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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
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
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
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
• 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
Understanding of Radiation Driving New Data Products
Rate of SEP events that may cause regolith breakdown
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