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Proton Beams of Death

posted Mar 4, 2020, 7:42 PM by Jeremy Drake   [ updated Apr 24, 2020, 6:29 AM ]
The most numerous stars in the Universe are those of the lowest masses - the M dwarfs. They are so dim compared with stars like our own Sun that their so-called habitable zones, where any planets might habour water in liquid form, are very close in. Unfortunately, this proximity is potentially hazardous for any planets with ambitions of engendering life. M dwarfs emit proportionally much more of their power in energetic radiation, such as X-rays and extreme ultraviolet light, in addition to winds, coronal mass ejections and energetic particles, than more massive stars like the Sun does. This radiation can scour and evaporate the atmospheres of close-in planets, possibly leaving behind only barren, rocky cores.

Energetic particles - mostly protons - accelerated in flares or in shockwaves from coronal mass ejections could be especially dangerous, causing showers of secondary ionizing particles in an atmosphere and destroying UV-protecting ozone. It is very difficult to asses exactly what the threat of energetic protons is because they do not travel in straight lines, like X-rays. They are instead guided and deflected by the magnetic field carried out from the star by its plasma wind through interplanetary space.  

In a paper lead by University of Arizona and Smithsonian Astrophysical Observatory scientist Federico Fraschetti and published in the 2019 March edition of the Astrophysical Journal, we decided to try and work out where energetic protons from the star end up. A supercomputer magnetohydrodynamic model of the stellar wind and turbulent magnetic field of a TRAPPIST-1-like system was created, and we then fired protons into this and mapped the results. We found that particles are strongly focused toward the equatorial planetary orbital plane, potentially bombarding any planets with a proton flux up to a million times more intense than experienced by the present-day Earth.  Proton beams of death?