Asteroid Regolith Weathering: A Large-Scale Observational Investigation

As bodies lacking an atmosphere or significant protection from solar wind particles, asteroids are subject to processes that modify the physical state and spectral properties of their regoliths. By investigating the relevant factors that contribute towards asteroid regolith modification, this work will provide crucial insight into the nature of these processes. I propose and test two major hypotheses: 1) that physical (mechanical) breakdown is caused by both meteoroid bombardment and thermal fatigue cycling, and thus regolith grain size depends on asteroid size and rotation period, and 2) changes in spectral properties (space weathering) are due to solar wind bombardment and depend on an object\u27s mineralogy, sun-distance, and surface age.I develop and validate a thermophysical modeling (TPM) approach that analyzes multiepoch (pre- and post-opposition) thermal infrared observations for asteroids without prior shape or spin information, in order to determine various thermophysical properties -- chiefly the thermal inertia. This TPM approach is applied to over 250 asteroids to determine their thermal inertia. Combining other thermal inertia datasets with mine, for a total of over 300 objects, a characteristic grain size is estimated for each object. Next, a multiple linear model is used to quantify the grain size dependence on asteroid diameter and rotation period, which are both shown to be statistically-significant model predictors. I also identify grain size differences between spectral groups { namely the M-types, which exhibit 4 times larger regolith grains, on average.Spectral data from meteorite and irradiated samples, spanning the visible and near-infrared regions, are used to develop an index to quantify the degree of space weathering. This space weathering index is applied to asteroid spectral observations and used in a multi-linear model to determine the predictor variables that increase the perceived amount of asteroid space weathering. Perihelion distance, diameter, and the average sun distance are found as statistically-significant factors in the multiple linear model. I also present evidence that regolith grains smaller than 0.5 mm enhance the extent of space weathering

Thermal decomposition as an activity driver of near-Earth asteroid (3200) Phaethon

Near-Earth asteroid (3200) Phaethon is an active asteroid with a dust tail repeatedly observed over the past decade for 3 days during each perihelion passage down to a heliocentric distance of 0.14 au. The mechanism causing the activity is still debated, and the suggested mechanisms lack clear supporting evidence. Phaethon has been identified as the likely parent body of the annual Geminid meteor shower, making it one of the few active asteroids associated with a meteoroid stream. Its low albedo and B-type reflectance spectrum indicates that Phaethon's composition is similar to carbonaceous chondrite meteorites, but a connection to a specific meteorite group is ambiguous due to the lack of diagnostic absorption features. In this study, we analyze the mid-infrared emissivity spectrum of Phaethon and find that it is closely associated with the Yamato-group (CY) of carbonaceous chondrites. The CY chondrites represent primitive carbonaceous material that experienced early aqueous alteration and subsequent late-stage thermal metamorphism. Minerals in these meteorites, some of which we identify in Phaethon's spectrum, show evidence of thermal decomposition; notably, the dehydroxylation and transformation of phyllosilicates into poorly crystalline olivine. Additionally, sulfides and carbonates in CYs are known release S2and CO2 gas upon heating to ~700oC. We show that Phaethon's surface temperature during its observed window of activity is consistent with the thermal decomposition temperatures of several components in CY meteorites. All of these lines of evidence are strong indicators that gas release from thermal decomposition reactions is responsible for Phaethon's activity. The results of this study have implications for the formation of the Geminid meteoroid stream, the origins of thermally-altered primitive meteorites, and the destruction of low-perihelion asteroids.Comment: in revie

