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Microwave emission is influenced by regolith thermophysical properties that can reveal the geological evolution of the Moon. Lunar near-surface microwave emission has been systematically investigated by the microwave radiometer (MRM) onboard Chinese Chang'E-2 (CE-2) lunar satellite. However, recent work showed that global calibration issues were causing discrepancies between CE-2 observations and theoretical simulations at 3.0- and 7.8-GHz channels, which influences data interpretations and applications. In this study, we use a new method to improve thermal models by employing the bolometric brightness temperature and thermophysical property of subsurface structure derived from high quality and repeated coverage Diviner data. The derived subsurface temperatures make it possible for us to improve the accuracy of microwave brightness temperature (TB) simulation within 70°N/S latitudes. We evaluate the MRM data quantitatively by comparing the global TB between modeled values and CE-2 observations (i.e., offset values) at different local times (LTs) and latitudes. The results show that offset values of the two channels vary significantly with LT, especially near 06:00 and 18:00. However, the 7.8-GHz channel presents greater (~12k in average) calibration uncertainties than the 3.0-GHz channel. In addition, the offset of both the two channels becomes complex at high latitudes but presents an obvious north-south asymmetry. Finally, we modify the MRM data according to different offsets at different LTs and latitudes. The modified global TB maps provide us a new view to characterize the lunar near-surface thermal environment, especially for low-TB spots that are related to the elevated rock abundance and crater degradation.

The composition of Bolides acts somewhat like a series of snapshots or a diary of my life between March 2020 and December 2021, and for me evokes geographical and temporal cues that are very specific for that particular point in time. The source material includes underwater recordings of kelp forests, captured by homemade hydrophones, the ululations of grey seal pups, and an improvised percussion performance on plate steel. The compositional methodology was guided by an aural discourse, and the structural decisions throughout the process were informed by the materials as they presented themselves, there were no abstract processes involved. Sound objects were chosen for their gestural and sonic properties, and then further processed using a mixture of real-time interaction facilitated by a Leap motion sensor and a multitouch-surface MIDI controller. Both of these devices were mapped to parameters of various DSP devices, some of which were created using Csound, some of which are native to Ableton Live 11. A series of performances were recorded using this configuration and the results of these gesturally-driven performances were further developed into the library of sound objects that make up this piece.

Recent advances in peroxidase‐mediated biotin tyramide (BT) signal amplification technology have resulted in high‐resolution and subcellular compartment‐specific mapping of protein and RNA localization. Horseradish peroxidase (HRP) in the presence of H2O2 is known to activate phenolic compounds for phenoxy radical reaction with nucleic acids, where biotinylation by BT is a practical example. BT reactivity with RNA and DNA is not understood in detail. We report that BT phenoxy radicals react in a sequence‐independent manner with guanosine bases in RNA. In contrast, DNA reactivity with BT cannot be detected by our methods under the same conditions. Remarkably, we show that fluorescein conjugates DNA rapidly and selectively reacts with BT phenoxy radicals, allowing convenient and practical biotinylation of DNA on fluorescein with retention of fluorescence., Enzyme‐catalyzed phenoxy radical biotinylation, an increasingly important tool in biotechnology and molecular biology applications, is here shown to label guanosine bases in RNA, but not in DNA, under defined conditions. Remarkably, common fluorescein conjugates of synthetic DNA oligonucleotides are found to undergo facile biotinylation on fluorescein with retention of fluorescence. This convenient observation points to a variety of practical applications of peroxidase‐catalyzed chemistry for analysis of DNA conjugates in vitro and in cells.

Deciphering paleoclimate on Mars has been a driving goal of Martian science for decades. Most research has addressed this issue by studying Mars' large polar layered deposits (PLDs) as a paleoclimate proxy, but the certainty to which we know the link between climate and orbit is debated. Here, we instead consider the record of other, smaller ice deposits located within craters separated from the PLDs using images from NASA's High Resolution Imaging Science Experiment camera and signal processing techniques. We show that the climate record in Burroughs Crater (72.3°S, 116.6°E) contains robust evidence of orbital forcing, with periodicities that have wavelengths of 15.6 and 6.5 m. The ratio of these dominant wavelengths is 2.4, the same as the ratio between the periods of Mars' obliquity changes and orbital precession. This result suggests orbital control of recent Mars climate, and would imply an average ice accumulation rate of 0.13 mm/yr over 4.5 Myr in this region.

