I r 

THE BEHAVIOR OF WATER ON MARS 

NAGW-552 

PROGRESS REPORT 

25 MAR 1987 

BRUCE M. JAKOSKY 

LABORATORY FOR ATMOSPHERIC AND SPACE PHYSICS 

UNIVERSITY OF COLORADO, BOULDER, CO 80309-0392 

(NASA-CR-180249) TEE EEfiAVICE CE WAITEf CN NE7- 193 24 

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CSCL 038 

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63/91 43762 
Our recent focus in Mars research has been in the area of the seasonal 

behavior of water in the atmosphere, surface, and polar caps, and exchange of 

water between these reservoirs. Below, we summarize some of our recent 

results. 

We have analyzed the behavior of water in the atmosphere and on the 

surface in the vicinity of the Viking-2 lander on Mars, with an emphasis on 

understanding the stability of H,O and CO, frosts. The analysis consisted of 

examining surface and atmospheric temperatures measured by the Viking Infrared 

Thermal Mapping experiment in order to constrain the physical properties and 

processes in the vicinity of the lander site, followed by modeling of the 

sublimation rates of CO, and H,O frosts based on these properties. We show 

via an equilibrium surface energy balance calculation that C02 frost is not 

stable when frost is observed on the surface. We estimate the stability of 

H,O frost based on sublimation rates controlled by the surface temperature; 

water frost was stable during the period when frost was actually observed, but 

was not stable after the frost actually disappeared. Results on these 

calculations, estimates of the amount of water actually involved in exchange 

with the surface, and discussion of the implications for the seasonal cycle of 

water in the atmosphere are contained in a paper by Hart and Jakosky (1986). 

The relationship between atmospheric water and ozone is an especially 

interesting one. Both species can play a role in impacting the seasonal 

weather patterns and current-epoch climate. Therefore, computer simulations 

of the behavior of ozone have been conducted. Photochemistry in the winter 

polar atmosphere of Mars has been examined for several latitudes, cloud types, 

and dust abundances. Computer simulation reproduces the ozone abundances 

observed by the Mariner 9 ultraviolet spectrometer experiment. Clouds change 

ozone abundances by only a few percent; however, typical dust abundances 
induce 10 to 30% increases in ozone abundances, primarily because 

photodissociation rates are drastically reduced by dust absorption. 

Furthermore, annual, latitudinal, and seasonal variations in dust opacity 

cause variations of 30% or greater in the ozone abundance. Results of these 

calculations have been reported in a paper submitted for publication by 

Li ndner (1987). 

Interactions between subsurface and atmospheric water play a major role 

in controlling the seasonal water cycle. Observations of the subsurface water 

abundance can constrain both the interactions between the surface and the 

atmosphere and the physical state of any near-surface water. The gamma-ray 

spectrometer on the upcoming Mars Observer spacecraft will contain a neutron 

spectrometer mode which will allow estimates of subsurface hydrogen to be 

made. 

water can be measured by such an investigation. 

We have done a preliminary study of the efficacy with which subsurface 

Results of these calculations 

have been reported in a paper submitted for publication by Drake et al. 

(1987). 

Our ongoing research is currently centered on two specific areas. First, 

a re-analysis of the radiance data obtained by the Viking atmospheric water 

detection experiment will provide updated information on the atmospheric water 

abundance. Second, physical modeling of the sublimation and transport of 

water from the summer residual north polar cap will constrain the physical 

processes which control the seasonal water cycle. 

The radiance data consist of measurements of the solar flux reflected 

from the martian surface in five channels, two of which are in continuum 

regions and three of which are in water vapor absorption bands. We are 

pursuing the goal of using the three band absorption measurements to derive 

simultaneously the column water vapor abundance as well as the effective 
temperature and pressure of line formation. Error analyses provide us with 

the information that we need in order to properly choose the data which can be 

averaged together to improve the signal-to-noise ratio enough to allow 

successful inversion. Additionally, the role of dust scattering and 

absorption must be taken into account at the level of accuracy desired. 

Finally, we are correcting problems in the earlier inversions of the MAWD data 

in terms of failing to correct properly for the variations of the solar flux 

with wavelength. The end result will be a better estimate of the abundance of 

water vapor in the martian atmosphere, an estimate of the vertical 

distribution of the water, and, perhaps most importantly, a better estimate of 

the uncertainties in the data inversion and analysis. Preliminary results 

have been reported by Hart and Jakosky (1987). 

Physical modeling of the sublimation and transport of water from the 

vicinity of the north polar cap during northern hemisphere summer season on 

Mars is important in order to understand the processes which control the 

current seasonal cycles on Mars. Previous analysis suggests that water 

appears in the atmosphere over the north polar cap as the cap heats up during 

summer and is transported equatorward by the circulation of the atmosphere. 

We have used Viking IRTM measurements of the temperature of the cap to 

calculate the amount of water sublimed into the atmosphere, using previously 

described models of the sublimation process. For realistic estimates of the 

boundary layer properties, it is possible to sublime sufficient water to 

explain the global increase in atmospheric water content. Interestingly, if 

the dark lanes or the circumpolar debris deposits contain water which is 

capable of subliming into the atmosphere, this source of water could dominate 

the polar behavior of water. Calculations of the transport equatorward of 

this polar water, using the two-dimensional, axisymmetric model developed by 
R. Haberle, cannot explain the apparent migration of water, however. This 

results due to the sluggish circulation in the polar region; once water can be 

moved to the region near 60" latitude, the cross-equatorial Hadley cell can 

move the water efficiently. Aspects of the seasonal cycle of water can be 

reproduced if the atmosphere contains a non-axisymmetric source of mixing; the 

only currently known mechanism for such eddy mixing is the near-polar cyclonic 

motions suggested by spiral wave clouds seen at these seasons. Preliminary 

results of these investigations have been presented by Jakosky (1987) and 

Haberle and Jakosky (1987). 
REFERENCES 

Drake, D.M., W.C. Feldman, and B.M. Jakosky, Martian neutral albedo spectra, 

submitted for publication, 1987. 

Haberle, R.M. and B.M. Jakosky, Transport of water from the residual north 

polar cap on Mars (abstract), Lunar Planetary Science Conference, 1987. 

Hart, H.M. and B.M. Jakosky, Composition and stability of the condensate 

observed at the Viking Lander 2 site on Mars, Icarus, 66, 134-142, 1986. 

Hart, H.M. and B.M. Jakosky, Vertical distribution of water vapor in the 

atmosphere of Mars: Error analysis and preliminary results (abstract), 

Lunar P1 anetary Science Conference, 1987. 

Jakosky, B.M., Sublimination of water from the residual north polar cap on 

- Mars (abstract), Lunar Planetary Science Conference, 1987. 

Lindner, B.L., Ozone on Mars: The effects of clouds and airborne dust, 

submitted for publication, 1987.