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Since 2012, the Curiosity rover has been diligently studying rocky outcrops on Mars, looking for clues about past water, climate, and habitability. Grotzinger et al. describe the analysis of a huge section of sedimentary rocks near Gale crater, where Mount Sharp now stands (see the Perspective by Chan). The features within these sediments are reminiscent of delta, stream, and lake deposits on Earth. Although individual lakes were probably transient, it is likely that there was enough water to fill in low-lying depressions such as impact craters for up to 10,000 years. Wind-driven erosion removed many of these deposits, creating Mount Sharp. Science , this issue p. 10.1126/science.aac7575 , see also p. 167 Mount Sharp now stands where there was once a large intercrater lake system. [Also see Perspective by Chan ] The landforms of northern Gale crater on Mars expose thick sequences of sedimentary rocks. Based on images obtained by the Curiosity rover, we interpret these outcrops as evidence for past fluvial, deltaic, and lacustrine environments. Degradation of the crater wall and rim probably supplied these sediments, which advanced inward from the wall, infilling both the crater and an internal lake basin to a thickness of at least 75 meters. This intracrater lake system probably existed intermittently for thousands to millions of years, implying a relatively wet climate that supplied moisture to the crater rim and transported sediment via streams into the lake basin. The deposits in Gale crater were then exhumed, probably by wind-driven erosion, creating Aeolis Mons (Mount Sharp).

The distribution and origin of serpentine on Mars can provide insights into the planet's aqueous history, habitability, and past climate. In this study, we used dynamic aperture factor analysis/target transformation applied to 15,760 images from the Compact Reconnaissance Imaging Spectrometer for Mars, followed by validation with the radiance ratio method, to construct a map of Mg‐serpentine deposits on Mars. Although relatively rare, Mg‐serpentine was detected in diverse geomorphic settings across Noachian and Hesperian‐aged terrains in the southern highlands of Mars, implying that serpentinization was active on early Mars and that multiple formation mechanisms may be needed to explain its spatial distribution. We also calculated the amount of H2 produced during the formation of the observed deposits and conclude that serpentinization was likely more widespread on Mars than indicated by the observed distribution.

The NASA Perseverance rover discovered light-toned float rocks scattered across the surface of Jezero crater that are particularly rich in alumina ( ~ 35 wt% Al 2 O 3 ) and depleted in other major elements (except silica). These unique float rocks have heterogeneous mineralogy ranging from kaolinite/halloysite-bearing in hydrated samples, to spinel-bearing in dehydrated samples also containing a dehydrated Al-rich phase. Here we describe SuperCam and Mastcam-Z observations of the float rocks, including the first in situ identification of kaolinite or halloysite on another planet, and dehydrated phases including spinel and apparent partially dehydroxylated kaolinite. The presence of spinel in these samples is likely detrital in origin, surviving kaolinitization, pointing to an ultramafic origin. However, the association of low hydration with increased Al 2 O 3 abundances suggests heating-induced dehydration which could have occurred during the lithification or impact excavation of these rocks. Given the orbital context of kaolinite-bearing megabreccia in the Jezero crater rim, we propose an origin for these rocks involving intense aqueous alteration of the parent material, followed by dehydration/lithification potentially through impact processes, and dispersion into Jezero crater through flood or impact-related processes. Aqueous alteration followed by dehydration and dispersion into Jezero crater is indicated by the identification of kaolinite or halloysite, spinel and a dehydrated Al-rich phase in spectroscopic observations of light-toned float rocks by the Perseverance rover

We use the crystallinity of hydrated silica, represented by the 1.4 μm absorption position in orbiter spectroscopic data, as a proxy for the longevity of water–rock interaction in the Syrtis Major region. Geological maps and crater size–frequency distribution analyses are employed to contextualize mineral detections and estimate surface ages. Hydrated silica is detected within two distinct geological units: a younger “volcanic terrain” (vt) unit (∼2.4 Ga) and an older “highland terrain” (ht) unit (3.5–3.7 Ga). Hydrated silica in the vt unit typically has a band position <1.41 μm, consistent with amorphous opal‐A, suggesting these younger terrains have experienced limited interaction with water. In contrast, hydrated silica in the older highlands typically has a band position >1.41 μm, indicating opal‐CT, suggesting that these deposits have had more time to interact with water, while also producing accessory minerals such as kaolinite and Fe/Mg phyllosilicates. Plain Language Summary This study explores the interactions between water and rocks in a region on Mars known as Syrtis Major by investigating a mineral‐like substance called hydrated silica. The structure of hydrated silica helps us estimate the extent of water interaction and its effects on the rocks. We used satellite data to locate this mineral across Syrtis Major and infer its crystal structure. Furthermore, we developed detailed geological maps and estimated surface ages to understand the geological context. We found that hydrated silica is located in two different types of areas: (a) a younger volcanic region; and (b) an older highland region. In the younger volcanic areas, it appears that less crystalline hydrated silica formed by interaction with small amounts of water, possibly during later volcanic activity. In the older highlands, more crystalline hydrated silica likely interacted with water for a longer duration or in larger amounts. This information aligns with the idea that the older highlands experienced more extensive or long‐lasting interactions with water compared to the younger volcanic regions. It provides insights into different wet periods in Mars' past, aiding our understanding of the planet's geological history and the role water played in shaping its surface. Key Points We analyzed the crystallinity of hydrated silica in Syrtis Major to infer the extent and longevity of water–rock interaction Amorphous silica is found in young volcanic terrains within Nili and Meroe Paterae and more crystalline silica in the older highlands Older highland regions likely underwent a longer interaction with water compared to younger volcanic terrains