Evidence of surface heterogeneity on active asteroid (3200) Phaethon

Thermal infrared emission and thermophysical modeling techniques are powerful tools in deciphering the surface properties of asteroids. The near-Earth asteroid (3200) Phaethon is an active asteroid with a very small perihelion distance and is likely the source of the Geminid meteor shower. Using a thermophysical model with a non-convex shape of Phaethon we interpret thermal infrared observations that span ten distinct sightings. The results yield an effective diameter of 5.4 +/- 0.1 km and independent thermal inertia estimates for each sighting. We find that the thermal inertia varies across each of these sightings in a way that is stronger than the theoretical temperature-dependent expectation from radiative heat transfer within the regolith. Thus, we test whether the variation in thermal inertia can be explained by the presence of a regolith layer over bedrock, or by a spatially heterogeneous scenario. We find that a model in which Phaethon's hemispheres have distinctly different thermophysical properties can sufficiently explain the thermal inertias determined herein. In particular, we find that a boundary is located between latitudes -30(o) and +10(o) that separates two regions: a fine-grained southern latitudes and a northern hemisphere that is dominated by coarse-grained regolith and/or a high coverage of porous boulders. We discuss the implications related to Phaethon's activity, potential association with 2005 UD, and the upcoming DESTINY+ mission.Peer reviewe

Patient-reported Experience of Diagnosis, Management, and Burden of Renal Cell Carcinomas : Results from a Global Patient Survey in 43 Countries

Funding/Support and role of the sponsor: This project was funded by equal unrestricted grants from Bristol-Myers Squibb, Ipsen Pharma, Novartis, and Pfizer according to the IKCC code of conduct governing corporate funding (ikcc.org). The sponsors were not involved in the design or analysis of the survey or approval of the final manuscript.Peer reviewedPublisher PD

Observational and Dynamical Characterization of Main-Belt Comet P/2010 R2 (La Sagra)

We present observations of comet-like main-belt object P/2010 R2 (La Sagra) obtained by Pan-STARRS 1 and the Faulkes Telescope-North on Haleakala in Hawaii, the University of Hawaii 2.2 m, Gemini-North, and Keck I telescopes on Mauna Kea, the Danish 1.54 m telescope at La Silla, and the Isaac Newton Telescope on La Palma. An antisolar dust tail is observed from August 2010 through February 2011, while a dust trail aligned with the object's orbit plane is also observed from December 2010 through August 2011. Assuming typical phase darkening behavior, P/La Sagra is seen to increase in brightness by >1 mag between August 2010 and December 2010, suggesting that dust production is ongoing over this period. These results strongly suggest that the observed activity is cometary in nature (i.e., driven by the sublimation of volatile material), and that P/La Sagra is therefore the most recent main-belt comet to be discovered. We find an approximate absolute magnitude for the nucleus of H_R=17.9+/-0.2 mag, corresponding to a nucleus radius of ~0.7 km, assuming an albedo of p=0.05. Using optical spectroscopy, we find no evidence of sublimation products (i.e., gas emission), finding an upper limit CN production rate of Q_CN<6x10^23 mol/s, from which we infer an H2O production rate of Q_H2O<10^26 mol/s. Numerical simulations indicate that P/La Sagra is dynamically stable for >100 Myr, suggesting that it is likely native to its current location and that its composition is likely representative of other objects in the same region of the main belt, though the relatively close proximity of the 13:6 mean-motion resonance with Jupiter and the (3,-2,-1) three-body mean-motion resonance with Jupiter and Saturn mean that dynamical instability on larger timescales cannot be ruled out.Comment: 23 pages, 13 figures, accepted for publication in A

Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA

Space missions and ground-based observations have shown that some asteroids are loose collections of rubble rather than solid bodies. The physical behaviour of such ‘rubble-pile’ asteroids has been traditionally described using only gravitational and frictional forces within a granular material. Cohesive forces in the form of small van der Waals forces between constituent grains have recently been predicted to be important for small rubble piles (ten kilometres across or less), and could potentially explain fast rotation rates in the small-asteroid population. The strongest evidence so far has come from an analysis of the rotational breakup of the main-belt comet P/2013 R3, although that was indirect and poorly constrained by observations. Here we report that the kilometre-sized asteroid (29075) 1950 DA is a rubble pile that is rotating faster than is allowed by gravity and friction. We find that cohesive forces are required to prevent surface mass shedding and structural failure, and that the strengths of the forces are comparable to, though somewhat less than, the forces found between the grains of lunar regolith

