# Presentation: 506902

## The Distribution of Hydrogen on Mars Bill Feldman

- A major goal of the NASA and ESA space programs is to find
- evidence for extraterrestrial life.  A prime requirement for the
- genesis and support of life as we know it is water.  A
- determination of the distribution of water on Mars has therefore
- been a prime objective of all missions to Mars.

## Key Science Questions

- What is the Geographic Distribution of
- Martian Water
- What is the Form of Water on Mars
- Is there an Aquifer
- What does the Water Abundance Distribution
- Tell us about Climate Change on Mars

**Key Science Questions**

## Topography Map

**Mars Orbiter**
**Laser Altimeter**

**Northern**
**Plains**

**Tharsis**

**Hellas**
**Basin**

**Southern**
**Highlands**

**Valles**
**Marinaris**

**Argyre**

**Olympus**
**Mons**

## RiverbedsonMars

**Riverbeds****on****Mars**

## This view of Gusev shows that Mars surface is heterogeneous and dry

## Once an Ocean on Mars?

-   Hidden Ice
-   Escaped the planet
-   Chemically incorporated
-   Deep down hydrosphere

**Where is All the Water Now?**

- Topography:  MOLA Team

## Movement of H2O and Ice by Obliquity

## The process of learning anything about planets is not exact.

- One must first choose to measure a quantity that
- is related to a phenomenon of interest.
- One then chooses a model of the environment that
- allows the translation of that measurement to physical reality.
- Oftentimes the chosen model does not mirror the actual
- environment and/or contains parameters that are not known.
- The only way out of this predicament is to compare the
- new measurements with those made using other methods
- in the hopes of getting a clearer picture of the actual
- physical conditions on and below the ground.

## Natural radiation from planetary bodies can be

- 

**Inelastic**
**collision**

- 

**Neutron**
**capture**

**Fast neutrons**

**Moderation**
**(neutrons loose energy**
**in successive collisions, eventually achieving thermal equilibrium with the surface)**

**Thermal and **
**epithermal neutrons**
**(H, C, Gd+Sm)**

**Fast neutron**
**<Atomic number>**

**Cosmic ray**

**Natural**
**radioactivity**

- 

** ****Th**

**Gamma rays**
**(Fe, Mg, Ti, Si, O, Al, Ca,**
**K, Th, U)**

- used to determine the composition of their
-  outermost layers

## Simulated Neutron leakage energy spectra for

- a range of soil water content

-  Flux x Energy

## The Mars Odyssey Neutron Spectrometer (MONS) was designed to detect and map deposits of hydrogen on Mars.
The detector measures escaping neutron currents in three energy ranges, Thermal, Epithermal, and Fast.
These currents can be used to constrain three parameters of a simple 1-D model of Water-Equivalent Hydrogen (WEH) distributions if the elemental composition of matrix soil material is known.
These parameters are the WEH content of an upper layer, Wup, the thickness of this layer, D, and the WEH content of an assumed semi-infinite lower layer, Wdown. 
Our analysis proceeds in two steps; the first assumes only one layer, D = 0, which gives a lower bound to the WEH abundance, and the second expands to two layers.

- The detector measures escaping neutron currents in three energy ranges, Thermal, Epithermal, and Fast.
- These currents can be used to constrain three parameters of a simple 1-D model of Water-Equivalent Hydrogen (WEH) distributions if the elemental composition of matrix soil material is known.
- These parameters are the WEH content of an upper layer, Wup, the thickness of this layer, D, and the WEH content of an assumed semi-infinite lower layer, Wdown.
- Our analysis proceeds in two steps; the first assumes only one layer, D = 0, which gives a lower bound to the WEH abundance, and the second expands to two layers.

## 12

- 6

- 6

- 18

- 24

- 30

- 36

## Slide 13

## Spirit Wheel Track from Tyrone to Winterhavenshowing white evaporite layer covered by dust

## Slide 15

## Water-Equivalent Hydrogen abundance of the lower layer 

- Water-Equivalent Hydrogen abundance of the lower layer
- in a two-layer model of the near surface regolith

## Slide 17

## Polar projections of the WEH content of the lower layer with a low

- abundance cutoff of 5 weight %.  The region south of -75o is
- omitted to avoid contamination by high thermal neutron currents
- from the south polar residual, CO2-covered water-ice cap

## Slide 19

## Slide 20

## Observed WEH near the equator is consistent with recharge 

- Longitude

- Latitude

- -60             0           60

- -60            0            60

- -60            0            60

- -180

- 180

- Observed WEH near the equator is consistent with recharge
-                                                                from the atmosphere

- H2O in atmosphere is centered north of the equator

- Atmospheric H2O emplacement using Ames MGCM - close to the observed pattern of WEH

- Distribution of WEH
- observed using MONS

##  Peak WEH is in the north

-  Peak WEH is in the north
-  Cut off from south residual cap by deep boundary canyons.

- Solis Planum and
- Tempe Terra

- Argyre and
- Xanthe Terra

## Comparison between longitude scans of the WEH of the lower layer, and burial depths

- for five latitudes between 60o and 70o north and south latitudes.  These scans can be
- separated into three longitudinal sectors.  Each has a relative maximum and relative
- minimum in WEH(dn), and a relatively flat portion, identified by the horizontal lines.

## Anticorrelation between WEH (down) and burial depth

- The correlation is good with a zero-depth asymptote of WEH=0.92

## Mangold, Icarus, 2005 

## 60.7o N, -2.9o E, Mars

- 60.7o N, -2.9o E, Mars
- Mangold et al., 2002

- Beacon Valley,  Marchant et al., 2002

## Mellon et al., 2007

## HiRISE image 

- HiRISE image
- of patterned
- ground  at 69o N
- and 130o E.

## Slide 29

##     Burial Depth

- MONS Thermal-
- Epithermal Data

- Patterned Ground
- Mangold et al., 2004

## Slide 31

## Icy textures

- Sand vs. ice-wedge polygons, evidence of freeze thaw, deformation of icy material:

- Ice lenses

## Summary of Single-Layer Results

- Mars has two distinct domains of hydrogen; large deposits at high latitudes and more modest, yet significant deposits near the equator.
- 2.	Atmospheric H2O is concentrated generally north of the equator.
- WEH is found preferentially on north-facing slopes of northern
- 	 portions of highest terrain in the southern highlands.
- 4.   The pattern of H2O deposition predicted by the Ames MGCM is
-        generally similar to the observed distribution of WEH.
- 5.  WEH near the equator appears to be delivered through the
- 	 atmosphere, not an aquifer fed by the southern water-ice cap.
- 6.  At high latitudes, WEH is high and most likely exists as water ice.

## Summary of Two-Layer Results

- 1.	The WEH abundance of the top layer is in the range between 1% and 5% by mass, but is generally closer to 2% by mass on average.
- 2.	The WEH abundance in the lower layer generally increases with increasing latitude between 55o and 75o.  The lone exception is in Scandia Colles in the north and Promethei Terrae in the south.
- 3.	The apparent burial depth decreases with increasing latitude poleward of 60o in both hemispheres.
- 4.	Zonal bands of high apparent burial depth at +/- 60o are consistent with a transition from WEH contained in hydrous minerals at lower latitudes, to WEH in water ice and water of hydration at higher latitudes.
- 5.	The anticorrelation between WEH (down) and Depth at high latitudes suggests that average regolith pore volumes decrease with increasing depth.