NEEP 533 Lecture #12

NEEP533 Course Notes (Spring 1999)
Resources from Space

Lecture #12: The End of Lunar Evolution and New Info!

Title: Maturity after Three Billion Years

Stage Seven: The Mature Surface - 3.0(?) to present. Formation of rayed impact craters and the regolith continued in all regions and included the implantation of solar wind gases in the regolith materials.

Changes to Major Lunar Features: Mature Surface Stage

Rayed crater formation and degradation

Stage characterized by continued impact activity, but by the absence of impact events that could form craters more than about 200 km in diameter. Significantly larger impact basins have formed on the Earth during this same period.
Copernicus,a typical rayed crater about 1 b.y. old

Rayed Craters as a Window into the Crust: The improvements in remote sensing techniques using earth-based telescopes and Clementine multispectral photographs have greatly improved our understanding of the rock units exposed in and around rayed craters such as Copernicus, Tycho, and Aristarchus.

		Clementine visual mosaic of the 93 km diameter crater Copernicus.

		Clementine false color image of the eastern half of Copernicus with a visual mirror image of the same half, showing yellow-green iron-rich materials on the southern rim and wall and reddish anorthositic norite on the north floor and wall (from 20-30km depth, the deepest level of excavation) and light colored olivine-bearing rocks in the central peak (rebound emplacement from depths >20-30km) (Pieters, et al, 1994).

		Clementine images of the 85 km crater Tycho showing, from right to left, enhancement in the blue, false color, and a ratio image to show iron and magnesium-rich (gabbroic/basaltic) materials in the central peak (rebound emplacement from depths >20-30 km) (Pieters, et al, 1994).

The detection of non-crustal material in Copernicus and Tycho suggest the presence of "splash intrusions" in the crust, as postulated in the discussion of Stage One in lecture 10, and their variety due to in situ crystal differentiation like that of similar rocks in the Apollo samples, suggest that these intrusions have undergone extensive in situ mineral differentiation during crystallization.

Interesting Issue: Why does the farside of the Moon have about twice as many rayed craters under 10 km in diameter than predicted by crater counts on the nearside (Moore, J.M., and McEwen, A.S., 1996, as reported in Science News, v 149, 235).

SUMMARY

RAYED CRATERS

WINDOW INTO THE CRUST

SPLASH INTRUSIONS REVEALED!

IRREGULAR DISTRIBUTION OF MATERIALS FOR UP TO 1000S OF KILOMETERS

TYCHO RAY OVER APOLLO 17 SITE

CONTRIBUTE TO DEVELOPMENT OF REGOLITH

Regolith: Regolith constitutes the most important material with respect resources on the Moon. It covers most of the surfaces of the Moon and is the most logical material to process for volatiles, metals, non-metals, and aggregate.

Regolith "...is a terrestrial term, also used for the Moon. It has been defined as 'a general term for the layer or mantle of fragmental and unconsolidated rock material, whether residual or transported and of highly varied character, that nearly everywhere forms the surface of the land and overlies or covers bedrock. It includes rock debris of all kinds, including volcanic ash .. '... lunar regolith consists of particles <1 cm in size although larger cobbles and boulders, some as much as several meters across, are commonly found at the surface....much of the pulverized material is melted and welded together to produce breccias (fragmental rocks) and impact melt rocks, which make up a significant portion of the regolith ..." (Heiken, et al, 1991)

Shoemaker, et al., 1968, is a particularly important reference in regard to characterization of the lunar regolith.

A particularly important part of the lunar regolith consists of aggregates of rock, mineral, and glass fragments, held together by impact melt glass, called agglutinates. Further, the lunar regolith contains adsorbed solar wind gases, meteoritic material, and the products of solar and cosmic radiation.

Lateral mixing of the regolith derived from various bedrock materials is a function of the age of the separating contact.

