CHARACTER OF CHARACTER OF FREE WATER (ICE)FREE WATER (ICE) SPREDING IN THE MARTIAN SURFACE SPREDING IN THE MARTIAN SURFACE REGOLITH ON THE BASE OFREGOLITH ON THE BASE OF HEND/ODYSSEYHEND/ODYSSEY DATA.DATA.

by Kuzmin R.O.1, I.G. Mitrofanov, M.L. Litvak, W. Boynton, R. S. Saunders.

1 - Vernadsky Institute of Geochemistry and Analytical Chemistry, RAS, Moscow, 119991, Russia rok@geokhi.ru ; 2 - Institute for Space Research, RAS, Moscow, 117997, Russia; 3 - University of Arizona, Tucson, AZ 85721, USA; 4 – NASA HQ, Washington, USA.

What it was known about the superficial layer of the Martian What it was known about the superficial layer of the Martian cryolithosphere before the HEND/ODYSSEY data ?cryolithosphere before the HEND/ODYSSEY data ?

A - Spatial spreading of the fresh meteorite crater (2-km diameter) with fluidized (blue) and dry ejecta (yellow). B – Cross-section of relative ice content in cryolithosphere (versus latitude and depth), compiled on the base parameter Dejecta/Dcrater for fluidized ejecta craters; C – The structure of the cryolithosphera superficial layer structure.

B

A C

Map of the epithermal neutrons counts rate values during the period from18 February to 17 April, 2002

(end of summer in southern hemisphere

Counts/sec

Analysis of the HEND/ODYSSEY data, accumulated during 10 months of global mapping

Epithermal neutrons (EN): 0.4 eV – 100 keV (regolith layer 1.5-2 m) Fast neutrons (FN): 3.4 – 7.3 MeV (regolith layer 0.2-0.3 m)

Main focus on free water neutron’ signature

Average counts rate of EN (a) and FN (b) vs. latitudes for N-winter (1),N-spring/summer transit (2) and beginning of N-summer (3).

Dynamics of the neutron counts rates during the period From February 18 to December 10, 2002.

Epithermal neutrons

Fast neutrons

Northern subpolar region: decreasing of the neutrons flux

Southern subpolar region: increasing of the neutrons flux

Scatter plots, showing the clustering of EN and FN counts rate for subpolar regions (2,3) in different HEND mapping periods

During summer season the neutrons flux clusters looks very similar for both hemisphere (with the average counts rate mostly lower than 0.12 counts/sec).

Global maps showing the seasonal dynamics of the neutron’s signature of free water presence (counts rate <0.12) in the subpolar regions (within the surface layer 1-2m), resulted by accumulation and sublimation of the seasonal cap from CO2-ice. Counts rate values in the range 0.12-0.14 may to charaterize the presence of both free and bound water amounts in different proportions.

Global map, showing the areal spread of free water (ice) neutron’s signature (with counts rate <0.12), mapped by HEND during summerseason in each hemispheres

Correlation of free water neutron’s signature spreadwith the Martian permafrost features distribution (on the example of the polygonal terrains).

Earth Mars

HEND: fast neutron map

TES data: bound water index map ( 6.1μm)

HEND: epithermal neutrons map

Are the fast neutrons sensitive to bound water in the Martian regolith?

Seemingly yes!