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Dark Dune Spots: Possible current habitats on MarsEörs Szathmáry
Collegium Budapest
Eötvös University Budapestszathmary@colbud.hu
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… Water was lost due to radiation decay and Water was lost due to radiation decay and
loss of hydrogen to spaceloss of hydrogen to space A large oxygen sink must be presentA large oxygen sink must be present More than 3 billion years ago conditions for More than 3 billion years ago conditions for
the origin of life seem to have been the origin of life seem to have been favourablefavourable
Could anybody have survived till today?Could anybody have survived till today?
An ancient lake and outflow
Loire Vallis
lake
Cataclysmic flood channels
Cyclic and episodic changes
Viking lander: no evidence for life
It is easy to land in the equatorial desert, BUTIt is easy to land in the equatorial desert, BUT It is very hard to find even traces of life thereIt is very hard to find even traces of life there The soil seems oxidisingThe soil seems oxidising BUT some oxidized organic compounds may have escaped BUT some oxidized organic compounds may have escaped
detectiondetection
Claims of past life remain controversial
Is this magnetite biogenic?
Dark Dune Spots (DDSs): a candidate habitat (2001)?
Analyzed DDS sites in the south polar region (Mars Global Surveyor data) MOC images
Dark dunes
Malin Space Science Systems
DDSs stick to the dunes…
…and have inner structure
Mere frosting-defrosting of the CO2 ice cover
Albedo decreases as frost thinsAlbedo decreases as frost thins Positive feedback: faster sublimationPositive feedback: faster sublimation
MUST mean:MUST mean: Start spot formation at sites with strong Start spot formation at sites with strong
exposure to insolationexposure to insolation Otherwise at Otherwise at random sitesrandom sites (wind, etc.) (wind, etc.)
Simple frosting-defrosting does NOT work, because…
Spot formation begins at the bottom, not at the top!
Simple frosting-defrosting does NOT work, because…
Spots do not develop on exposed sites!
Simple frosting-defrosting does NOT work, because…
There is annual recurrence (>75%) at the same sites!
Simple frosting-defrosting does NOT work, because…
On slopes flows On slopes flows originate from the originate from the DDSsDDSs
Which always flow Which always flow downwardsdownwards
From elongated spotsFrom elongated spots Gravitation is a Gravitation is a
formative causeformative cause
Flows may be due to water runoff
The dry planet is much wetter than thoughtThe dry planet is much wetter than thought There is plenty of water:There is plenty of water:
In both ice capsIn both ice caps In the upper layer of the polar region In the upper layer of the polar region
(permafrost)(permafrost) In liquid form in the gulliesIn liquid form in the gullies
Mars Odyssey HEND measurements
High Energy Neutron DetectorHigh Energy Neutron Detector Deficit of high-energy neutronsDeficit of high-energy neutrons Hydrogen is concentrated in the subsurfaceHydrogen is concentrated in the subsurface Water-rich layers tens of centimetres thickWater-rich layers tens of centimetres thick
Frozen water in polar regions
Recent gullies by melting snow Occur in clusters on slopesOccur in clusters on slopes Between 30 and 70 latitude in Between 30 and 70 latitude in
both hemispheres both hemispheres Consist of alcoves several Consist of alcoves several
hundred metres wide, hundred metres wide, Channels up to several Channels up to several
kilometres long and several tens kilometres long and several tens of metres deep of metres deep
Typically originate within Typically originate within several hundred metres of the several hundred metres of the slope crest,slope crest,
Can occur on crater walls that Can occur on crater walls that are raised above the are raised above the surrounding terrain or near the surrounding terrain or near the summit of isolated knobs.summit of isolated knobs.
North
Christensen’s mechanism (2003) (1(1) Water is transported from the poles to mid-) Water is transported from the poles to mid-
latitudes during periods of high obliquity, forming latitudes during periods of high obliquity, forming a water-rich snow layer a water-rich snow layer
(2) Melting occurs at low obliquity as mid-latitude (2) Melting occurs at low obliquity as mid-latitude temperatures increase, producing liquid water that temperatures increase, producing liquid water that is stable beneath an insulating layer of overlying is stable beneath an insulating layer of overlying snow. snow.
(3) Gullies form on snow-covered slopes through (3) Gullies form on snow-covered slopes through erosion by melt water or as a result of melt water erosion by melt water or as a result of melt water seeping into the loose slope materials and seeping into the loose slope materials and destabilizing them. destabilizing them.
