Astronomers have discovered a “super-Earth” planet in the habitable zone of a red dwarf star just 18.2 light-years away. The planet, named GJ 251c, could be one of the most promising targets for future studies of the existence of life beyond our solar system.
The planet GJ 251c orbits a red dwarf star PHOTO: NASA
GJ 251c orbits a red dwarf star in the constellation Gemini and has a mass about four times that of Earth. This size puts it in the category of “super-Earths,” rocky planets larger and more massive than Earth.
“Although we cannot yet confirm the presence of an atmosphere or life on GJ 251c, the planet represents a promising target for future exploration“, said Suvrath Mahadevan, professor of astronomy at Penn State University, according to Space.com.
The planet is in the so-called “habitable area”or “goldilocks zone”where conditions could allow liquid water to exist on the surface if the atmosphere is right.
Two decades of observations
The discovery was made possible thanks to observations that spanned more than 20 years. Scientists tracked a small “oscillation” of the parent star, caused by the planet’s gravity. This subtle motion to and from Earth produces a detectable change in the star’s radial velocity, measurable with spectrographs.
The GJ 251 system also contains another planet, GJ 251b, discovered in 2020. Using archived data from telescopes around the world, the team led by Mahadevan was able to refine the measurements for this planet.
The astronomers then combined this data with new, highly precise observations made with the Habitable-Zone Planet Finder (HPF) instrument on the Hobby-Eberly Telescope in Texas. Thus, a second signal was identified, that of the planet GJ 251c, which orbits the star every 54 days. The discovery was confirmed with additional data obtained from the NEID spectrograph on the WIYN telescope in Arizona.
A difficult discovery
Although it seems simple, the process of detecting such a planet is extremely complex. Red dwarf stars are very active, their surface “boiling” constant, with convective bubbles and eruptions producing intense background noise.
“It’s a tricky game, where we have to discount the effects of stellar activity and distinguish the planet’s subtle signals from what is basically a boiling magnetospheric cauldron”, explained Mahadevan.
What’s next for GJ 251c
Astronomers hope that future telescopes will be able to study this world’s atmosphere. The James Webb Space Telescope (JWST) probably won’t be able to analyze the planet, being too far from its star to be effectively observed. However, new giant 30-meter telescopes under development could detect light reflected from the planet’s atmosphere or surface.
“We are at the limit of current technology,” said Corey Beard, a researcher at the University of California, Irvine, who participated in the study. “We need the next generation of telescopes to directly image this candidate planet”.
A “temperamental” star
Although GJ 251c looks like a promising place, there is one major problem: its star. At only 36% of the mass of the Sun, GJ 251 is a red dwarf, a type of star known for its powerful outbursts that can, over time, destroy the atmospheres of surrounding planets.
Astronomers have already discovered several habitable planets around similar stars, such as Proxima Centauri b or TRAPPIST-1e, but observations by the JWST telescope have shown that these worlds do not appear to have a stable atmosphere.
In the case of GJ 251c, however, there is hope. The planet is slightly further from its star than other similar worlds, and this may be enough to shield it from intense radiation. If it has a dense atmosphere and a strong magnetic field, it could resist the stellar wind.
For now, everything remains at the level of hypothesis. “We made an exciting discovery”said Mahadevan, “but we still have a lot to learn about this planet“.