Lateral mixing between the Apollo 17 light mantle material (109 m.y) and older mare is on the order of 10s of meters.
Lateral Mixing between mare basalts (3-4 b.y.) and older highlands is on the order of 100s of kilometers (Fischer and Pieters, 1995)

Pit bottomed crater in the regolith.

Normal regolith exposed in shallow trench

Incompletely mixed regolith units.

Mass wasting

Movement of regolith down slope,triggered by impacts, gravitationally mobilized, and possibly lubricated and buoyed by solar wind volatiles released through particle interaction during motion.

Taurus-Littrow Mare from 60 nm.

The plume-like landslide from the South Massif, Valley of Taurus-Littrow, shown above, was probably caused by the impact of ray-forming material from the Tycho cratering event, ~2000 km to the southwest.

SUMMARY

REGOLITH (mantle of fragmental, unconsolidated material overlying bedrock)

AVERAGES ~10M DEEP ON 3.8 BY OLD SURFACES

CONSTITUENTS:

ROCK FRAGMENTS

AGGLUTINATES (IMPACT GLASS WELDING ROCK AND MINERAL FRAGMENTS)

MINERAL FRAGMENTS

VOLCANIC GLASS SPHERES AND FRAGMENTS

METEORITIC CONTAMINATION (<2%)

ADSORBED SOLAR WIND VOLATILES (H2 AND HE)

PRODUCTS OF SOLAR AND COSMIC RADIATION

LATERAL MIXING RATE

ON THE ORDER OF 10S OF METERS PER 100 MY

~100 KILOMETERS PER BILLION YEARS

VERTICAL MIXING IRREGULAR

3M DRILL CORES INDICATE NO SIGNIFICANT CHANGE WITH DEPTH

EARLY RESOURCE BASE

CONSUMABLES

POWER

METALS

SOLAR CELLS

GEOTECHNICAL PARAMETERS

DENSITY ~1.9 GM/CM3

HIGH BEARING STRENGTH

MODERATE COHESION

>60% PARTICLES <100m

HIGHLY ABRASIVE

DISSEMINATED, FINE GRAIN NATIVE IRON

HIGHLY REDUCING (HYDROGEN)

The light colored swirls

Major Issue: What created the light-colored swirls that have formed on, and probably in, the regolith, particularly in regions east of Smythii.

Alterations of the regolith due to the impact of cometary material.

Alterations of the regolith due to out-gassing of the deep interior of the Moon, possibly the relatively undifferentiated lower mantle (below ~500 km).

There are some suggestions that the largest areas of swirls are antipodal to young large basins, such as Orientale for those east of Smythii.

Field of light colored swirls east of Smythii

Overhead view of zoned swirl east of Smythii

SUMMARY

LIGHT COLORED SWIRLS

ALTERATIONS OF THE REGOLITH

COMETARY MATERIAL ?

OUT-GASSING OF THE DEEP INTERIOR (HYDROGEN) ?

SHOCK INDUCED (ANTIPODAL TO YOUNG LARGE BASINS (ORIENTALE-REGION EAST OF SMYTHII)

LOCAL CONCENTRATION OF SOLAR WIND FLUX (REMANENT MAGNETIC FIELDS)

The possibility of polar ice.

Major Issue: Has cometary ice been deposited in the permanently shadowed regions of the South Pole during this final stage of lunar evolution?

More than 15,000 sq. km. of area has been shown by Clementine to be in presently in permanent shadow in the present phase of precession of the lunar pole (Shoemaker, et al, 1994, in Nozette, et al, 1994)
Theory predicts that 20 to 50 percent of any water and other volatiles released on the lunar surface by cometary impacts (or lunar out-gassing) would be precipitated in these very cold shadowed areas (Watson, et al., 1961, Arnold, 1979).
Limited data from a bi-static radar experiment is consistent with but not conclusive of ice being present in this region (Nozette, et al, 1996)
- Radar mapping of the South Polar region from Earth suggests that very rough surfaces are responsible for the ice-like returns from the Clementine data (Stacy, et al, 1997)