Christensen’s mechanism II
(4) Gullies incised into the substrate are observed (4) Gullies incised into the substrate are observed where the snow layer has been completely where the snow layer has been completely removed. removed.
(5) Patches of snow remain today where they are (5) Patches of snow remain today where they are protected against sublimation by a layer of protected against sublimation by a layer of desiccated dust/sediment desiccated dust/sediment
(6) Melting could be occurring at present in (6) Melting could be occurring at present in favourable locations in these snowpacks.favourable locations in these snowpacks.
Clow’s (1987) model for melting
Melting occurs beneath the surface at temperatures Melting occurs beneath the surface at temperatures well below freezing, because sunlight is absorbed well below freezing, because sunlight is absorbed at depth rather than at the surface, and this at depth rather than at the surface, and this absorption is substantially increased by the absorption is substantially increased by the incorporation of minor amounts of dust. incorporation of minor amounts of dust.
Can occur for a wide range of snow properties and Can occur for a wide range of snow properties and atmospheric pressures, and occurs under current atmospheric pressures, and occurs under current conditions in mid-latitudes if dust abundances are conditions in mid-latitudes if dust abundances are greater than 1,000 parts per million by mass. greater than 1,000 parts per million by mass.
Clow’s model II
Meltwater moving downwards under gravity will Meltwater moving downwards under gravity will encounter lower temperatures and refreeze. encounter lower temperatures and refreeze.
Conduction and latent heat transfer will gradually Conduction and latent heat transfer will gradually warm the snow and substrate, allowing liquid warm the snow and substrate, allowing liquid water to accumulate and be available for erosionwater to accumulate and be available for erosion
Subsurface erosion and collapse of the snow Subsurface erosion and collapse of the snow mantle will occur, with liquid water potentially mantle will occur, with liquid water potentially reaching and eroding the substrate as the snow reaching and eroding the substrate as the snow layer continues to melt.layer continues to melt.
Clow’s model III
Liquid water will begin to be generated 100 d after Liquid water will begin to be generated 100 d after the spring equinox under current conditions for the spring equinox under current conditions for snow with a dust content of 1,000 p.p.m.m.snow with a dust content of 1,000 p.p.m.m.
Will reach a depth of 20 cm approximately 25 d Will reach a depth of 20 cm approximately 25 d later. later.
Up to 0.33 mm of snowmelt runoff is produced Up to 0.33 mm of snowmelt runoff is produced each day for 50 d each martian year.each day for 50 d each martian year.
Compare HEND with DDS sites!
DDSs are different from gullies, because… They reappear annuallyThey reappear annually Frost/snow cover above them is re-established Frost/snow cover above them is re-established
each year and disappears by midsummereach year and disappears by midsummer Crater slopes and alcoves are NOT necessaryCrater slopes and alcoves are NOT necessary BUT the dune material ISBUT the dune material IS Channels from DDSs on slopes are also thought to Channels from DDSs on slopes are also thought to
form below the snowform below the snow Slow melting, NOT gas outbreak: complete lack of Slow melting, NOT gas outbreak: complete lack of
explosive formationsexplosive formations Salinity unknown, could be importantSalinity unknown, could be important
Layered frost on the dunes (2002)
Water ice, clathrate Water ice, clathrate and COand CO22 ice are ice are
deposited in that orderdeposited in that order Dunes are the first to Dunes are the first to
frost and the last to frost and the last to defrostdefrost
Total frost between Total frost between 0.2-1 m (laser 0.2-1 m (laser altimeter)altimeter)
Dark spots are transformed to summer grey spots
The biological hypothesis
Annual reactivation and Annual reactivation and growth of photosynthetic growth of photosynthetic organismsorganisms
Ice: excellent shield Ice: excellent shield against cold, UV and against cold, UV and drynessdryness
Organisms must go to Organisms must go to dormancy before water ice dormancy before water ice shield melts through shield melts through (‘adaptive sporulation’)(‘adaptive sporulation’)
Looking for partial analogues on Earth (extremophiles)
The Dry Valleys of The Dry Valleys of AntarcticaAntarctica
Cold, dryCold, dry High UV due to High UV due to
continuous solar continuous solar exposureexposure
Ozone depletionOzone depletion
Bacterial activity in lake ice
These bacteria are permanently buried in ice!
Photosynthetic microorganisms
At the centre of a rich consortium
Ice and snow lake covers in mountains (Alps, etc.)