Before the Perseverance rover landing, the acoustic environment of Mars was unknown. Models predicted that: (1) atmospheric turbulence changes at centimetre scales or smaller at the point where molecular viscosity converts kinetic energy into heat1, (2) the speed of sound varies at the surface with frequency2,3 and (3) high-frequency waves are strongly attenuated with distance in CO2 (refs. 2,3,4). However, theoretical models were uncertain because of a lack of experimental data at low pressure and the difficulty to characterize turbulence or attenuation in a closed environment. Here, using Perseverance microphone recordings, we present the first characterization of the acoustic environment on Mars and pressure fluctuations in the audible range and beyond, from 20 Hz to 50 kHz. We find that atmospheric sounds extend measurements of pressure variations down to 1,000 times smaller scales than ever observed before, showing a dissipative regime extending over five orders of magnitude in energy. Using point sources of sound (Ingenuity rotorcraft, laser-induced sparks), we highlight two distinct values for the speed of sound that are about 10 m s−1 apart below and above 240 Hz, a unique characteristic of low-pressure CO2-dominated atmosphere. We also provide the acoustic attenuation with distance above 2 kHz, allowing us to explain the large contribution of the CO2 vibrational relaxation in the audible range. These results establish a ground truth for the modelling of acoustic processes, which is critical for studies in atmospheres such as those of Mars and Venus.

The Perseverance rover has collected seven oriented samples of sedimentary rocks, all likely older than the oldest signs of widespread life on Earth, at the exposed base of the western fan in Jezero crater, Mars. The samples include a sulfate‐ and clay‐bearing mudstone and sandstone, a fluvial sandstone from a stratigraphically low position at the fan front, and a carbonate‐bearing sandstone deposited above the sulfate‐bearing strata. All samples contain aqueously precipitated materials and most or all were aqueously deposited. Although the rover instruments have not confidently detected organic matter in the rocks from the fan front, the much more sensitive terrestrial instruments will still be able to search for remnants of prebiotic chemistries and past life, and study Mars's past habitability in the samples returned to Earth. The hydrated, sulfate‐bearing mudstone has the highest potential to preserve organic matter and biosignatures, whereas the carbonate‐bearing sandstones can be used to constrain when and for how long Jezero crater contained liquid water. Returned sample science analyses of sulfate, carbonate, clay, phosphate and igneous minerals as well as trace metals and volatiles that are present in the samples acquired at the fan front would provide transformative insights into past habitable environments on Mars, the evolution of its magnetic field, atmosphere and climate and the past and present cycling of atmospheric and crustal water, sulfur and carbon. Plain Language Summary The Perseverance rover collected seven oriented samples of bedrock at the front of the apron‐like sediment deposit in the western side of Jezero crater, Mars. Grains and cements in these sedimentary rocks were likely deposited by water or formed in the presence of water in a range of past environments that predate the first signs of life on Earth. This study describes the geologic context and chemical composition of these samples and discusses how, upon return to Earth, they can be used to search for potential signs of past life, understand when and for how long Mars was habitable and why its climate changed. Studies of the returned samples would seek to detect and analyze organic compounds that may be present below the detection limit of the rover instruments, particularly in the finest‐grained rocks, and look for the traces of prebiotic processes or past life in all collected samples of sedimentary rocks. Additional analyses can also constrain tell us when, why and for how long the rivers and lakes existed in Jezero crater. The presence of diverse materials in rocks that were deposited by or into water can transform current views of Mars science and habitability outside of Earth. Key Points The Perseverance rover has collected seven cores of aqueously deposited sandstones and siltstones at the front of Jezero's western fan Hydrated sulfate, clay and carbonate minerals in the cores record the history of Mars's volatiles and surface habitability The same minerals may preserve organic and inorganic signals of abiotic, prebiotic and biological processes

