1. PRELIMINARY STUDY OF UV RADIATION ON MARS FROM SPICAM RESULTS AND ITS RELATION TO SURFACE HABITABILITY
C. Depiesse , N. Mateshvili , C. Muller , D. Fussen , D. Gillotay , D. Moreau, D. Fonteyn , Belgian Institute for Space Aeronomy, Belgium
S. Perrier, J.-L. Bertaux, Service d’Aéronomie du C.N.R.S., France.

2. Life on Earth Formation of earth :
years
Begin of life into the earth oceans :
years
Life at surface on ground :
years, enough O3 to stop UV radiation destructing DNA

3. Habitability of Mars ? Current Martian conditions :
Ground temperature, ~ -100°…0° C
Surface pressure, <6 mbar below triple point of water
UV ground radiation, depending on CO2 and O3 abundance in atmosphere…
 SPICAM mission

4. SPICAM mission to Mars
Mars-Express has reached Mars orbit in early 2004 and since, its instruments have measured during an entire Martian year.
SPICAM, in particular, has measured the nadir reflected and backscattered solar light as well as solar occultations with an almost complete planetary coverage. The UV instrument (ranging from 118 nm to 320 nm) covers the entire band of UV sterilizing radiation that could affect survivability on Mars surface.

8. Model to analyze Spectra
2D model from Dr. Moreau (1996, IASB, Belgium) includes :
Extended Chemistry including organic chemistry, sulfur and chlorine chemistry.
Radiative transfer (based on CCM1, NCAR adapted to Mars)
Dynamical Transport (including atmospheric waves)
Evolution of polar caps
Dust multiple scattering

9. Strong UV transmission
Mars Ground Radiation
Irradiance (mW m-2 nm-1)
UV-A
UV-B
UV-C
[O3]=2µm atm
Earth
Mars
± 350 mW m-2
± 970 mW m-2
~ 0 mW m-2
±265 mW m-2
Strong UV transmission
DNA absorption

10. Possible resistant forms of life on Mars ?
Surface life is confronted to aggressions by UV radiation and an effective oxidant, detected by the in situ experiments on VIKING but not yet identified.
Low temperature
Low pressure
No liquid water
Strong UV radiation

11. Possible resistant forms of life on Mars
The FOTON LICHEN of Sancho et al (2006) gives an estimated half life time of 8000 years in exposed space for Rhizocarpon geographicum and Xanthoria elegans, these lichens are high altitude species and come from the Monte Perdido national park in Spain. Lichens are a symbiotic association of a fungus and a green algae

12. What is the basis for protecting lichens?
Parietin forms under influence of UV exposure inside the fungus and
thus protects the alga, algae have their own carotenoids which are
unfortunately less efficient.
Parietin is essentially a blue
Screen and nobody knows that
If it is “on purpose” that it is
a UV screen efficient in UV-B and C,
the production of parietin is an adaptation
UV-A triggers it.
Lichens are also extreme examples of
Metabolic antifreeze: (Kappen, 1993):
Xanthoria candelaria and
Rhizoplaca melanophthalma
tolerated freezing to -196 ºC, and even
after being stored for up to several years,
resumed normal photosynthetic rates when
warmed and wetted.
K.A. Solhaug , Y. Gauslaa, 2006.

13. Are other vegetal species more resistant?
Yes, Deschamipia Antarctica, the Antarctic weed is protected by luteolin, a
flavonoïd , its seeds can resist indefinitely to UV, more, luteolin is also an efficient antifreeze and allows vascular plants to survive .
Even cyanobacteria have a pigment that could prove to be a UV filter: Phycobilins

14. Contamination of Mars surface ?
Metallophile bacteria:
Radiodurans: - UV and γ resistant
- but rapidly oxidized
Metallidurans: - UV resistant
- oxidant resistant
- protected by their metallic neighbourhood
Ralstonia metallidurans
- Spirit
- Opportunity

15. Back to 1873: Flammarion’s map of Mars.
However since, no vegetation has
ever been observed on Mars
Dust has
a deep influence
on Mars colour
(picture from Viking I)
Back to 1873: Flammarion’s map of Mars.

16. Close future… Not so far future… Long perspective…
Reactivation of the Moreau model
Complete UV climatology and mapping using SPICAM nadir observations and comparison with model
Search of new atmospheric molecules (H2O2, HNO3, oxidant,…)
Not so far future…
Preparation of the EXOMARS mission to Mars (collaboration with Open University, UK) which will contain a UV-Vis spectrometer on the Pasteur payload
Long perspective…
Determine the characteristics of protection against UV for the future human mission to Mars…

17. Thanks to… Belgian Institute for Space Aeronomy, Belgium :
N. Mateshvili , C. Muller , D. Fussen , D. Gillotay , D. Moreau, D. Fonteyn ,F. Daerden
Service d’Aéronomie du C.N.R.S., France.
S. Perrier, J.-L. Bertaux
Complutense University of Madrid, Spain
L. Sancho
Minnesota State University, USA
C. T. Ruhland