The Climates of Other Worlds: Searching for the Next Habitable Planet

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

KITP Friends May 15, 2019

Credit: NASA Radial Velocity (m/s) Velocity Radial

Mayor & Queloz 1995 Phase We are in the Earth-sized regime

Credit: NASA Credits: NASA Ames / W. Stenzel; Princeton University / T. Morton NASA’s Kepler Mission Transit Technique

Credit: NASA Spitzer TESS Transiting Exoplanet Survey Satellite Credit: George Ricker TESS will identify the best and smallest exoplanet targets for characterization of atmospheres James Webb Space Telescope

Starlight filters through the planet’s absorption line spectrum atmosphere

Credit: Northrop Grumman • Habitable planet

• hosting life? Proxima Centauri b

Credit: ESO/M. Kornmesser Credit: NASA-JPL/Caltech LHS 1140b

Credit: ESO Which ones do we follow up on?

16 Contact (1997) New era, new approach • Observational data AND computer models

NASA +

Koshland Science Museum Life’s Requirements

A Liquid (H2O) Bioessential Elements (SPONCH) Energy (Stellar or chemical)

Photo: Frans La

Aomawa Shields The Climates of Other Worlds The Habitable Zone

) Runaway greenhouse 

Maximum CO2 greenhouse Stellar Mass (M

Distance from Star (AU) Snowball Earth Many factors can affect planetary habitability Aomawa Shields The Climates of Other Worlds Galactic Location Composition & Structure

Stellar Effects

Spectral Liquid water Energy Distribution Planetary Properties Dynamics

Surface

Atmosphere Interior

Aomawa Shields The Climates of Other Worlds Galactic Location Orbital Composition Evolution & Structure

Stellar Planetary Effects System Sibling Planets Spectral Liquid water Energy Distribution Planetary Properties Dynamics

Surface

Atmosphere Credit: Victoria Interior Meadows

Aomawa Shields The Climates of Other Worlds Isotopic Birth Tides Orbit Abundance Environ. Elem. Galactic Abundance Location Impact Flux Orbital Composition Evolution & Structure Luminosity Magnetic Dust Eccen. Metallicity Field Minor Oscillations Planets Stellar Rotation Planetary Activity Effects System Orbits

Companions Sibling Satellites Planets Spectral Liquid water Energy Masses Distribution Obliquity Radius Planetary Orbit Properties Dynamics Albedo Surface Temps Rotation Clouds Oblatenes rate Outgassing Surface Composition Liquids Magnetic Atmosphere Field Surface Credit: Victoria UV Pressure Interior Meadows Shielding Atm. Structure Density Aomawa Shields Structure The Climates of Other Worlds . 1-D line-by-line radiative transfer models Models . 1-D in height . Atmospheric gas absorption

. Radiative convective climate models

. Energy Balance Models (EBMs) . 0-D or 1-D (in latitude) usually

. 3-D General Circulation Models (GCMs) . Sophisticated treatment of atmospheric circulation, ocean- atmosphere processes Aomawa Shields The Climates of Other Worlds PREDICTING FUTURE CLIMATE ON EARTH IPCC, 2018: Summary for Policymakers Snowball Earth Artist concept

Exploring thaw criteria for Snowball Earth

Abbot and Pierrehumbert 2010

Aomawa Shields The Climates of Other Worlds Abbot et al. 2011

Aomawa Shields The Climates of Other Worlds

Warming Early Mars

Credit: ESA

Aomawa Shields The Climates of Other Worlds Forget and Pierrehumbert 1997 Credit:

Aomawa Shields The Climates of Other Worlds Credit: NASA, ESA, and S. Beckwith (STScI) and the HUDF Team

Aomawa Shields The Climates of Other Worlds

Aomawa Shields The Climates of Other Worlds M-dwarf planets

Image credit: ESO/L. Calçada Aomawa Shields The Climates of Other Worlds Red dwarf Sun The Sun

Stellar

Brightness 100% Small planets are easier to detect around small stars small around detect to easier are planets Small G Dwarf M Dwarf Credit: Victoria Meadows Credit: Victoria The Habitable Zone )  Stellar Mass (M

Distance from Star (AU) Snowball Earth

Aomawa Shields The Climates of Other Worlds Synchronous rotation and surface pressure (Joshi, Haberle, and Reynolds 1997)

Host star

Aomawa Shields The Climates of Other Worlds Synchronous rotation can be a benefit for climate and habitability (Yang et al. 2013)

Night side Night side Day side

Credit: Jun Yang Aomawa Shields The Climates of Other Worlds Aomawa Shields The Climates of Other Worlds M-dwarf planets could lose oceans during PMS phase

(Luger and Barnes 2015)

Aomawa Shields The Climates of Other Worlds

Starlight BINGO Aomawa Shields The Climates of Other Worlds Ice-albedo Feedback Courtesy of NASA Shutterstock Photo: Stephen Warren Ice Ice

Photo courtesy of Stephen Warren

Shields et al. (2013) Ice absorbs where M-dwarfs emit strongly Warren et al. (2002) Grenfell et al. (1994) No ice! PAL (“present

atm level”) CO2

Snowball!

