In this paper we present an in-depth study of the distributions of various neutral species in Titan's upper atmosphere, between 950 and 1500 km for abundant species (N
2, CH
4, H
2) and between 950 ...and 1200 km for other minor species. Our analysis is based on a large sample of Cassini/INMS (Ion Neutral Mass Spectrometer) measurements in the CSN (Closed Source Neutral) mode, obtained during 15 close flybys of Titan. To untangle the overlapping cracking patterns, we adopt Singular Value Decomposition (SVD) to determine simultaneously the densities of different species. Except for N
2, CH
4, H
2 and
40Ar (as well as their isotopes), all species present density enhancements measured during the outbound legs. This can be interpreted as a result of wall effects, which could be either adsorption/desorption of these molecules or heterogeneous surface chemistry of the associated radicals on the chamber walls. In this paper, we provide both direct inbound measurements assuming ram pressure enhancement only and abundances corrected for wall adsorption/desorption based on a simple model to reproduce the observed time behavior. Among all minor species of photochemical interest, we have firm detections of C
2H
2, C
2H
4, C
2H
6, CH
3C
2H, C
4H
2, C
6H
6, CH
3CN, HC
3N, C
2N
2 and NH
3 in Titan's upper atmosphere. Upper limits are given for other minor species.
The globally averaged distributions of N
2, CH
4 and H
2 are each modeled with the diffusion approximation. The N
2 profile suggests an average thermospheric temperature of 151 K. The CH
4 and H
2 profiles constrain their fluxes to be
2.6
×
10
9
cm
−
2
s
−
1
and
1.1
×
10
10
cm
−
2
s
−
1
, referred to Titan's surface. Both fluxes are significantly higher than the Jeans escape values. The INMS data also suggest horizontal/diurnal variations of temperature and neutral gas distribution in Titan's thermosphere. The equatorial region, the ramside, as well as the nightside hemisphere of Titan appear to be warmer and present some evidence for the depletion of light species such as CH
4. Meridional variations of some heavy species are also observed, with a trend of depletion toward the north pole. Though some of the above variations might be interpreted by either the solar-driven models or auroral-driven models, a physical scenario that reconciles all the observed horizontal/diurnal variations in a consistent way is still missing. With a careful evaluation of the effect of restricted sampling, some of the features shown in the INMS data are more likely to be observational biases.
The flyby measurements of the Cassini spacecraft at Saturn's moon Rhea reveal a tenuous oxygen (O₂)-carbon dioxide (CO₂) atmosphere. The atmosphere appears to be sustained by chemical decomposition ...of the surface water ice under irradiation from Saturn's magnetospheric plasma. This in situ detection of an oxidizing atmosphere is consistent with remote observations of other icy bodies, such as Jupiter's moons Europa and Ganymede, and suggestive of a reservoir of radiolytic O₂ locked within Rhea's ice. The presence of CO₂ suggests radiolysis reactions between surface oxidants and organics or sputtering and/or outgassing of CO₂ endogenic to Rhea's ice. Observations of outflowing positive and negative ions give evidence for pickup ionization as a major atmospheric loss mechanism.
The Lower to Middle Paleolithic transition (~400,000 to 200,000 years ago) is marked by technical, behavioral, and anatomical changes among hominin populations throughout Africa and Eurasia. The ...replacement of bifacial stone tools, such as handaxes, by tools made on flakes detached from Levallois cores documents the most important conceptual shift in stone tool production strategies since the advent of bifacial technology more than one million years earlier and has been argued to result from the expansion of archaic Homo sapiens out of Africa. Our data from Nor Geghi 1, Armenia, record the earliest synchronic use of bifacial and Levallois technology outside Africa and are consistent with the hypothesis that this transition occurred independently within geographically dispersed, technologically precocious hominin populations with a shared technological ancestry.
The Cassini Ultraviolet Imaging Spectrograph (UVIS) observed an occultation of the Sun by the water vapor plume at the south polar region of Saturn's moon Enceladus. The Extreme Ultraviolet (EUV) ...spectrum is dominated by the spectral signature of H2O gas, with a nominal line‐of‐sight column density of 0.90 ± 0.23 × 1016 cm−2 (upper limit of 1.0 × 1016 cm−2). The upper limit for N2 is 5 × 1013 cm−2, or <0.5% in the plume; the lack of N2 has significant implications for models of the geochemistry in Enceladus' interior. The inferred rate of water vapor injection into Saturn's magnetosphere is ∼200 kg/s. The calculated values of H2O flux from three occultations observed by UVIS have a standard deviation of 30 kg/s (15%), providing no evidence for substantial short‐term variability. Collimated gas jets are detected in the plume with Mach numbers of 5–8, implying vertical gas velocities that exceed 1000 m/sec. Observations at higher altitudes with the Cassini Ion Neutral Mass Spectrometer indicate correlated structure in the plume. Our results support the subsurface liquid model, with gas escaping and being accelerated through nozzle‐like channels to the surface, and are consistent with recent particle composition results from the Cassini Cosmic Dust Analyzer.
Key Points
N2 upper limit
Mach number of jets ranges from 5 to 8, more collimated than previous estimate
Flux of water vapor stable over last 6 years at 200 kg/sec
Jets of water ice from surface fractures near the south pole of Saturn's icy moon Enceladus produce a plume of gas and particles. The source of the jets may be a liquid water region under the ice ...shell-as suggested most recently by the discovery of salts in E-ring particles derived from the plume-or warm ice that is heated, causing dissociation of clathrate hydrates. Here we report that ammonia is present in the plume, along with various organic compounds, deuterium and, very probably, (40)Ar. The presence of ammonia provides strong evidence for the existence of at least some liquid water, given that temperatures in excess of 180K have been measured near the fractures from which the jets emanate. We conclude, from the overall composition of the material, that the plume derives from both a liquid reservoir (or from ice that in recent geological time has been in contact with such a reservoir) as well as from degassing, volatile-charged ice.
