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Recipe for a Habitable

Aomawa Shields Clare Boothe Luce Associate Professor Shields Center for Climate and Interdisciplinary Education (SCECIE) University of , Irvine

ASU School of and (SESE) December 2, 2020 A moment to pause… Leading effectively during COVID-19

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Ill. Niklas Elmehed. Ill. Niklas Elmehed. © Nobel Media.

© Nobel Media. RadialVelocity (m/s)

Nobel Prize in Physics 2019

Mayor & Queloz 1995 https://exoplanets.nasa.gov/

As of December 2, 2020

Aomawa Shields Recipe for a Habitable World Credit: NASA NNASA’sASA’s KKeplerepler MMissionission TESS Transiting Exoplanet Survey Satellite Credit: NASA-JPL/Caltech b

Credit: ESO/M. Kornmesser LHS 1140b

Credit: ESO TOI 700d

Credit: NASA TESS in the Earth-sized regime

Credit: NASA’s Goddard Space Flight Center Which ones do we follow up on?

20 The Habitable Zone (Kasting et al. 1993, Kopparapu et al. 2013)

) Runaway greenhouse 

Maximum CO2 greenhouse (M Mass Stellar

Distance from (AU) Many factors can affect Aomawa Shields Recipe for a Habitable World Liquid

Aomawa Shields Recipe for a Habitable World Isotopic Birth Abundance Environ. Elem. Galactic Abundance Location Impact Flux Orbital SCECIE Composition Evolution & Structure Magnetic Dust Eccen. Field Minor Oscillations Planets Stellar Planetary Activity Effects System

Companions Sibling SCECIE Satellites Planets SCECIE Spectral Liquid water Masses Distribution SCECIE Obliquity Radius Planetary Orbit Properties SCECIE Dynamics SCECIE Albedo Surface Temps Rotation Clouds Oblatenes rate SCECIE Surface Composition SCECIE Liquids Magnetic Field Surface Credit: After Meadows and Barnes UV Pressure Interior 2018 Shielding Atm. Structure Density Structure Credit: AniaBuckle 1-D Energy Balance Model Global Climate Model (EBM) (GCM)

Broadband albedos Two-band albedos (for example – Vis/IR)

Weight by host star spectrum

EBM needs a separate R-T model to incorporate atmosphere into broadband planetary albedo calculation

Based on McGuffie and Henderson-Sellers (2005) Koshland Science Museum Global Climate Model (GCM) (Ex. CCSM4 (Gent et al. 2011), LMD Generic GCM (Hourdin et a. 2006))

Koshland Science Museum Conservation of momentum

Mass continuity

Conservation of energy (1st law of thermo)

Equation of state for the atmosphere PREDICTING FUTURE CLIMATE ON EARTH (Smagorinsky et al. 1965, Manabe et al. 1965, Holloway & Manabe 1971, Manabe & Wetherald 1975)

IPCC, 2018: Summary for Policymakers Waterbelt Snowball Earth as refuge for photosynthetic Abbot et al. 2011

Aomawa Shields Recipe for a Habitable World Warming Early Forget and Pierrehumbert 1997, Colaprete & Toon 2003, Forget et al. 2013, Kitzmann 2016, Wordsworth et al. 2017

Credit: ESA Aomawa Shields Recipe for a Habitable World Forget and Pierrehumbert 1997 Aomawa Shields Recipe for a Habitable World “Eyeball Earth” scenario for g

Pierrehumbert 2011 Habitable climates on

Turbet et al. 2016 Starlight Ice-albedo Courtesy of NASA

Aomawa Shields Recipe for a Habitable World M-dwarf planets

Image credit: ESO/L. Calçada Aomawa Shields Recipe for a Habitable World

M-dwarf planets exhibit more stable climates in simulations

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Wolf, Shields+ (2017)

Aomawa Shields Recipe for a Habitable World M-dwarf planets

Sodium chloride dihydrate (“hydrohalite”)

Image credit: ESO/L. Calçada NaCl ·2H2O

Aomawa Shields Recipe for a Habitable World Hydrohalite precipitation in sea ice T < -23∘ C

Carns et al. 2015 Hydrohalite is highly reflective in the IR

Shields and Carns 2018

Aomawa Shields Hydrohalite parameterization matters in the HZ, and climate sensitivity increases as instellation is lowered