Topographic depressions within permanently shadowed regions (PSRs) on low-obliquity planetary bodies can be shielded not only from direct illumination, but also from scattered sunlight and thermal emission from nearby sunlit surfaces. We apply an illumination model to high-resolution topography data to produce the first map of double shadows at the lunar poles. The total doubly shadowed area resolved at the 30 m scale is 1.47 km2 in the northern hemisphere and 5.37 km2 in the southern hemisphere, predominantly contained within small craters on the floors of large permanently shadowed craters. In total, ∼0.04% of PSR area is permanently double shadowed, but the largest double shadows are nearly 600 m across, potentially large enough to be resolved in remote sensing temperature measurements. In the absence of secondary heating sources, double shadows are predicted to be significantly colder than singly shadowed areas and could sequester highly volatile compounds like carbon dioxide. Future in situ investigation of the regions identified in this work can elucidate the origin and distribution of the Moon’s most volatile deposits.

The surfaces of airless bodies like the Moon are bombarded by a steady stream of small impactors that lead to erosion of the topography over time. However, the rate of degradation from small impacts, a key parameter in interpreting the ages of present-day lunar surface features, is not well constrained. Here we demonstrate, using a numerical mass transport model, that impact erosion is a nonlinear diffusion process, in contrast to past studies of crater degradation that have assumed that the downslope mass flux of ejecta is linearly proportional to hillslope gradient. Nonlinearity is a consequence of the asymmetric shape of ejecta blankets on sloped surfaces, and as a result, the degradation rate on steep slopes is over 40% greater than on nearly flat surfaces. Using measurements of the morphology and formation rate of small primary and secondary craters, the kilometer-scale lunar landscape diffusivity is computed and compared to the value inferred from topographic profiles of degraded craters. We show that the abundance of decameter-scale craters forming on the Moon over the past decade is consistent with small impacts dominating the erosion of the lunar landscape, but only if the primary size−frequency distribution remains steep down to the submillimeter scale.

Mars Polar Science is an integrated, compelling system that serves as a nearby analogue to numerous other planets, supports human exploration, and habitability. Mars possesses the closest and most easily accessible layered ice deposits outside of Earth, and accessing those layers to read the climate record would be a triumph for planetary science.

Mars exhibits diverse surface changes at all latitudes and all seasons. Active processes include impact cratering, aeolian sand and dust transport, a variety of slope processes, changes in polar ices, and diverse effects of seasonal CO

1. Introduction In 2008, the High Resolution Imaging Science Experiment (HiRISE) on board NASA’s MRO fortuitously captured several discrete clouds of material (Fig.1) in the process of cascading down a steep scarp of the water-ice-rich north polar layered deposits (NPLD). The events were only seen during a period of ~4 weeks, near the onset of northern spring, when the seasonal cover of CO2 is beginning to sublimate from the north polar regions. Russell et al. [1] analyzed the morphology of the clouds, inferring that the particles involved were mechanically analogous to terrestrial “dry, loose snow or dust”, making the events similar to terrestrial “powder avalanches” [2]. HiRISE confirmed the seasonality of these avalanches the following spring, and has been monitoring them (Fig.2) for a total of 7 Mars Years (MY29–MY35). We will present observations from this monitoring. We seek to: (1) quantify the frequency of these events (2) quantify their effect on the mass balance of the NPLD (especially with respect to competing processes such as viscous deformation and other mass-wasting events [3-5], and (3) investigate possible trigger mechanisms. 2. Observations The avalanches often appear as dense clouds of reddish, air-lofted material moving down scarps of the NPLD margins. The scarps are steep (>50º) and appear fractured (Fig.1), and the clouds themselves range in extent from just a few tens of meters to over 200 m. Observations of many avalanche events at different stages allow us to deduce the course of a typical event. Avalanches start at a discrete point on the steep face and remain small and optically thick as they descend (Fig.1a,b). Upon reaching the basal unit they spread outward at speeds of several m/s (measured from color fringing in HiRISE images [1]), become optically thinner, and develop a more diffuse boundary (Fig1.c,d). The avalanches then transition to near-stationary clouds close to, but detached from the scarp, which presumably slowly settle onto the exposed basal unit (Fig.1e). A total of 57 events have been captured in action on the so-called “Discovery Scarp” (Fig.2) since the first five events were captured here in a single HiRISE image. On average, 8 events are captured on this scarp per year, and they tend to occur on its steepest sections (50–70º), and preferentially on SW-facing scarps. Figure 2 shows the location of the Discovery Scarp and all other scarps along the NPLD margins where avalanches have been observed. An average of 20 new events are observed every year. Avalanches have only been observed to occur between Ls 5º and 70º, and thus are an exclusively “springtime” event. This time of year coincides with both the sublimation of seasonal CO2 ice over the north polar region, and with a peak in subsurface compressional stresses in the scarp walls, as shown by [6]. 3. Trigger mechanisms In accordance with the seasonality of the avalanches, trigger mechanisms to consider are (1) sublimation-driven collapse of sections of the scarp wall (material in the avalanches would most likely be a combination of CO2 and surface dust), and (2) thermal stress-driven collapse, similar to exfoliation of granitic domes on Earth [6] (material would mostly be pulverized dusty water ice, i.e. the material that makes up NPLD beds). To examine the first mechanism, we acquired HiRISE images early in the season, before the events occurred. Images of the discovery scarp at Ls 350º (Fig.3a) and Ls 1º appear to show that the CO2 has already sublimated from the steepest parts of the wall by this time. However, CRISM spectra of this location (Fig.3b,c) show absorption bands diagnostic of CO2 until after Ls 50º. Though the bands are weak, their presence suggests CO2 persists until this time. We also used a 1D thermal balance model [7] to calculate the amount of CO2 frost that accumulates on a steep surface throughout the year. With conservative estimates for thermal properties (i.e., assumed an exposed wall of water ice), model results show that on a 50º SW-facing slope, all CO2 frost has sublimated by Ls 10º, matching HiRISE observations but contradicting CRISM. This thermal model is extremely sensitive to dust cover on the scarp wall however, and a few cm of dust can accumulate, and maintain wintertime CO2. It is also possible that the steepness of the scarp makes it difficult to isolate in the CRISM data, and that the absorption bands correspond to influence from adjacent, flatter terrains. 4. Results and Future Work Our study shows that north polar cap avalanches occur frequently on steep, marginal scarps of the NPLD, and likely have a substantial effect in eroding the NPLD. There are contradicting observations of CO2 frost on the steepest areas of the scarps, which we will further investigate with CRISM observations at high-roll angles that view the scarp more head-on. Even if CO2 is present in small amounts on the scarps early in the year, we have found that it is the fractured scarps that show a much higher frequency of avalanches than those that show little to no fracturing. Thus, although CO2 may be present in the clouds mixed with the avalanche material as it moves over the basal unit, a more likely trigger seems to be the springtime peak in compressional stresses that fractures the scarps [6]. In the future, we will quantify the mass wasted by the events with flow models used for terrestrial processes, and further investigate the triggers with improved detail in the thermal and stress models. References [1] Russell et al. (2008) GRL. 35, L23204. [2] McClung and Schaerer (2006), Mountaineers, Seattle Wash. [3] Sori, et al., GRL, 43. [4] Herkenhoff et al. (2020) 7th ICMPSE [5] Fanara et al. 2020, Icarus [6] Byrne et al. (2016), 6th ICMPSE [7] Dundas and Byrne (2010) Icarus 206, 716.

Highlights • First study providing evidence of equivalence of self-collection for SARS-CoV-2 • Self-collection has potential to increase accessibility and detection of SARS-CoV-2 • Self-collection has potential to preserve PPE supplies • Self-collection has potential to reduce exposure to others • Self-collection was easy to perform and preferred by the majority of participants, Objectives To evaluate the reliability of self-collection for SARS-CoV-2 and other respiratory viruses because swab collections for SARS-CoV-2 put health workers at risk of infection and require use of personal protective equipment (PPE). Methods In a prospective study, patients from two states in Australia attending dedicated COVID-19 collection clinics were offered the option to first self-collect (SC) throat and nasal swabs (SCNT) prior to health worker collect (HC) using throat and nasal swabs (Site 1) or throat and nasopharyngeal swabs (Site 2). Samples were analysed for SARS-CoV-2 as well as common respiratory viruses. Concordance of results between methods was assessed using Cohen's kappa (κ) and Cycle threshold (Ct) values were recorded for all positive results as a surrogate measure for viral load. Results Of 236 patients sampled by HC and SC, 25 had SARS-CoV-2 (24 by HC and 25 by SC) and 63 had other respiratory viruses (56 by HC and 58 y SC). SC was highly concordant with HC (κ = 0.890) for all viruses including SARS-CoV-2 and more concordant than HC to positive results by any method (κ = 0.959 vs 0.933). Mean SARS-CoV-2 E-gene and N-gene, rhinovirus and parainfluenza Ct values did not differ between HC and SCNT. Conclusions Self-collection of throat and nasal swabs offers a reliable alternative to health worker collection for the diagnosis of SARS-CoV-2 and other respiratory viruses and provides patients with easier access to testing, reduces exposure of the community and health workers to those being tested and reduces requirement for PPE.

In its polar layered deposits (PLD), Mars possesses a record of its recent climate, analogous to terrestrial ice sheets containing climate records on Earth. Each PLD is greater than 2 ​km thick and contains thousands of layers, each containing information on the climatic and atmospheric state during its deposition, creating a climate archive. With detailed measurements of layer composition, it may be possible to extract age, accumulation rates, atmospheric conditions, and surface activity at the time of deposition, among other important parameters; gaining the information would allow us to “read” the climate record. Because Mars has fewer complicating factors than Earth (e.g. oceans, biology, and human-modified climate), the planet offers a unique opportunity to study the history of a terrestrial planet’s climate, which in turn can teach us about our own planet and the thousands of terrestrial exoplanets waiting to be discovered. During a two-part workshop, the Keck Institute for Space Studies (KISS) hosted 38 Mars scientists and engineers who focused on determining the measurements needed to extract the climate record contained in the PLD. The group converged on four fundamental questions that must be answered with the goal of interpreting the climate record and finding its history based on the climate drivers. The group then proposed numerous measurements in order to answer these questions and detailed a sequence of missions and architecture to complete the measurements. In all, several missions are required, including an orbiter that can characterize the present climate and volatile reservoirs; a static reconnaissance lander capable of characterizing near surface atmospheric processes, annual accumulation, surface properties, and layer formation mechanism in the upper 50 ​cm of the PLD; a network of SmallSat landers focused on meteorology for ground truth of the low-altitude orbiter data; and finally, a second landed platform to access ~500 ​m of layers to measure layer variability through time. This mission architecture, with two landers, would meet the science goals and is designed to save costs compared to a single very capable landed mission. The rationale for this plan is presented below. In this paper we discuss numerous aspects, including our motivation, background of polar science, the climate science that drives polar layer formation, modeling of the atmosphere and climate to create hypotheses for what the layers mean, and terrestrial analogs to climatological studies. Finally, we present a list of measurements and missions required to answer the four major questions and read the climate record. 1. What are present and past fluxes of volatiles, dust, and other materials into and out of the polar regions? 2. How do orbital forcing and exchange with other reservoirs affect those fluxes? 3. What chemical and physical processes form and modify layers? 4. What is the timespan, completeness, and temporal resolution of the climate history recorded in the PLD?

The ages of terrains on other planetary bodies are chiefly determined using crater size–frequency distributions. However, primary impacts can generate numerous secondary craters that can affect the crater population. Classifying impact craters as primary or secondary is commonly done via time-consuming manual inspection, which limits the areas that can be analyzed at high resolution. We present a parametric model for characterizing small (100–600 m diameter) impact craters, where the model parameters have implications for describing the physical processes involved in their formation and modification. We infer these parameters from craters in images captured by the high-resolution imaging science experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter. For each crater within the appropriate size range, our algorithm creates a 3-D surface for a parametrically modeled crater and a 2-D rendering using illumination metadata, including emission, phase, and solar incidence angles at the time when the image was captured. A function describes the likelihood of each set of model parameters in terms of the geometry of craters in a given HiRISE image. These values are then optimized using a Metropolis–Hasting Markov chain Monte Carlo sampler. We evaluated three different prior probability distributions over the parameter space and two different likelihoods: one for digital terrain models and the other for images. We show that after applying t-distributed stochastic neighbor embedding (t-SNE) over the inferred crater parameters, t-SNE is able to project the multidimensional crater parameters into a 2-D space where secondary craters cluster together and are separable from primary craters.

