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Dark Dune Spots: Possible current habitats on Mars. Eörs Szathmáry. Collegium Budapest. s zathmary@colbud.hu. Eötvös University Budapest. Mars: a dead planet (?). Very dry: no water Very cold (minus 13 0 C) High UV radiation (above 190 nm) Thin atmosphere (6 mbar).

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Dark dune spots possible current habitats on mars
Dark Dune Spots: Possible current habitats on Mars

Eörs Szathmáry

Collegium Budapest

szathmary@colbud.hu

Eötvös University Budapest


Mars a dead planet
Mars: a dead planet (?)

  • Very dry: no water

  • Very cold (minus 130 C)

  • High UV radiation (above 190 nm)

  • Thin atmosphere (6 mbar)


There may have been plenty of water in the past
There may have been plenty of water in the past…

  • Water was lost due to radiation decay and loss of hydrogen to space

  • A large oxygen sink must be present

  • More than 3 billion years ago conditions for the origin of life seem to have been favourable

  • Could anybody have survived till today?


An ancient lake and outflow
An ancient lake and outflow

lake

Loire Vallis




Viking lander no evidence for life
Viking lander: no evidence for life

  • It is easy to land in the equatorial desert, BUT

  • It is very hard to find even traces of life there

  • The soil seems oxidising

  • BUT some oxidized organic compounds may have escaped detection


Claims of past life remain controversial
Claims of past life remain controversial

Is this magnetite biogenic?



Analyzed dds sites in the south polar region mars global surveyor data
Analyzed DDS sites in the south polar region (Mars Global Surveyor data)

MOC images

Dark dunes

Malin Space Science Systems




Mere frosting defrosting of the co 2 ice cover
Mere frosting-defrosting of the CO Surveyor data)2 ice cover

  • Albedo decreases as frost thins

  • Positive feedback: faster sublimation

    MUST mean:

  • Start spot formation at sites with strong exposure to insolation

  • Otherwise at random sites (wind, etc.)


Simple frosting defrosting does not work because
Simple frosting-defrosting does NOT work, because… Surveyor data)

Spot formation begins at the bottom, not at the top!


Simple frosting defrosting does not work because1
Simple frosting-defrosting does NOT work, because… Surveyor data)

Spots do not develop on exposed sites!


Simple frosting defrosting does not work because2
Simple frosting-defrosting does NOT work, because… Surveyor data)

There is annual recurrence (>75%) at the same sites!


Simple frosting defrosting does not work because3
Simple frosting-defrosting does NOT work, because… Surveyor data)

  • On slopes flows originate from the DDSs

  • Which always flow downwards

  • From elongated spots

  • Gravitation is a formative cause


Flows may be due to water runoff
Flows may be due to water runoff Surveyor data)

  • The dry planet is much wetter than thought

  • There is plenty of water:

    • In both ice caps

    • In the upper layer of the polar region (permafrost)

    • In liquid form in the gullies


Mars odyssey hend measurements
Mars Odyssey HEND measurements Surveyor data)

  • High Energy Neutron Detector

  • Deficit of high-energy neutrons

  • Hydrogen is concentrated in the subsurface

  • Water-rich layers tens of centimetres thick



Recent gullies by melting snow
Recent gullies by melting snow Surveyor data)

  • Occur in clusters on slopes

  • Between 30 and 70 latitude in both hemispheres

  • Consist of alcoves several hundred metres wide,

  • Channels up to several kilometres long and several tens of metres deep

  • Typically originate within several hundred metres of the slope crest,

  • Can occur on crater walls that are raised above the surrounding terrain or near the summit of isolated knobs.

 North


Christensen s mechanism 2003
Christensen’s mechanism (2003) Surveyor data)

  • (1) Water is transported from the poles to mid-latitudes during periods of high obliquity, forming a water-rich snow layer

  • (2) Melting occurs at low obliquity as mid-latitude temperatures increase, producing liquid water that is stable beneath an insulating layer of overlying snow.

  • (3) Gullies form on snow-covered slopes through erosion by melt water or as a result of melt water seeping into the loose slope materials and destabilizing them.


Christensen s mechanism ii
Christensen’s mechanism II Surveyor data)

  • (4) Gullies incised into the substrate are observed where the snow layer has been completely removed.

  • (5) Patches of snow remain today where they are protected against sublimation by a layer of desiccated dust/sediment

  • (6) Melting could be occurring at present in favourable locations in these snowpacks.


Clow s 1987 model for melting
Clow’s (1987) model for melting Surveyor data)

  • Melting occurs beneath the surface at temperatures well below freezing, because sunlight is absorbed at depth rather than at the surface, and this absorption is substantially increased by the incorporation of minor amounts of dust.

  • Can occur for a wide range of snow properties and atmospheric pressures, and occurs under current conditions in mid-latitudes if dust abundances are greater than 1,000 parts per million by mass.


Clow s model ii
Clow’s model II Surveyor data)

  • Meltwater moving downwards under gravity will encounter lower temperatures and refreeze.

