Astronomers Detect Second Planet Orbiting Nearest Star

Scientists used to wonder how common planets were throughout the universe, and now we know — they’re everywhere. Even with our relatively rudimentary methods of detecting exoplanets, we’ve identified thousands of alien worlds, including some in our own backyard. In 2016, astronomers discovered an exoplanet around Proxima Centauri, the nearest star to the sun. Now, it looks like there might be a second “super-Earth” exoplanet orbiting that star. 

Proxima Centauri sits a mere 4.2 light-years away from Earth. It’s part of a triple star group along with the nearby Alpha Centauri AB binary system. Proxima Centauri is smaller and cooler than those stars — it’s what’s known as a red dwarf, the most common type of star in the Milky Way galaxy. 

While Proxima Centauri is very close in cosmic terms, its planetary plane doesn’t align with Earth. That means the common transit method of exoplanet detection doesn’t work. Instruments like Kepler and the new TESS satellite use the transit method to detect small dips in light output as planets pass in front of their home stars. Since that doesn’t work with Proxima Centauri, astronomers used the star’s radial velocity (also called Doppler spectroscopy) to spot Proxima b in 2016. An international team of astronomers used the same “solar wobbles” to detect the new Proxima c exoplanet candidate. 

Image by Wikipedia. Alpha Centauri AB is on the left, Beta Centauri on the right, and Proxima Centauri is at the center of the red circle.

Proxima c is a relatively low-mass exoplanet, believed to be about six times more massive than Earth. Whereas Proxima b orbits the star once every 11 Earth days, Proxima c has an orbital period of five years. It’s 50 percent farther from Proxima Centauri than Earth is from the sun, and Proxima Centauri is a much cooler star. As a result, scientists predict Proxima c is far outside the star’s habitable zone with temperatures as low as -388 degrees Fahrenheit. Proxima b is inside the habitable zone, but radiation from the red dwarf might render it inhospitable. 

The team analyzed 17 years of data from the HARPS (High Accuracy Radial Velocity Planet Searcher) and the UVES (Ultraviolet and Visual Echelle Spectrograph) instruments to identify Proxima c. The study reports that the new exoplanet best explains Proxima Centauri’s peculiar gravitational wobble. Now, it’s up to other teams to study the star and confirm the findings. Even if there’s no chance for life on Proxima c, it could be a real boon to the study of exoplanets to have a system with two of them right on our cosmic doorstep.

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