The Ol Doinyo Lengai volcano, Tanzania, as an analogue for Carbon Planets

Jani Radebaugh, Rory Barnes, Jeff Keith Department of Geological Sciences, Brigham Young University, Department of Physics, University of Washington Field Analogues are Valuable • Knowledge of landforms on other planets is incomplete • Similar physics, materials can be found on Earth • Earth landscapes can yield important information about other planets

MEDUSA FOSSE FORMATION, MARS DUNHUANG, CHINA, 40 N 93 E Field Analogues are Valuable • Knowledge of landforms on other planets is incomplete • Similar physics, materials can be found on Earth • Earth landscapes can yield important information about other planets

TITAN Field Analogues are Valuable • Knowledge of landforms on other planets is incomplete • Similar physics, materials can be found on Earth • Earth landscapes can yield important information about other planets

DUNHUANG, CHINA, 40 N 93 E Field Analogues are Valuable • Yardangs: Wind important, but also bedrock, rainfall, gravels

LUT DESERT, IRAN Field Analogues of exoplanets?? • We’ve yet to even “see” an exoplanet • They are planetary surfaces worth studying as we do for our solar system

TRAPPIST-1 Carbon Planets • Postulated to form in carbon-rich nebular environments (Seager and Kuchner 2005) • When C/O>0.8 in the disk (Bond et al. 2010) • May reach >75% carbon in the habitable zone!

ARTIST LUYTEN Carbon Planets • Even in our solar system, carbon is enriched in certain locations • Mercury may have had graphite crust on magma ocean (Peplowski et al. 2016)

Mercury MESSENGER M-dwarf Carbon Planets

• Carbon planets orbiting M-dwarf stars could spend millions/billions of years closer than the habitable zone during pre-main-sequence (e.g. Baraffe et al. 2015) • Planet in runaway greenhouse, water is photolyzed in stratosphere, leaving large, oxygen-rich atmosphere JPL/CALTECH M-dwarf Carbon Planets

 What happens when an oxygen-rich atmosphere reacts with surface carbon?  How does this affect surface albedo and atmospheric composition over time? NASA JPL/CALTECH G-type Star Carbon Planets

• Planets in the habitable zone around G-type stars, like Earth, may experience a reducing, Archean-like atmosphere early in its history  How carbon surfaces interact with Archean atmospheres may reveal how conditions evolved to be right for life K2-138 – NASA JPL/CALTECH Ol Doinyo Lengai Tanzania • Currently erupting carbon-rich lavas of CO2, Na2O, K2O, CaO • High degrees of partial melt of enriched mantle (de Moor et al. 2013) • Cool (600 C), erupts black changes to white Ol Doinyo Lengai Tanzania • Similar flow morphology to basalt • Viscosity 10x lower than basalt (like mud) • Field and lab studies explored rheology, etc. (Pinkerton et al. 1995; Norton and Pinkerton 1996) Ol Doinyo Lengai Tanzania • Similar flow morphology to basalt • Viscosity 10x lower than basalt (like mud) • Field and lab studies explored rheology, etc. (Pinkerton et al. 1995; Norton and Pinkerton 1996) Ol Doinyo Lengai Tanzania • Stratovolcano with gas-rich silicate eruptions • Cone repeatedly fills and empties on decadal timescales • Full in 1990s, collapsed, filling again

~1995 - Marc Szeglat Ol Doinyo Lengai Tanzania

GeoEye/GoogleEarth Ol Doinyo Lengai – Colors • What causes lavas to be black or white? • If oxygen, then for carbon planet albedos:

• O2-rich = white • O2-poor Archean = black • High volcanic output = mix

Marc Szeglat Ol Doinyo Lengai – Colors • What causes lavas to be black or white? • If oxygen, then for carbon planet albedos:

• O2-rich = white • O2-poor Archean = black • High volcanic output = mix  Do field studies to monitor changes • Buried, unaltered lavas? • Devitrification (return to crystals)?  Do lab studies on lavas – control atmosphere, gradually add O2

Marc Szeglat Ol Doinyo Lengai – Resurfacing Rate  Use lava flow rates, topography and temperature distribution to determine resurfacing rate • Temps from near-IR • Topography from drone or handheld along rim • Flow rates from field observations • Extrapolate to carbon planets, see how quickly new lavas exposed to atmosphere

Kilauea, Carling et al. 2016 Carbon Planet Tectonism

• On Earth, plate tectonics cycles CO2, stabilizing surface temperature • On carbon worlds, low melting temps, viscosities • => Convection in mantle, maybe plate tectonics Carbon Planet Tectonism • Add Silicon, create SiC • Hard, high-temperature, insulating (Kite et al. 2019 EPSC) • Not likely to convect • May act under heat pipe mechanism (Moore 2019)

Marc Szeglat Carbon Planet Atmospheres

• Both tectonic models remove O2 and CO2 and help make atmosphere habitable (Foley and Smye 2018)

• Free O2 is reactive, may prevent large biomolecules from forming • No global tectonism, no atmosphere removal (i.e. Venus) Carbon Planet Atmospheres

• Both tectonic models remove O2 and CO2 and help make atmosphere habitable (Foley and Smye 2018)

• Free O2 is reactive, may prevent large biomolecules from forming • No global tectonism, no atmosphere removal (i.e. Venus) Akatsuki, IR Carbon Planet Atmospheres • Can carbon surfaces absorb oxygen?

 Use model with lab experiments for rates of O2 uptake compared with production in upper atmosphere • VLPlanet (Virtual Planet Laboratory) Barnes et al. 2016

Nour Almejadi Carbon Planets in our Backyard • Ol Doinyo Lengai is a strong analogue for carbon planets • Field, lab and modeling studies can reveal important aspects of these postulated worlds • May reveal progression of early Earth towards habitability

 Atmospheric stability is a delicate balance  If no atmospheric sinks, runaway greenhouse can occur, rendering planet uninhabitable – e.g. Venus