  • Conduction and latent heat transfer will gradually warm the snow and substrate, allowing liquid water to accumulate and be available for erosion

  • Subsurface erosion and collapse of the snow mantle will occur, with liquid water potentially reaching and eroding the substrate as the snow layer continues to melt.


Clow s model iii
Clow’s model III Surveyor data)

  • Liquid water will begin to be generated 100 d after the spring equinox under current conditions for snow with a dust content of 1,000 p.p.m.m.

  • Will reach a depth of 20 cm approximately 25 d later.

  • Up to 0.33 mm of snowmelt runoff is produced each day for 50 d each martian year.



Ddss are different from gullies because
DDSs are different from gullies, because… Surveyor data)

  • They reappear annually

  • Frost/snow cover above them is re-established each year and disappears by midsummer

  • Crater slopes and alcoves are NOT necessary

  • BUT the dune material IS

  • Channels from DDSs on slopes are also thought to form below the snow

  • Slow melting, NOT gas outbreak: complete lack of explosive formations

  • Salinity unknown, could be important


Layered frost on the dunes 2002
Layered frost on the dunes (2002) Surveyor data)

  • Water ice, clathrate and CO2 ice are deposited in that order

  • Dunes are the first to frost and the last to defrost

  • Total frost between 0.2-1 m (laser altimeter)



The biological hypothesis
The biological hypothesis Surveyor data)

  • Annual reactivation and growth of photosynthetic organisms

  • Ice: excellent shield against cold, UV and dryness

  • Organisms must go to dormancy before water ice shield melts through (‘adaptive sporulation’)


Looking for partial analogues on earth extremophiles
Looking for partial analogues on Earth (extremophiles) Surveyor data)

  • The Dry Valleys of Antarctica

  • Cold, dry

  • High UV due to continuous solar exposure

  • Ozone depletion


Bacterial activity in lake ice
Bacterial activity in lake ice Surveyor data)

These bacteria are permanently buried in ice!


Photosynthetic microorganisms
Photosynthetic microorganisms Surveyor data)

At the centre of a rich consortium



Uv protection by snow
UV protection by snow Surveyor data)


Thermal tolerance on earth
Thermal tolerance on Earth Surveyor data)

  • Temperatures go down to –70 °C in the Antarctic valleys

  • Spores can be cooled down arbitrarily

  • Photosynthesis is possible under the snow down to –20 °C, when the temperature above is a lot colder

  • You do not need liquid water, only positive water potential

  • Extremely fast rehydration in cyanobacteria

  • Many cyanobacteria are halophilic



More on uv resistance
More on UV resistance Surveyor data)

  • There are bacteria (e.g. Deinococcus radiodurans) on Earth, extremely resistant to radiation and dryness

  • Martian organisms must have undergone billions of years of adaptation

  • Dead cells in the upper layer efficiently protect viable cells in the lower layer

  • Viable stock may also endure as endoliths

  • Efficient external and internal shields (e.g. black in cyanobacteria: “sunglass”)


A mars chamber simulation is being prepared
A Mars chamber simulation is being prepared… Surveyor data)

at Centro di Astrobiologia (CAB) in Madrid


Objective of the chamber experiments
Objective of the chamber experiments Surveyor data)

  • To prove that there is a layered structure of the frost under simulated Martian conditions

  • To see whether spots form by simple frosting-defrosting or not

  • To introduce biological material (e.g. cyanobacteria) into the simulation


Summary
Summary Surveyor data)

  • DDSs are a potential habitat for life on Mars today

  • They may be actual habitats

  • Earthly analogues are encouraging

  • Chamber simulations have to be carried out

  • Looking for pigments by appropriate spectroscopy (resolution, wavelengths!)

  • Sending landers to interesting sites!


Some further thoughts
Some further thoughts Surveyor data)

  • Those who consider this story scandalous must also ultimately think that life is improbable!

  • If life is probable, this story is not against parsimony at all

  • We are faced with NON-abundant life

  • We are in a lucky period, because the phenomenon may disappear in the future


Main collaborators
Main collaborators Surveyor data)

  • András Horváth, astronomer and planetologist

  • Tibor Gánti chemical engineer and theoretical biologist (Principles of the Living State OUP, in a week)

  • Susanna Manrubia physicist (CAB) to coordinate the Spanish group (incl. chamber)


Reading
Reading Surveyor data)

Horváth, A., et al. (2001) Probable evidence of recent biological activity on Mars: Appearance and growing of dark dune spots in the South Polar Region, Lunar Planet Sci.XXXII, #1543,

Horváth, A., et al. (2002) Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Interpretation, Lunar Planet. Sci.XXXIII, #1108.

Horváth, A., et al. (2002) The “Inca City” Region of Mars: Test field for Dark Dune Spots Origin,Lunar Planet. Sci.XXXIII, #1109.

Gánti et al. (2003) Origins of Life and Evolution of the Biosphere in press