LOW ALBEDO SURFACES OF LAVA WORLDS ZAHRA ESSACK, SARA SEAGER TESS SCIENCE CONFERENCE I HOT SUPER EARTHS LAVA-OCEAN EXOPLANETS What causes the high geometric albedos on some hot super Earths?

• Rplanet < 1.6 Rearth • Tidally locked • Low pressure atmospheres (< 0.1 bar) • Substellar temperature > 850 K • Surface lava oceans due to

NASA intense stellar irradiation

2 LAVA-OCEAN EXOPLANET CANDIDATES

• Kepler-10 b 0.4 < Ag < 0.5

• Kepler-21 b 0.4 < Ag < 0.5

• K2-141 b 0.2 < Ag < 0.4

Demory (2014)

Malavolta et al. (2018) 3 SURFACES AS A SOURCE OF HIGH ALBEDOS

NASA 4 A (SIMPLE) THEORETICAL SURFACE OF A LAVA-WORLD Malavolta et al. , 2019 K2-141 b

NASA

Winn, 2010 5 GEOMETRIC ALBEDO OF A PLANET

Malavolta et al. , 2018 K2-141 b

Reflected angle: η Incidence angle ζ cos(��������) cos(���������) cos(��������) cos ��������� − α

To Star Reflection coefficient To Observer

Sobolev, 1975 Winn, 2010 6 MEASURING SPECULAR REFLECTION FROM QUENCHED GLASS Malavolta et al. , 2018 K2-141 b

Smooth quenched glass Rough quenched glass

Essack et al. (in prep) Winn, 2010 7 SPECULAR ALBEDO VS. η (ROUGH GLASS)

Lab measurements of reflectionMalavolta from et al. , 2018 K2-141Incidence b Angle = quenched glass Reflected Angle (η)

Fit data from lab measurements to get reflection +0.03 coefficient Ag = 0.09 function: � �, �, � – 0.01

Integrate reflection coefficient function over all latitudes and longitudes on the Substellar planet dayside point hemisphere to get = cos(latitude)cos(longitude) albedo: Ag Essack et al. (in prep) Winn, 2010 8 GEOMETRIC ALBEDO OF A COMBINATION LAVA-GLASS PLANET Malavolta et al. , 2018 K2-141 b

Babylon.js Andrew Cooper

Lava: Specular reflection value Quenched Glass: Specular from non-crystalline solids reflection values measured literature. experimentally. Winn, 2010 9 GEOMETRIC ALBEDO OF A COMBINATION LAVA-GLASS PLANET Malavolta et al. , 2018 K2-141 b

Specular reflection from lava and quenched glass cannot explain the high geometric albedos of hot super Earths.

Essack et al. (in prep) Winn, 2010 10 REFLECTION FROM ATMOSPHERES

Malavolta et al. , 2018 K2-141 b

NASA Combining results from Zebger et al. (2005); Hu et al. (2012). Winn, 2010 11 FUTURE WORK: MEASURING THE ALBEDO OF LAVA Malavolta et al. , 2018 K2-141 b

FURNACE May 2018 Z. Essack Winn, 2010 12 FUTURE WORK: LAVA WORLDS FROM TESS

Malavolta et al. , 2018 K2-141 b

June 2019 Winn, 2010 13 CONCLUSION

• LavaMalavoltaworlds et al. , 2018with solid (quenched glass) or liquidK2-141(lava) b surfaces have low specular albedos (< 0.1), and hence a negligible contribution to the high geometric albedos of some hot super Earths. • The high geometric albedos of hot super Earths are likely explained by atmospheres with reflective clouds. • Validating and characterizing lava planet candidates from TESS will allow us to better understand their atmospheres, surfaces, and other properties.

Winn, 2010 14 ADDITIONAL SLIDES

15 HIGH ALBEDO SURFACE MATERIALS

65 % Al2O3, 35% CaO

Rouan et al. (2011); Morang et al. (2018) Clay minerals

(illite, kaolinite, montmorillonite) 16 SECONDARY ECLIPSE DEPTH DEGENERACY KEPLER-10 b Malavolta et al. , 2018 K2-141 b

Winn, 2010 17 GEOMETRIC ALBEDO OF A COMBINATION LAVA-GLASS PLANET Malavolta et al. , 2018 K2-141 b

Babylon.js Andrew Cooper

Lava: Specular reflection value Quenched Glass: Specular from non-crystalline solids reflection values measured literature. experimentally. Winn, 2010 18 SPECULAR ALBEDO VS. η (SMOOTH GLASS)

Lab measurements Incidence Angle = of reflectionMalavolta from et al. , 2018 K2-141Reflected b Angle (η) quenched glass

Fit data from lab measurements to get reflection A = 0.07 ± 0.01 coefficient g function: � �, �, �

Integrate reflection coefficient function over all latitudes and Substellar longitudes on the planet dayside point hemisphere to get = cos(latitude)cos(longitude) albedo: A g Winn, 2010 19 EXPONENTIAL MODEL FIT: MOTIVATION

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