We have measured the thermal conductivity at low temperatures (5–300
K) of six meteorites representing a range of compositions, including the ordinary chondrites Cronstad (H5) and Lumpkin (L6), the ...enstatite chondrite Abee (E4), the carbonaceous chondrites NWA 5515 (CK4 find) and Cold Bokkeveld (CM2), and the iron meteorite Campo del Cielo (IAB find). All measurements were made using a Quantum Design Physical Properties Measurement System, Thermal Transport Option (TTO) on samples cut into regular parallelepipeds of ∼2–6
mm dimension. The iron meteorite conductivity increases roughly linearly from 15
W
m
−1
K
−1 at 100
K to 27
W
m
−1
K
−1 at 300
K, comparable to typical values for metallic iron. By contrast, the conductivities of all the stony samples except Abee appear to be controlled by the inhomogeneous nature of the meteorite fabric, resulting in values that are much lower than those of pure minerals and which vary only slightly with temperature above 100
K. The L and CK sample conductivities above 100
K are both about 1.5
W
m
−1
K
−1, that of the H is 1.9
W
m
−1
K
−1, and that of the CM sample is 0.5
W
m
−1
K
−1; by contrast the literature value at 300
K for serpentine is 2.5
W
m
−1
K
−1 and those of enstatite and olivine range from 4.5 to 5
W
m
−1
K
−1 (which is comparable to the Abee value). These measurements are among the first direct measurements of thermal conductivity for meteorites. The results compare well with previous estimates for meteorites, where conductivity was derived from diffusivity measurements and modeled heat capacities; our new values are of a higher precision and cover a wider range of temperatures and meteorite types. If the rocky material that makes up asteroids and provides the dust to comets, Kuiper Belt objects, and icy satellites has the same low thermal conductivities as the ordinary and carbonaceous chondrites measured here, this would significantly change models of their thermal evolution. These values would also lower their thermal inertia, thus affecting the Yarkovsky and YORP evolution of orbits and spin for solid objects; however, in this case the effect would not be as great, as thermal inertia only varies as the square root of the conductivity and, for most asteroids, is controlled by the dusty nature of asteroidal surfaces rather than the conductivity of the material itself.
Measurements of the low‐temperature thermodynamic and physical properties of meteorites provide fundamental data for the study and understanding of asteroids and other small bodies. Of particular ...interest are the CM carbonaceous chondrites, which represent a class of primitive meteorites that record substantial chemical information concerning the evolution of volatile‐rich materials in the early solar system. Most CM chondrites are petrographic type 2 and contain anhydrous minerals such as olivine and pyroxene, along with abundant hydrous phyllosilicates contained in the meteorite matrix interspersed between the chondrules. Using a Quantum Design Physical Property Measurement System, we have measured the thermal conductivity, heat capacity, and thermal expansion of five CM2 carbonaceous chondrites (Murchison, Murray, Cold Bokkeveld, Northwest Africa 7309, Jbilet Winselwan) at low temperatures (5–300 K) which span the range of possible surface temperatures in the asteroid belt and outer solar system. The thermal expansion measurements show a substantial and unexpected decrease in CM2 volume as temperature increases from 210 to 240 K followed by a rapid increase in CM2 volume as temperature rises from 240 to 300 K. This transition has not been seen in anhydrous CV or CO carbonaceous chondrites. Thermal diffusivity and thermal inertia as a function of temperature are calculated from measurements of density, thermal conductivity, and heat capacity. Our thermal diffusivity results compare well with previous estimates for similar meteorites, where conductivity was derived from diffusivity measurements and modeled heat capacities; our new values are of higher precision and cover a wider range of temperatures.
We report here time-domain infrared spectroscopy and optical photometry of the HD 145263 silica-rich circumstellar-disk system taken from 2003 through 2014. We find an F4V host star surrounded by a ...stable, massive 1022-1023 kg (MMoon to MMars) dust disk. No disk gas was detected, and the primary star was seen rotating with a rapid ∼1.75 day period. After resolving a problem with previously reported observations, we find the silica, Mg-olivine, and Fe-pyroxene mineralogy of the dust disk to be stable throughout and very unusual compared to the ferromagnesian silicates typically found in primordial and debris disks. By comparison with mid-infrared spectral features of primitive solar system dust, we explore the possibility that HD 145263's circumstellar dust mineralogy occurred with preferential destruction of Fe-bearing olivines, metal sulfides, and water ice in an initially comet-like mineral mix and their replacement by Fe-bearing pyroxenes, amorphous pyroxene, and silica. We reject models based on vaporizing optical stellar megaflares, aqueous alteration, or giant hypervelocity impacts as unable to produce the observed mineralogy. Scenarios involving unusually high Si abundances are at odds with the normal stellar absorption near-infrared feature strengths for Mg, Fe, and Si. Models involving intense space weathering of a thin surface patina via moderate (T < 1300 K) heating and energetic ion sputtering due to a stellar super-flare from the F4V primary are consistent with the observations. The space-weathered patina should be reddened, contain copious amounts of nanophase Fe, and should be transient on timescales of decades unless replenished.
