Global geologic map of asteroid (101955) Bennu indicates heterogeneous resurfacing in the past 500,000 years

Global geologic maps are useful tools for efficient interpretation of a planetary body, and they provide global context for the diversity and evolution of the surface. We used data acquired by the OSIRIS-REx spacecraft to create the first global geologic map of the near-Earth asteroid (101955) Bennu. As this is the first geologic map of a small, non-spherical, rubble-pile asteroid, we discuss the distinctive mapping challenges and best practices that may be useful for future exploration of similar asteroids, such as those to be visited with the Hera and Janus missions. By mapping on two centimeter-scale global image mosaics (2D projected space) and a centimeter-scale global shape model (3D space), we generated three input maps respectively describing Bennu's shape features, geologic features, and surface texture. Based on these input maps, we defined two geologic units: the Smooth Unit and the Rugged Unit. The units are differentiated primarily on the basis of surface texture, concentrations of boulders, and the distributions of lineaments, mass movement features, and craters. They are bounded by several scarps. The Rugged Unit contains abundant boulders and signs of recent mass movement. It also has fewer small (<20 m), putatively fresh craters than the Smooth Unit, suggesting that such craters have been erased in the former. Based on these geologic indicators, we infer that the Rugged Unit has the younger surface of the two. Differential crater size-frequency distributions and the distribution of the freshest craters suggest that both unit surfaces formed ~10–65 million years ago, when Bennu was located in the Main Asteroid Belt, and the Smooth Unit has not been significantly resurfaced in the past 2 million years. Meanwhile, the Rugged Unit has experienced resurfacing within the past ~500,000 years during Bennu's lifetime as a near-Earth asteroid. The geologic units are consistent with global diversity in slope, surface roughness, normal albedo, and thermal emission spectral characteristics. The site on Bennu where the OSIRIS-REx mission collected a regolith sample is located in the Smooth Unit, in a small crater nested within a larger one. So although the Smooth Unit is an older surface than the Rugged Unit, the impact-crater setting indicates that the material sampled was recently exposed. Several similarities are apparent between Bennu and asteroid (162173) Ryugu from a global geologic perspective, including two geologic units distinguishable by variations in the number density of boulders, as well as in other datasets such as brightness

Development of an UPLC mass spectrometry method for measurement of myofibrillar protein synthesis: application to analysis of murine muscles during cancer cachexia

Cachexia, characterized by skeletal muscle mass loss, is a major contributory factor to patient morbidity and mortality during cancer. However, there are no reports on the rate of myofibrillar protein synthesis (MPS) in skeletal muscles that vary in primary metabolic phenotype during cachexia, in large part because of the small-size muscles and regional differences in larger muscles in the mouse. Here, we describe a sensitive method for measurement of MPS and its application to analysis of MPS in specific muscles of mice with (Apc(Min/+)) and without (C57BL/6) cancer cachexia. Mice were injected with a loading dose of deuterated phenylalanine (D5F), and myofibrillar proteins were extracted from skeletal muscles at 30 min. The relative concentrations of D5F and naturally occurring phenylalanine (F) in the myofibrillar proteins and the amino acid pool were quantified by ultra-performance liquid chromatograph (UPLC) mass spectrometry (MS). The rate of MPS was determined from D5F-to-F ratio in the protein fraction compared with the amino acid pool. The rate of MPS, measured in 2-5 mg of muscle protein, was reduced by up to 65% with cachexia in the soleus, plantaris, diaphragm, and oxidative and glycolytic regions of the gastrocnemius. The rate of MPS was significantly higher in the oxidative vs. glycolytic gastrocnemius muscle. A sufficiently sensitive UPLC MS method requiring a very small amount of muscle has been developed to measure the rate of MPS in various mouse muscles. This method should be useful for studies in other animal models for quantifying effects of cancer and anti-cancer therapies on protein synthesis in cachexia, and particularly for analysis of sequential muscle biopsies in a wide range of animal and human studies

Comparative methodologies for measuring metabolizable energy of various types of resistant high amylose corn starch

Energy values of high amylose corn starches high in resistant starch (RS) were determined in vivo by two different methodologies. In one study, energy values were determined according to growth relative to glucose-based diets in rats fed diets containing RS2, heat-treated RS2 (RS2-HT), RS3, and amylase predigested versions to isolate the RS component. Net metabolizable energy values ranged from 2.68 to 3.06 kcal/g for the RS starches, and 1.91-2.53 kcal/g for the amylase predigested versions. In a second study, rats were fed a diet containing RS2-HT and the metabolizable energy value was determined by bomb calorimetry. The metabolizable energy value was 2.80 kcal/g, consistent with Study 1. Thus, high amylose corn based RS ingredients and their amylase predigested equivalents have energy values approximately 65-78% and 47-62% of available starch (Atwater factor), respectively, according to the RS type (Garcia, T. A.; McCutcheon, K. L.; Francis, A. R.; Keenan, M. J.; O'Neil, C. E.; Martin, R. J.; Hegsted, M. The effects of resistant starch on gastrointestinal organs and fecal output in rats. FASEB J. 2003, 17, A335). ©2009 American Chemical Society

Validation of stereophotoclinometric shape models of asteroid (101955) Bennu during the OSIRIS-REx mission

NASA’s OSIRIS-REx mission to asteroid (101955) Bennu relied on the production of real-time shape models for both spacecraft navigation and scientific analysis. The primary method of constructing shape models during the early phases of the mission was image-based stereophotoclinometry (SPC). The SPC shape models were used for operational planning, navigation, sample site selection, and initial scientific investigations. To this end, detailed analyses of the quality of each shape model and a thorough documentation of all sources of error were vital to ensure proper considerations of the limitations of each model. In this paper, we present methods used during the OSIRIS-REx mission to validate the SPC shape models and construct the associated quality reports. Although developed for the OSIRIS-REx mission, these validation techniques can be applied to SPC-derived shape models of other planetary bodies. © 2021. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

OSIRIS-APEX: An OSIRIS-REx Extended Mission to Asteroid Apophis

The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft mission characterized and collected a sample from asteroid (101955) Bennu. After the OSIRIS-REx Sample Return Capsule released to Earth’s surface in 2023 September, the spacecraft diverted into a new orbit that encounters asteroid (99942) Apophis in 2029, enabling a second mission with the same unique capabilities: OSIRIS-Apophis Explorer (APEX). On 2029 April 13, the 340 m diameter Apophis will draw within ∼32,000 km of Earth’s surface, less than 1/10 the lunar distance. Apophis will be the largest object to approach Earth this closely in recorded history. This rare planetary encounter will alter Apophis’s orbit, will subject it to tidal forces that change its spin state, and may seismically disturb its surface. APEX will distantly observe Apophis during the Earth encounter and capture its evolution in real time, revealing the consequences of an asteroid undergoing tidal disturbance by a major planet. Beginning in 2029 July, the spacecraft’s instrument suite will begin providing high-resolution data of this “stony” asteroid—advancing knowledge of these objects and their connection to meteorites. Near the mission’s end, APEX will use its thrusters to excavate regolith, a technique demonstrated at Bennu. Observations before, during, and after excavation will provide insight into the subsurface and material properties of stony asteroids. Furthermore, Apophis’s material and structure have critical implications for planetary defense. © 2023. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]