Scientists used to wonder how ordinary planets were everywhere in the universe and now we know they are everywhere. Even with our relatively rudimentary methods to detect exoplanets, we have identified thousands of alien worlds, including some in our own backyard. In 2016, astronomers discovered an exoplanet around Proxima Centauri, the star closest to the sun. Now it seems that maybe a second “super-earth” exoplanet revolves around that star.
Proxima Centauri is only 4.2 light-years away from the earth. It is part of a triple star group together with the nearby binary system Alpha Centauri AB. Proxima Centauri is smaller and cooler than those stars – it is what is known as a red dwarf, the most common type of star in the Milky Way.
Although Proxima Centauri is very close in cosmic terms, its planetary plane is not in line with the earth. This means that the general transit method for exoplanet detection does not work. Instruments such as Kepler and the new TESS satellite use the transition method to detect small dips in light output while planets pass in front of their home stars. Because that does not work with Proxima Centauri, astronomers used the radial speed of the star (also called Doppler spectroscopy) to spot Proxima b in 2016. An international team of astronomers used the same “sun wobbles” around the new Proxima c exoplanet candidate to detect.
Proxima c is a relatively small mass exoplanet, which is believed to be around six times the size of the Earth. While Proxima revolves around the star every 11 Earth Days, Proxima c has a turnaround time of five years. It is 50 percent farther from Proxima Centauri than the earth from the sun, and Proxima Centauri is a much cooler star. As a result, scientists predict that Proxima c is far beyond the habitable zone of the star with temperatures up to -388 degrees Fahrenheit. Proxima b is in the habitable zone, but radiation from the red dwarf can make it inhospitable.
The team analyzed 17 years of data from the HARPS (High Accuracy Radial Velocity Planet Searcher) and the UVES instruments (Ultraviolet and Visual Echelle Spectrograph) to identify Proxima c. The study reports that the new exoplanet best explains the special gravity swing of Proxima Centauri. Now it’s up to other teams to study the star and confirm the findings. Even if there is no chance of life on Proxima c, it could be a real blessing for the study of exoplanets to have a system with two of them right outside our door.