After DART: Using the First Full-scale Test of a Kinetic Impactor to Inform a Future Planetary Defense Mission

NASA’s Double Asteroid Redirection Test (DART) is the first full-scale test of an asteroid deflection technology. Results from the hypervelocity kinetic impact and Earth-based observations, coupled with LICIACube and the later Hera mission, will result in measurement of the momentum transfer efficiency accurate to ∼10% and characterization of the Didymos binary system. But DART is a single experiment; how could these results be used in a future planetary defense necessity involving a different asteroid? We examine what aspects of Dimorphos’s response to kinetic impact will be constrained by DART results; how these constraints will help refine knowledge of the physical properties of asteroidal materials and predictive power of impact simulations; what information about a potential Earth impactor could be acquired before a deflection effort; and how design of a deflection mission should be informed by this understanding. We generalize the momentum enhancement factor β, showing that a particular direction-specific β will be directly determined by the DART results, and that a related direction-specific β is a figure of merit for a kinetic impact mission. The DART β determination constrains the ejecta momentum vector, which, with hydrodynamic simulations, constrains the physical properties of Dimorphos’s near-surface. In a hypothetical planetary defense exigency, extrapolating these constraints to a newly discovered asteroid will require Earth-based observations and benefit from in situ reconnaissance. We show representative predictions for momentum transfer based on different levels of reconnaissance and discuss strategic targeting to optimize the deflection and reduce the risk of a counterproductive deflection in the wrong direction

The ESA Hera Mission: Detailed Characterization of the DART Impact Outcome and of the Binary Asteroid (65803) Didymos

Hera is a planetary defense mission under development in the Space Safety and Security Program of the European Space Agency for launch in 2024 October. It will rendezvous in late 2026 December with the binary asteroid (65803) Didymos and in particular its moon, Dimorphos, which will be impacted by NASA’s DART spacecraft on 2022 September 26 as the first asteroid deflection test. The main goals of Hera are the detailed characterization of the physical properties of Didymos and Dimorphos and of the crater made by the DART mission, as well as measurement of the momentum transfer efficiency resulting from DART’s impact. The data from the Hera spacecraft and its two CubeSats will also provide significant insights into asteroid science and the evolutionary history of our solar system. Hera will perform the first rendezvous with a binary asteroid and provide new measurements, such as radar sounding of an asteroid interior, which will allow models in planetary science to be tested. Hera will thus provide a crucial element in the global effort to avert future asteroid impacts at the same time as providing world-leading science

A Holocene climatic record from arid northwestern China

The history of climatic changes during the interval 8500-3000 cal. yr B.P. has been reconstructed from stratigraphical and chronological studies and the results of Total Organic Carbon (TOC), Total Inorganic Carbon (TIC), element composition, pollen, and stable isotope analyses of a section along the Hongshui River, in the southern Tengger Desert, NW China. The record suggests that from 8450 (bottom of the studied section) to 7500 yr B.P., the climate was characterized by instability. From 7500 to 5070 yr B.P., the climatic conditions improved and can be divided into two parts: a warm-humid sped between 7290 and 6380 yr B.P., during which the average temperature was 3-4 degrees C higher than that of today, and a warm-dry spell lasting from 5950 to 5720 yr B.P. The climate deteriorated between 6380 and 5950 yr B.P. From 5720 to 5070 yr B.P., the temperature decreased, but humidity increased. An abrupt temperature drop occurred between 5340 and 5290 yr B.P. that indicated the decline of the warmer and humid Mid-Holocene climate. From 5070 yr B.P. onward, the climate oscillated significantly and there were three large temperature decreases coinciding with high mountain glacier advances between 5070-4670 yr B.P., 4300-3740 yr B.P. and 3410-3230 yr B.P. (top of the section), respectively. The climatic fluctuations recorded in the southern Tengger Desert appear in-phase with climatic changes recognized in the Tibetan Plateau, suggesting that the period between 7290 and 6380 yr B.P. was the most warm-humid spell. One extremely dry event occurred at ca. 3000 yr B.P., and subsequently the fluvial-lacustrine depositional process terminated and wind action prevailed in the area; both of these features can be attributed to the rapid strengthening and weakening of the summer monsoon circulation, which are closely connected with global changes. (C) 2000 Elsevier Science B.V. All rights reserved

Lacustrine radiocarbon reservoir ages in Co Ngoin and Zige Tangco, central Tibetan Plateau

A series of C-14 ages were made in two lake sediment cores from Co Ngoin and Zige Tangco, central Tibetan Plateau, China, using bulk organic carbon, plant remains, chitin of cladocera, and carbonates. The old C-14 ages of the surface sediments in both cores suggests that there is a significant reservoir effect in these lakes. The magnitude of the reservoir age of different material is variable. Authigenic carbonate has the largest reservoir age, while plant remains and chitin show smaller deviations. Due to a lack of terrestrial macrofossils at most depths, a regression approach was used to obtain the approximate C-14 reservoir correction for bulk organic matter, which is 3260 C-14 BP and 2010 C-14 BP for Co Ngoin and Zige Tingco respectively. (C) 2009 Elsevier Ltd and INQUA. All rights reserved

Lake level and climate changes between 42,000 and 18,000 C-14 yr BP in the Tengger Desert, Northwestern China

