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 channels @ high elevation– Groundwater sources• 1/3 surface in standing bodies

– Ice covered ocean in north

Alternate

• Above theories based on outflows being water driven

• CO2 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

• 330-85, 80-160– 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*106

• Outflows ~4*106

• 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 CO2

• Needs a lot of CO2

• 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*104

Reconciliation

• VBF and floods very similar in age/volume/location– 156m GEL ?

• More than enough in megaregolith– Only 11-28%

• Fluvial channels• 107-4*109 km3 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)