Stars like Ross 128 move ever so slightly because of the gravitational tug of nearby objects. These tiny movements can be seen as changes in a star’s light spectrum; when the star moves toward an observer—in this case, the HARPS instrument—its light looks slightly bluer, and when it moves away, it turns redder. If these shifts occur in regular patterns, that means there’s an exoplanet lurking. Astronomers can analyze this information to determine some of the planet’s properties. Nicola Astudillo-Defru, an astronomer at the University of Geneva and Bonfils’s coauthor, said he reacted with “a big wow” when the data showed a rocky and temperate world. “I feel so excited that I mailed Xavier minutes later with a clear URGENT in the subject,” he said in an email.

Astronomers say Ross 128 b completes an orbit around its star every 9.9 days. They estimate the exoplanet has an equilibrium temperature somewhere between -60 degrees and 20 degrees Celsius (-76 degrees to 68 degrees Fahrenheit).

Astronomers don’t know whether Ross 128 b resides in its star system’s habitable zone, that sweet spot where temperatures are just right for liquid water to pool on the surface of a rocky world. But they’re still hopeful that it might be able to support life. Red dwarfs like Ross 128 are dimmer than sun-like stars, emitting infrared instead of visible light. So while Ross 128 orbits 20 times closer to its star than the Earth does to the sun, the exoplanet receives only 1.38 times more stellar radiation than Earth. Bonfils said Ross 128 is “quieter” than other red dwarfs, like Proxima Centauri, which can unleash flares that bathe orbiting planets in ultraviolet and X-ray radiation.

“Some even think that the atmosphere can erode, can evaporate, due to these activities,” Bonfils said. The quiet nature of Ross 128 may have created a comfortable cosmic environment for life on the exoplanet to take hold, despite its planet’s close proximity to the star.

Ross 128 popped into headlines in July of this year, when astronomers at the Arecibo Observatory in Puerto Rico said they had detected a mysterious radio transmission coming from the star for about 10 minutes in mid-May. Stars can emit electromagnetic radiation in the form of radio waves, but this signal was recorded at a frequency scientists hadn’t seen before in red dwarfs. Arecibo and other telescopes quickly trained their eyes on Ross 128 for more observations, but the transmission never appeared again. The astronomers entertained several possible explanations, including—much to the internet’s delight—extraterrestrials. They eventually said the signal probably came from one or more geostationary satellites. But the discovery of an Earth-sized exoplanet around the star could restart some of that conversation.

“We are considering additional follow-up in light of the new discovery at radio and optical wavelengths,” said Andrew Siemion, the director of the Berkeley SETI Research Center who runs the Breakthrough Listen Initiative, aimed at finding evidence of extraterrestrial civilizations. The Breakthrough Listen team helped Arecibo astronomers observe Ross 128 this spring. “Nearby exoplanets are particularly exciting from a SETI perspective as they permit us to search for and potentially detect much weaker signals than from more distant targets.”