– In our ongoing survey of meteorite physical properties, we have to date measured the thermal conductivity for seventeen stony meteorites at temperatures ranging from 5 K to 300 K. Here, we report ...new results for nine ordinary chondrites, one enstatite chondrite, and the basaltic achondrites Frankfort (howardite) and Los Angeles (shergottite). We find that thermal conductivity is significantly lower than would be expected from averaging the laboratory conductivities of their constituent minerals, with a dependence on temperature different from the expected conductivity of pure minerals. In addition, we find a linear relationship between the inverse of the porosity of the samples measured and their thermal conductivity, regardless of meteorite composition or type. We conclude that thermal conductivity is controlled by the presence of shock‐induced microcracks within the meteorites, which provide a barrier to the transmission of thermal energy via phonons. In contrast to conductivity, our first measurement of heat capacity as a function of temperature (on Los Angeles) suggests that heat capacity is primarily a function of oxide composition and is not strongly affected by the physical state of the sample.
Lunar meteorites are the most diverse and readily available specimens for the direct laboratory study of lunar surface materials. In addition to informing us about the composition and heterogeneity ...of lunar material, measurements of their thermo‐physical properties provide data necessary to inform the models of the thermal evolution of the lunar surface and provide data on fundamental physical properties of the surface material for the design of exploration and resource extraction hardware. Low‐temperature data are particularly important for the exploration of low‐temperature environments of the lunar poles and permanently shadowed regions. We report low‐temperature‐specific heat capacity, thermal conductivity, and linear thermal expansion for six lunar meteorites: Northwest Africa NWA 5000, NWA 6950, NWA 8687, NWA 10678, NWA 11421, and NWA 11474, over the range 5 ≤ T ≤ 300 K. From these, we calculate thermal inertia and thermal diffusivity as functions of temperature. Additionally, heat capacities were measured for 15 other lunar meteorites, from which we calculate their Debye temperature and effective molar mass.
Non-destructive, non-contaminating, and relatively simple procedures can be used to measure the bulk density, grain density, and porosity of meteorites. Most stony meteorites show a relatively narrow ...range of densities, but differences within this range can be useful indicators of the abundance and oxidation state of iron and the presence or absence of volatiles. Typically, ordinary chondrites have a porosity of just under 10%, while most carbonaceous chondrites (with notable exceptions) are more than 20% porous. Such measurements provide important clues to the nature of the physical processes that formed and evolved both the meteorites themselves and their parent bodies. When compared with the densities of small solar system bodies, one can deduce the nature of asteroid and comet interiors, which in turn reflect the accretional and collisional environment of the early solar system.
The nucleus of the Jupiter-family comet 19P/Borrelly was closely observed by the Miniature Integrated Camera and Spectrometer aboard the Deep Space 1 spacecraft on 22 September 2001. The ...8-kilometer-long body is highly variegated on a scale of 200 meters, exhibiting large albedo variations (0.01 to 0.03) and complex geologic relationships. Short-wavelength infrared spectra (1.3 to 2.6 micrometers) show a slope toward the red and a hot, dry surface (≤345 kelvin, with no trace of water ice or hydrated minerals), consistent with ∼10% or less of the surface actively sublimating. Borrelly's coma exhibits two types of dust features: fans and highly collimated jets. At encounter, the near-nucleus coma was dominated by a prominent dust jet that resolved into at least three smaller jets emanating from a broad basin in the middle of the nucleus. Because the major dust jet remained fixed in orientation, it is evidently aligned near the rotation axis of the nucleus.
Background Studies have failed to identify characteristics of women who have been diagnosed with ductal carcinoma in situ (DCIS) and have a high or low risk of subsequent invasive cancer. Methods We ...conducted a nested case–control study in a population-based cohort of 1162 women who were diagnosed with DCIS and treated by lumpectomy alone from 1983 to 1994. We collected clinical characteristics and information on subsequent tumors, defined as invasive breast cancer or DCIS diagnosed in the ipsilateral breast containing the initial DCIS lesion or at a regional or distant site greater than 6 months after initial treatment of DCIS (N = 324). We also conducted standardized pathology reviews and immunohistochemical staining for the estrogen receptor (ER), progesterone receptor, Ki67 antigen, p53, p16, epidermal growth factor receptor-2 (ERBB2, HER2/neu oncoprotein), and cyclooxygenase-2 (COX-2) on the initial paraffin-embedded DCIS tissue. Competing risk models were used to determine factors associated with risk of subsequent invasive cancer vs DCIS, and cumulative incidence survival functions were used to estimate 8-year risk. Results Factors associated with subsequent invasive cancer differed from those associated with subsequent DCIS. Eight-year risk of subsequent invasive cancer was statistically significantly (P = .018) higher for women with initial DCIS lesions that were detected by palpation or that were p16, COX-2, and Ki67 triple positive (p16+COX-2+Ki67+) (19.6%, 95% confidence interval CI = 18.0% to 21.3%) than for women with initial lesions that were detected by mammography and were p16, COX-2, and Ki67 triple negative (p16−COX-2−Ki67−) (4.1%, 95% CI = 3.4% to 5.0%). In a multivariable model, DCIS lesions that were p16+COX-2+Ki67+ or those detected by palpation were statistically significantly associated with subsequent invasive cancer, but nuclear grade was not. Eight-year risk of subsequent DCIS was highest for women with DCIS lesions that had disease-free margins of 1 mm or greater combined with either ER−ERBB2+Ki67+ or p16+COX-2−Ki67+ status (23.6%, 95% CI = 18.1% to 34.0%). Conclusion Biomarkers can identify which women who were initially diagnosed with DCIS are at high or low risk of subsequent invasive cancer, whereas histopathology information cannot.
