A New Exoplanet For Proxima Centauri, the Solar System’s Closest Celestial Neighbor

 A New Exoplanet For Proxima Centauri, the Solar System’s Closest Celestial Neighbor

by Mckenzie Golden

3/1/21

A group of Portuguese astronomers appear to have discovered a third exoplanet orbiting around the closest star to our Sun, as their research was published to the public in the Astronomy and Astrophysics Journal on February 10, 2022. The red dwarf Proxima Centauri, just 4.3 light years from our solar system, appears to bear at least three exoplanets in its system, with the new one appropriately labeled Proxima Centauri d. It joins Proxima Centauri b (disc. 2016) and c (disc. 2020) as the only discovered planets orbiting Proxima Centauri. 

Fig. 1: Approximate location of Proxima Centauri d to its star and much larger neighbor Alpha Centauri.

Candidate d is believed to be one of the lightest exoplanets ever discovered, measuring only one quarter of the mass of Earth. It is orbiting Proxima Centauri with extreme proximity at only one tenth of the distance between Mercury and the Sun. It was discovered via a recurring 5 day signal (see Fig. 2), which corresponded to a five day orbital period (which makes sense with its proximity to the star). Now that peer review has confirmed its existence, more research will likely take place to determine if Proxima Centauri d has an atmosphere or what its composition may be.

Fig. 2: Graphs assessing the orbital period of Proxima Centauri d from the original research submission to the Astronomy and Astrophysics Journal. We can observe in the middle graph that there appears to be a trend of recurrence every five days.

Proxima Centauri d orbits slightly outside the inner edge of the star’s habitable zone (the region in which a rocky planet could contain liquid water), indicating that it probably could not support life. Interestingly enough, despite this, if candidate d has no atmosphere, it is believed that it’s temperature at equilibrium could be around 200 degrees Fahrenheit, probably due to its close proximity to the habitable zone. This system’s habitable zone is much closer to the star itself than our Solar System’s HZ– this is because Proxima Centauri is only about 12.5% of the mass of our Sun, so it is a much smaller and less hot star.

The machinery in question used for the discovery was an attachment to the ESO’s Very Large Telescope in Chile, called the Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (and comically acronymed ESPRESSO). The initial signal picked up by the VLT was relatively weak, most likely due to the planet’s small size, so the ESPRESSO modification was used to determine if the cause of the signal was planetary in nature, or if the star’s activity was throwing off the instruments. ESPRESSO is a precise spectroscopic instrument, in that it collects light and is able to separate it into wavelengths and records the resulting spectrum (aka modern telescopes). 

There are many interesting prospects with Proxima Centauri d– especially in the realm of uncovering the immediate observable universe. Exoplanet discovery has increased exponentially in the last twenty years, but the discovery of an exoplanet that could be a traversable distance away in the near future opens the door to a whole new level of studying exoplanets and phenomena outside of our solar system. The discovery of lighter and lighter exoplanets shows that human instrumentation is becoming more advanced and reliable. Perhaps one of the great draws of astronomy research is how much of the universe is still left to be discovered– and discoveries like Proxima Centauri d are just scratching a very exciting and promising surface. 

Cover picture

Links:

https://earthsky.org/space/3rd-possible-planet-proxima-d-proxima-centauri/ 

https://www.aanda.org/articles/aa/full_html/2022/02/aa42337-21/aa42337-21.html 

https://www.eso.org/sci/facilities/paranal/instruments/espresso.html 

https://exoplanets.nasa.gov/faq/15/what-is-the-habitable-zone-or-goldilocks-zone/#:~:text=The%20habitable%20zone%20is%20the,of%20its%20atmosphere%20would%20freeze. 

https://nasa.fandom.com/wiki/Orbital_period