could directly image its light within the next decade. Directly measuring the light from a planet in its star’s habitable zone could reveal chemical “biosignatures” in its atmosphere, which may reveal biological activity on the planet. If confirmed, such a detection could represent the first discovery of extraterrestrial life.
While Professor Mahadevan cautioned that any image captured by next-generation telescopes would be only “a spot of light,” the data carried within that light would likely clarify whether the planet currently maintains an atmosphere. The professor said the ability to directly image the planet this close to Earth could also allow astronomers to search any atmosphere for “possible biosignatures.”
“The planet lies within the Habitable Zone of its host star, i.e., in the region around the star where liquid water could exist on a planet, given suitable atmospheric properties,” Dr. Mahadevan told The Debrief. “This, coupled with the proximity of the host star, and the fact that our future ground-based telescopes have a good chance of being able to detect the light from this planet, makes it a good place to search for atmospheric biosignatures.”
When asked what type of chemical signature or signatures from GJ 251 c’s atmosphere would constitute signs of biological activity, the professor noted that what exactly does, or does not, constitute an actual biosignature “is a very active area of research.”
“On Earth, the simultaneous presence of oxygen and Methane in the atmosphere is a biosignature, since those exist together only due to the presence of life on our planet,” Dr. Mahadevan told The Debrief. “However, it is only in context with what the atmosphere of GJ 251c is made of that one could discuss ‘what is a biosignature?’ and what could be caused by abiotic processes.”
Before that step, the professor said astronomers would need to “unambiguously detect” the presence of an atmosphere around GJ 251 c. Unfortunately, current observatories do not have the necessary capabilities to measure and characterize the atmosphere of a habitable-zone exoplanet today.
“We are at the cutting edge of technology and analysis methods with this system,” explained Corey Beard, corresponding author on the paper who conducted the research while earning a doctorate in astrophysics from the University of California, Irvine. “We need the next generation of telescopes to directly image this candidate, but what we also need is community investment.”
When asked which planned observatories may offer that capability, Dr. Mahadevan noted three ground-based observatories that could be completed within the next decade. Of the three “next-generation” ground-based telescopes in the 30m class, Beard told The Debrief that the Thirty Meter Telescope (TMT) is “likely to be the best suited for observations of this planet” since it will be in the Earth’s northern hemisphere.
The researcher also noted that the Giant Magellan Telescope (GMT) and the European Southern Observatory’s Extremely Large Telescope (ELT), which will feature a primary mirror of about 39 meters, could directly measure the light from GJ 251 c. However, due to their locations in the southern hemisphere, Mahadevan said these observatories would be observing the planet “at high airmass.” This means that, unlike the TMT in the northern hemisphere, these two observatories would have to try to image GJ 251 c through significantly more of the Earth’s atmosphere, which would add unnecessary interference to any data.
When asked about space-based observatories, Dr. Mahadevan noted that the proposed LIFE mission will be equipped with an interferometer at “thermal wavelengths” that should also be able to directly observe GJ 251 c and any potential atmosphere.
Scientists often note that a better understanding of a planet’s atmosphere should offer a better understanding of its surface chemistry. This type of data could help future observers distinguish which chemical signatures are from naturally occurring processes and which might represent biological activity from life beyond Earth.
“While we can’t yet confirm the presence of an atmosphere or life on GJ 251 c, the planet represents a promising target for future exploration,” Mahadevan said. “We made an exciting discovery, but there’s still much more to learn about this planet.”
The study “Discovery of a nearby Habitable Zone Super-Earth Candidate Amenable to Direct Imaging” was published in The Astronomical Journal.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.