AbstractBefore the Perseverance rover landing, the acoustic environment of Mars was unknown. Models predicted that: (1) atmospheric turbulence changes at centimetre scales or smaller at the point where molecular viscosity converts kinetic energy into heat1, (2) the speed of sound varies at the surface with frequency2,3and (3) high-frequency waves are strongly attenuated with distance in CO2(refs. 2–4). However, theoretical models were uncertain because of a lack of experimental data at low pressure and the difficulty to characterize turbulence or attenuation in a closed environment. Here, using Perseverance microphone recordings, we present the first characterization of the acoustic environment on Mars and pressure fluctuations in the audible range and beyond, from 20 Hz to 50 kHz. We find that atmospheric sounds extend measurements of pressure variations down to 1,000 times smaller scales than ever observed before, showing a dissipative regime extending over five orders of magnitude in energy. Using point sources of sound (Ingenuity rotorcraft, laser-induced sparks), we highlight two distinct values for the speed of sound that are about 10 m s−1apart below and above 240 Hz, a unique characteristic of low-pressure CO2-dominated atmosphere. We also provide the acoustic attenuation with distance above 2 kHz, allowing us to explain the large contribution of the CO2vibrational relaxation in the audible range. These results establish a ground truth for the modelling of acoustic processes, which is critical for studies in atmospheres such as those of Mars and Venus. 

When does a statute grant powers to the President as opposed to other officials? Prominent theories of presidential power argue or assume that any statute granting authority to an executive officer also implicitly confers that authority upon the President. This Article challenges that statutory construction. It argues that the President has statutory authority to direct the administration of the laws only under statutes that grant to the President in name. Congress's enduring practice of granting power to executive officers subject to express conditions of presidential control supports a strong negative inference that the President has no directive authority when a statute grants authority to an executive officer without any mention of presidential control. Such a construction also has significant institutional advantages: Not only is Congress generally ill equipped to police the validity of the President's assertions of statutory authority, but the President has strong incentives to claim that his actions are authorized by existing statutes. Limiting the occasions for the President to claim statutory power to those statutes in which Congress has expressly granted him authority helps to restrict the President's adventurous assertions of statutory power and provides a check on the President internal to the executive branch, while still recognizing Congress's important interests in placing certain matters in the President's own hands. This statutory conclusion further implies-contrary to the suggestion of Dean Elena Kagan-that presidential direction of administrative agency action may not qualify for judicial deference under Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc. unless the statute expressly grants authority to the President. It also provides an account of the legal status of executive orders and other presidential directives that lack independent constitutional authorization: Those directives may legally bind the discretion of executive officials and the public only if the President acts under a statute granting power to the President in name.

Collection of samples that could be returned to Earth from the floor of Jezero crater is a major goal of the Mars 2020 mission. Laboratory analyses of these will expand exploration of Jezero, a Noachian crater on Mars characterized by a delta–lake system with high potential for habitability. The samples will also be used to test current ideas about the early planetary evolution of Mars. The Perseverance rover has collected samples from two members of the Máaz formation, mapped in orbital images as the Crater floor fractured rough unit by [1]. Type localities of the Roubion and Rochette members have been targeted and abraded prior to sample collection. Here we summarize these sampling activities and the potential of sampling the Chal member of Máaz. A similar summary for samples collected from the Séítah formation is described in Hickman-Lewis et al. (this meeting).

BackgroundIntra-articular narcotics have proven efficacy for providing pain relief following knee arthroscopy. This effect is short-lived. Methadone, with its long serum half-life (thirty-five hours, compared with two hours for morphine) could provide improved and prolonged pain relief. The purpose of the present study was to examine the effects of an intra-articular injection of methadone on postoperative analgesia following arthroscopic anterior cruciate ligament reconstruction.MethodsSixty-five skeletally mature patients undergoing primary anterior cruciate ligament reconstruction were randomly assigned to one of three groups, all of which received an intra-articular injection consisting of 9.5 mL of 0.5% bupivacaine with 1:200,000 epinephrine at the completion of the procedure. In addition, the remaining 0.5 mL of the syringe was filled with one of three substances. The study group (twenty-five patients) received 5 mg of methadone, the comparison group (twenty-one patients) received 5 mg of morphine, and the control group (nineteen patients) received 0.5 mL of saline solution. All supplemental pain medications were given on an as-needed basis, recorded, and converted to morphine equivalents. Specific variables that were measured included supplemental analgesia requirements during both the inpatient period and the outpatient period (from the time of discharge to the seventh postoperative day) and pain scores.ResultsThere was no significant difference in inpatient (p = 0.998) or outpatient (p = 0.887) supplemental analgesic requirements or pain scores between the methadone group (Group 1) and the control group (Group 3). The morphine group (Group 2) required significantly less inpatient (p = 0.014) and outpatient (p = 0.044) supplemental analgesia compared with the control group (Group 3). There were no complications.ConclusionsThe present report represents the first known study of the use of intra-articular methadone and establishes that this analgesic is safe at a single dose of 5 mg. At this dose, however, methadone does not provide improved postoperative analgesia following arthroscopic anterior cruciate ligament reconstruction. In contrast, intra-articular morphine does appear to be effective for decreasing postoperative pain.Level of EvidenceTherapeutic Level I. See Instructions to Authors for a complete description of levels of evidence.