Hydrogen/water on the Moon - Lunar and Planetary Institute · 2009-11-30 · page 13 Meeting of...

Meeting of LEAG

November 16-18, 2009

Hydrogen/water on the Moon

Igor Mitrofanov,

on behalf of LEND/LRO Team

Meeting of LEAG


Meeting of LEAG


Data from Clementine and Lunar Prospector

the model of water ice deposits at Permanently Shadowed Regions (PSRs)

Meeting of LEAG


LRO

LCROSS

NASA’s Lunar Reconnaissance Orbiter и LCROSS

Meeting of LEAG


Meeting of LEAG


LRO Mission Requirement

Instrument Requirement LEND: Required Data Products

The LRO shall obtain high spatial

resolution hydrogen mapping of the

Moon's surface to a 20% accuracy and 5 km resolution at the

poles.

LEND IMR 1:

Hydrogen mapping

Surface Composition Data Product (I): The content of Hydrogen in subsurface at polar regions with spatial resolution from 5 km (Half-

Width at Half-Maximum) and with variation sensitivity from 100 parts per million (ppm)

The LRO shall identify putative

deposits of appreciable surface

or near surface water ice in the Moon’s

polar cold traps at 100m scale spatial

resolution

LEND IMR 2:

Testing for water ice

Surface Composition Data Product (II): The water ice column density on polar regions of

the Moon with spatial resolution from 5-20km.

The LRO shall characterize the deep

space radiation environment in lunar

orbit, including neutron albedo.

LEND IMR 3:

Radiation environment

Radiation Data Product (III): Global distribution of neutrons at Moon’s orbit with

spatial resolution of 50 km at different energy ranges from thermal energy up to >15 MeV

separately for periods of quiet Sun and for periods of Solar Particle Events.

Meeting of LEAG


LEND LRO:

smoothing to 50 km resolution South Pole <-75°

Lunar Prospector (Feldman et al)

Slide - 7

4 collimated sensors of LEND are validated for mapping with high spatial resolution

Meeting of LEAG


LEND LRO:

smoothing to 50 km resolution

South Pole <-75°

LOLA data used for relief

Meeting of LEAG


LEND LRO:

smoothing to 30 km resolution

South Pole <-75°

LOLA data used for relief

Meeting of LEAG


QUESTION 1: Testing the model of PSRs, as the major contributors into the “Lunar Prospector” effect of polar suppression of neutron emission from the Moon

Meeting of LEAG


Lunar Prospector effect and its model of PSRs major contribution

4.4%

4.4%

>>4.4%

Meeting of LEAG


BGD2 BGD1

BGD2

BGD1

PSR

Testing the PSR model of “Lunar Prospector” effect by LEND data analysis

Testing sample of PSRs:

> 100 km2 > 300 counts

Δ1 and Δ2

Meeting of LEAG


Example of PSR

Observed variation of neutron emission

Estimation for Hydrogen

Shoemaker (- 4.4 ± 1.6) % About 100 ppm of H more than outside

PSR at this latitude

(- 8.3 ± 1.6) % About 200-300 ppm of H more than outside at moderate latitudes

Hawthon (- 3.8 ± 1.8) % About 100 ppm of H more than outside



Faustini (- 10.8 ± 3.2) % About 300 ppm of H more than outside



Shackelton (+ 3.1 ± 2.0) % About 100 ppm of H less (!?) than

outside PSR at this latitude

(- 0.2 ± 2.0) % About the same H content as at moderate latitudes

Cabeus (- 15.3 ± 5.6) % About 400-500 ppm of H more than

outside PSR at this latitude

(- 18.2 ± 5.6) % About 500 ppm of H more than outside at moderate latitudes

Meeting of LEAG


“Lunar Prospector” effect as seen by LEND for South with and without contribution of all selectable PSRs

Meeting of LEAG



REASULT 1: PSRs are not the major contributors into the LP effect in comparison with illuminated surface at similar polar latitudes

Meeting of LEAG



RESULT 1: PSRs are not the major contributors into the LP effect in comparison with illuminated surface at similar polar latitudes

QUESTION 2: Are there any local Suppressed Neutron Regions (SNR) at polar latitudes, which manifest the most pronounced signature of hydrogen/water at subsurface?

Meeting of LEAG


Regions at

Cabeus

Suppression Effect of epi-

thermal neutrons in respect to

moderate latitudes

Estimation of

Hydrogen

SNR at

6 km (- 24.7 ± 5.6) % >800 ppm

SNR at

12 km (- 13.2 ± 2.5) % >300 ppm

SNR at

24 km (- 12.1 ± 1.6) % > 300 ppm

PSR (- 18.2 ± 5.6) % >500 ppm

6 km

24 km

12 km

LCROSS

Meeting of LEAG


D. Crider and R.Vondrak, 2003

Model of formation of subsurface layer with H/H2O

Meeting of LEAG


h

h

1

100

Water Content (%)

1 meter

SNR

0

Estimation for SNR @ Cabeus: 800 ppm of H 2 – 3 wt% of water ice

Model-dependent estimation of H/H2O content

Meeting of LEAG



RESULT 1: There is NO strong suppression of epithermal neutron emission at south pole due to selectable PSRs in comparison with overall suppressed emission of illuminated surface at similar polar latitudes

QUESTION 2: Are there any local Suppressed Neutron Regions (SNR) at polar latitudes, which manifest the most pronounced signature of hydrogen/water at subsurface?

RESULT 2: Yes, they are. SNR at Cabeus is one of them. It is not coincident with the PSR at Cabeus. It may contain water ice under the top layer of dry regolith with a content of about 2 – 3 wt%

Meeting of LEAG


CONCLUSIONS:

1) LEND measurements of H spatial distribution correspond to LRO mission requirements (100 ppm detection limit with resolution of 10 km at poles).

2) LEND data for South pole does not support the model that water ice at current PSRs produces the effect of overall suppression of epithermal neutrons at poles (Lunar Prospector effect). Content of hydrogen in current PSRs is similar with the content at illuminated surface at the same polar latitudes (or only marginally higher) .

3) Suppressed Neutron Regions are detected at poles, which boundaries are not coincident with PSR. Cabeus SNR was suggested for LCROSS, as the best southern spot. The estimated content of hydrogen at Cabeus SNR corresponds to >800 ppm, or to 2 – 3 wt% of water in case of postulated burial depth of tens of centimeters.

4) Existence of SNRs outside PSRs requires more accurate physical models of lunar surface, which take into account active processes of its formation and transformation.

5) LEND detection of SNRs outside PSRs is good news for future program of Moon exploration (no activity in permanent darkness).

Hydrogen/water on the Moon - Lunar and Planetary Institute · 2009-11-30 · page 13 Meeting of...

Documents

Transcript of Hydrogen/water on the Moon - Lunar and Planetary Institute · 2009-11-30 · page 13 Meeting of...