Mid-ocean ridge jumps associated with hotspot magmatism

Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 266 (2008): 256-270, doi:10.1016/j.epsl.2007.10.055.Hotspot-ridge interaction produces a wide range of phenomena including excess crustal thickness, geochemical anomalies, off-axis volcanic ridges and ridge relocations or jumps. Ridges are recorded to have jumped toward many hotspots including, Iceland, Discovery, Galapagos, Kerguelen and Tristan de Cuhna. The causes of ridge jumps likely involve a number of interacting processes related to hotspots. One such process is reheating of the lithosphere as magma penetrates it to feed near-axis volcanism. We study this effect by using the hybrid, finite-element code, FLAC, to simulate two-dimensional (2-D, cross-section) viscous mantle flow, elasto-plastic deformation of the lithosphere and heat transport in a ridge setting near an off-axis hotspot. Heating due to magma transport through the lithosphere is implemented within a hotspot region of fixed width. To determine the conditions necessary to initiate a ridge jump, we vary four parameters: hotspot magmatic heating rate, spreading rate, seafloor age at the location of the hotspot and ridge migration rate. Our results indicate that the hotspot magmatic heating rate required to initiate a ridge jump increases non-linearly with increasing spreading rate and seafloor age. Models predict that magmatic heating, itself, is most likely to cause jumps at slow spreading rates such as at the Mid-Atlantic Ridge on Iceland. In contrast, despite the higher magma flux at the Galapagos hotspot, magmatic heating alone is probably insufficient to induce a ridge jump at the present-day due to the intermediate ridge spreading rate of the Galapagos Spreading Center. The time required to achieve a ridge jump, for fixed or migrating ridges, is found to be on the order of 105-106 years. Simulations that incorporate ridge migration predict that after a ridge jump occurs the hotspot and ridge migrate together for time periods that increase with magma flux. Model results also suggest a mechanism for ridge reorganizations not related to hotspots such as ridge jumps in back-arc settings and ridge segment propagation along the Mid-Atlantic Ridge.Mittelstaedt, Ito and Behn were funded by NSF grant OCE03-51234 and OCE05-48672

Rare copy number variation in cerebral palsy

As per publisher: published online 22 May 2013Recent studies have established the role of rare copy number variants (CNVs) in several neurological disorders but the contribution of rare CNVs to cerebral palsy (CP) is not known. Fifty Caucasian families having children with CP were studied using two microarray designs. Potentially pathogenic, rare (<1% population frequency) CNVs were identified, and their frequency determined, by comparing the CNVs found in cases with 8329 adult controls with no known neurological disorders. Ten of the 50 cases (20%) had rare CNVs of potential relevance to CP; there were a total of 14 CNVs, which were observed in <0.1% (<8/8329) of the control population. Eight inherited from an unaffected mother: a 751-kb deletion including FSCB, a 1.5-Mb duplication of 7q21.13, a 534-kb duplication of 15q11.2, a 446-kb duplication including CTNND2, a 219-kb duplication including MCPH1, a 169-kb duplication of 22q13.33, a 64-kb duplication of MC2R, and a 135-bp exonic deletion of SLC06A1. Three inherited from an unaffected father: a 386-kb deletion of 12p12.2-p12.1, a 234-kb duplication of 10q26.13, and a 4-kb exonic deletion of COPS3. The inheritance was unknown for three CNVs: a 157-bp exonic deletion of ACOX1, a 693-kb duplication of 17q25.3, and a 265-kb duplication of DAAM1. This is the first systematic study of CNVs in CP, and although it did not identify de novo mutations, has shown inherited, rare CNVs involving potentially pathogenic genes and pathways requiring further investigation.Gai McMichael, Santhosh Girirajan, Andres Moreno-De-Luca, Jozef Gecz, Chloe Shard, Lam Son Nguyen, Jillian Nicholl, Catherine Gibson, Eric Haan, Evan Eichler, Christa Lese Martin and Alastair MacLenna