An Earth-mass world located within the habitable zone orbiting the closest star to Earth? Sounds exciting, huh? It is. A team of astronomers used ESO telescopes to find clear evidence of a planet orbiting the closest star. And it sits within the star’s (Proxima Centauri) habitable zone.
What do we know about the planet dubbed Proxima B?
Proxima B size and orbit
Astronomers used the Doppler effect to identify and learn more about the planet. They were looking for “the tiny back and forth wobble of the star that would be caused by the gravitational pull of a possible orbiting planet.” The small wobble in Proxima Centauri’s spectrum of light came towards (blueshift) and moved away (redshift) from Earth at around 3 MPH every 11.2 days. This was the signal the team of astronomers were waiting to find. They had just found Proxima B.
Close study of the Doppler shifts indicated a planet with a mass at least 1.3 times of Earth and a tight orbit of just 7 million kilometers from Proxima Centauri. That’s just 5% of the Earth-Sun distance and much closer to its star than Mercury is to our Sun. It takes just 11.2 Earth days to complete an orbit.
One of the telescopes used to detect Proxima B.
Guillem Anglada-Escudé, who led the team of astronomers, was ecstatic about the data. “I kept checking the consistency of the signal every single day during the 60 nights of the Pale Red Dot campaign. The first 10 were promising, the first 20 were consistent with expectations, and at 30 days the result was pretty much definitive, so we started drafting the paper!”
Proxima B’s potential hurdles
Is Proxima B habitable? That’s the big question. And one astronomers don’t quite have a definitive answer to.
Let’s talk about what works in the planet’s favor first.
The type of star it is orbiting. Proxima Centauri is a red dwarf. That means it is much cooler than our Sun, hence the closer habitable zone around it. A separate paper states the planet receives about two-thirds of the energy from its star as Earth does from the Sun.
So Proxima B looks like Earth (mass-wise), orbits like Earth (within the habitable zone) and receives a similar amount of energy. What’s the problem?
Not all energy is created equal. Right now, Proxima B receives 60 times more high-energy radiation than Earth according to researchers. And the total from the time of formation is about 7 to 16 times higher compared to Earth. Here’s the big question: does Proxima B have an atmosphere, which would help it preserve water? That’s what future research will attempt to answer. Today, researchers can’t rule out the presence of water on the planet’s surface.
Proxima B is likely tidally locked. You know how you walk outside at night and see the same face of the moon? That’s tidal locking. It’s likely Proxima B is also tidally locked given it’s proximity to its star. One side of the planet sits in permanent daylight, while the other sits in permanent darkness. Now, if the planet has an atmosphere it could redistribute the heat from the day side to the night side. This all hinges on the planet having an atmosphere, though. Without it, Proxima B will look more like a wasteland.
Researchers can’t discount any possibility. The only thing we know for sure is that a rock orbits Proxima Centauri at a distance that would allow liquid water. The fact that this planet is this close to Earth is incredible.
Guillem Anglada-Escudé is excited about the future. “Many exoplanets have been found and many more will be found, but searching for the closest potential Earth-analogue and succeeding has been the experience of a lifetime for all of us. Many people’s stories and efforts have converged on this discovery. The result is also a tribute to all of them. The search for life on Proxima b comes next…”
The next generation of telescopes will help astronomers probe the potential atmospheres of Proxima B and exoplanets like it. Today, we talk about exoplanets. Tomorrow, their atmospheres.
You can read more about Proxima B at the Pale Red Dot website.