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Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos...

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Schedule Remember: Papers are due November 4
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Page 1: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Schedule• Remember: Papers are due November

4

Page 2: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Regolith • Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock material that nearly everywhere overlies bedrock.

• This includes the soil of the Earth.

• On rocky objects, particularly asteroids and moons, what you see on the surface is regolith.

Page 3: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Almost all Solid Objects Have Regolith

• Asteroids are essentially all regolith or mega-regolith– Most are likely rubble piles– Some may include accreted

fragments from impactors (example Almahata Sitta)

– Only very rapidly spinning asteroids may be regolith-free

• Mars • Moon• Mercury• Earth

Page 4: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

• During the early phases of the Apollo Moon landing program, Tommy Gold of Cornell raised a concern that the dust layer at the top of the regolith would be very thick (10’s of meters), low density, and fluffy.

• The worry was that the lunar landing module (with the astronauts) would sink beneath the surface.

• This caused NASA to fly the a lunar robotic lander program (Surveyor), at a cost ~ $3 billion, before Apollo.

Page 5: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

The Lunar Regolith• We know the most about the Moon, so

lets start there.• Impacts at all scales form and alter the

regolith.• Micrometeorites form a fine (<1mm) soil)• Basin-forming impacts excavate a

colossal amount of material….this is what forms the surface units of the Moon and other planets.– Take the Imbrian basin

• 1200 km in diameter• Ejecta was up to 400 meters thick 600 km from ring

edge.• Fractured the crust down to ~25 km

– With smaller bodies, a single major impact can resurface the entire object (i.e. Vesta)

Page 6: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Terms• Regolith “Soil”: The upper layer of regolith.

– Fine particles, very loose, very fluffy, created by micrometeorite bombardment.

– About 20 cm deep– Density about 0.9-1.1 g/cm3. Increases with

depth to about 1.9 g/cm3. Porosity about 45%.– The regolith becomes progressively more

compacted with depth.

• Depth of regolith varies with the age of the surface– On the moon Mare has about 4-5 meters,

Highlands about 10 meters– Overturn is very slow, 7 cm of overturn can

take 109 years.

• Megaregolith: Deep shattered layer – The rubble from basin and heavy

bombardment ejecta. About 2 km deep in highlands

– Structurally disturbed and displaced crust. Between 2~10 km deep.

– Bedrock fracturing from the impacts. About 25 km deep.

Page 7: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.
Page 8: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Lunar Soils• Accumulate at a rate of ~1.5

mm/million years

• Dominated by <1 mm particles

• Mean particle size between 40 to 130 μm

• Average particle size of ~65 to 70 μm

• Grain density of 3.1 g/cm3

• Bulk density ranges from 1.45 to 1.79 g/cm3, depending on depth

Page 9: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Regolith Processes: Comminution • Comminution: breaking

of rocks and minerals into smaller particles – Impacts at all scales

grind down particle size.– Major impacts produce

ejecta blocks – Micrometeorites grind

down gravel and blocks to dust (remember they impact with an order of magnitude more force than a bullet)

Page 10: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Regolith Processes: Agglutination• Agglutination: welding of mineral and

rock fragments together by micrometeorite-impact-produced glass.

• High-velocity impacts produce enough heating in Lunar soils to melt material and weld fragments.

• This process is limited to the Moon (and probably Mercury) since impact speeds need to be ~10 km/s

• Agglutinates are NOT found in meteorites….. Average impact velocities in the asteroid belt are ~ 5 km/s. Too low to produce melting and agglutinates.

Page 11: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Regolith Processes: Agglutination

• Agglutination works against comminution since it joins small particles to form bigger particles.

• This is why Tommy Gold was proved to be wrong…..

Page 12: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Impact Gardening

• Ejecta is excavated by the impacts and spread over the surface, adding to the regolith.

• This process mixes the upper layers of the regolith, depositing fresh material on the surface.

• With impact basins, the gardening can be huge…..

Page 13: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Regolith Processes: Comminution • For asteroids

comminution has an additional twist– Low gravity– Low escape velocity

• As asteroids get smaller– Low gravity allows

progressively larger ejecta debris to escape

– Smaller asteroids should have courser regoith soil

Eros

Itokawa

6 meters

Page 14: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Regolith Processes: Solar Wind Effects

• Spallation: formation of elements as a result of cosmic ray impacts that cause protons and neutrons to spall off.

• Implantation: See next slide

• Vaporization: See next slide

• Sputtering: atoms are ejected from a solid target material due to bombardment of the target by energetic particles. The sputtered atoms mostly recondense on grain surfaces.

• Charging: Solar ultraviolet and X-ray radiation are energetic enough to knock electrons out of the lunar soil. Positive charges build up until the tiniest particles of lunar dust are repelled and lofted anywhere from m’s to km’s high. Eventually they fall back toward the surface where the process is repeated. On the night side, the dust is negatively charged by electrons in the solar wind.

Page 15: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Regolith Processes: Solar Wind Implantation and Vaporization

• The elements making up the solar wind are implanted onto the surfaces and shallow interiors of the regolith.

– The wind is mostly H and He, so these dominate

• The buildup of solar wind H can change the chemistry of the regolith, creating reducing conditions.

• When the regolith is briefly heated by impacts, the implanted H drives reduction reactions.

– Iron-rich silicates (olivine and pyroxene) are converted to reduced iron and iron-poor ensitite.

– This produces particles of submicron Fe which when suspended in agglutinate glass is a powerful reddening agent.

• Vaporization: Low-temperature phases can be vaporized during impact and will recondense on surfaces

Page 16: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Space Weathering• This term covers the alterations suffered by solid

materials when exposed to the space environment.– Crystal damage and spallation from cosmic rays– Irradiation, implantation, and sputtering from solar wind

particles– Bombardment and vaporization by different sizes of

meteorites and micrometeorites.– Or almost any regolith process…..

• The effects of space weathering depend on the chemistry of the target material. For lunar materials and ordinary chondrites, one effect is to darken the material and reddening the spectra.

Page 17: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

PSRD http://www.psrd.hawaii.edu/Aug09/solarwind.helium.html

presents

Space Weathering Agent: Solar Wind Space Weathering Agent: Solar Wind

• Bombardment of helium ions on olivine under vacuum conditions in the lab simulates space weathering of asteroids and other airless bodies.

• The observed effects are:– reddening of the spectral slope– slight darkening of the olivine– attenuation of the 1 μm

absorption band– formation of metallic iron in the

outer layer of the mineral surface in powder and flat slab

Page 18: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

PSRD http://www.psrd.hawaii.edu/Aug09/solarwind.helium.html

presents

Space Weathering Agent: Solar Wind Space Weathering Agent: Solar Wind

The more we understand the processes and timescales of space weathering, the better we can:

• Interpret reflectance spectra of the surfaces of airless planetary bodies

• Compare spectra of meteorites to spectra of asteroids, to determine meteorite parent bodies

Page 19: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Our “Type Section” for Space Weathering has been the Moon

• Lunar weathering generates nano-phase Fe (amongst other things) on the grain surfaces and in glassy rims.

• This is EXTREMELY optically active and produces the characteristic lunar “red slope” in the visible and near-IR spectra.

• Another effect is the darkening of the reflectance and attenuation of the absorption bands.

Page 20: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

• But it is not just the Moon that is exposed to this environment.

• Space weathering can be viewed as the response to energetic inputs that drive the surface composition away from equilibrium. – The result are chemical reactions

and evolution that can be understood from underlying thermodynamic driving forces.

Try a little forward modeling

Page 21: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Look at the Chemistry….• By using techniques and insights developed in

materials science and physics we can: – Assess the environment of the common asteroidal and

planetary materials– Forward model the weathering reactions– Make testable predictions about processes and

products.

• Start with the idea that key weathering reactions are driven by: – The chemical environment of space (hard vacuum, low

fO2, solar wind H, sputtering) – Thermal energy supplied by micrometeorite impacts.– Follow the chemical products……

Page 22: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Take Olivine• Turns out that the

thermodynamics of olivine make it very susceptible to weathering.

• In a reducing environment when you add energy (heat) olivines lose oxygen and metallic cations (producing nano-phase Fe)– The mineral becomes more

disordered and less optically active. – At the same time, the weathering

product (npFe0) creates a powerful optical component (i.e. lunar red slope).

Page 23: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

We have done a few experiments

• Olivine weathering has been simulated a number of ways.– Most commonly with laser

zapping.

• We did this by changing the chemistry and the kinetics (reducing environment and warming things up)

• The result is lunar-like spectra

From T. Kohout et al., Icarus 2014

Page 24: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

But this is just a start….

• Turns out that surfaces with exposed npFe0 are an ideal environment for catalyzing further reactions.

• Mineral decompostion (and the production of catalitic materials) can be thought of as the first stage of space weathering.

• The problem on the Moon is that there is nothing much to catalyze.

From T. Kohout et al., Icarus 2014

Page 25: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

But what if you do have something else to react with?

• The second stage of weathering depends upon the presence of “feedstock” components that can participate in catalyzed chemical reactions on exposed surfaces.

• On Volatile-rich Asteroids…..– Reactive surfaces use the volatiles

coming out of frost-line small bodies as the feed-stock (CO, H20, NH3) for catalytic reactions (for example: Fischer-Tropsch Type (FTT)).

Page 26: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Fischer-Tropsch Reactions?• Developed in Germany in the 1920s, this is

a catalytic technology to convert hydrogen and CO into liquid hydrocarbons.

– The process has widespread industrial applications, particular in the generation of liquid fuels from coal or gas.

• (2n + 1) H2 + n CO CnH(2n+2) + n H2O

• Can use iron, cobalt, and ruthenium as catalysts.

• Varying pressure and temperature varies the reaction outputs, typically long-chained alkanes.

• BUT, if NH3 is in the feedstock FTT can produce amino acids.

Page 27: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Weathering on Volatile-rich Carbonaceous Asteroids

• Fischer-Tropsch Type (FTT) reactions using the heat supplied by micrometeorite bombardment would “weather” volatile-rich surfaces, producing…..– Long-chain hydrocarbons, polyaromatic

hydrocarbons, amino acids, various complex organics.

– “Maturity” in this case probably relates to the abundance and variety of organics.

• Space weathering on volatile-rich asteroids produces organics…– Which is what we see in CI and CM

carbonaceous chondrites.

Page 28: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

How does the “weathered” surface survive?

• This is a surface effect…..how can we end up with this stuff as part of the interior of a meteorite and survive atmospheric entry?

• Remember that asteroids are mostly (almost all) rubble piles. – They go thru cycles of disruption and reaccretion.– Impact ejecta buries surface material.– The stratigraphy gets inverted all the time.

• For example, about 12% of OC falls have solar wind implanted gases. They are samples of the regolith.

Page 29: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

A few examples

Tysnes Island (H4)

Mifflin (L5)

Fayetteville (H4~6)

Page 30: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Conclusions: A Theory of Space Weathering

• The basic scheme can be applied to ANY airless body– Thermodynamics and mineral kinetics are the drivers.– Outputs depend on the chemistry of the available inputs.– Decomposition of common rock-forming minerals can create

strongly catalytic regoliths.

• The range of weathering products are not random, but the predictable (and testable) outcome of the source’s mineral kinetics and chemical feedstock.

• Weathering products do not have to be optically active.– Probably most weathering products are spectrally neutral or

even suppress an object’s reflectance spectrum because decomposition makes the minerals more disordered.

Page 31: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Conclusions: Volatile-Rich Asteroids

• For volatile-rich asteroids, major weathering products include a range of carbon-rich compounds– Weathering in the presence of catalysts transforms

“feedstock” materials into a range of products including long-chain organics and amino acids.

• The generation of pre-biotic compounds are probably a routine and predictable by-product of common space weathering processes.– The precursors of life are probably abundant in any space-

weathered asteroid belt, in any solar system, and only wait being accreted to a hospitable environment.

Page 32: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Asteroid, Meteor, MeteoriteAsteroid, Meteor, Meteorite

http://www.psrd.hawaii.edu/April10/AlmahataSitta.html

In the early morning of October 6, 2008 an asteroid close to Earth was detected by a Catalina Sky Survey (CSS) telescope at Mount Lemmon, Arizona. It entered and broke up in Earth's atmosphere 19 hours later leaving behind a luminous train of clouds in the sky and meteorites on the desert floor.

CSS telescope discovery images

of asteroid TC3

Train station sign in the Nubian Desert

Page 33: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Asteroid, Meteor, MeteoriteAsteroid, Meteor, Meteorite

http://www.psrd.hawaii.edu/April10/AlmahataSitta.html

280 meteorite fragments (weighing 3.95 kilograms) have been found.

Almahata Sitta is an anomalous polymict ureilite: A spectacular mixture of lithologies giving new clues to the mineralogy, density, thermal history, magnetism, and geologic evolution of its parent body.

Page 34: Schedule Remember: Papers are due November 4. Regolith Regolith: Greek rhegos (blanket) + lithos (stone) the mantle of fragmental and unconsolidated rock.

Asteroid, Meteor, MeteoriteAsteroid, Meteor, Meteorite

http://www.psrd.hawaii.edu/April10/AlmahataSitta.html


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