Astronomers have found that Proxima Centauri, the star closest to our solar system, is surrounded by a ring of cosmic dust. This indicates that Proxima Centauri may host a planetary system that we have yet to discover.
An illustration of Proxima Centauri and its dust ring [Image by ESO/M. Kornmesser]
It turns out that Proxima Centauri has been keeping secrets from us. Proxima Centauri is a low-mass red dwarf situated only 4.25 light years away from our Sun in the constellation Centaurus. At this relatively close distance, Proxima Centauri is the closest known star to our solar system. Thus, it’s also host to the closest known Earth-sized exoplanet, Proxima b, which researchers discovered just last year. Proxima b seems to be in the habitable zone of its planetary system, indicating that liquid water may exist on its surface.
Since discovering the dusty ring around Proxima Centauri, however, astronomers now think that Proxima b may not be the only planet circling the star.
Hubble Telescope image of Proxima Centauri [Image by ESA/Hubble]
According to a new study (linked is a pre-print copy), researchers used the Atacama Large millimeter/submillimeter Array (ALMA) in Chile to study Proxima Centauri. The researchers found a ring of dust about 1% the mass of Earth encircling the star.
There are a few similarities between our Sun and its closest neighbor. For one thing, both are about the same age. Both have similar-sized planets in their habitable zones. The Sun has the Kuiper Belt, a ring of composed of icy celestial bodies. Proxima Centauri’s dust ring, meanwhile, has a temperature of about -230 degrees Celsius, similar to the temperature of the Kuiper Belt.
An illustration of Proxima b [Image by ESO/M. Kornmesser]
Proxima Centauri’s dust ring lies about a few hundred million kilometers away from its host star, far beyond the orbit of Proxima b. Though astronomers are calling it a dust ring, it’s actually not entirely made of dust. It’s likely that the ring is composed materials ranging in size, from dust grains to asteroid-like objects that measure several kilometers in width. According to the researchers, these materials were likely unable to band together and form planets.
However, the secrets don’t end there. ALMA researchers also say that they found indications that there may be a second ring surrounding Proxima Centauri. It’s likely that this second ring, if it exists, is about 10 times farther from the star than the first ring. However, astronomers haven’t yet confirmed that this second ring does exist.
The orange circle tagged as "Unknown source?" is the possible giant planet [Illustration by Anglada et. al, Astrophysical Research Letters (2017)]
The discovery of Proxima Centauri’s first ring of dust is now telling astronomers that there may be more planets hanging around in the Proxima Centauri system. After all, dust rings like this are usually composed of the leftover materials of planetary formation. “The dust around Proxima is important because [..] 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,” says Guillem Anglada, the study’s lead researcher.
Anglada and his colleagues also say that the existence of a giant planet further away from Proxima Centauri than Proxima b is possible. However, existing data on the star doesn’t indicate that a planet such as this may exist. Still, researchers are open to the possibility.
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