424 research outputs found
Freeze-Thaw Cycling as a Chemical Weathering Agent on a Cold and Icy Mars
Liquid water was abundant on early Mars, but whether the climate was warm and wet or cold and icy with punctuated periods of melting is still poorly understood. Modern climate models for Mars tend to predict a colder, icier early climate than previously imagined. In addition, ice and glaciation have been major geologic agents throughout the later Hesperian and Amazonian eras. One process that can act in such climates is repeated freezing and thawing of water on the surface and in the subsurface, and is significant because it can occur anywhere with an active layer and could have persisted for a time after liquid water was no longer stable on Mars surface. As freeze-thaw is the dominant mechanical weathering process in most glacial/periglacial terrains, it was likely a significant geomorphologic driver at local to regional scales during past climates, and would potentially have been most active when day-average surface temperatures exceeded 0 C for part of the year. Indeed, freeze-thaw involving liquid water in the Amazonian is evidenced by abundant geomorphic features including polygonal ground and solifluction lobes requiring seasonal thawing. In addition to physical modification, freezing can drive solutions towards supersaturation and force dissolved solutes out as precipitates. In Mars-like terrains, dissolved solutes are typically dominated by silica. In polar regions on Earth, freeze-thaw cycles have been shown to promote deposition of silica, and freeze-thaw experiments on synthetic solutions found stable amorphous silica that built up over multiple cycles. Freeze-thaw may therefore be an important but overlooked chemical weathering process on Mars. However, our ability to assess its impact on alteration of martian terrains is majorly limited by the current lack of understanding of the alteration phases produced (and formation rates) under controlled freeze-thaw weathering of Mars-relevant materials. To address this knowledge gap, we report results from (1) freeze-thaw weathering products found at a glacial Mars analog site at the Three Sisters, Oregon, and (2) new controlled freeze-thaw experiments on basaltic material
Forensic DNA phenotyping: Developing a model privacy impact assessment
© 2018 Elsevier B.V. Forensic scientists around the world are adopting new technology platforms capable of efficiently analysing a larger proportion of the human genome. Undertaking this analysis could provide significant operational benefits, particularly in giving investigators more information about the donor of genetic material, a particularly useful investigative lead. Such information could include predicting externally visible characteristics such as eye and hair colour, as well as biogeographical ancestry. This article looks at the adoption of this new technology from a privacy perspective, using this to inform and critique the application of a Privacy Impact Assessment to this emerging technology. Noting the benefits and limitations, the article develops a number of themes that would influence a model Privacy Impact Assessment as a contextual framework for forensic laboratories and law enforcement agencies considering implementing forensic DNA phenotyping for operational use
Large parallel and perpendicular electric fields on electron spatial scales in the terrestrial bow shock
Large parallel ( 100 mV/m) and perpendicular ( 600 mV/m) electric
fields were measured in the Earth's bow shock by the vector electric field
experiment on the Polar satellite. These are the first reported direct
measurements of parallel electric fields in a collisionless shock. These fields
exist on spatial scales comparable to or less than the electron skin depth (a
few kilometers) and correspond to magnetic field-aligned potentials of tens of
volts and perpendicular potentials up to a kilovolt. The perpendicular fields
are amongst the largest ever measured in space, with energy densities of
of order 10%. The measured parallel electric field
implies that the electrons can be demagnetized, which may result in stochastic
(rather than coherent) electron heating
Mineralogical Signatures of Cold and Icy Climates on Ancient and Modern Mars
Liquid water was abundant on early Mars, but whether the climate was warm and wet or cold and icy with punctuated periods of melting is still poorly understood. Modern climate models for Mars tend to predict a colder, icier early climate than previously imagined [e.g., 1]. However, any model for the early climate on Mars must be reconciled with the chemical record. We currently do not understand how alteration mineralogy formed in snow and ice dominated conditions compares to that of warmer climates, and it is unclear whether cold climate weathering could form all or any of the aqueous alteration phases expressed on early martian surfaces [2]. To help resolve this knowledge gap, we synthesize results from glacial Mars analog sites at the Three Sisters, Oregon and mafic regions of the Antarctic ice sheet, and compare them to the surface mineralogy of Mars. These sites provide the opportunity to investigate weathering in environments analogous to glacial environments on Mars throughout geologic time, including snowpacks or smaller wet-based or polythermal glaciers [3, 4] as well as the proposed extensive ice sheets of the late Noachian icy highlands mode
Spectral Interpretation of Magmatic Evolution, Oxidation, and Crystallinity in a Volcanic Planetary Analog System
Volcanic surfaces are common and varied throughout the terrestrial planets. Remote spectroscopy is often the only method for determining surface chemistry and mineralogy of such provinces, and is thus critical for understanding petrologic processes and constraining planetary interior evolution and chemistry. Natural volcanic systems exhibit variability in magmatic chemical evolution, crystallinity, oxidation, and eruption-related alteration (e.g. hydrothermal). The extent to which spectroscopy can identify these characteristics alongside each other is thus a key question for interpreting volcanic processes from orbit. While the effects of each of these on visible/near infrared (VNIR) and thermal infrared (TIR) spectra of igneous rocks has been studied separately to varying degrees, their combined spectral effects (and interpretability of such spectra) are understudied
