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Earth's closest 'super' neighbor, Proxima Centauri, a star, may be home to second planet, study suggests

It appears to be at least 5.8 times as massive as Earth, earning it the name 'super-earth'. It could be orbiting its star about once every five years, say scientists who led the planet-hunting mission hunt
Proxima Centauri (ESA/Hubble & NASA)
Proxima Centauri (ESA/Hubble & NASA)

The closest star to our sun, Proxima Centauri, may have given away one of its secrets: a 'super-earth' planet.

A new study suggests that the star, which is only 4.2 light-years away, could be home to a planet dubbed Proxima C. If scientists confirm its existence, it will be the second planet orbiting the star.

It appears to be at least 5.8 times as massive as Earth, giving it the name'super-earth'. It could be orbiting its star about once every five years, say scientists who led the planet-hunting-  'mission hunt'.

"Proxima Centauri is the nearest star to the sun, and this detection would make it the closest multi-planetary system to us," Fabio Del Sordo, study author and a postdoctoral researcher in the department of physics at the University of Crete, told CNN.

This artist's concept contrasts our familiar Earth with a super-earth named 55 Cancri e. (NASA/JPL-Caltech/R. Hurt SSC))

Proxima Centauri is a red dwarf star, with only about an eighth of the mass of the sun. Only recently, in 2016, scientists detected the first planet circling the star: Proxima b. Astronomers believe this planet could host life.

Proxima c, on the other hand, may not be habitable. It is too far from the influence of its host star, meaning the planet may not be receiving enough heat to keep water on its surface in a liquid state. 

The team caught a glimpse of the planet's presence using the Atacama Large Millimeter/ submillimeter Array (ALMA), an astronomical observatory in northern Chile. When scientists pointed the observatory towards Proxima Centauri, they spotted fluctuating light signals coming from the star -- this could be the sign of a second planet, say, scientists.

These fluctuations happen due to moving objects, more specifically, when the star and the second planet are moving toward or away from each other. Planets use their gravity to cause their host stars to move in small circles. 

When these objects move, scientists observe a shift in light signals of the star, making it appear in colors between red and blue, depending on the location of the planet. By keeping an eye on the shifts in the colors, astronomers find planets.

Using the same method, Del Sordo and the team detected Proxima c. But this does not mean their find is conclusive: they have not been able to rule out one important factor that could be influencing the changing light signals: the star's magnetic field.

"Even the closest planetary system to us may retain interesting surprises. Proxima Centauri hosts a planetary system that is much more complex than we knew, and we do not know how many unknown features are waiting to be discovered," Del Sordo said.

To confirm whether the star is indeed home to the second planet, Proxima c, scientists will have to carry out follow-up studies using next-generation direct imaging instrumentation, says the team. This, in turn, may provide insights into how low-mass planets form around low-mass stars.

The study has been published in Science Advances.