Resolving the era of wet climates on Mars: Stratigraphy and paleohydrology of Aeolis Dorsa Edwin Kite (Princeton), Antoine Lucas (U. Paris), John Armstrong (Weber State University), Oded Aharonson (Weizmann), Michael Lamb (Caltech), Alan Howard (U. Virginia) Rationale: River-deposit dimensions constrain Early Mars hydrology, but stratigraphy is essential to constrain Mars climate evolution models Today, use measurements of Early Mars river-deposit dimensions versus stratigraphic elevation to: 1)Constrain intermittency of wet conditions 2)Constrain climate models. wavelength width

River deposits record constraints sorely needed for Mars climate evolution models  Environmental scenarios for precipitation-fed runoff on Early Mars vary widely: e.g. Haberle et al. 2012, Kite et al. Icarus 2013, Mischna et al. 2013, Segura et al. 2012, Urata & Toon 2013, Wordsworth et al. 2013, Andrews-Hanna & Lewis 2011, Kite et al. Nature Geoscience mbar atmosphere needed to suppress evaporitic cooling  Key geologic constraint – intermittency of wet conditions: e.g. Burr et al. 2010, Palucis et al. 2014, Irwin et al. 2005, Hoke et al. 2011, Williams et al. 2011, Morgan et al. 2014, Grant & Wilson 2012, Fassett et al.2010, Hobley et al. 2014, Hauber et al Need error bars on geologic constraints to avert climate model overfitting Intermittent “One-pass” Intermittent Long timescales (> 10 6 yr) : Short timescales (< 10 6 ) thick-atmosphere greenhouse; transient high eccentricity impact cataclysm impact-triggered metastable wet states; volcanic forcing orbital forcing volcanic forcing IMPORTANCE OF INTERMITTENCY One-pass Intermittent Orbital forcing Volcanic forcing Impact-triggered metastable wet states Impact cataclysm Thick early greenhouse

NASA/JPL/MSSS Williams et al. Science 2013 Palucis et al. JGR 2014 ESP_027807_1765 PSP_008002_1750 F2 MSL rover This Talk )E longitude latitude Tharsis Hellas Early Mars water-availability model output (Kite et al., Icarus 2013a) Zimbelman & Scheidt, Science 2012 Kite et al., Nature Geosci Aeolis Dorsa river deposits in global context: Gale Aeolis Dorsa alluvial fans Kite et al., in prep. geosci.uchicago.edu/~kite/stereo 1 cm rhythmite Relatively young, post-Noachian (?) 0E 360E 60S 60N

>10 8 yr time gap (embedded craters) R-2 B20_017548_1739_XI R-1 Howard PNAS m e.g. Burr et al & 2010 Kite et al & in prep. Stratigraphic context of river deposits suggests wet-dry alternations Channel deposits >3.2 km stratigraphic thickness rhythmite alluvial fans rivers >400 km E-W extent

Getting from stereopairs to stratigraphic logs Errors: Stratigraphic Measurement Outcrop variance Measurement correlation

Meander wavelengths tighten upwards Small meanders rare/absent below 0m, common above 0m (4-20) Myr (Kite et al., Icarus 2013b) X transect 1 (153.5 º E) transect 2 (155 º E) transect 3 (151 º E) strat. error 1. Meander wavelengths (λ) poor exposure

Channel widths narrow upwards Narrow channels rare/absent below 0m, common above 0m strat. error X transect 1 (153.5 º E) transect 2 (155 º E) transect 3 (151 º E) 2. Channel widths (w) (4-20) Myr (Kite et al., Icarus 2013b) poor exposure

# data points Stratigraphic elevation (m) 0 Also: intermittency at 10m scale (correlatable basinwide using marker bed; Burr et al., 2010) ESP_034189_1740 higher channel-deposit proportion lateral-accretion deposits Logs show basin-wide discharge (Q) variability Wavelength λ (m) Width w (m)

Constraints on models of post-Noachian Mars climate evolution: Both short term intermittency and long-term intermittency. A thicker atmosphere – and a way of removing it Escape-to-space, or loss-to-ground (carbonate formation)? Stochastic Mars climate evolution model: Uniform initial conditions: 3.5 Gya, 100 mbar Liquid water availability model (e.g. Kite et al. Icarus 2013) Liquid water availability model (e.g. Kite et al. Icarus 2013) Supply-limited carbonate weathering in area of H 2 O(l) update atmospheric pressure, solar luminosity escape to space scaled using ASPERA-3 data scaled to UV flux of young Sunlike stars Variable 3.5 Gyr orbital forcings (n = 100) Armstrong et al Ensemble approach Obliquity eccentricity Ls of perihelion

Obliquity (°) / Patm (mbar) Late bursts of habitability on Mars-like planets: 1 example atmospheric pressure normalized area of liquid-water obliquity Preliminary long, globally-dry interval patchily, intermittently wet area of liquid water obliquity atmospheric pressure Metz et al. 2009, Edgar et al. 2014, Andrews-Hanna & Lewis 2011, Head et al. 2009, Toon et al … Dry spells: Aeolian supply/ deflation? (e.g. Kocurek & Bridges, 2012) Wet spells: Cementation? (e.g. Milliken et al., 2014) Obliquity (°) / Patm (mbar) Model Age (Gyr) 20 Myr

Long dry intervals common – Laskar et al. Icarus 2004, Li & Batygin ApJL 2014 Late-stage carbonate drawdown? – 100x less carbonate than in Pollack et al. (1987), consistent with SAM δ 13 C – Still need young, voluminous sedimentary reservoir for carbonate long globally-dry interval long, globally- dry interval Preliminary Late bursts of habitability on Mars-like planets: 3 different, equally likely scenarios Obliquity (°) / Patm (mbar) wet Obliquity (°) / Patm (mbar)

Testing late-stage carbonate drawdown requires an extended Curiosity traverse MAVEN  Test escape-to-space hypothesis Upper Gale mound - above the sulfates: A representative sample of the only geochemical reservoir adequate to explain the loss of habitability via carbonate drawdown  Test loss-to-ground hypothesis:

Conclusions Aeolis Dorsa records 1.5-2x reduction in river-deposit dimensions at or near R-1/R-2 contact - Consistent with 3-4x reduction in peak discharge across the contact m stratigraphy, (4-20) Myr total depositional interval Intermittency at multiple timescales (regional unconformities, river- deposit dimensions, marker beds). Constrains quantitative models linking sed. & strat. to climate evolution e.g. Kite et al., ‘Seasonal melting,’ Icarus 2013, Kite et al., ‘Growth and form …’, Geology 2013, Kite et al., ‘Low paleopressure …,’ Nature Geoscience 2014 With thanks to: Devon Burr, Kevin Lewis, Rebecca Williams, Robert Jacobsen, Lynn Carter, Bill Dietrich, Laura Kerber, Frederik Simons, Nicolas Mangold, Ross Irwin, Bill Dietrich, Alexandra Lefort, & Noah Finnegan for discussions, ideas, and inspiration. More information: