Oceans on Mars By Carr and Head Presented by Mark Popinchalk An assessment of the observational evidence and possible fate

Northern Lowlands North-South dichotomy – High standing cratered terrain – South – Low standing, sparsely cratered – North – Crust generally thicker in south Generally 5km lower

Time Scale Post Noachian – Outflows/“Ocean” areas Mainly Hesperian Era Post Noachian landforms will be preserved – Low erosion Mariner 9 found outflow channels – Late 80’s – where? and how big?

Northern Depressions Surface mostly Hesperian Possibly Large Impacts What caused the features? – Debris blankets – Pervasive Ground Ice – Volcano-ice interactions ‘86 Lucchitta et al. first to suggests stand water – Polygon fractured ground

Parker ’89, ’93 Former shorelines – Cliffs in terrain – Plains with “thumb print” textures – Backflow – Massifs with stepped slopes Identified two possible shorelines – Multiple bodies Meridiani shoreline, 1.5 km

Outflows And Olympus Olympus Mons aureole deposits – Submarine landslides 2.5 km GEL Outflow high elevation – Groundwater sources 1/3 surface in standing bodies – Ice covered ocean in north

Alternate Above theories based on outflows being water driven CO 2 for some, Lava, Wind There is doubt This paper assumes outflows were water.

Mars Global Surveyor Arrived in optimal orbit in 1999 MOLA – Contact 1, too varied – Contact 2 better candidate 150m MOC Little support, no evidence

Aims Geomorphic evidence of shorelines Examine areas that were covered, modification due to water Reconcile appearance and disappearance

Basins Utopia Basin – -5000m North Polar Basin – -5200m Amazonis Plaitia – Extremely flat, not really a basin Isidis basin – -3900m

Age Lack of craters -> Upper Hesperian Low hills, remnants of large craters -> Noachian Noachian, with something on top

Features Ridges – Thought to be volcanic in origin Low slopes – Oceanic Abyssal plain? Volcanic Amazonis Planitia – Supremely Flat MOC images – Lava flows Fluvial Channels feed in

Textured Highly textured at a few kilometers – Hills, ridges, cones, polygons Geologically young, latitude dependent, ice/dust rich layer of mantle – Superposed on Vastitas Borealis Formation

Possible Shorelines MOLA map Used Clifford and Parker as a baseline Interpreted features and elevations Arabia, Deuteronilus

Arabia Shoreline ~ Contact 1 – Age ~ 4 Ga Largest possible ocean Plains upland Boundary -2090±1400m

Problems , – Huge scatter, generalized, numerous cliffs, mesas, knobs and valleys Mean elevation changes on stretches Areas are volcanic flows

Debunked Argued for debris flows found in Deuteronilus Mensae – Explained with Mass Wasting

Deuteronilus ~Contact 2 Age between 2-4 Ga – Between age of youngest and oldest shoreline Upper Hesperian

Elevation Hiesinger (2000)– – Varies only 110m – Two other random points vary more Break in the slope Volcanic Activity breaks it up past Elysium Half its length is VBF border

VBF Border Large Overlap with Contact 2

For Completeness Other Contacts

Shorelines ? Contact’s do vary in height No MOC back up Equivocal What about the features within the shorelines?

Ridges Northern Basin – Ridges smaller, farther apart, lower elevation Difference between Contact 1 and Contact 2

VBF Stealth Craters 3 Levels and ages Baseline Noachian Lower Hesperian ridged plains Upper Hesperian draped over Depends on scale Head et al. 2002, modeled deposits Matched ridge spreading, wrinkle ridges

VBF deposited? Many features which imply “cover” of 100m MOC images reveal better If VBF was deposited, volume ~ 3*10 6 Outflows ~4*10 6 Also evidence of ice

No Erosion… Water would have to move between basins. – North-Utopian Many small events… Inherited ice lakes…

Utopia-Isidis

VBF Features

Fate of the ocean Would be frozen under current conditions – Outflow brings CO 2 Needs a lot of CO 2 Would lose heat 7-20 K per year – Ice cover forms Heat loss reduced – Freezes solid – Sublimates away ~10*5 years Heat loss due ~1-2*10 4

Reconciliation VBF and floods very similar in age/volume/location – 156m GEL ? More than enough in megaregolith – Only 11-28% Fluvial channels *10 9 km 3 s -1 – Flood rates not strong enough ~ 10 % Multiple Floods

Where does the water go Ice caps Ground ice layer? No, would return to atmosphere Water to space – 50m GEL Total in Ice Caps and Loss to Space – 70m GEL – Atmosphere? Basal belting? Return to ground water?

Conclusions Evidence of large bodies of water – Near Contact 2/Deuteronilus/VBF Shorelines inconclusive – Features within the contact main proponent VBF interpreted as sublimation residue of flood/ocean. – 150m GEL required Water volume needed a mystery – 50m lost to space, 30m caps, 70?

References Parker, T. J., Mapping of ‘‘Oceanus Borealis’’ shorelines on Mars Carr, M. H., and Head, J.W. “Ocean on Mars” an assessment of the observational evidence and possible fate Wikipedia – Mars article (Images)