Evryscope flares as probes of the habitability of Proxima b and the nearest rocky exoplanets
Abstract
In March 2016, the Evryscope observed the first superflare from Proxima Centauri. The Evryscope array of small optical telescopes recorded the superflare as part of an ongoing survey of all bright southern stars, monitored simultaneously at 2 minute cadence since 2015. Evryscope flares act as probes of the space weather environment and potential habitability of nearby exoplanets in three ways: by constraining their UV surface environments, by looking for planetary magnetic fields via star-planet interaction and flares that phase up with planet orbits, and by monitoring optical counterparts to radio flare observations. We will illustrate each of these probes for Proxima Centauri, and go on to discuss the first results from our ongoing program to measure the long-term flare behavior of all TESS planet-search targets. By modeling the photochemical effects of particle events accompanying large flares, we find Proxima's repeated flaring is sufficient to reduce the ozone column of an Earth-like atmosphere at the orbit of Proxima b by 90% within five years. Surface UV-C levels during the Evryscope superflare reached 100× the intensity required to kill simple UV-hardy microorganisms without ozone, suggesting that life would struggle to survive in the areas of Proxima b exposed to these flares.
Across the sky, we report 2× the previous largest number of 1034 erg high-cadence flares from nearby cool stars. We find 8 flares with amplitudes of 3+ magnitudes, with the largest reaching 5.6 magnitudes and releasing 1036 erg. We measure the superflare rate per flare-star and quantify the superflare properties of TESS-planet-search stars as a function of spectral type. We observe 14.6±2% of the stars around which TESS may discover temperate rocky planets emit flares large enough to significantly affect the potential habitability of those planets. We found 17 stars that may deplete an Earth-like atmosphere via repeated flaring, and we will discuss observations of a superflare with sufficient energy to photo-dissociate all ozone in an Earth-like atmosphere in a single event.- Publication:
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AAS/Division for Extreme Solar Systems Abstracts
- Pub Date:
- August 2019
- Bibcode:
- 2019ESS.....433118L