Shields and Carns 2018 Stronger climate sensitivity to hydrohalite parameterization on synchronously-rotating M-dwarf planets

Shields and Carns 2018 Aomawa Shields Trenberth diagram

Credit: Kevin Trenberth, John Fasullo and Jeff Kiehl M-dwarf planet 108%

88% 100% G-dwarf planet

F-dwarf planet

InstellationStarlight (%(% ofof what Modern Earth gets Solar from Constant) the ) Shields et al. 2019 F-dwarf planet

29% reflected 14% absorbed

16% reflected

Shields et al. 2019 G-dwarf planet

27% 19% reflected absorbed

10% reflected

Shields et al. 2019 M-dwarf planet

18% 34% reflected absorbed

7% reflected

Shields et al. 2019 F-dwarf planet

29% reflected 14% absorbed

16% reflected

Shields et al. 2019 M-dwarf planet

18% 34% reflected absorbed

7% reflected

Shields et al. 2019 Surface Albedo Ice Fraction

Shields et al. 2019 Difference in Specific Surface Temperature Humidity

Shields et al. 2019

1-D Energy Balance Model (EBM)

Based on McGuffie and Henderson-Sellers (2005) EBM North and Coakley (1979) Heat Ocean and land Dependence of OLR Planetary response transport temperature gradients on Temperature SMART (Spectral Mapping Atmospheric Radiative Transfer model) Meadows & Crisp, 1997; Crisp 1997 SMART (Spectral Mapping Atmospheric Radiative Transfer model) Meadows & Crisp, 1997; Crisp 1997 1.0

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Planets dominated by land reflect more starlight and have lower surface temperatures than ocean- covered worlds. But, land planets orbiting M stars are still warmer than their counterparts orbiting stars with more visible and UV light

Based on Rushby, Shields, and Joshi, The Astrophysical Journal, 2019 Temporal habitability and water loss on eccentric planets Recipe for a Habitable World TOO HOT

TOO COLD Eccentricity

The Earth

Instellation Planets orbiting cooler stars are thawed for Palubski, Shields, and Deitrick, The Astrophysical Journal, 2020 larger fractions of the year ` Recipe for a Habitable World Different land surfaces will have different albedos and resulting effects on the climate of TRAPPIST-1 planets

Rushby, Shields, Wolf, et al. ApJ, in review Differences of 50 K across lowest (granite) to highest (calcite) albedo land surface

Rushby, Shields, Wolf, et al. ApJ, in review Surface Temperature TRAPPIST-1d most capable of supporting life (with low albedo surface (ex. igneous rock)

Rushby, Shields, Wolf, et al. ApJ, in press cross-equatorial energy transport increased for lower-albedo planets

Rushby, Shields, Wolf, et al. ApJ, in press Aomawa Shields Recipe for a Habitable World Take –away points • Surface composition affects planetary climate and habitability

• Important to incorporate spectral dependence of ice, snow, salt, and land albedos into GCMs

• Allows for more realistic assessments of possible climates and habitability of Acknowledgments • UCI • National Science Foundation • NASA Habitable Worlds Program • Clare Boothe Luce Foundation • UC President’s Postdoctoral Fellowship Program • Virtual Planetary Laboratory • Collaborators –Eric Agol, , Rory Barns, Cecilia Bitz, Regina Carns, Benjamin Charnay, Russell Deitrick, John Johnson , Manoj Joshi, Victoria Meadows, Igor Palubski , Ray Pierrehumbert, Tyler Robinson, Andrew Rushby, Vidya Venkatesan, Eric Wolf Thank you!

NASA Ames/JPL-Caltech/Tim Pyle Take –away points • Surface composition affects planetary climate and habitability

• Important to incorporate spectral dependence of ice, snow, salt, and land albedos into GCMs

• Allows for more realistic assessments of possible climates and habitability of exoplanets

M-dwarf planet (synchronous)

Shields et al. 2019 Synchronous rotation is possible for Kepler-62f

e=0.00 e=0.32

Shields et al. (2016a) Surface Temperature freezing freezing point point Obliquity = 60° Obliquity = 23°

Shields et al. (2016a) Southern hemisphere summer

Aomawa Shields Recipe for a Habitable World Shields et al. (2016a) Rising Stargirls