•Europa plumes may feed a global exosphere with complex structure and dynamics•Water and organics may be enhanced on the dayside during polar plume activity•Prior plumes or chemically enriched ...terrain may yield detectable exospheric signs•Model gives species density criteria for plume or enriched terrain detection
A Europa plume source, if present, may produce a global exosphere with complex spatial structure and temporal variability in its density and composition. To investigate this interaction we have integrated a water plume source containing multiple organic and nitrile species into a Europan Monte Carlo exosphere model, considering the effect of Europa's gravity in returning plume ejecta to the surface, and the subsequent spreading of adsorbed and exospheric material by thermal desorption and re-sputtering across the entire body. We consider sputtered, radiolytic and potential plume sources, together with surface adsorption, regolith diffusion, polar cold trapping, and re-sputtering of adsorbed materials, and examine the spatial distribution and temporal evolution of the exospheric density and composition. These models provide a predictive basis for telescopic observations (e.g. HST, JWST) and planned missions to the Jovian system by NASA and ESA. We apply spacecraft trajectories to our model to explore possible exospheric compositions which may be encountered along proposed flybys of Europa to inform the spatial and temporal relationship of spacecraft measurements to surface and plume source compositions. For the present preliminary study, we have considered four cases: Case A: an equatorial flyby through a sputtered only exosphere (no plumes), Case B: a flyby over a localized sputtered ‘macula’ terrain enriched in non-ice species, Case C: a south polar plume with an Enceladus-like composition, equatorial flyby, and Case D: a south polar plume, flyby directly through the plume.
Background
Pregnant and postpartum women with severe hypertension are at increased risk of stroke and require blood pressure (BP) reduction. Parenteral antihypertensives have been most commonly ...studied, but oral agents would be ideal for use in busy and resource‐constrained settings.
Objectives
To review systematically, the effectiveness of oral antihypertensive agents for treatment of severe pregnancy/postpartum hypertension.
Search strategy
A systematic search of MEDLINE, EMBASE and the Cochrane Library was performed.
Selection criteria
Randomised controlled trials in pregnancy and postpartum with at least one arm consisting of a single oral antihypertensive agent to treat systolic BP ≥ 160 mmHg and/or diastolic BP ≥ 110 mmHg.
Data collection and analysis
Cochrane RevMan 5.1 was used to calculate relative risk (RR) and weighted mean difference by random effects.
Main results
We identified 15 randomised controlled trials (915 women) in pregnancy and one postpartum trial. Most trials in pregnancy compared oral/sublingual nifedipine capsules (8–10 mg) with another agent, usually parenteral hydralazine or labetalol. Nifedipine achieved treatment success in most women, similar to hydralazine (84% with nifedipine; relative risk RR 1.07, 95% confidence interval 95% CI 0.98–1.17) or labetalol (100% with nifedipine; RR 1.02, 95% CI 0.95–1.09). Less than 2% of women treated with nifedipine experienced hypotension. There were no differences in adverse maternal or fetal outcomes. Target BP was achieved ~ 50% of the time with oral labetalol (100 mg) or methyldopa (250 mg) (47% labetelol versus 56% methyldopa; RR 0.85 95% CI 0.54–1.33).
Conclusions
Oral nifedipine, and possibly labetalol and methyldopa, are suitable options for treatment of severe hypertension in pregnancy/postpartum.
By traversing the plume erupting from high southern latitudes on Saturn's moon Enceladus, Cassini orbiter instruments can directly sample the material therein. Cassini Plasma Spectrometer, CAPS, data ...show that a major plume component comprises previously‐undetected particles of nanometer scales and larger that bridge the mass gap between previously observed gaseous species and solid icy grains. This population is electrically charged both negative and positive, indicating that subsurface triboelectric charging, i.e., contact electrification of condensed plume material may occur through mutual collisions within vents. The electric field of Saturn's magnetosphere controls the jets' morphologies, separating particles according to mass and charge. Fine‐scale structuring of these particles' spatial distribution correlates with discrete plume jets' sources, and reveals locations of other possible active regions. The observed plume population likely forms a major component of high velocity nanometer particle streams detected outside Saturn's magnetosphere.
Gravitational waves were discovered with the detection of binary black-hole mergers and they should also be detectable from lower-mass neutron-star mergers. These are predicted to eject material rich ...in heavy radioactive isotopes that can power an electromagnetic signal. This signal is luminous at optical and infrared wavelengths and is called a kilonova. The gravitational-wave source GW170817 arose from a binary neutron-star merger in the nearby Universe with a relatively well confined sky position and distance estimate. Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC 4993, which is spatially coincident with GW170817 and with a weak, short γ-ray burst. The transient has physical parameters that broadly match the theoretical predictions of blue kilonovae from neutron-star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 ± 0.01 solar masses, with an opacity of less than 0.5 square centimetres per gram, at a velocity of 0.2 ± 0.1 times light speed. The power source is constrained to have a power-law slope of -1.2 ± 0.3, consistent with radioactive powering from r-process nuclides. (The r-process is a series of neutron capture reactions that synthesise many of the elements heavier than iron.) We identify line features in the spectra that are consistent with light r-process elements (atomic masses of 90-140). As it fades, the transient rapidly becomes red, and a higher-opacity, lanthanide-rich ejecta component may contribute to the emission. This indicates that neutron-star mergers produce gravitational waves and radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements.
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