Differentiating Hydrothermal, Pedogenic, and Glacial Weathering in a Cold Volcanic Mars-Analog Environment
Although the current cold, dry environment of Mars extends back through much of its history, its earliest periods experienced significant water- related surface activity. Both geomorphic features (e.g., paleolakes, deltas, and river valleys) and hydrous mineral detections (e.g., clays and salts) have historically been interpreted to imply a "warm and wet" early Mars climate. More recently, atmospheric modeling studies have struggled to produce early climate conditions with temperatures above 0degC, leading some studies to propose a "cold and icy" early Mars dominated by widespread glaciation with transient melting. However, the alteration mineralogy produced in subglacial environments is not well understood, so the extent to which cold climate glacial weathering can produce the diverse alteration mineralogy observed on Mars is unknown. This summer, we will be conducting a field campaign in a glacial weathering environment in the Cascade Range, OR in order to determine the types of minerals that these environments produce. However, we must first disentangle the effects of glacial weathering from other significant alteration processes. Here we attempt a first understanding of glacial weathering by differentiating rocks and sediments weathered by hydrothermal, pedogenic, and glacial weathering processes in the Cascades volcanic range
Silica Dissolution and Precipitation in Galciated Volcanic Environments and Implications for Mars
The surface of Mars exhibits strong evidence for a widespread and long-lived cryosphere. Observations of the surface have identified phases produced by water-rock interactions, but the contribution of glaciers to the observed alteration mineralogy is unclear. To characterize the chemical alteration expected on an icy early Mars, we collected water and rock samples from terrestrial glaciated volcanics. We related geochemical measurements of meltwater to the mineralogy and chemistry of proglacial rock coatings. In these terrains, water is dominated by dissolved silica relative to other dissolved cations, particularly at mafic sites. Rock coatings associated with glacial striations on mafic boulders include a silica-rich component, indicating that silica precipitation is occurring in the subglacial environment. We propose that glacial alteration of volcanic bedrock is dominated by a combination of high rates of silica dissolution and precipitation of opaline silica. On Mars, cryosphere-driven chemical weathering could be the origin of observed silica-enriched phases
Crowdsourced and crowdfunded: the future of forensic DNA?
© 2018 Informa UK Limited, trading as Taylor & Francis Group Forensic DNA analysis is dependent on comparing the known and the unknown. Expand the number of known profiles, and the likelihood of a successful match increases. Forensic use of DNA is moving towards comparing samples of unknown origin with publicly available genetic data, such as the records held by genetic genealogy providers. Use of forensic genetic genealogy has yielded a number of recent high-profile successes but has raised ethical and privacy concerns. Navigating family trees is complex, even more so when combined with a comparison of genetic relationships. This intelligence-gathering process has led to occasional false leads, and its use also risks a public backlash, similar to concerns over Cambridge Analytica. A cautious approach to use of this technique is therefore warranted
Sediment Transport and Aqueous Alteration in a Mars-Analog Glacial System
The bulk of the Martian crust is basaltic with a wide variety of subsequently derived aqueous alteration phases. Study of analogue terrains is vital to better understand the weathering of such mafic bedrock at a range of surface temperatures. Moreover, climatic models have suggested that the early Martian climate was not warm and wet, but cold and icy, with some of the apparent fluvial and lacustrine features attributable to transient melting of ice sheets as opposed to persistent surface water. This study examines sediment samples from Collier glacial valley, Three Sisters, Oregon (OR), with the aim of better characterizing erosion, transport, and in situ aqueous alteration in a glaciated Mars-analogue terrain
Basalt Weathering in a Cold and Icy Climate: Three Sisters, Oregon as an Analog for Early Mars
There is abundant evidence for liquid water on early Mars, but the debate remains whether early Mars was warm and wet or cold and icy with punctuated periods of melting. To further investigate the hypothesis of a cold and icy early Mars, we collected rocks and sediments from the Collier and Diller glacial valleys in the Three Sisters volcanic complex in Oregon. We analyzed rocks and sediments with X-ray diffraction (XRD), scanning and transmission electron microscopies with energy dispersive spectroscopy (SEM, TEM, EDS), and visible, short-wave infrared (VSWIR) and thermal-IR (TIR) spectroscopies to characterize chemical weathering and sediment transport through the valleys. Here, we focus on the composition and mineralogy of the weathering products and how they compare to those identified on the martian surface. Phyllosilicates (smectite), zeolites, and poorly crystalline phases were discovered in pro- and supra-glacial sediments, whereas Si-rich regelation films were found on hand samples and boulders in the proglacial valleys. Most phyllosilicates and zeolites are likely detrital, originating from hydrothermally altered units on North Sister. TEM-EDS analyses of the <2 um size fraction of glacial flour samples demonstrate a variety of poorly crystalline (i.e., no long-range crystallographic order) phases: iron oxides, devitrified volcanic glass, and Fe-Si-Al phases. The CheMin XRD on the Curiosity rover in Gale crater has identified significant amounts of X-ray amorphous materials in all samples measured to date. The amorphous component is likely a combination of silicates, iron oxides, and sulfates. Although we have not yet observed amorphous sulfate in the samples from Three Sisters, the variety of poorly crystalline weathering products found at this site is consistent with the variable composition of the X-ray amorphous component identified by CheMin. We suggest that these amorphous phases on Mars could have formed in a similarly cold and icy environment
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