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