So far, an impressive 5,000 exoplanets have been discovered. In the hunt for an Earth analogue, of these thousands of planets, only ∼50 have been found to be in the so-called habitable zone (HZ) of their stellar host. Only 20 of these are considered to be the size of the Earth.

A team of astronomers led by MPIA scientist Diana Kossakowski has discovered an Earth-mass exoplanet orbiting the habitable zone of the red dwarf star Wolf 1069. the parent star, the team is optimistic it can provide stable habitable conditions in much of its dayside.

The likelihood that Wolf 1069 b retained most of its atmosphere increases in the absence of any visible stellar activity or strong UV radiation. Therefore, the planet is one of the few promising targets to search for biosignatures and signs of habitability.

Diana Kossakowski of MPIA. She is the lead author of the underlying article and said: “When we analyzed the data from the star Wolf 1069, we found a clear, low-amplitude signal from what appears to be a planet about the mass of Earth. It orbits the star in 15.6 days at a distance equal to one-fifteenth of the distance between the Earth and the Sun.”

Wolf 1069 b receives only about 65% of the incident radiation power Earth receives from the sun, despite being so close to it. Wolf 1069 emits significantly less energy and has a colder surface temperature than the Sun, giving it an orange appearance. Reduced heating power is the result of these characteristics.

Wolf 1069 b is the sixth closest Earth-mass planet to its host star’s habitable zone, at a distance of 31 light-years. It is one of the few illustrious targets to search for biosignatures due to its promising chances of being habitable, along with Proxima Centauri b and TRAPPIST-1 e.

kossakowski said: “This shifts the so-called habitable zone inwards. Therefore, planets around red dwarf stars like Wolf 1069 may be habitable even though they are much closer to the sun than Earth.”

temperature map of Wolf 1069 b
Simulated surface temperature map of Wolf 1069 b, assuming a modern Earth-like atmosphere. The map is centered on the point that always faces the central star. The temperatures are given in Kelvin (K). 273.15 K corresponds to 0 °C. Liquid water would be possible on the surface of the planet within the red line. ©Kossakowski et al. (2023) /MPIA

Co-author Jonas Kemmer from the University of Heidelberg adds: “The CARMENES instrument was built to make it easier to discover as many potentially habitable worlds as possible.”

Like Earth, Wolf 1069 b may have a natural greenhouse effect, which could help raise its average temperature above 250 Kelvin (-23 °C). This value assumes a simple barren rocky planet. According to the scientists’ calculations, the average temperature could even rise to 286 Kelvin (+ 13 °C), if it had an atmosphere similar to that of Earth, allowing liquid water to spread over a significant area on the side of the Earth. planet would survive. looks at the star.

The team concludes that the planet can tolerate moderate temperatures and liquid surface water under different atmospheric conditions and surface types based on computer simulations using advanced climate models.

In addition, Wolf 1069 seems benign. There is no evidence of harmful star activity based on the observations. Even still, it’s too early to be overly optimistic.

MPIA scientist Remo Burn, a team member of the study, said: “Our computer simulations show that about 5% of all evolving planetary systems around low-mass stars like Wolf 1069 end up with a single detectable planet. The simulations also reveal a phase of violent encounters with planetary embryos during the construction of the planetary system, which occasionally led to catastrophic consequences.”

Wolf 1069 b is one of those unusually isolated planets. Based on their measurements, astronomers rule out new planets with an orbital period of less than 10 days and at least one Earth mass. It’s less than the 15.6 days they calculated for Wolf 1069 b. However, they cannot rule out planets with larger orbits.

While Wolf 1069 b is an intriguing candidate to further narrow down its habitability conditions, it shares a distinctive feature with nearly all planets in the habitable zones of red dwarf stars. Most likely it is tidally locked in the orbit of the parent star. In other words, one rotation around an object’s axis is equivalent to one complete revolution. It always has a day on the side that faces the star, while it’s always dark in the other hemisphere because that side always faces the star.

Magazine reference:

  1. D. Kossakowski, M. Kürster et al. The CARMENES search for exoplanets around M dwarfs, Wolf 1069 b: Earth-mass planet in the habitable zone of a nearby very low-mass star. Astronomy & Astrophysics. DOI: 10.48550/arXiv.2301.02477