Wolf 1069b is the sixth closest Earth-mass exoplanet situated in the conservative habitable zone of its parent star, after Proxima Centauri b, Gliese 1061d, Teegarden’s Star c, and Gliese 1002b and c.

An artist’s conception of the surface of the Earth-mass exoplanet Wolf 1069b. Image credit: NASA’s Ames Research Center / Daniel Rutter.

“An impressive 5,000 exoplanets and counting have been detected thus far, largely thanks to the past and ongoing radial-velocity and transit surveys,” said lead author Dr. Diana Kossakowski from the Max Planck Institute for Astronomy and colleagues.

“On the hunt for an Earth analog, out of these thousands of planets, only 50 have been found to sit in the so-called habitable zone of their stellar host, which is defined to be the circumstellar region in which liquid water could potentially exist on the surface of the planet.”

“Only 20 of these are considered to be Earth-sized, defined by radii between 0.8 and 1.6 Earth radii or by masses between 0.5 and 3 Earth masses.”

“Moreover, a majority of them have been discovered around M-dwarf (red dwarf) stellar hosts, most likely due to the ease in detectability considering the higher planet-to-star mass and radius ratios.”

The newly-discovered Earth-mass exoplanet orbits Wolf 1069, a slowly rotating, high-proper motion M-dwarf star discovered in 1920.

Also known as Gliese 1253, GJ 1253, or Karmn J20260+585, the star is located 31.3 light-years away in the constellation of Cygnus.

“When we analyzed the data of Wolf 1069, we discovered a clear, low-amplitude signal of what appears to be a planet of roughly Earth mass,” Dr. Kossakowski said.

“The planet orbits the star within 15.6 days at a distance equivalent to one-fifteenth of the separation between the Earth and the Sun.”

“Despite the close range, it only receives about 65% of the incident radiant power of what the Earth obtains from the Sun.”

This illustration compares Wolf 1069, Proxima Centauri and TRAPPIST-1 planetary systems; the green rings indicate the individual habitable zones around the parent stars. Image credit: MPIA Graphics Department / J. Neidel.

Named Wolf 1069b, the newfound planet is about 1.36 times more massive than Earth.

Sitting at a separation of 0.07 astronomical units (AU) away from the host star puts Wolf 1069b in the habitable zone.

“While Wolf 1069b is a promising candidate to constrain further its conditions concerning habitability, there is one peculiar property it shares with virtually all planets in the habitable zones of red dwarf stars,” the astronomers said.

“The planet’s rotation is likely tidally locked to its orbit around the host star.”

“In other words, one rotation about its axis takes as long as one complete revolution. As the same side always faces the star, it experiences eternal day while there is always night on the opposite hemisphere.”

The planetary signal from Wolf 1069b was detected using radial-velocity data from the CARMENES spectrograph, an instrument installed on the 3.5-m telescope at the Calar Alto Observatory in Spain.

“The CARMENES instrument was built for the very purpose of making it easier to discover as many potentially habitable worlds as possible,” said Dr. Jonas Kemmer, an astronomer at Heidelberg University.

After Proxima Centauri b, Gliese 1061d, Teegarden’s Star c, and Gliese 1002b and c, Wolf 1069b is the sixth closest Earth-mass planet situated in the conservative habitable zone of its parent star.

“Wolf 1069b is a noteworthy discovery that will allow further exploration into the habitability of Earth-mass planets around M dwarfs, as well as case study in testing planetary formation theories,” the researchers concluded.