The flyby of Pluto and Charon by the New Horizons spacecraft provided high-resolution images of cratered surfaces embedded in the Kuiper belt, an extensive region of bodies orbiting beyond Neptune. ...Impact craters on Pluto and Charon were formed by collisions with other Kuiper belt objects (KBOs) with diameters from ~40 kilometers to ~300 meters, smaller than most KBOs observed directly by telescopes. We find a relative paucity of small craters ≲13 kilometers in diameter, which cannot be explained solely by geological resurfacing. This implies a deficit of small KBOs (≲1 to 2 kilometers in diameter). Some surfaces on Pluto and Charon are likely ≳4 billion years old, thus their crater records provide information on the size-frequency distribution of KBOs in the early Solar System.
ABSTRACT
The mutual gravitational interaction of binary asteroids, which make up approximately 15 per cent of the near-Earth asteroid (NEA) population, provides a continuous tidal force, creating ...ground motion. We explore the potential of kilometre-sized binary asteroids as targets for seismological studies of their interior structure. We use a numerical model wherein each body is constructed of discrete particles interacting via gravity and contact forces. The system's orbital properties are modelled based on those of typical binary NEAs: a secondary body orbits a primary body at a distance of a few to 10 primary radii, resulting in orbital periods of a few tens of hours. We varied the elastic moduli (stiffness) of the constituent particles and measured a strain of a few micrometres caused by the orbiting satellite. Over eight orbital periods, the acceleration of the strain vector along the primary body's equatorial axis indicates that tidally induced ground motion generated by a binary asteroid system is detectable by modern seismometers, like the instruments deployed on the InSight mission to Mars. Owing to the relatively short orbital period of the satellite – a mean of 25.8 h for known binary NEAs – only a modest mission lifetime would be required for a seismometer to adequately characterize an asteroid's interior through tidally induced deformation. Future deployment of seismometers on binary asteroids will allow for a detailed characterization of the structure of these objects.
Impacts into marine targets are known to create abnormal crater morphologies. We investigate the formation of the ~4 km diameter Flynn Creek marine target impact crater using the iSALE hydrocode. We ...compare simulation results to topographic profiles, mineral pressure indicators, and breccia sequencing from drill cores to determine the most likely sea depth at this location at the time of impact (~360 Ma, Tennessee, USA): 700–800 m. Both the peak shock pressure produced by the impact and the mechanism(s) of central peak formation differ with sea depth. The large central mound of Flynn Creek could have been produced in three distinct ways, all requiring the presence of an ocean: (1) a relatively cohesive rim collapse deposit that reached the crater center as part of a ground flow and came to rest on top of the existing crater stratigraphy; (2) chaotic resurge of ejecta with the returning ocean that deposited at the crater center; (3) large uplift facilitated by the removal of overburden pressure from a deep ocean. The first two of these mechanisms create “false peaks” in which high‐shock uplifted material and original crater floor are buried beneath > 200 m of relatively low shock material. Our simulations suggest that drilling of marine impact sites might require deeper than expected drill cores, so that any high‐pressure mineralogical indictors at depth can be accessed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•New study of impact melt deposits exterior to crater rims on the Moon.•Exterior melt deposits are more common in the highlands than the mare.•Simple craters have the longest relative melt flow ...length.•Pre-existing topography plays an important role in melt emplacement.
In this study, we analyzed the distribution and properties of 146 craters with impact melt deposits exterior to their rims. Many of these craters were only recently discovered due to their unusual radar properties in the near-global Mini-RF data set. We find that most craters with exterior deposits of impact melt are small, ⩽20km, and that the smallest craters have the longest melt flows relative to their size. In addition, exterior deposits of impact melt are more common in the highlands than the mare. This may be the result of differing target properties in the highlands and mare, the difference in titanium content, or the greater variation of topography in the highlands. We find that 80% of complex craters and 60% of simple craters have melt directions that are coincident or nearly coincident with the lowest point in their rim, implying that pre-existing topography plays a dominant role in melt emplacement. This is likely due to movement during crater modification (complex craters) or breached crater rims (simple craters). We also find that impact melt flows have very high circular polarization ratios compared to other features on the Moon. This suggests that their surfaces are some of the roughest material on the Moon at the centimeter to decimeter scale, even though they appear smooth at the meter scale.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Tidal interactions between planets or stars and the bodies that orbit them dissipate energy in their interiors. The dissipated energy heats the interior and a fraction of that energy will be released ...as seismic energy. Here we formalize a model to describe the tidally-driven seismic activity on planetary bodies based on tidal dissipation. To constrain the parameters of our model we use the seismic activity of the Moon, driven by tidal dissipation from the Earth-Moon interactions. We then apply this model to predict the amount of seismic energy release and largest seismic events on other moons in our Solar System and exoplanetary bodies. We find that many moons in the Solar System should be more seismically active than the Earth's Moon and many exoplanets should exhibit more seismic activity than the Earth. Finally, we examine how temporal-spatial variations in tidal dissipation manifest as variations in the locations and timing of seismic events on these bodies.
•Tidal dissipation provides the energy to drive seismic activity.•Tidal dissipation can be linked mathematically to seismicity.•The Lunar seismic record can constrain tidally-driven seismicity.•All tidally-active worlds should experience seismic activity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•ctDNA decrease at one month was an early predictor for radiological response.•Patients with CTC and ctDNA decrease had better survival outcomes.•ctDNA and CEA rise preceded radiological evidence of ...disease progression.•Mutation detection in ctDNA was highly concordant compared with tissue biopsy.
To determine the predictive and prognostic roles of three blood-based biomarkers: circulating tumour DNA (ctDNA), circulating tumour cells (CTC) and carcinoembryonic antigen (CEA), in patients with advanced epidermal growth factor receptor-mutated (EGFR+) lung cancer.
