Energetic flares in the search for habitable exoplanets

Exoplanet searchers will, I suspect, find the article “Warm planets orbiting cool stars” by John Johnson (Physics Today, March 2014, page 31 ) interesting and encouraging.

In his section on habitable zones, I wish Johnson had considered the effect of flares among low-mass stars of the M-class main sequence. The internal structure of those stars, coupled with rapid spin, can produce frequent energetic flares. They are important to the discussion because a planet whose temperature places it within the habitable zone would be vulnerable to carbon-chemistry damage from the flares’ ionizing radiation. “Life on a planet near one of these flare stars might be quite difficult.” ¹

Earth is shielded from the Sun’s less-frequent flares by its magnetic fields. An extrasolar planet orbiting a flare star and having any hope of life-producing chemistry would need even stronger, more persistent magnetic fields. Those fields might even be detectable in searches of extrasolar planets.