Lunar Prospector Mission
The Lunar Prospector Mission includes a neutron spectrometer (Feldman, et al, 1998) that measures the orbital flux of neutrons produce by the interaction of lunar surface materials and cosmic rays. Low energy thermal neutrons are absorbed by the nuclei of Fe, Ti, K, Gd, and Sm. High energy "fast neutrons" are produced by cosmic ray interaction with Fe and Ti nuclei. Intermediate energy "epithermal neutrons" are absorbed by interaction with hydrogen nuclei (protons).
Of immediate interest is the data displayed graphically in the following figure (Feldman, et al, 1998) :

This figure shows the averages and standard deviations of all epithermal counts and illustrates the pronounced reduction in counts over the poles with the adsorption about twice as great at the north pole as the south.

The data in this picture has been interpreted by the Lunar Prospector Team as indicating the presence of water at the poles. Such an interpretation is obviously premature as the measurement is of hydrogen, not water. Even though the theory that a significant amount of any released cometary water would be deposited in the permanently shadowed cold trap at the poles, the hydrogen we know is present in lunar soils is embedded solar wind hydrogen.

Apollo samples examined in the laboratory contained up to 150 ppm hydrogen which is 5-10 times less than that reported by Lunar Prospector Team. Solar wind hydrogen and other solar wind volatiles, both primary and re-accelerated after thermal release elsewhere on the Moon, also may be preferentially retained in cold traps at poles (about -230^o C versus a maximum of 123^o C at the equator for a maximum differential of 253^oC). In addition, no special care was taken to prevent the loss of hydrogen from lunar samples during handling in the long path from collection, through transport back to Earth and the Lunar Receiving Laboratory, through many splits before distribution to principle investigators, and finally in the initial laboratory handling. Some investigators (Carrier, et al, 1972) have reported hydrogen loss during mechanical handling of regolith samples and strong evidence exists for hydrogen fluidization of a regolith avalanche in the Valley of Taurus-Littrow (Schmitt, 1991). On the other hand, as the atoms are actually embedded in the mineral and glass grains, it would be surprising if the actual hydrogen content of a given sample was more than a factor of 2 greater than that measured.

Several issues need to be investigated before the possibility of increased polar concentrations of solar wind hydrogen can be fully assessed. They include:
- Another issue yet to be addressed relative to the possibility of water ice at the poles is the longevity of any ice deposits in an environment of micrometeor impact and solar wind sputtering (protons [96%], helium ions [4%], and electrons). Regolith surfaces at the Apollo landing sites appear to be fully mixed and exposed to solar wind at a rate of about 1 cm depth per l million years, a rate for the regolith that obviously decreases with time as more and more energetic impacts are required to penetrate that already mixed.
  - In the case of exposed water ice, micrometeor impact and solar wind sputtering will erode the ice at a rate that combines loss of thermalized water and ionized hydrogen and oxygen and redeposition in other cold trap locations. How long a layer of water ice would remain in this environment has not been determined, however, a loss rate approaching 1 cm per million years would not be surprising.

The figure below (Feldman, et al, 1998) shows the global distribution of counting rates and probably reflects the distribution of solar wind hydrogen as no water has been detected in the lunar samples.

One intriguing aspect of this presentation is the apparent enhancement of hydrogen in the Cratered Highlands, both southern and farside. The Apollo 16 sample with the most retained solar wind hydrogen measured, 146 ppm, also came from the southern highlands (Heiken, et al, 1991). One area of investigation might be to examine the potential for feldspar retention of hydrogen as a Ca and/or Na cation substitution (H-feldspar) in the same way that feldspars are chemically altered at their exposed surfaces in the hydrous weathering environment on Earth.