We recruited 28 patients with 103 serial blood samples. We performed mutational analyses for EGFR mutations using droplet digital PCR (ddPCR) on ctDNA. We evaluated the accuracy of EGFR mutation detection in ctDNA compared with tissue biopsy. We also quantified CTCs, ctDNA and CEA in serially collected blood samples, and evaluated the baseline and changes in these blood-based biomarkers with clinical outcomes.
EGFR mutation detection in plasma was highly concordant as compared with tissue biopsy. Detectable baseline ctDNA was associated with higher disease burden (p < 0.01). Early disappearance of ctDNA at 4 weeks was associated with radiological response at 12 weeks of treatment (p = 0.01) and improved progression free survival (PFS) (HR 5.47, 95%CI 1.32–22.72, p = 0.02) and overall survival (OS) (HR 5.46, 95%CI 1.28–23.22, p = 0.02). A decrease in CTC count at 4 weeks was associated with improved PFS (HR 3.81, 95%CI 1.13–12.79, p = 0.03) but not OS. 85% of patients with radiological progression had a ctDNA rise compared with 22% of patients with stable disease (p=0.01). ctDNA rise was seen on average 170 days prior to radiological progression. There is a significant association between the rise of CEA level with radiological progression (p=0.001).
Early change in ctDNA, CTC and CEA levels may be long-term predictors of treatment benefit and failure prior to availability of radiological response data.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Background
We estimated clinically important, group-level differences in self-reported cognitive function for the Functional Assessment of Cancer Therapy-Cognitive Function (FACT-Cog) instrument. We ...also investigated individual level change that could be considered meaningful for cancer survivors affected by cognitive impairment following chemotherapy, and that could be used for responder analyses. We used data from a multi-site randomized controlled trial in 242 participants that evaluated a web-based intervention for improving self-reported cognitive functioning in adult cancer survivors who reported cognitive impairment and who had adjuvant chemotherapy in the previous 6–60 months. We used anchor and distribution methods to estimate a range of clinically important differences (CIDs) and investigated meaningful change thresholds (MCTs) for the FACT-Cog and the Perceived Cognitive Impairments (PCI) subscale, post-intervention and at six-month follow-up with empirical cumulative distribution functions. Our primary anchor was the patient reported cognitive function subscale of the European Organization for Research and Treatment of Cancer Quality of Life-Cognitive Functioning Scale (EORTC-CF).
Results
Most participants were female (95%) breast cancer survivors (89%). Correlation of changes in the FACT-Cog and the EORTC-CF were 0.55 post-intervention and 0.61 at follow-up. Anchor-based CID estimates for the FACT-Cog using our primary anchor were 11.3 points (post) and 8.8 (follow-up), which corresponds to a standardized effect size of 0.49 and 0.38; 8.6% and 6.6% of the total scale’s range. Anchor-based CID estimates for the FACT-Cog PCI subscale were 7.4 (post) and 4.6 points (follow-up), which corresponds to a standardized effect size of 0.50 and 0.31; 10.3% and 6.4% of the PCI range). Empirical cumulative distribution functions of change in FACT-Cog demonstrating possible MCTs showed that anchor change of none, minimally better and much better were well separated.
Conclusions
The CID and MCT estimates from this manuscript can help in the design, analysis and interpretation of self-reported cognitive function in cancer patients and survivors.
•We model the fluvial degradation of impact craters on Titan.•This process can modify craters such that they would be unrecognizable from orbit.•It also removes central uplifts, explaining their ...infrequent occurrence on Titan.•Latitudinal differences in erosion rate may explain Titan’s crater distribution.
There are few identifiable impact craters on Titan, especially in the polar regions. One explanation for this observation is that the craters are being destroyed through fluvial processes, such as weathering, mass wasting, fluvial incision and deposition. In this work, we use a landscape evolution model to determine whether or not this is a viable mechanism for crater destruction on Titan. We find that fluvial degradation can modify craters to the point where they would be unrecognizable by an orbiting spacecraft such as Cassini, given enough time and a large enough erosion rate. A difference in the erosion rate between the equator and the poles of a factor of a few could explain the latitudinal variation in Titan’s crater population. Fluvial erosion also removes central peaks and fills in central pits, possibly explaining their infrequent occurrence in Titan craters. Although many craters on Titan appear to be modified by aeolian infilling, fluvial modification is necessary to explain the observed impact crater morphologies. Thus, it is an important secondary modification process even in Titan’s drier equatorial regions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
10.
Crater Morphometry on Callisto Bray, V. J.; Schenk, P. M.
The planetary science journal,
08/2024, Volume:
5, Issue:
8
Journal Article
Peer reviewed
Open access
Abstract Impact crater formation is affected by the physical properties of planetary crusts, allowing comparison of crater dimensions to serve as a proxy for comparing the crustal properties of ...different planetary bodies. New topographic profiles of Callisto craters, derived from Galileo-based digital terrain models, are presented, and the crater dimensions recorded. These data were used to derive crater morphometry scaling trends, which were then compared to the established trends of Ganymede and the Moon. Our comparative study suggests that the upper brittle portion of Callisto’s ice crust allows for the retention of steep-sided and elevated rim scarps, while subsurface warmer ice leads to an enhanced uplift and shallowing of the crater bowl. Crater dimensions are similar between Callisto and Ganymede, suggesting that the bulk properties of their near-surface crusts are comparable. The most notable difference between craters on these two Galilean moons were the smaller central pit diameters on Callisto. This difference can be explained if the pit formation on these bodies is controlled by the presence and movement (drainage and/or volatile loss) of impact melt water: the lower impact velocity and/or lower expected crustal heat flow on Callisto will result in less impact melt generation, and thus smaller central pits.
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