Summary
Background
Blocking of lymphocyte trafficking to bile ducts is a potential mechanism to alter the disease course of patients with primary sclerosing cholangitis (PSC).
Aim
To describe the ...effect of the α4β7 integrin antibody, vedolizumab, on liver biochemistry and disease activity in patients with PSC and inflammatory bowel disease (IBD).
Methods
This is a retrospective multi‐centre study of adult patients with a diagnosis of both IBD and PSC. The primary outcome was change in serum alkaline phosphatase level at weeks 14 and 30. Secondary outcomes included changes in other liver biochemistries and in clinical outcomes for the bowel disease. A safety analysis for adverse events was performed.
Results
Thirty‐four patients (16 Crohn's disease, 18 ulcerative colitis) were included. Nine (26%) had a history of liver transplant. Median follow‐up on vedolizumab was 9 months (IQR: 7‐16). There was no overall change in serum alkaline phosphatase level with vedolizumab therapy (median 268 IQR: 105‐551 IU/L at baseline versus 249 IQR: 183‐634 IU/L, P = 0.99 at week 30). No significant changes in other liver biochemistries or the Mayo PSC Risk Score were demonstrated at week 30. Clinical remission was achieved at week 30 in 55% of Crohn's disease and 29% of ulcerative colitis patients. Seven (21%) patients ceased vedolizumab; six patients stopped therapy due to persistent IBD activity and one for worsening of liver biochemistries.
Conclusion
Vedolizumab treatment in patients with PSC and IBD did not improve liver biochemistry but was associated with improvement in bowel disease and a favourable safety profile.
Linked ContentThis article is linked to Pavlidis et al and Christensen et al papers. To view these articles visit https://doi.org/10.1111/apt.14603 and https://doi.org/10.1111/apt.14638.
Evidence from Arrokoth and comets strongly suggests a very low density for this and similar small Kuiper belt objects. Plausible compositions imply high porosities, in excess of 70%, and low ...compaction crush strengths. If so, impact craters on Arrokoth (especially Sky, its largest) formed largely by compaction of pore space and material displacement. This is consistent with geological evidence from New Horizons imaging. High porosity reduces cratering efficiency in the gravity regime whereas compaction moves it toward crush strength scaling and increased efficiency. Compaction also guarantees that most impactor kinetic energy is taken up as waste heat near the impact point, with momentum transferred to the rest of the body by elastic waves only. Monte Carlo simulations of Sky‐forming conditions indicate that the momentum imparted likely separated Arrokoth's two lobes, but displacement was limited by dissipation at the neck between them. Unusual strength properties are not required to preserve Arrokoth's bilobate configuration.
Plain Language Summary
It has become apparent over the last few years that small asteroids and comets are very underdense compared with the materials they are made of. This means that their total porosities are likely quite high, in excess of 70%, both as tiny voids within particles (so‐called microscopic porosity) and spaces between particles (macroscopic porosity). But none are likely as porous as the distant denizens of the Kuiper belt such as Arrokoth (visited by the New Horizons spacecraft in 2019). This paper concerns impact craters on Arrokoth and similar small bodies, and the rather unusual effects expected. Imagine a fluffy (fine powder) snowball striking a much larger fluffy snowball, only that the snow is not pure ice but a mixture of porous icy, rocky, and carbon‐rich particles. Even at high velocities (>100 s of m/s) craters should mostly form by compacting pore space and pushing material away from the impact point, not the traditional blasting of ejecta back into space. Similar to crush‐up of an automobile bumper, compaction helps to protect from the potentially catastrophic effects of large impacts, such as complete disruption of the target or breakup of bilobate bodies like Arrokoth, and should be incorporated in future collisional evolution studies.
Key Points
Arrokoth is likely a low density, highly porous, contact binary planetesimal
Impact craters on Arrokoth, and particularly its largest, likely formed as compaction craters, with modest or little ejecta
High porosity acted to protect Arrokoth from catastrophic disruption, ejecta recoil, and lobe dislocation and rearrangement
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