Multiple lines of stratigraphic, geochemical, and fossil data suggest that fresh-mesohaline paleolakes were widespread in the Tengger Desert of northwestern China and underwent major fluctuations during the late Pleistocene. The paleolakes started to develop at ca. 42,000 C-14 yr B.P. The lake levels were the highest between 35,000 and 22,000 C-14 yr B.P., during which Megalake Tengger dominated the landscape. The climatic conditions at this time were unique for this area and have no modem analogue. After an episode of decline between 22,000 and 20,000 C-14 yr B.P. and an episode of rebound between 20,000 and 18,600 C-14 yr B.P., the paleolakes started to desiccate and completely disappeared around 18,000 C-14 yr B.P. The environmental proxy data indicate that the Megalake Tengger formed under warm-humid climates. The reconstructed climatic variations appear to be correlative with the abrupt climatic events reconstructed for the North Atlantic. (C) 2002 University of Washington

Holocene moisture evolution in Arid Central Asia and its out-of-phase relationship with Asian monsoon history

We synthesize palaeoclimate records from the mid-latitude arid Asian region dominated today by the Westerlies ("arid central Asia" (ACA)) to evaluate spatial and temporal patterns of moisture changes during the Holocene. Sediment records from I I takes with reliable chronologies and robust proxies were selected to reconstruct moisture histories based on a five-class ordinal wetness index with assigned scores from the driest to wettest periods at individual sites for 200-year time slices. The proxies used in these records include pollen and diatom assemblages, sediment lithology, lake levels, and geochemistry (mainly isotope) data. The results of our synthesis show that ACA as a whole experienced synchronous and coherent moisture changes during the Holocene, namely a dry early Holocene, a wetter (less dry) early to mid-Holocene, and a moderately wet late Holocene. During the early Holocene most of the lakes experienced very low water levels and even dried out before ca 8 ka (1 ka = 1000cal a BP). Hence the effective-moisture history in ACA is out-of-phase with that in monsoonal Asia as documented by numerous palaeoclimate records. In monsoonal Asia, a strong summer monsoon and humid climate characterized the early Holocene, and a weakened summer monsoon and drier climate prevailed during the late Holocene, which were mainly controlled by changes in low-latitude summer insolation. In contrast, we propose that the pattern of Holocene effective-moisture evolution in the westerly dominated ACA was mainly determined by North Atlantic sea-surface temperatures (SSTs) and high-latitude air temperatures that affect the availability, amount and transport of water vapor. Also, topography of the Tibetan Plateau and adjacent Asian highlands could have contributed to the intensification of dry climate in ACA during the early Holocene, as a result of strengthening the subsidence of dry air masses, associated with stronger uplift motion on the plateau by intense heating under a stronger summer insolation. Summer insolation might have played a key role in directly controlling moisture conditions in ACA but only after the northern hemisphere ice-sheets had disappeared in the mid- and late Holocene. (C) 2007 Elsevier Ltd. All rights reserved

Candidate Gene Resequencing in a Large Bicuspid Aortic Valve-Associated Thoracic Aortic Aneurysm Cohort: SMAD6 as an Important Contributor

Contains fulltext : 176973.pdf (publisher's version ) (Open Access)Bicuspid aortic valve (BAV) is the most common congenital heart defect. Although many BAV patients remain asymptomatic, at least 20% develop thoracic aortic aneurysm (TAA). Historically, BAV-related TAA was considered as a hemodynamic consequence of the valve defect. Multiple lines of evidence currently suggest that genetic determinants contribute to the pathogenesis of both BAV and TAA in affected individuals. Despite high heritability, only very few genes have been linked to BAV or BAV/TAA, such as NOTCH1, SMAD6, and MAT2A. Moreover, they only explain a minority of patients. Other candidate genes have been suggested based on the presence of BAV in knockout mouse models (e.g., GATA5, NOS3) or in syndromic (e.g., TGFBR1/2, TGFB2/3) or non-syndromic (e.g., ACTA2) TAA forms. We hypothesized that rare genetic variants in these genes may be enriched in patients presenting with both BAV and TAA. We performed targeted resequencing of 22 candidate genes using Haloplex target enrichment in a strictly defined BAV/TAA cohort (n = 441; BAV in addition to an aortic root or ascendens diameter >/= 4.0 cm in adults, or a Z-score >/= 3 in children) and in a collection of healthy controls with normal echocardiographic evaluation (n = 183). After additional burden analysis against the Exome Aggregation Consortium database, the strongest candidate susceptibility gene was SMAD6 (p = 0.002), with 2.5% (n = 11) of BAV/TAA patients harboring causal variants, including two nonsense, one in-frame deletion and two frameshift mutations. All six missense mutations were located in the functionally important MH1 and MH2 domains. In conclusion, we report a significant contribution of SMAD6 mutations to the etiology of the BAV/TAA phenotype

The science return of the ESA Hera Misson: The European component of the AIDA collaboration that will combine Hera and NASA DART missions data

Hera is a planetary defence mission with mission goals dedicated to that field. However, the data it collects will provide significant insights into asteroidal science and the evolutionary history of our Solar System. The uniqueness of the Hera target in the history of Solar System exploration - a small binary asteroid - will allow several current models and paradigms in planetary science to be tested. Hera will thus provide world-leading science at the same time as providing a crucial element in the global effort to avert future asteroid impacts