Instellation (% of what Earth receives)

M-dwarf planets less susceptible to snowball Shields et al. (2013) F-dwarf planets more susceptible to snowball Aomawa Shields The Climates of Other Worlds M-dwarf planet is more stable against convection

Shields et al. (2013) Albedo Surface Temperature

G-dwarf planet (100%)

M-dwarf planet (90%)

Shields et al. (2013)

Climate Stability No ice!

Warm start

Cold start

Snowball! Shorter jump in ice line Higher jump in ice line Shields et al. (2014) M-dwarf planets have Better for life? more stable climates

Aomawa Shields The Climates of Other Worlds http://sparce.evac.ou.edu/q_and_a/air_circulation.htm, SPaRCE Transports heat from equator to higher latitudes Aomawa Shields The Climates of Other Worlds Hadley circulation on deglaciating planets Northern hemisphere winter

) 645 × 109 kg/s 623 × 109 kg/s 489 × 109 kg/s mb Pressure ( Pressure

Latitude Shields et al. (2014)

Weaker Hadley circulation helps M-dwarf planet thaw more easily

Aomawa Shields The Climates of Other Worlds Identifying Multiple Possible Climate Regimes

Wolf, Shields+ (2017)

Aomawa Shields The Climates of Other Worlds Sodium chloride dihydrate (“hydrohalite”)

NaCl ·2H2O

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 Targeted planet studies

Aomawa Shields The Climates of Other Worlds “Eyeball Earth” scenario for Gliese 581 g

Pierrehumbert 2011 Multiple-planet systems

First place to look for a habitable, Earth-like planet?

Aomawa Shields The Climates of Other Worlds Image credit: NASA Ames/JPL-Caltech

? Too hot

Aomawa Shields The Climates of Other Worlds Kepler-62f

Needs CO2

Aomawa Shields Image credit: NASA Ames/JPLThe-Caltech Climates of Other Worlds Stable eccentricities

e_fmax = 0.32

stable Stable ecc for Kepler-62f 0.00 ≤ e ≤ 0.32

unstable

Shields et al. (2016a) Aomawa Shields The Climates of Other Worlds Surface Temperature

High

CO2

Earth- Open water like axial tilt Shields et al. Circular 2016a orbit Global mean surface temps similar to Earth! Aomawa Shields The Climates of Other Worlds Insolation

PAL CO2

Shields et al. 2016a

Aomawa Shields The Climates of Other Worlds Surface Temperature freezing freezing point point Obliquity = 60° Obliquity = 23°

Shields et al. (2016a) Southern hemisphere summer

Aomawa Shields The Climates of Other Worlds Shields et al. (2016a) Surface Temperature 3 bar CO2

Shields et al. (2016a) Aomawa Shields The Climates of Other Worlds Credit: NASA/JPL-Caltech Courtesy of ESO/L. Calçada Credit: Ansel Adams Take away point Combining observations AND theory = How we will most accurately assess planetary habitability

Aomawa Shields The Climates of Other Worlds Rising Stargirls More than the eye can see

IRAS

Axel Mellinger www.risingstargirls.org Acknowledgments • UCI • KITP • 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, , John Johnson , Manoj Joshi, Victoria Meadows, Igor Palubski , Ray Pierrehumbert, Tyler Robinson, Andrew Rushby Thank you!

NASA Ames/JPL-Caltech/Tim Pyle Email: [email protected] Aomawa Shields Website: http://faculty.sites.uci.edu/shields/ Minimum land fraction for glaciations increases with redder host star SED

Andrew Rushby

Rushby et al. in prep M-dwarf planets G-dwarf planets

Igor Palubski

Palubski et al. in prep Planets orbiting cooler stars are thawed for larger fractions of the year for lower eccentricities NEW WORK (Here at KITP) “Trenberth diagram”

Synchronous rotation is possible

e=0.00 e=0.32

Shields et al. (2016a)