Edwin L. Aguirre
When astronomers announced last summer that they had discovered a rocky, Earth-like planet orbiting the star Proxima Centauri, researchers around the world were excited. Proxima Centauri
is the closest star to our solar system, so interest is high in our cosmic neighbor. What’s more, the new planet — called Proxima b
— is situated within the star’s habitable zone, where Proxima b’s atmosphere, if it’s dense enough, can sustain liquid water on the planet’s surface.
Scientists believe that, owing to Proxima Centauri’s close distance, they may actually find direct evidence of life on Proxima b. However, advanced mathematical 3-D modeling conducted by Physics
Asst. Prof. Ofer Cohen
of the university’s Lowell Center for Space Science and Technology
, as well as researchers from the Harvard-Smithsonian Center for Astrophysics, demonstrates that Proxima b doesn’t have an atmosphere; hence, the chances of finding extraterrestrial life on the alien world’s surface have become less likely.
The team’s findings were published in “The Astrophysical Journal Letters
” and were reported in the December issue of Physics Today
. Cohen’s part of the study is supported by a five-year, $500,000 grant from the NASA Nexus for Exoplanet System Science (NExSS) Program.
A Pale Red Dot
Proxima Centauri is a red dwarf star in the southern constellation Centaurus that is much smaller, dimmer and cooler than the sun. It lies 4.25 light-years from us — a mere “stone’s throw away” in terms of the cosmic scale. (One light-year is approximately 6 trillion miles.)
The Proxima Centauri system is different from TRAPPIST-1
star system that was announced by NASA on Feb. 22. This newly discovered stellar system consists of an ultra-cool dwarf star orbited by seven rocky, Earth-size planets within the star’s habitable zone. TRAPPIST-1 is located 40 light-years away in the constellation Aquarius.
Cohen and his colleagues modeled Proxima Centauri’s “stellar wind,” the steady stream of charged particles emanating from the star, and its effect on Proxima b. According to their model, Proxima b is buffeted by wind from Proxima Centauri that is more than 2,000 times stronger than what Earth experiences from the sun’s wind because Proxima b lies 20 times closer to its parent star than Earth is to the sun.
“Even though Proxima b resides in the habitable zone and might have a magnetic field than can deflect some of the stellar wind, whatever atmosphere the alien planet had initially possessed was probably stripped away by stellar wind a long time ago,” explains Cohen. “With the atmosphere all gone, there’s no way to shield the planet’s surface from the star’s intense ultraviolet and X-ray radiation.”
Still, Cohen isn’t completely ruling out the possibility of extraterrestrial life on the neighboring planet, however remote.
“Here on Earth, we can find ‘extremophiles’ — organisms living in some of our planet’s most hostile and extreme environments,” he says. “Life finds a way.”