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Effects of stellar flares on atmospheres of habitable planets
Project Investigators: James Kasting, Victoria Meadows, Antigona Segura, Suzanne Hawley, Lucianne Walkowicz, John Scalo
Other Project Members
Samraat Pawar (Doctoral Student)Francisco Javier Martin-Torres (Collaborator)Summary
Stellar flares, sudden energy bursts from a star, produce a cascade of particles and radiation that can affect that can affect the atmospheres of orbiting planets. Our research is focused on understanding how the atmospheric chemistry of a planet is affected by flares. We want to know if flares can modify the concentrations of compounds that are produced by life and released to the planetary atmosphere and if the ultraviolet radiation during a flare can reach the planetary surface and damage the possible organisms on that planet.
Astrobiology Roadmap Objectives:
- Objective 1.1: Models of formation and evolution of habitable planets
- Objective 4.3: Effects of extraterrestrial events upon the biosphere
- Objective 7.2: Biosignatures to be sought in nearby planetary systems
Project Progress
The habitability of terrestrial planets orbiting low-luminosity yet highly-active M stars, still hinges largely on the fact that such planets will be irradiated by intense and frequent UV flares. The severity of the resulting fluctuating atmospheric composition and UV levels at the planetary surface is usually assumed to be large, but has never been examined. We are taking a few of the apparently severe problems with the radiation and stellar wind environment of M stars (and, to a lesser extent, the young Sun) and examining them quantitatively. These include 1. The erosion or creation of an ozone layer, 2. Whether an atmosphere will be constantly driven far from its time-independent state; and 3. The magnitude of the UV variations at the surface.
The effects of a single flare on an orbiting planet
To address these issues we have used data on a large stellar flare output by AD Leonis to create time-resolved stellar spectra during that flare to use as input of a time dependent 1-D coupled radiative–convective/photochemical model. This model was then used to simulate the effect of that flare on an Earth-like planet in the habitable zone of AD Leonis. The planetary atmospheric and surface consequences of this single flare are being prepared for publication.
Synthetic flare time series’
In preparation for full-scale photochemistry calculations with realistic flare flux variations, we have prepared a suite of synthetic time series’ giving the flux of radiation from a flaring M star, using statistical sampling of large numbers of flares of various energies, durations, rise/fall ratios, distributed randomly (a Poisson process). We match the exponent of a power-law relation between flare rate and flare energy, and the mean time between flares of a given amplitude, to available data for a number of M flare stars that are candidates for future spectrally resolved detection missions. The observed characteristics of the most frequently-flaring M stars led to the construction of time series’ of flare amplitudes lasting many days with a resolution of about a fraction of a second, set by considerations of characteristic chemical timescales with much larger photodissociation rates than ever encountered on Earth.
An example of a set of four independent realizations of time series’ whose amplitude-frequency statistical distribution was set to match EUVE observations of the star AD Leo is shown in Fig. 2.
A library of data files containing a large number of these time series’ will be made available to the general community, supplemented with spectral time variation data generated from a not-yet-set prescription. These should be useful to researchers studying the effects of energetic particle events or EUVE and X-ray flares on atmospheric loss, or other groups studying irradiation of atmospheres.
Evolution on time of the spectra of the big 1985 AD Leo flare. The time in seconds corresponding to each spectrum is shown on the right-lower corner of each panel. Quiescent state (black) is shown for comparison.Four independent realizations of flare time series’ for identical parameters. Square root of flare relative fluxes are displayed to bring out the low-amplitude structure. ? = -2.2 is the power law slope of the frequency-energy relation, <?W> = 2.2 days is the mean waiting time between flares of amplitude 10, <?D> = 30 minutes is the average duration of a flare, and <?> is the average value of the decay time/rise time ratio. The quantities ?W, ?D, ? were sampled from exponential, exponential, and positive Gaussian frequency distributions, respectively.Mission Involvement
Terrestrial Planet FinderWe may be able to determine if high activity stars (like M main sequence stars) would affect the planetary atmospheric chemistry in such a way that destroy or eliminate possible biosignatures and if the ultraviolet surface environment of planets around these stars is safe for life. This will help to choose possible targets for the TPF mission and analyze its observations.Cross-Team Collaborations
This work was done in collaboration with Jim Kasting, who is also a member of the Penn State team.
- Astronomical Observations of Terrestrial Planet Atmospheres
- Earth as an Extrasolar Planet
- Effects of stellar flares on atmospheres of habitable planets
- Hydrodynamic Escape from Planetary Atmospheres
- Modeling Early Earth Environments
- Planet Formation and Dynamical Modeling
- Planetary Habitability
- Planetary Surface and Interior Models and Super Earths
- Stromatolites in the Desert: Analogs to Other Worlds
- The Virtual Planetary Laboratory – The Life Modules - Photosynthesis
- VPL Climate and Radiative Transfer Models
- VPL Model Interfaces and the Community Tool