UV protection by snow
Thermal tolerance on Earth Temperatures go down to –70 Temperatures go down to –70 °C in the °C in the
Antarctic valleysAntarctic valleys Spores can be cooled down arbitrarilySpores can be cooled down arbitrarily Photosynthesis is possible Photosynthesis is possible underunder the snow the snow
down to –20 °C, when the temperature down to –20 °C, when the temperature above is a lot colderabove is a lot colder
You do not need liquid water, only positive You do not need liquid water, only positive water potentialwater potential
Extremely fast rehydration in cyanobacteriaExtremely fast rehydration in cyanobacteria Many cyanobacteria are halophilicMany cyanobacteria are halophilic
Snow and ice UV protection
More on UV resistance
There are bacteria (e.g. There are bacteria (e.g. Deinococcus Deinococcus radioduransradiodurans) on Earth, extremely resistant ) on Earth, extremely resistant to radiation and drynessto radiation and dryness
Martian organisms must have undergone Martian organisms must have undergone billions of years of adaptationbillions of years of adaptation
Dead cells in the upper layer efficiently Dead cells in the upper layer efficiently protect viable cells in the lower layerprotect viable cells in the lower layer
Viable stock may also endure as endolithsViable stock may also endure as endoliths Efficient external and internal shields (e.g. Efficient external and internal shields (e.g.
black in cyanobacteria: “sunglass”)black in cyanobacteria: “sunglass”)
A Mars chamber simulation is being prepared…
at Centro di Astrobiologia (CAB) in Madrid
Objective of the chamber experiments
1.1. To prove that there is a layered structure To prove that there is a layered structure of the frost under simulated Martian of the frost under simulated Martian conditionsconditions
2.2. To see whether spots form by simple To see whether spots form by simple frosting-defrosting or notfrosting-defrosting or not
3.3. To introduce biological material (e.g. To introduce biological material (e.g. cyanobacteria) into the simulationcyanobacteria) into the simulation
Summary
DDSs are a DDSs are a potentialpotential habitat for life on habitat for life on Mars todayMars today
They may be They may be actualactual habitats habitats Earthly analogues are Earthly analogues are encouragingencouraging Chamber Chamber simulationssimulations have to be carried out have to be carried out Looking for pigments by appropriate Looking for pigments by appropriate
spectroscopyspectroscopy (resolution, wavelengths!) (resolution, wavelengths!) Sending Sending landers landers to interesting sites!to interesting sites!
Some further thoughts
Those who consider this story scandalous Those who consider this story scandalous must also ultimately think that life is must also ultimately think that life is improbable!improbable!
If life is probable, this story is not against If life is probable, this story is not against parsimony at allparsimony at all
We are faced with NON-abundant lifeWe are faced with NON-abundant life We are in a lucky period, because the We are in a lucky period, because the
phenomenon may disappear in the futurephenomenon may disappear in the future
Main collaborators
András HorváthAndrás Horváth, astronomer and , astronomer and planetologistplanetologist
Tibor Tibor GántiGánti chemical engineer and chemical engineer and theoretical biologist (theoretical biologist (Principles of the Principles of the Living StateLiving State OUP, in a week) OUP, in a week)
Susanna Manrubia physicist (CAB) to Susanna Manrubia physicist (CAB) to coordinate the Spanish group (incl. coordinate the Spanish group (incl. chamber)chamber)
Reading Horváth, A., Horváth, A., et al. et al. (2001) Probable evidence of recent (2001) Probable evidence of recent
biological activity on Mars: Appearance and growing biological activity on Mars: Appearance and growing of dark dune spots in the South Polar Region, of dark dune spots in the South Polar Region, Lunar Lunar Planet Sci.Planet Sci. XXXIIXXXII, #1543, , #1543,
Horváth, A., Horváth, A., et al. et al. (2002) Morphological Analysis of the (2002) Morphological Analysis of the Dark Dune Spots on Mars: New Aspects in Biological Dark Dune Spots on Mars: New Aspects in Biological Interpretation, Interpretation, Lunar Planet. Sci.Lunar Planet. Sci. XXXIIIXXXIII, #1108., #1108.
Horváth, A., Horváth, A., et al. et al. (2002) The “Inca City” Region of (2002) The “Inca City” Region of Mars: Test field for Dark Dune Spots Origin,Mars: Test field for Dark Dune Spots Origin, Lunar Lunar Planet. Sci.Planet. Sci. XXXIIIXXXIII, #1109., #1109.
Gánti Gánti et al.et al. (2003) (2003) Origins of Life and Evolution of the Origins of Life and Evolution of the BiosphereBiosphere in press in press
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