Expanded representations of the polar absorption of epithermal neutrons (Feldman, et al, 1998) are given the the following figures:

	Orbital relations in the Earth-Moon system. Note that lunar spin axis is nearly perpendicular to ecliptic, resulting in the sun always being near the horizon at the poles.
	Mosaic of ~1500 Clementine images of the south pole of the Moon. Note relatively large area of darkness near pole. This dark region suggests that permanently shadowed zones may exist here.
	Visual and radar images of the lunar south pole. Radar image is from Arecibo Observatory and shows landscape detail in the non-sunlit areas
	Geometric relations between Earth, Moon and Clementine spacecraft. Using the onboard S-band radio, radio was beamed into the dark areas near the poles. The coherent opposition backscatter effect (CBOE) is caused by radio penetration of ice and is seen when the source (spacecraft) is aligned with the target (Moon) and receiver (Earth). This condition is called beta=0.
	Mosaic of south pole showing permanent shadow (red), and the beta=0 groundtracks for orbits 234 and 235. Note that orbit 234 tracked directly over the dark areas of the pole while orbit 235 was confined to zones containing no permanent shadow.
	Radar results (ratio of RCP/LCP) for all 4 orbits. Orbits 301 and 302 were over the north pole (very small area of permanent darkness) and orbit 235 was over the non-dark portion of the south pole (see figure above). Only orbit 234, directly over the south pole, shows the CBOE effect. The magnitude of 1 dB indicates that roughly 1 km3 of ice may exist here (= 10^9 m^3 = 1 mT). Note that the absence of any evidence of ice at the north pole by this technique in contrast to the neutron data which indicates twice as much hydrogen there.

REMEMBER WHEN CONSIDERING ICE ON THE MOON:

o Apollo sample measurements show no definitive evidence of indigenous or solar proton-induced water, although theory would predict that some small quantity of solar proton-induce water should form continuously. The work of Epstein and Taylor (1973) on Deuterium and 18O relationships indicates that no water in lunar samples other than terrestrial water contamination and solar wind hydrogen reaction with the soils.

o Steady state flux of impacts would release and cause some or all water precipitated permanently shadowed areas to be ionized and thermally accelerated to escape velocities.

o Sputtering of ice by charged particles, within the isotropic particle environment of the tail of the Earth's magnetosphere, may cause water loss unless mixing of ice and regolith is rapid enough to offer protection (Arnold, 1979).

o Radar investigations from Earth-based radio telescopes suggest that rough surfaces may have given the ice-like returns seen by the Clementine bistatic radar experiment (Stacy, et al., 1997).

SUMMARY

POLAR WATER-ICE DEPOSITS?

>6000 SQ. KM. IN PERMANENT SHADOW

-230o C

THEORY PREDICTS THAT 20-50% OF VOLATILE RELEASED WOULD PRECIPITATE IN COLD TRAPS

COMETS

VOLCANIC OUTGASSING

THERMAL RELEASE OF SOLAR WIND VOLATILES

BI-STATIC RADAR EXPERIMENT WITH CLEMENTINE

SUGGESTED WATER ICE AT SOUTH POLE

NONE AT NORTH POLE

EARTH RADAR MAPPING SUGGESTS ROUGH SURFACES RATHER THAN ICE

LUNAR PROSPECTOR NEUTRON SPECTROMETER

INTERPRETATION OF EPITHERMAL NEUTRON ADSORPTION

15% GREATER AT THE NORTH POLE AS THE SOUTH

EQUIVALENT TO ABOUT 700-1500 PPM HYDROGEN

0.6-2% WATER EITHER DISPERSED IN UPPER 50CM OF THE POLAR REGOLITH OR AS DISCRETE LAYER IN THIS DEPTH

PROSPECTOR TEAM ESTIMATES 6 BILLION TONS OF WATER ICE, UP BY 10X FROM ORIGINAL ESTIMATE

NASA AND PROSPECTOR TEAM WANT VERY MUCH FOR THIS TO BE WATER

LONGEVITY OF ICE LAYER MAY NOT BE GREAT

EROSION MAY APPROACH 1 CM/1MY

VERIFICATION

POLAR ORBITING RADAR

POLAR ORBITING ³HE SENSITIVE GAMMA-RAY SPECTROMETER

SURFACE MISSION

ALTERNATIVE EXPLANATION IS DISPERSED SOLAR WIND HYDROGEN

APOLLO 16 SAMPLES CONTAINED UP TO 150 PPM

MAY BE FACTOR OF TWO HIGHER DUE TO LOSSES DURING HANDLING

PROSPECTOR DATA SHOWS HYDROGEN CONCENTRATED IN HIGHLANDS

PREFERENTIALLY RETAINED IN CA-FELDSPAR?

