Proxima Centauri may be a multi-planet system

Dust belt found orbiting the star could have been created by a gas giant.
By Laurel Kornfeld | Nov 07, 2017
Proxima Centauri, the closest star to our Sun, already known to have one orbiting planet, is surrounded by a ring of icy dust that could have been created by a gas giant planet not yet discovered.

The disk was discovered by a team of researchers at the European Southern Observatory (ESO) through observations of the star in various wavelengths using multiple telescopes, especially the Atacama Large Millimeter/submillimeter Array (ALMA) radio telescope in Chile.

Up to three circumstellar rings might be surrounding the star, the scientists believe. The closest one, which is also the largest and brightest, orbits between one and four astronomical units (AU, with one AU equal to the average Earth-Sun distance or 93 million miles) from the star.

A second, cold belt of material may be orbiting Proxima Centauri at a distance of approximately 30 AU though evidence for this one remains circumstantial.

Evidence is also circumstantial for a possible third ring, a hot one orbiting 0.4 AU from the star.

Scientists compared the bright ring to our solar system's asteroid belt and Kuiper Belt, where small rocky and icy materials were shepherded by Jupiter and Neptune respectively.

A hidden gas giant could be acting the same way in the Proxima Centauri system.

When ALMA observed the star in the far infrared and in high frequency microwave light, scientists saw the cold, bright debris disk, which could indicate the presence of additional planets.

Because dust rings have a higher surface area than individual planets, the former are easier to spot than the latter.

Approximately 1.6 AU from Proxima b, the one known planet orbiting the star, scientists have observed a "thermal blob" that could be a Saturn-mass ringed planet of up to 100 Earth masses.

A gas giant that size could be shepherding material and creating the dust belt.

"Our ALMA data reveal also an intriguing faint compact source at a distance less than two Astronomical Units from the star and that could be interpreted as a ring of dust surrounding a giant planet 100 times more massive than the Earth," noted ALMA program manager Itziar de Gregorio-Monsalvo.

To date, no planet has been found in that location by another planet-hunting project known as RedDots, which studies three red dwarf stars, including Proxima Centauri.

The researchers are also puzzled by the presence of debris disks surrounding this star, which is five billion years old, as these disks are usually found orbiting either new stars or old, dead ones.

"In my opinion, what we found in Proxima Centauri suggests an elaborate system that might be harboring several planets," said Mayra Osorio of the Instituto de Astrofisica de Andalucia.

A paper describing the findings has been published in The Astrophysical Journal.

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