Science & Technology

Newfound dust belts suggest that Proxima Centauri has more than one alien planet

Astronomers created a stir last year when they reported that the closest star beyond our own solar system harbors a potentially habitable planet, but now fresh evidence hints that there could be even more worlds around Proxima Centauri.

The ALMA Observatory’s array of antennas in Chile has picked up the thermal glow from cold clouds of dust surrounding the red dwarf star, which lies just 4.2 light-years away in the constellation Centaurus. The clouds show up in a region that’s about one to four times as far away from the star as Earth is from our own sun.

There’s also evidence of a second dust belt farther out from the star. Such belts are thought to contain the remains of material left behind by the planet formation process, consisting of particles ranging in size from flecks of earthly dust to miles-wide asteroids.

Both belts are farther out than Proxima Centauri b, the planet whose detection was announced last year.

“The dust around Proxima is important because, following the discovery of the terrestrial planet Proxima b, it’s the first indication of the presence of an elaborate planetary system, and not just a single planet, around the star closest to our sun,” Spanish astronomer Guillem Anglada, lead author of a study to be published in Astrophysical Journal Letters, said today in a news release.

Anglada’s name is similar to that of Guillem Anglada-Escudé, an astronomer at Queen Mary University of London who led the team behind Proxima b’s discovery, but the two are not related. To make things even more complicated, Anglada-Escudé is a co-author of the ALMA study. (Anglada is a relatively common surname in Spain, where both men grew up.)

The research team estimates that the inner dust belt extends a few hundred million kilometers (miles) out from Proxima Centauri, and has a total mass that adds up to a hundredth of Earth’s heft. Temperatures in the belt are about 380 degrees below zero Fahrenheit. That would make it about as cold as Pluto and the Kuiper Belt on the icy edge of our solar system. The farther-out belt would be even colder.

The entire Proxima Centauri system is cooler than our own solar system because the red dwarf star is so much dimmer than our own sun. Even though Proxima b’s orbit would fit well within Mercury’s orbit, that planet’s surface temperature is thought to range from minus-22 degrees F on its dark side to 86 degrees F on its light side.

Assuming that the planet has an atmosphere, water could conceivably exist in liquid form. And if that’s the case, Proxima b could sustain life as we know it, provided that such life forms could survive the occasional high-energy blast of stellar radiation.

Farther-out planets would be even less hospitable. Nevertheless, ALMA’s observations are likely to lead astronomers to take closer looks.

“Further observations will give us a more detailed picture of Proxima’s planetary system,” said study co-author Pedro Amado — who, like Anglada, is an astronomer at the Instituto de Astrofisica de Andalucia in Granada, Spain. “In combination with the study of protoplanetary discs around young stars, many of the details of the processes that led to the formation of the Earth and the Solar System about 4,600 million years ago will be unveiled. What we are seeing now is just the appetizer, compared to what is coming.”

ALMA won’t be the only instrument turned in Proxima Centauri’s direction. There’s a whole range of telescopes that could provide insights, ranging from NASA’s James Webb Space Telescope, due for launch in 2019, to a proposed Colossus Telescope or an ExoLife Finder Telescope. In the decades ahead, the Breakthrough Starshot project intends to send nano-sized, beam-propelled probes zooming past Proxima.

Anglada, Amado and Anglada-Escudé are among 22 authors of the paper published in Astrophysical Journal Letters, titled “ALMA Discovery of Dust Belts Around Proxima Centauri.”

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