LRO/CRaTER’s Discoveries of the Lunar Radiation Environment and Lunar Regolith Alteration by

Radiation

N. A. Schwadron, H. E. Spence, J. K. Wilson, A. Jordan, R. Winslow, C. Joyce, M. Looper, A. W. Case, N. E. Petro,

M. S. Robinson, T. J. Stubbs, C. Zeitlin, J. B. Blake, J. Kasper, J. E. Mazur, S. S. Smith and L. Townsend

H. E. Spence - K. D. Wood Colloquium

CRaTER Concept of Operations

28 April 20102

Quick CRaTER Overview• Measures > 12 MeV/nuc particles• 6 detectors (D1-D6) with Tissue Equivalent Plastic

(TEP) between pairs of detectors– Thick and thin detectors with different gains

allow a large range of Linear Energy Transfer (LET) to be sampled

– TEP mimics absorption of energy by human tissue as radiation passed through telescope

• Senses particles from zenith and nadir directions• Any energy deposit in any detector triggers an

‘event’, in which all energy deposits from all detectors are recorded

• Data products are in terms of LET, the amount of energy deposited per path-length (ΔE/Δx) as a particle transits through detector

Recent PublicationsCRaTER Special Issue of Space Weather - 10 Articles on CRaTER Measurements and Implications

– Schwadron, N. A., S. Smith and H. E. Spence, The CRaTER Special Issue of Space Weather: Building the observational foundation to deduce biological effects of space radiation, Space Weather, 11, 47, doi:10.1002/20026, 2013

– Case, A.W., The Deep-space Galactic Cosmic Ray Lineal Energy Spectrum, 2013, Space Weather, doi:10.1002/swe.20051 – Looper, M.D. et al., The Radiation Environment Near the Lunar Surface: CRaTER Observations and Geant4 Simulations. Space Weather,

Vol. 11, 142-152, doi:10.1002/swe.20034, 2013 – Joyce, C.J., et al., Validation of PREDICCS Using CRaTER/LRO Observations During Three Major Solar Events in 2012 using CRaTER and the

EMMREM Model. Space Weather, Vol. 11, pp. 1-11, doi:10.1002/swe.20059, 2013 – Spence, H. E., et al., Relative contributions of galactic cosmic rays and lunar proton "albedo" to dose and dose rates near the Moon,

Space Weather, 11, 643, 2013 – Porter, J. A., et al., Radiation environment at the Moon: Comparisons of transport code modeling and measurements from the CRaTER

instrument, Space Weather, 12, 329, 2014 – Joyce, C. J., et al., Radiation modeling in the Earth and Mars atmospheres using LRO/CRaTER with the EMMREM Module, Space Weather,

12, 112, 2014 – Zeitlin, C.;et al. Measurements of Galactic Cosmic Ray Shielding with the CRaTER Instrument. Space Weather, Vol. 11, pp. 284-296,

doi:10.1002/swe.20043, 2013– Schwadron, N., Bancroft, C., Bloser, P., Legere, J., Ryan, J., Smith, S., Spence, H., Mazur, J., and Zeitlin, C., Dose spectra from energetic

particles and neutrons, Space Weather, 11, 547, 2013 – Schwadron et al., Does the Worsening Galactic Cosmic Radiation Environment Preclude Future Manned Deep Space Exploration,

Space Weather, In Press, 2014

3 Additional Articles on Charging of Regolith and Changing Space Environment

• Jordan, A. P., T. J. Stubbs, J. K. Wilson, N. A Schwadron, H. E. Spence and C. J. Joyce, Deep dielectric charging of regolith withn the Moon’s permanently shadowed regions, JGR Planets, 119, doi:10.1002/2014JE004648.

• Jordan, A. P., T. J. Stubbs, J. K. Wilson, N. A. Schwadron, and H. E. Spence (2015), Dielectric breakdown weathering of the Moon’s polar regolith, J. Geophys. Res. Planets, in press, doi: 10.1002/2014JE004710.

• Smith, C. W., McCracken, K. G., Schwadron, N. A., and Goelzer, M. L., The heliospheric magnetic flux, solar wind proton flux, and cosmic ray intensity during the coming solar minimum, Space Weather, 12, 499, 2014

Recent Results

• Radically New Radiation Environment, Implications for Human Exploration

• New Insights on Energetic Particle Albedo Protons

• Lunar Subsurface Charging and Dielectric Breakdown – Implications for Regolith

• Causes and Effects of SEP Anisotropies at the Moon

http://crater-web.sr.unh.eduData Products

Protracted Min (23) and Mini Max (24)

• Dropping solar wind• Flux• Pressure• Magnetic Field

• Continues trend observed by Ulysses

McComas et al., ApJ, 2013

Long-term Record of Magnetic Field & SSN

• SSN (black)• Predicted (red)• OMNI (blue)• 10Be (green)• Magnetic Flux

Balance (Schwadron et al.,, 2010)

Goelzer et al., ApJ, 2013

Continued Decay of Magnetic Flux in the Dalton-like Minimum

Goelzer et al., ApJ, 2013

Comparison of Total Radiation Dose Equivalent measured by RAD to modeled

Historic SPE Events

RAD Cruise

GCR (6 mo)

RAD Cruise SPEs (total)

RAD Mars SPEs

Feb 1956 SPE

July 1959 SPE

Nov 1960 SPE

Aug 1972 SPE

Oct 1989 SPE

0

100

200

300

400

500

600

700

Contribution of SPEs to Total Dose Eq. (mSv) (behind 5 g/cm2 Al shielding)

RAD Mea-surements (to

date)

No

signi

fican

t SP

Es to

dat

e

Dos

e Eq

uiva

lent

(mSv

)

*SPE Dose Equivalent values modeled behind 5 g/cm2 Aluminum by M.-H. Kim, F. Cucinotta, et al. (AGU, 2012).

