LOW ALBEDO SURFACES OF LAVA WORLDS

ZAHRA ESSACK SARA SEAGER, MIHKEL PAJUSALU

ROCKY WORLDS, CAMBRIDGE UK 8 JANUARY 2020 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

0.4 < Ag < 0.5

0.2 < Ag < 0.4

0.4 < Ag < 0.5

Demory (2014) Malavolta et al. (2018)

Ag = Geometric Albedo 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(푙푎푡푖푡푢푑푒) cos(푙표푛푔푖푡푢푑푒) cos(푙푎푡푖푡푢푑푒) cos 푙표푛푔푖푡푢푑푒 − α

To Star Reflection coefficient To Observer

Sobolev (1975) Winn, 2010 6 MEASURING REFLECTION FROM QUENCHED GLASSES Malavolta et al. , 2018 K2-141 b

Winn, 2010

Essack et al. (in review) (in Essack al. et 7 BASALT AND FELDSPAR QUENCHED GLASSES

Malavolta et al. , 2018 K2-141 b

Reference Basalt Standard

Feldspar

Essack et al. (in review) Winn, 2010 8 BASALT: REFLECTANCE VS. η (ROUGH GLASS) Essack et al. (in review) Lab measurements of reflection from quenched glass Incidence Angle = Reflected Angle η

Fit data from lab measurements to get reflection A = 0.09+0.02 coefficient g – 0.01 function: 훠 훈, 훈, 훑

Integrate reflection coefficient function over all latitudes and longitudes on the planet dayside Substellar hemisphere to get point albedo: A g 9 FELDSPAR: REFLECTANCE VS. η (ROUGH GLASS) Essack et al. (in review) Lab measurements of reflection from quenched glass Incidence Angle = Reflected Angle η

Fit data from lab measurements to get reflection +0.02 coefficient Ag = 0.02 function: 훠 훈, 훈, 훑 – 0.01

Integrate reflection coefficient function over all latitudes and longitudes on the planet dayside Substellar hemisphere to get point albedo: A g 10 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: Reflection from non-crystalline solids values measured literature. experimentally. Winn, 2010 11 GEOMETRIC ALBEDO OF A COMBINATION LAVA-GLASS PLANET Malavolta et al. , 2018 K2-141 b

Reflection from lava and quenched glasses cannot explain the high geometric albedos of hot super Earths.

Essack et al. (in review) Winn, 2010 12 OTHER SOURCES OF REFLECTION

MalavoltaATMOSPHERES et al. , 2018 EVOLVED HIGH ALBEDO SURFACES

Al2O3 ; CaO

NASA READE

Combining results from Zebger et al. (2005); Hu et al. (2012); Kite et al. (2016). Winn, 2010 13 FUTURE WORK:

MEASURINGMalavolta et al. , 2018 THE ALBEDO OF LAVAK2-141 b LASER

SPECTROMETER FIBER

CRUCIBLE Sept. 2019 W/LAVA FURNACE Z. Essack Winn, 2010 14 FUTURE WORK: LAVA WORLDS FROM TESS

Malavolta et al. , 2018 K2-141 b

Essack et al. (in review) WinnDecember, 2010 2019 15 CONCLUSION

• LavaMalavoltaworlds et al. , 2018with solid (quenched glass) or liquidK2-141(lava) b surfaces have low 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 or evolved surfaces. • Validating lava planet candidates from TESS and characterizing them with JWST will allow us to better understand their atmospheres, surfaces, and other properties. Winn, 2010 16