Evryscope and K2 Constraints on TRAPPIST-1 Superflare Occurrence and Planetary Habitability

Abstract

The nearby ultracool dwarf TRAPPIST-1 possesses several Earth-sized terrestrial planets, three of which have equilibrium temperatures that may support liquid surface water, making it a compelling target for exoplanet characterization. TRAPPIST-1 is an active star with frequent flaring, with implications for the habitability of its planets. Superflares (stellar flares whose energy exceeds 10^33 erg) can completely destroy the atmospheres of a cool star's planets, allowing ultraviolet radiation and high-energy particles to bombard their surfaces. However, ultracool dwarfs emit little ultraviolet flux when quiescent, raising the possibility of frequent flares being necessary for prebiotic chemistry that requires ultraviolet light. We combine Evryscope and Kepler observations to characterize the high-energy flare rate of TRAPPIST-1. The Evryscope is an array of 22 small telescopes imaging the entire Southern sky in g' every two minutes. Evryscope observations, spanning 170 nights over 2 years, complement the 80-day continuous short-cadence K2 observations by sampling TRAPPIST-1's long-term flare activity. We update TRAPPIST-1's superflare rate, finding a cumulative rate of 4.2 (+1.9 -0.2) superflares per year. We calculate the flare rate necessary to deplete ozone in the habitable-zone planets' atmospheres, and find that TRAPPIST-1's flare rate is insufficient to deplete ozone if present on its planets. In addition, we calculate the flare rate needed to provide enough ultraviolet flux to power prebiotic chemistry. We find TRAPPIST-1's flare rate is likely insufficient to catalyze some of the Earthlike chemical pathways thought to lead to RNA synthesis, and flux due to flares in the biologically relevant UV-B band is orders of magnitude less for any TRAPPIST-1 planet than has been experienced by Earth at any time in its history.

arXiv comment12 pages, 9 figures. Accepted to The Astrophysical Journal, in press

References in corpus (35)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Astropy: A Community Python Package for Astronomy
• The NumPy array: a structure for efficient numerical computation
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• Habitable Zones Around Main-Sequence Stars: New Estimates
• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• Temperate Earth-sized planets transiting a nearby ultracool dwarf star
• Correcting systematic effects in a large set of photometric lightcurves
• The Effect of a Strong Stellar Flare on the Atmospheric Chemistry of an Earth-like Planet Orbiting an M dwarf
• Kepler Flares I. Active and Inactive M dwarfs
• The nature of the TRAPPIST-1 exoplanets
• Stellar Flares from the First Tess Data Release: Exploring a New Sample of M-dwarfs
• The Habitability of Planets Orbiting M-dwarf Stars
• Kepler Flares II: The Temporal Morphology of White-Light Flares on GJ 1243
• Modeling Repeated M-dwarf Flaring at an Earth-like Planet in the Habitable Zone: I. Atmospheric Effects for an Unmagnetized Planet
• Magnetic Cycles and Rotation Periods of Late Type Stars from photometric time series
• Multiple and changing cycles of active stars II. Results
• Frequent flaring in the TRAPPIST-1 system - unsuited for life?
• The Origin of RNA Precursors on Exoplanets
• Connecting Flares and Transient Mass Loss Events in Magnetically Active Stars
• A White Light Megaflare on the dM4.5e Star YZ CMi
• The MUSCLES Treasury Survey. V. FUV Flares on Active and Inactive M Dwarfs
• UV Surface Environment of Earth-like Planets Orbiting FGKM Stars Through Geological Evolution
• The First Naked-Eye Superflare Detected from Proxima Centauri
• Evryscope science: exploring the potential of all-sky gigapixel-scale telescopes
• MOST Observations of our Nearest Neighbor: Flares on Proxima Centauri
• Evolution of coexisting long and short period stellar activity cycles
• EvryFlare I: Long-term Evryscope Monitoring of Flares from the Cool Stars Across Half the Southern Sky
• K2 Ultracool Dwarfs Survey. III. White Light Flares are Ubiquitous in M6-L0 Dwarfs
• The Stellar Activity of TRAPPIST-1 and Consequences for the Planetary Atmospheres
• The largest M dwarfs flares from ASAS-SN
• Impact of Stellar Superflares on Planetary Habitability
• ASASSN-16ae: A Powerful White-Light Flare on an Early-L Dwarf
• Building the Evryscope: Hardware Design and Performance
• Stellar energetic particles in the magnetically turbulent habitable zones of TRAPPIST-1-like planetary systems

Cited by in corpus (13)

• No Such Thing as a Simple Flare: Substructure and QPPs Observed in a Statistical Sample of 20 Second Cadence TESS Flares
• Extending Optical Flare Models to the UV: Results from Comparing of TESS and GALEX Flare Observations For M Dwarfs
• Activity of TRAPPIST-1 analogue stars observed with TESS
• A Study of Flares in the Ultra-Cool Regime from SPECULOOS-South
• The Flaring TESS Objects of Interest: Flare Rates for all Two Minute Cadence TESS Planet Candidates
• Point Spread Function Estimation for Wide Field Small Aperture Telescopes with Deep Neural Networks and Calibration Data
• Eta-Earth Revisited II: Deriving a Maximum Number of Earth-like Habitats in the Galactic Disk
• Lower-than-expected flare temperatures for TRAPPIST-1
• Separating flare and secondary atmospheric signals with RADYN modeling of near-infrared JWST transmission spectroscopy observations of TRAPPIST-1
• Interaction of Trappist-1 exoplanets with coronal mass ejections: Joule heating, Poynting fluxes and the role of magnetic fields
• Bioverse: Potentially Observable Exoplanet Biosignature Patterns Under the UV Threshold Hypothesis for the Origin of Life
• Activity and Rotation of Nearby Field M Dwarfs in the TESS Southern Continuous Viewing Zone
• Evryscope-South Survey of Upper- and Pre-main Sequence Solar Neighborhood Stars