RAD cruise measurements from Jan-July 2012.

Nov. 60 SPE includes contributions from 2 events.

Oct. 89 SPE includes contributions from 5 events over 1 month.

Historical SPE Events (Modeled)

Longitudinal Dependence and Anisotropy of SEPs

STEREO ASTEREO B

CRaTER

ESP Event

ShockPassage

Joyce et al., 2015

Context provided by ENLIL simulations (CCMC)

• Dose rate for skin/eye and BFO for four different levels of shielding which correspond to spacesuit, heavy spacesuit, spacecraft and heavy protective shielding.

• Average background GCR dose rate measured by CRaTER during this time is also shown.• NASA 30 day dose limits for skin and eye exceeded for both levels of spacesuit shielding

and the heaviest shielding reduces the total accumulated dose by more than an order of magnitude.

• BFO limit is not exceeded for any level of shielding, though we see that heavier shielding is less effective at reducing the total dose.

BFO Limit

Skin Limit

CRaTERGCR

Carrington Event?!

The Moon as a Beam Stop: Estimating Anisotropies!

7DOY of 20146 8

Example of oscillations during 6 January 2014 event.

Consistent with previous observations of small events (e.g. Reames et al. 2001), where the anisotropy persists, as opposed to larger events where proton-generated Alfven waves scatter the particles to isotropy.

Joyce et al., 2015

First energetic particle albedo maps of Moon

Wilson, J. K., et al. , The first cosmic ray albedo proton map of the Moon, J. Geophys. Res. – Planets, 117, DOI: 10.1029/2011JE003921, 2012.

(from Wilson et al., 2012)

Possible composition dependence of albedo sources

(Wilson et al., 2013, work in progress)Wilson et al., 2015

Beam runs (HIMAC & MGH) with CRaTER EM confirm nuclear evaporation concept

Zeitlin, C., et al., Measurements of Galactic Cosmic Ray Shielding with the CRaTER Instrument, Space Weather, DOI: 10.1002/swe.20043, 2013.

2012, HIMAC beam testing

(Zeitlin et al., 2013)

2013, HIMAC beam testing

Albedo test

Regolith Simulant

“GCR” beam

CRaTEREM

Lunar“albedo”

Beam runs with CRaTER and Simulations confirm nuclear evaporation concept

Suppression of Radiation Albedo from H-rich material

Suppression of albedo

Geant Simulations by Mark Looper

Search for Compositional

Gradients due to Proton Albedo

• Plots and linear fits of albedo proton yield from CRaTER versus elemental abundance derived from the Lunar Prospector Gamma Ray Spectrometer and Neutron Spectrometer, and binned by 30°.

• High-yield spots A and B and low-yield spots C, D and E are single pixels at this resolution and are labeled. The plots are as follows:

• (a) iron, which is enhanced throughout all of the lunar maria;

• (b) titanium, which is relatively efficient at absorbing neutrons and which is most abundant in northern Mare Tranquilitatus;

• (c) potassium, which is representative of the elements in KREEP material (“K, Rare Earth Elements, and Potassium”) that are most abundant in Mare Vaporum.

The five named spots are not exceptional locations in terms of elemental abundances. Although we do see a statistically significant difference in proton yields from the maria and highlands, elemental abundances in the regolith do not explain the entire trend.

Iron

Titanium

Potassium

Investigations of chemical alteration of regolith by energetic particles and cosmic rays

• Schwadron, N. A., et al., Lunar radiation environment and space weathering from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER), J. Geophys. Res. – Planets, 117, DOI: 10.1029/2011JE003978, 2012.

• Jordan, A. P, et al., The formation of molecular hydrogen from water ice in the lunar regolith by energetic charged particles, J. Geophys. Res. – Planets, DOI:10.1002/jgre.20095, 2013.

(Jordan et al., 2013)(Schwadron et al., 2012)

H2O H2 + O

Observed amount of H2 wrt H2O molecules in LCROSS impact: 8% (+10%/-4%)

After 1 billion years, GCR and SEP radiolysis likely accounts for 10-100% of observed H2

Published investigation on deep dielectric charging by energetic particles and cosmic rays

Understanding of Radiation Driving New Data Products

Rate of SEP events that may cause regolith breakdown

We expect regolith in lunar PSRs to have lower albedo in colder regions.

How does breakdown weathering compare to meteorite weathering?

Weathering process Energy Flux [m-2 yr-1] Breakdown vapor/melt

production [kg m-2 yr-1]Meteoroid

impacts 12 1.8 x 10-7

SEP breakdown 0.27 5.5 x 10-8

Breakdown weathering may be comparable to meteoritic weathering in PSRs

Instrument Observation of PSR regolithLCROSS Increased porosity in Cabeus (Schultz et al., 2010)LRO/LAMP Darker plane albedo / increased porosity

(Gladstone et al., 2012)LRO/LOLA Brighter normal albedo (Lucey et al., 2014)

PSR observations suggest “an environmental control on these [optical]

properties”(Lucey et al., 2014)

Breakdown weathering, which would preferentially occur in PSRs, may help explain

these properties by enhancing vapor deposition and by melting and fracturing the regolith

LRO/CRaTER Summary

• Deepest Solar Minimum and Weakest Maximum more than 80 years– Increased GCR radiation intensity in solar minima– Lower probability of SEP events Enabler for launching missions

near solar maxima

• Radiation Effects on the Moon– Chemical modification of Lunar Regolith– Deep dielectric charging grain fragmentation in PSRs

and changes in regolith porosity• Development of new LRO derived mapping

products and Understanding of SEPs