COLD TRAPS WOULD ALSO HOLD OTHER VOLATILES, E.G., ³HE, AND ⁴HE

THERMAL REMOBILIZATION WOULD BE MEANS OF CONCENTRATION

253^oC DIFFERENCE BETWEEN EQUATOR AND POLES AT LUNAR NOON

FUTURE MODELING STUDIES TO ASSESS POTENTIAL OF SOLAR WIND VOLATILES AT THE POLES

SOLAR WIND PROTON FLUX

SECONDARY HYDROGEN RELEASE AT THE LUNAR SURFACE

SECONDARY HYDROGEN RE-INTRODUCTION TO THE SOLAR WIND

SECONDARY HYDROGEN TRAPPING AND RELEASE AT THE POLES

WATER ICE LONGEVITY AT THE POLES

Tidal interaction with the Earth and Sun.

The investigation of tidal rhythmites on Earth indicate that the Earth's rotation has slowed during at least the last 900 m.y., increasing the length of the day from about 18 hours to the current 24 hours and an increase in the semimajor axis of the Moon's orbit by about 10% or 34,400 km (Sonett, et al, 1996) as angular momentum has been transferred, minus losses due to tidal heating.

SUMMARY

TIDAL INTERACTION WITH THE EARTH

TIDAL RHYTHMITES (SPECIAL SEDIMENTARY ROCKS)

900 MY AGO MOON WAS 10% (34,400 KM) CLOSER

EARTH DAY WAS 18 HOURS

EVOLUTION OF THE MOON: SUMMARY

Lunar Evolution: The Apollo Model The figure summarizes what is known about the internal structure and properties of the Moon, based on a synthesis of geophysical, petrological, and geochemical data from Apollo. A schematic cross section of the Moon as it probably exists today

Space weathering. (see Clark and Johnson, l996)

Micrometeorites

Erosion of rock surfaces by ejection of impact melt, fractured rock and minerals, and vapor.

Reduction of Fe⁺² to iron in the presence of solar wind hydrogen.

Microfracturing of rock surface minerals beneath "zap" pits.

Rounding of rock edges

Gardening and maintenance of optical uniformity (high back-scatter structure) of upper millimeter or so of the regolith surface.

Creation and redistribution of a thin, irregular brownish glass patina on rock surfaces.

Heat and cold (expansion and contraction)

Apparently minor particle movement and fracture working suggested by seismic noise patterns.

Sunlight (largely UV)

Likely cause of the production of sodium atoms observed a part of the lunar "atmosphere" (Medillo, M., and Baumgardner, J., 1995)

Solar wind and solar flare ions

Hydrogen and helium ions cause sputtering of ions from exposed mineral grains while at the same time they are embedded in the grain at depths of a few tens of Angstroms.

Galactic and extragalactic cosmic rays

Human activities

	Artist's conception (Pat Rawlings) of a Lunar Base (What's wrong with this picture? No radiation protection)
	Artist's (Pat Rawlings) conception of a Lunar Base (better).

o Having been on the surface and sampled lunar materials (ground truth), we know a great deal about the Moon's resources that could support long term settlement.

o Galileo, and Clementine - and some direct as well as indirect geochemical sensing from the Earth and Apollo lunar orbits. Stand by for analysis of Lunar Prospector data.