Cryovolcanism, defined here as the extrusion of icy material from depth, may be an important planetary phenomenon in shaping the surfaces of many worlds in the outer Solar System and revealing their thermal histories. However, the physics, chemistry and ubiquity of this geologic process remain poorly understood, especially in comparison to the better-studied silicate volcanism on the terrestrial planets. Ceres is the only plausibly cryovolcanic world to be orbited by a spacecraft up to now, making it the best opportunity to test the importance of cryovolcanism on bodies in the outer Solar System and compare its effects to silicate volcanism on terrestrial planets. Here, we analyse images from NASA’s Dawn mission and use the finite element method to show that Ceres has experienced cryovolcanism throughout its geologic history, with an average cryomagma extrusion rate of ~10^4 m^3 yr^(−1). This result shows that volcanic phenomena are important on Ceres, but orders of magnitude less so than on the terrestrial planets.

Landslides are among the most widespread geologic features on Ceres. Using data from Dawn's Framing Camera, landslides were previously classified based upon geomorphologic characteristics into one of three archetypal categories, Type 1(T1), Type 2 (T2), and Type 3 (T3). Due to their geologic context, variation in age, and physical characteristics, most landslides on Ceres are, however, intermediate in their morphology and physical properties between the archetypes of each landslide class. Here we describe the varied morphology of individual intermediate landslides, identify geologic controls that contribute to this variation, and provide first‐order quantification of the physical properties of the continuum of Ceres's surface flows. These intermediate flows appear in varied settings and show a range of characteristics, including those found at contacts between craters, those having multiple trunks or lobes; showing characteristics of both T2 and T3 landslides; material slumping on crater rims; very small, ejecta‐like flows; and those appearing inside of catenae. We suggest that while their morphologies can vary, the distribution and mechanical properties of intermediate landslides do not differ significantly from that of archetypal landslides, confirming a link between landslides and subsurface ice. We also find that most intermediate landslides are similar to Type 2 landslides and formed by shallow failure. Clusters of these features suggest ice enhancement near Juling, Kupalo and Urvara craters. Since the majority of Ceres's landslides fall in the intermediate landslide category, placing their attributes in context contributes to a better understanding of Ceres's shallow subsurface and the nature of ground ice., Key Points Landslides on Ceres have a wide range of morphologiesSubsurface ice affects the formation of most landslides on Ceres and influences their morphologyCeres has widespread ground ice with ice enhancements near the poles and within Juling and Kupalo craters

The modern climate of Mars has been well characterized from over a decade of orbiting spacecraft, in situ measurements via landers/rovers, and theoretical advances in climate modeling. Nonetheless, important questions remain unanswered, including the present-day mass balance of the north polar residual cap and its icy outliers. Exposed water-ice mounds are found in craters, and extend as far equatorward as 70.2°N. Due to their southerly location, these ice mounds are likely more sensitive to ongoing changes in climate. We analyze high-resolution images of the Louth crater ice mound, and employ a coupled 1-D thermal and atmospheric model to estimate annual mass balance of both Louth and Korolev water ice. We incorporate the effects of shallowly-sloping surfaces and seasonally-dependent water ice albedo. No clear trend in the advance or retreat of Louth crater water ice is observed in over 4 Mars years of repeat, high-resolution images. Secular changes are either sufficiently small as to not be detected, or the ice is in equilibrium. Modeled mass balance ranges from −6 to +2 mm of water ice per Mars year at both sites, with nominal cases being in near-equilibrium (

Recent liquid water flow on Mars has been proposed based on geomorphological features, such as gullies. Recurring slope lineae — seasonal flows that are darker than their surroundings — are candidate locations for seeping liquid water on Mars today, but their formation mechanism remains unclear. Topographical analysis shows that the terminal slopes of recurring slope lineae match the stopping angle for granular flows of cohesionless sand in active Martian aeolian dunes. In Eos Chasma, linea lengths vary widely and are longer where there are more extensive angle-of-repose slopes, inconsistent with models for water sources. These observations suggest that recurring slope lineae are granular flows. The preference for warm seasons and the detection of hydrated salts are consistent with some role for water in their initiation. However, liquid water volumes may be small or zero, alleviating planetary protection concerns about habitable environments.

National Science Foundation (NSF) [DGE-1143953]; NASA Earth and Space Sciences Fellowship (NESSF) [NNX16AP09H]; NASA Mars Data Analysis Program (MDAP) award [NNX15AM62G]

Dawn at Ceres Guest Investigator Program award [NNX15AI29G]; NSF Graduate Research Fellowship award [DGE-1143653]

Carbon dioxide has been detected on the trailing hemispheres of several Uranian satellites, but the exact nature and distribution of the molecules remain unknown. One such satellite, Umbriel, has a prominent high albedo annulus-shaped feature within the 131-km-diameter impact crater Wunda. We hypothesize that this feature is a solid deposit of CO 2 ice. We combine thermal and ballistic transport modeling to study the evolution of CO 2 molecules on the surface of Umbriel, a high-obliquity (∼98°) body. Considering processes such as sublimation and Jeans escape, we find that CO 2 ice migrates to low latitudes on geologically short (100s–1000 s of years) timescales. Crater morphology and location create a local cold trap inside Wunda, and the slopes of crater walls and a central peak explain the deposit's annular shape. The high albedo and thermal inertia of CO 2 ice relative to regolith allows deposits 15-m-thick or greater to be stable over the age of the solar system. We conclude that Wunda, located at low latitude (7.9° S) and near the center of the trailing hemisphere where CO 2 detections are strongest, likely contains a solid CO 2 ice deposit. We discuss prospects for similar CO 2 ice deposits on crater floors on the other major Uranian moons, and predict that they are present on Ariel, Titania, and possibly Oberon (but not Miranda or smaller satellites). Such deposits have likely not been observed due to the limited nature of Voyager 2 image coverage.

Excess ice is widespread throughout the martian mid-latitudes, particularly in Arcadia Planitia, where double-layer ejecta (DLE) craters also tend to be abundant. In this region, we observe the presence of thermokarstically-expanded secondary craters that likely form from impacts that destabilize a subsurface layer of excess ice, which subsequently sublimates. The presence of these expanded craters shows that excess ice is still preserved within the adjacent terrain. Here, we focus on a 15-km DLE crater that contains abundant superposed expanded craters in order to study the distribution of subsurface volatiles both at the time when the secondary craters formed and, by extension, remaining today. To do this, we measure the size distribution of the superposed expanded craters and use topographic data to calculate crater volumes as a proxy for the volumes of ice lost to sublimation during the expansion process. The inner ejecta layer contains craters that appear to have undergone more expansion, suggesting that excess ice was most abundant in that region. However, both of the ejecta layers had more expanded craters than the surrounding terrain. We extrapolate that the total volume of ice remaining within the entire ejecta deposit is as much as 74 km 3 or more. The variation in ice content between the ejecta layers could be the result of (1) volatile preservation from the formation of the DLE crater, (2) post-impact deposition in the form of ice lenses; or (3) preferential accumulation or preservation of subsequent snowfall. We have ruled out (2) as the primary mode for ice deposition in this location based on inconsistencies with our observations, though it may operate in concert with other processes. Although none of the existing DLE formation hypotheses are completely consistent with our observations, which may merit a new or modified mechanism, we can conclude that DLE craters contain a significant quantity of excess ice today.

NASA Earth and Space Science Fellowship [NNX13AO55H]; NASA's Mars Reconnaissance Orbiter project

Water ice cliffs on MarsSome locations on Mars are known to have water ice just below the surface, but how much has remained unclear. Dundaset al.used data from two orbiting spacecraft to examine eight locations where erosion has occurred. This revealed cliffs composed mostly of water ice, which is slowly sublimating as it is exposed to the atmosphere. The ice sheets extend from just below the surface to a depth of 100 meters or more and appear to contain distinct layers, which could preserve a record of Mars' past climate. They might even be a useful source of water for future human exploration of the red planet.Science, this issue p.199