LRO-LAMP Observations of Nighttime Illumination Conditions in the Lunar South

Polar Region

October 11, 2017

Kathleen Mandt, Tommy Greathouse, Erwan Mazarico, Yang Liu, Miriam Lemelin, Angela Stickle, J.-P. Williams, Kurt Retherford, Randy Gladstone, Ben Byron, G. W. Patterson, Dana Hurley and Amanda Hendrix

The LRO Lyman Alpha Mapping Project (LAMP)

Maps the Moon in the Far Ultraviolet (FUV)

Daytime using sunlight

Nighttime using starlight and the Interplanetary Medium (IMP) Lyman-α skyglow

Operational modes

Nighttime – door open

Daytime – pinhole mode reduces throughput to 0.13%

Recent change

Permanently opened failsafe door – daytime throughput now 10%

LRO-LAMP and the PSRs

Permanently Shaded Regions (PSRs)

Only mapped at night

Found to have up to 2% surface water frost

(Gladstone et al. 2012)

Comparison with Diviner temperature supports

water frost (Hayne et al., 2015)

Comparison with LOLA and Diviner (Fisher et

al. 2017)

Illumination in the PSRs

Increases temperature

Less volatile stability

3

3

Gladstone et al. (2012)

Hayne et al. (2015)

Nighttime FUV Illumination

LAMP STM 4

Focus on wavelengths where sunlight is

brighter than stellar illumination

NOTE: We are

intentionally using

data excluded from

Gladstone et al.

(2012)

Mazarico et al., 2011

Approach requires months of data

5

Total illumination within PSRs is estimated by

subtracting the average albedo for sza > 91 from the

full dataset using >36 months of observations

Average sza > 91 gives

Average unfiltered

Difference from average sza > 91

Illumination model – initial and updated

• Model

• Determine flux to surface

• Flux scattered back to LRO

• Same time period as LAMP

observations

Updated recently to

compute the direct

and scattered light

coming to LAMP

during actual

observations

Resampling illumination model

7

Haworth

Shoemaker

The role of phase function in what LRO should observe

• Original Model

• Simulated full PSR in 6-hour

increments

• Covered night and day

• Comparison method

• Selected time and location of

LAMP obs.

• Resample to LAMP lat/lon map

• Tested multiple phase functions

Comparison with other datasets

8

Comparison of LAMP maps of scattered sunlight

with other LRO datasets for Haworth:

(a) slopes from LOLA topography;

(b) elevation from LOLA topography;

(c) LAMP excess albedo showing scattered

sunlight;

(d) 1064 nm phase function

(e) 174 nm phase function

(f) 184 nm phase function

(g) LOLA normal albedo;

(h) West-looking Mini-RF CPR

(i) East-looking Mini-RF CPR;

(j) Minimum temperature

(k) Average temperature

(l) Maximum temperature from Diviner.

Correlation study of LAMP observations

Variable by Variable Haworth

Correlation Probability of Significance

Shoemaker Correlation

Probability of Significance

Model 1064 flux Excess Albedo -0.0309 0.0505 0.0203 0.2009

Model 1064 LRO Excess Albedo -0.0604 0.0001 0.023 0.1472

Model 174 flux Excess Albedo -0.0293 0.0637 -0.0023 0.885

Model 174 LRO Excess Albedo -0.0335 0.0339 0.0196 0.2172

Model 184 flux Excess Albedo -0.0226 0.152 -0.0024 0.8779

Model 184 LRO Excess Albedo -0.0407 0.0098 0.0195 0.2191

CPR West Excess Albedo -0.0392 0.0131 -0.0252 0.1115

Min temp Excess Albedo 0.0178 0.258 0.0262 0.0985

CPR East Excess Albedo 0.0246 0.1183

Max temp Excess Albedo 0.0725 <.0001 0.3014 <.0001

Temp Difference Excess Albedo 0.0759 <.0001 0.3508 <.0001

S1 West Excess Albedo 0.0847 <.0001 -0.0084 0.5948

LOLA Excess Albedo 0.166 <.0001 0.2988 <.0001

Average temp Excess Albedo 0.1956 <.0001 0.2595 <.0001

• Highly significant correlation between LAMP and the maximum

temperature

• Relationship to Mini-RF observations is unclear – surface

roughness?

• Does the model

correlate with

observations? – LAMP illumination is

anticorrelated with

the model in all

Haworth cases

– Poor correlation

based on p-value

with Shoemaker

• Correlation with

LOLA is

opposite to what

would be

expected for ice

Additional correlations

10

Variable by Variable Haworth

Correlation Probability of Significance

Shoemaker Correlation

Probability of Significance

Max temp On band 0.0751 <.0001 0.0330 0.0374

Min temp Off band 0.0585 0.0002 -0.0074 0.6420

Min temp CPR West 0.1125 <.0001 -0.1697 <.0001

Min temp Lyman alpha 0.0064 0.6865 0.0677 <.0001

Average temp Off band 0.0562 0.0004 0.0117 0.4607

CPR East LOLA 0.3067 <.0001

CPR West LOLA 0.1691 <.0001 0.2504 <.0001

LOLA Lyman alpha -0.0694 <.0001 -0.1914 <.0001

Max temp Off band 0.0568 0.0003 -0.0025 0.8734

Max temp CPR West 0.1594 <.0001 -0.4023 <.0001

Max temp LOLA 0.0443 0.0050 0.2520 <.0001

CPR West On band 0.0658 <.0001 0.0202 0.2025

Min temp LOLA -0.2507 <.0001 -0.0151 0.3396

Min temp CPR East -0.0565 0.0003

Average temp On band 0.0635 <.0001 0.0210 0.1855

Average temp LOLA -0.0368 0.0197 0.2766 <.0001

Average temp CPR West 0.0017 0.9122 -0.3115 <.0001

• Correlations with p-

values less than

0.001 – The risk of

concluding that a

correlation exists

when no correlation

exists, is < 0.1%

– Green supports

water ice, red

contradicts

• Temperature results

are mixed

• Is LOLA influenced

by surface

roughness?

Summary and Conclusions

Illumination observations vs model

Poor correlations between LAMP observations and model

The original illumination model is highly sensitive to the assumed

phase function – so how do we determine this for PSRs?

New model results coming

Correlations between LRO datasets

LAMP excess albedo agrees with maximum temperature observations

Interesting correlations between other datasets, but no clear sign of

multi-instrument water ice detection