Belts of dusty debris encircle closest star Proxima Centauri

Two belts of dust and ice have been detected around the closest star after the Sun, Proxima Centauri, suggesting it may be like a mini Solar System with more planets waiting to be found. And there are hints that one might resemble Saturn.

An artist’s impression, not to scale, shows how the newly discovered belts of dust around the closest star to the Solar System, Proxima Centauri, may look. Image credit: ESO/M. Kornmesser

Proxima is a red dwarf star, much smaller and cooler than our own Sun, which lies 4.2 light-years away – equivalent to 40 trillion km.

It hit the headlines in August, 2016, with the announcement of the discovery of a rocky planet just a little bigger than Earth in its habitable zone.

Astronomers made the latest detection by observing the glow from the bands of cold dust, using the ALMA telescope, an array of dishes high in Chile’s Atacama Desert.

One is being compared to the Kuiper Belt, which is a band of rock and ice beyond Neptune in our own Solar System. But Proxima’s lies much closer in, at only one to four times the distance of the Earth from the Sun. The Earth-Sun distance is called one Astronomical Unit (AU).

The belt’s temperature is estimated to be around -230° C, which compares to that of the Kuiper Belt. Less distinct in the data is a second dusty belt about 10 times farther out than the first, and even colder.

More planets?

Though the rocky planet dubbed Proxima b remains the only planet yet found orbiting Proxima Centauri, the presence of the dusty belts is tantalising evidence that there may be other smaller worlds in its own solar system.

They are thought to be made up of particles of rock and ice, ranging is size from tiny grains to large asteroids, that failed to collect together to form planets and moons.

The new study that detected the dusty belts was led by Guillem Anglada, from the Instituto de Astrofísica de Andalucía (CSIC), in Granada, Spain.

Commenting on the find, he said: “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.”

He added: “This result suggests that Proxima Centauri may have a multiple planet system with a rich history of interactions that resulted in the formation of a dust belt. Further study may also provide information that might point to the locations of as yet unidentified additional planets.”

Skymania asked Professor Anglada if Proxima Centauri’s environment could be thought of as a solar system in miniature.

He told us: “Yes. Because Proxima is colder, less massive and less luminous than our Sun we expected that a possible analogue to our Kuiper Belt should be located at only a few astronomical units (AU) from the star, in contrast with our Kuiper Belt that is found at 30-50 AU. And this is indeed what we found.

“So, we consider the dust clouds that we identify at distances 1-4 AU from Proxima as an analogue to our Kuiper Belt. At this distance from Proxima we expect the temperature and other physical conditions to be similar to those in our Kuiper Belt. In this sense, the planetary system around Proxima can be considered as a solar system in miniature, as you pointed out.”

An ESO video about the new discovery

But Anglada added: “What does not fit into this scheme is the possible outer belt at 30 AU. There is no known structure in our Solar System that can be considered an analogue to this belt. As far as I know, only some heterodox theories have considered the possibility of an equivalent distant structure in our Solar System. But, of course, it is possible that it remains still undiscovered . . . ”

A gas giant like Saturn?

We also asked whether observations so far had ruled out the existence of any larger gas giants, like Jupiter in this system? Would they not have shown up by now?

Anglada told us: “No, the current observations do not rule out the presence of gas giants. Actually, we find an excess of emission in the proximity of the star whose nature is unknown. As one of the possible explanations, we note that this emission is consistent with the expected emission from a ring of dust around a planet similar to Saturn, and located at a distance of 1.6 AU from the star.

“Such a planet might have remained undetected in the previous radial velocity observations that led to the detection of Proxima b. Future observations should clarify the nature of this source.”

Anglada’s colleague, Pedro Amado, who was also involved in the research, said that this observation would lead to further discoveries about the Proxima Centauri system.

He said: “These first results show that ALMA can detect dust structures orbiting around Proxima. Further observations will give us a more detailed picture of Proxima’s planetary system.

“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 4600 million years ago will be unveiled. What we are seeing now is just the appetiser compared to what is coming!”

Proxima Centauri may be the closest star to our Sun, but it would still take a conventional spacecraft many thousands of years to reach it. However, Professor Stephen Hawking and Facebook chief Mark Zuckerberg have announced the Starshot Project to send a fleet of tiny robotic probes that could accelerate to a quarter of the speed of light and get there in just 20 years.

Incidentally Anglada is not related to the similarly-named Dr Guillem Anglada-Escudé, of Queen Mary University of London, who led the discovery of planet Proxima b. However, Dr Anglada-Escudé also contributed to the new detection.

A video by ESO showing the dusty belts and planet Proxima b.

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