	Figure: AS 17 152 23311 Full Moon/Full self sufficiency needed!
	Figure: AS 17 134 20509 Living on the lunar surface

Non-metallic materials required for lunar construction: o Regolith cover for insulation and radiation protection; o Road aggregate (as a by-product from mining and processing of regolith); o Dry compacted regolith fines (Desai, 1993); o Sintered or cast regolith-based structural materials; o Regolith/metal fiber composites through thermal liquefaction (Desai, 1993)

	Relatively undisturbed regolith surface.
	Moderately disturbed regolith surface.

Figure: AS17 134 20394 Aggregate-rich regolith near Powell Crater.; Figure: AS17 146 22429 Local layered structure to regolith at Van Serg Crater
Metallic materials required for lunar operations and manufacturing.

	Lunar Soil Composition
	Comparison of compositions of lunar soil and the Earth's crust

Note: The overall availability of potential resources on a planet represents a critical baseline - if its not there, forget about it. Locating economically extractable concentrations of such resources, however, constitutes the difference between a potential resource and a commodity. In the following outline, the indicated concentration (grade) of a particular resource is in relation to the concentration in its best known host.; o Cr₂O₃-0.5-1 wt% from (Fe,Mg)(Cr,Al,Ti)₂O₄ (spinel in regolith); o MgO- wt% from (Mg,Fe)₂SiO₄ (olivine)
Other useful elements: o P₂O₅-0.5 wt% in phosphate minerals in KREEP; o Na₂O-1.2 wt% and K₂O-3.6 wt% in KREEP; o Rare Earth Elements, Hf, and Zr concentrated in KREEP related materials
Indigenous volatiles


In situ orange soil at Shorty Crater	Orange soil beads in transmitted light	Large deposits of orange soil along southwestern rim of Serenitatis

o Sulfur from FeS (troilite) in basaltic regolith
Mineral concentrations possible in differentiated cooling units in the maria: o Titanium (ilmenite), chromium (chromite), iron and sulfur (native iron and troilite)

Text:

Sullivan, et al., 1991, Using Space Resources, NASA Johnson Space Center, 27p.

Questions:

1. Taking the composition of any Apollo 11 or 17 Ti-rich basalt flow, describe possible mineral enrichments and their layered sequence due to slow cooling and gravitational differentiation in an appropriately thick flow.

2. Do modern applications of rare earth elements suggest that it might be worth while to seek concentrations of such elements for use on the Moon or in Space rather than continue to depend on terrestrial sources? Explain in some detail.

3. List and provide summary descriptions of potential additives necessary to sustain lunar regolith and/or hydroponic based agriculture.

References:

Alllen, C.C., Morris, R.V., and McKay, D.S., 1996 Oxygen Extraction from Lunar Soils and Pyroclastic Glass, Journal of Geophysical Research, 101, 26,085-26,095.

Criswell, D.R., 1996, Lunar Solar Power System: Review of the technology base of an operational LSP System, 47th International Astronautical Congress, October 7-11, Beijing (IAF-96-R.2.04

Desai, C.S., et al, 1993, Development and Mechanical Properties of Structural Materials from Lunar Simulants, in Lewis, J., Matthews, M.S., and Guerrieri, M.L., 1993, Editors, Resources of Near-Earth Space, University of Arizona Press.

Haskin, L.A., et al, 1993, A Geochemical Assessment of Possible Lunar Ore Formation, in Lewis, J., Matthews, M.S., and Guerrieri, M.L., 1993, Editors, Resources of Near-Earth Space, University of Arizona Press.

Heiken, G., et al, 1991, Lunar Source Book, Cambridge University Press, Cambridge, 736p.

Lewis, J., Matthews, M.S., and Guerrieri, M.L., 1993, Editors, Resources of Near-Earth Space, University of Arizona Press.

Sullivan, et al., 1991, Using Space Resources, NASA Johnson Space Center, 27p.

Taylor and Haskin

NEEP533 Syllabus

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Lecture #12: The End of Lunar Evolution and New Info!

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Questions:

References: