In order to find an additional quantitative way to estimate the petrographic type of unequilibrated ordinary chondrites (UOC), and one that can be used remotely in the study of asteroids, we have analyzed the near-infrared spectra of a suite of UOC observed falls. We obtained spectra from the RELAB database at Brown University and applied several methods for determining the amount of clinopyroxene (CPX) as a percentage of the total pyroxene in the meteorites. The presence of low-Ca CPX has long been known to be characteristic of little-metamorphosed ordinary chondrites. The methods we used were (1) naked-eye determination of the wavelength of the absorption features at similar to 1 mu m and similar to 2 mu m, (2) determination of the wavelengths of these features by fitting polynomial equations, and (3) determining the relative intensities of the CPX and OPX features after isolation by a curve fitting procedure. The measurements were then "calibrated" using data from the literature to obtain values for the amount of CPX in the total pyroxene. We find that there is an empirical relationship between the amount of CPX detected by these methods of spectrum analysis and the petrologic type. Petrologic type = + 4.402-0.019 x CPX% We explain this empirical relationship (1) as evidence that in pyroxene bearing rocks the spectrum of pyroxene dominates (this has been known in the 1970s), (2) that low-Ca CPX is so abundant in these meteorites (up to 40 vol%) that it is easily detected by reflectance spectroscopy, and (3) compositional effects caused by Ca and Fe in the pyroxenes partially cancel out or are small. We thus have a new method of quantitatively measuring the level of metamorphic alteration experienced by these important meteorites and of assigning them a petrologic type of 3.0 to 3.9. More importantly, unlike existing methods, this can be applied remotely so that chondritic asteroid surfaces (i.e. those of Q and S asteroids) can also be characterized in terms of their metamorphic history. As an example, (433) Eros and (25143) Itokawa were found to be types similar to 3.5 and similar to 3.4, respectively. We briefly discuss the implications of this for understanding the history of meteorites and asteroids.

It has been proposed that all L chondrites resulted from an ongoing collisional cascade of fragments that originated from the formation of the ~500 Ma old asteroid family Gefion, located near the 5:2 mean‐motion resonance with Jupiter in the middle Main Belt. If so, L chondrite pre‐atmospheric orbits should be distributed as expected for that source region. Here, we present contradictory results from the orbit and collisional history of the October 24, 2015, L6 ordinary chondrite fall at Creston, CA (here reclassified to L5/6). Creston's short 1.30 ± 0.02 AU semimajor axis orbit would imply a long dynamical evolution if it originated from the middle Main Belt. Indeed, Creston has a high cosmic ray exposure age of 40–50 Ma. However, Creston's small meteoroid size and low 4.23 ± 0.07° inclination indicate a short dynamical lifetime against collisions. This suggests, instead, that Creston originated most likely in the inner asteroid belt and was delivered via the ν6 resonance. The U‐Pb systematics of Creston apatite reveals a Pb‐Pb age of 4,497.1 ± 3.7 Ma, and an upper intercept U‐Pb age of 4,496.7 ± 5.8 Ma (2σ), circa 70 Ma after formation of CAI, as found for other L chondrites. The K‐Ar (age ~4.3 Ga) and U,Th‐He (age ~1 Ga) chronometers were not reset at ~500 Ma, while the lower intercept U‐Pb age is poorly defined as 770 ± 320 Ma. So far, the three known L chondrites that impacted on orbits with semimajor axes a <2.0 AU all have high (>3 Ga) K‐Ar ages. This argues for a source of some of our L chondrites in the inner Main Belt. Not all L chondrites originate in a continuous population of Gefion family debris stretching across the 3:1 mean‐motion resonance.

The Saricicek howardite meteorite shower consisting of 343 documented stones occurred on September 2, 2015 in Turkey and is the first documented howardite fall. Cosmogenic isotopes show that Saricicek experienced a complex cosmic-ray exposure history, exposed during 12-14Ma in a regolith near the surface of a parent asteroid, and that an 1m sized meteoroid was launched by an impact 22 +/- 2Ma ago to Earth (as did one-third of all HED meteorites). SIMS dating of zircon and baddeleyite yielded 4550.4 +/- 2.5Ma and 4553 +/- 8.8Ma crystallization ages for the basaltic magma clasts. The apatite U-Pb age of 4525 +/- 17Ma, K-Ar age of 3.9Ga, and the U,Th-He ages of 1.8 +/- 0.7 and 2.6 +/- 0.3Ga are interpreted to represent thermal metamorphic and impact-related resetting ages, respectively. Petrographic; geochemical; and O-, Cr-, and Ti-isotopic studies confirm that Saricicek belongs to the normal clan of HED meteorites. Petrographic observations and analysis of organic material indicate a small portion of carbonaceous chondrite material in the Saricicek regolith and organic contamination of the meteorite after a few days on soil. Video observations of the fall show an atmospheric entry at 17.3 +/- 0.8kms(-1) from NW; fragmentations at 37, 33, 31, and 27km altitude; and provide a pre-atmospheric orbit that is the first dynamical link between the normal HED meteorite clan and the inner Main Belt. Spectral data indicate the similarity of Saricicek with the Vesta asteroid family (V-class) spectra, a group of asteroids stretching to delivery resonances, which includes (4) Vesta. Dynamical modeling of meteoroid delivery to Earth shows that the complete disruption of a 1km sized Vesta family asteroid or a 10km sized impact crater on Vesta is required to provide sufficient meteoroids 4m in size to account for the influx of meteorites from this HED clan. The 16.7km diameter Antionia impact crater on Vesta was formed on terrain of the same age as given by the He-4 retention age of Saricicek. Lunar scaling for crater production to crater counts of its ejecta blanket show it was formed 22Ma ago.

Research is being conducted to understand the behavior of asteroids entering the atmosphere in order to help quantify their impact hazard. The strength of the body plays a critical role in determining the outcome of their impact events and is needed for many asteroid mitigation options. Meteorites are the physical material we have here to understand the larger parent body. Our objective is to scale flaw parameters in meteorites to their parent body, and therefore providing a way to scale strength from the smaller meteorites to the larger asteroids.

Meteorites, and their fall to Earth, have the potential to inform studies of the asteroid impact hazard and of impact mitigation. We describe six ways in which they have relevance to understanding the behavior of meteoroids in the atmosphere and thus impact mitigation. (1) Hundreds of meteorite falls have been described in the literature. While eyewitness observations are subjective, at their core there is unique information on which to build and test numerical models of an asteroid’s behavior as it passes through the atmosphere. (2) For 19 recovered meteorites, film or video recordings have been obtained and for most of these light curves have been derived which provide quantitative information on meteorite fall and fragmentation. (3) There are 188 known meteorite craters on Earth and in 10 cases fragments of the meteorite responsible have been recovered. In these cases numerical impact models can utilize the known properties of the projectile and the dimensions of the crater. (4) Studies of the meteorites provide information on their preatmospheric size, internal structure and physical properties (tensile strength, density, porosity, thermal conductivity etc.) which are essential for understanding the behavior of objects coming through the atmosphere. (5) The flow patterns on the fusion crust of the meteorite, and the shape of the recovered meteorite, provides information on orientation and physical behavior during flight. Petrographic changes under the fusion crust provide information on thermal history during the latter stages of flight. (6) The structure and composition of the so-called “gas-rich regolith breccias” provide information on the outermost layer of the parent asteroid from which the meteorites came. This information is critical to certain mitigation strategies. We conclude by describing initiatives for hazardous asteroid impact mitigation at Ames Research Center and Lawrence Livermore National Laboratory that will exploit and disseminate the information available from meteorites. This includes characterization of the meteorites likely to be analogous of incoming asteroids and the development of a website to advise the world-wide community of information available.

We have obtained near-infrared spectra for near-Earth asteroids (NEA) and Main Belt asteroids by using NASA's Infrared Telescope Facility. Most of the S complex classes of the Tholen-Bus-DeMeo scheme and the S(I)-S(VII) classes are represented. To help interpret the results, we examined visible/near-IR spectra for ordinary chondrites. The unequilibrated ordinary chondrites (UOC) spectra contain a 2.3 mu m feature which is absent in the spectra of the equilibrated ordinary chondrites (EOC). On the basis of literature data and new spectra low-Ca clinopyroxenes, we suggest that the 2.3 mu m in UOC is due to the presence of low-Ca clinopyroxene in the UOC which is absent in EOC. While this difference can be seen in the raw spectra, we confirmed this observation using a modified Gaussian model (MGM) for spectral analysis. Both the UOC and the EOC plot in the S(IV) field of the band area ratio plot for asteroids. We suggest that many or most S(IV) asteroids have material resembling UOC on their surfaces. An internally heated ordinary chondrite parent object would have EOC material at depth and UOC material on the surface. Cosmic ray exposure ages, and K-Ar ages for L chondrites, indicate that most EOC came from relatively few objects; however, the age distributions for UOC are unlike those of EOC. We suggest that while EOC come from the interiors of a limited number of S(IV) asteroids, the UOC come from the surfaces of a large number of S(IV) asteroids.

In order to gain further insight into their surface compositions and relationships with meteorites, we have obtained spectra for 17 C and X complex asteroids using NASA's Infrared Telescope Facility and SpeX infrared spectrometer. We augment these spectra with data in the visible region taken from the on-line databases. Only one of the 17 asteroids showed the three features usually associated with water, the UV slope, a 0.7 mu m feature and a 3 mu m feature, while five show no evidence for water and 11 had one or two of these features. According to DeMeo et al. (2009), whose asteroid classification scheme we use here, 88% of the variance in asteroid spectra is explained by continuum slope so that asteroids can also be characterized by the slopes of their continua. We thus plot the slope of the continuum between 1.8 and 2.5 mu m against slope between 1.0 and 1.75 mu m, the break at similar to 1.8 mu m chosen since phyllosilicates show numerous water-related features beyond this wavelength. On such plots, the C complex fields match those of phyllosilicates kaolinite and montmorillonite that have been heated to about 700 degrees C, while the X complex fields match the fields for phyllosilicates montmorillonite and serpentine that have been similarly heated. We thus suggest that the surface of the C complex asteroids consist of decomposition products of kaolinite or montmorillonite while for the X complex we suggest that surfaces consist of decomposition products of montmorillonite or serpentine. On the basis of overlapping in fields on the continuum plots we suggest that the CI chondrites are linked with the Cgh asteroids, individual CV and CR chondrites are linked with Xc asteroids, a CK chondrite is linked with the Ch or Cgh asteroids, a number of unusual CI/CM meteorites are linked with C asteroids, and the CM chondrites are linked with the Xk asteroids. The associations are in reasonable agreement with chondrite mineralogy and albedo data. (C) 2011 Elsevier Inc. All rights reserved.

To understand the nature of C asteroid surfaces, which are often related to phyllosilicates and C chondrites, we report near-infrared spectra for a suite of phyllosilicates, heated to 100-1100 degrees C in 100 degrees C intervals, and compare the results for telescope IRTF spectra for 11 C asteroids. As C asteroids have relatively featureless spectra, we focus on "continuum plots" (1.0-1.75 mu m slope against 1.8-2.5 mu m slope). We compare the continuum plots of the 11 C asteroids and our heated phyllosilicates with literature data for C chondrites. The CI, CR, CK, and CV chondrite meteorites plot in the C asteroid field, whereas CM chondrites plot in a close but discrete field. All are well separated from the large phyllosilicate field. Heating kaolinite and montmorillonite to >= 700 degrees C moves their continua slopes into the C asteroid field, whereas chlorite and serpentine slopes move into the CM chondrite field. Water losses during heating are generally 10-15 wt% and were associated with a 20-70% albedo drop. Our data are consistent with surfaces of the C asteroids consisting of the dehydration products of montmorillonite whereas the CM chondrites are the dehydration products of serpentine and chlorite. The presence of opaque minerals and evaporites does not provide quantitative explanations for the difference in continua slopes of the phyllosilicates and C asteroids. The CM chondrites can also be linked to the C asteroids by heating. We suggest that the CM chondrites are interior samples, and the presence of a 3 mu m feature in C asteroid spectra also indicates the excavation of material.

During 2015, a unique launch opportunity exists that allows for a New-Frontiers-class mission to discover a compositional gradient of small bodies in our solar system. The proposed seven year mission includes a flyby of main belt asteroid (108144) 2001 HM1, a flyby and impactor release (a la Deep Impact) at the Trojan asteroid (624) Hektor (a suspected contact binary) with companion P/2006, and a flyby with impactor release at the Centaur asteroid 39P/Oterma. The variety of types and positions of these small bodies will help answer some of the fundamental questions we have for the evolution and composition of our solar system. The Jet Propulsion Laboratory (JPL) Planetary Science Summer School team has designed a mission designed to address all of these scientific questions and design objectives. We will describe instrument selection, launch dates and mission timetables, measurement and encounter strategies, impactor design and benefits, data acquisition and communication tradeoffs and provide background into the mission science goals. Furthermore, cost estimates and a work breakdown will be provided to prove the practicality 978-1-4244-2622-5/09/$25.00 copy2009 IEEE. IEEEAC paper #1634, Version 2, Updated Jan 7, 2009 of meeting all the science objectives within a short period of time. A strategy for the development of our system based upon previously used instruments and hardware will also be presented.

We have studied the sublimation of ice and water vapor transport through various thicknesses of clay (<63 μm grain size). We experimentally demonstrate that both adsorption and diffusion strongly affect the transport of water, and that the processes of diffusion and adsorption can be separately quantified once the system comes to a steady state. At shallow depths of clay, water vapor transport is determined by diffusion through both the atmosphere and the clay layer, whereas at greater depth the rate of sublimation of the ice is governed only by diffusion through the clay. Using two different models, we determine the diffusion coefficient for water vapor through unconsolidated clay layer to be 1.08±0.04×10−4 and 1.29±0.06×10−4m2s−1. We also determined the adsorption isotherms for the clay layer, which follow the Langmuir theory at low water vapor pressure (<100 Pa, where a monolayer of water molecules forms on the surface of the clay) and the BET theory at higher pressure (where multiple water layers form). From our analysis of both types of isotherms we determined the adsorption constants to be α=4.9±1.0×10−2Pa−1 and c=30±10, respectively, and specific surface areas of 1.10±0.2×105 and 9.0±0.7×104m2kg−1, respectively. Finally, we report a theoretical kinetic model for the simultaneous diffusion and adsorption from which we determine adsorption kinetic constants according to the Langmuir theory of ka=2.5±0.5×10−4s−1 and kd=8.7±3.6×10−5s−1. If the martian regolith possesses diffusive properties similar to those of the unconsolidated montmorillonite soil we investigated here, it would not represent a significant barrier to the sublimation of subsurface ice. However, at the low subsurface temperatures of high latitude (180 K on average), ice could survive from the last glaciation period (about 300 to 400,000 years ago). Higher subsurface temperatures in the equatorial regions would prevent long-timescale survival of ice in the shallow subsurface. In agreement with previous work, we show that adsorption of water by a clay regolith could provide a significant reservoir of subsurface water and it might account for the purported diurnal cycle in the water content of the atmosphere.