A spectral comparison of (379) Huenna and its satellite

We present near-infrared spectral measurements of Themis family Asteroid (379) Huenna (D ∼ 98 km) and its 6 km satellite using SpeX on the NASA IRTF. The companion was farther than 1.5″ from the primary at the time of observations and was approximately 5 magnitudes dimmer. We describe a method for separating and extracting the signal of a companion asteroid when the signal is not entirely resolved from the primary. The spectrum of (379) Huenna has a broad, shallow feature near 1 μm and a low slope, characteristic of C-type asteroids. The secondary’s spectrum is consistent with the taxonomic classification of C-complex or X-complex. The quality of the data was not sufficient to identify any subtle feature in the secondary’s spectrum.     

Why are climate policies of the present decade so crucial for keeping the 2 °C target credible?

Decision-makers have confirmed the long term objective of preventing a temperature increase greater than 2 °C. This paper aims at appraising by means of a cost-benefit analysis whether decision makers’ commitment to meet the 2 °C objective is credible or not. Within the framework of a cost-benefit type integrated assessment model, we consider that the economy faces climate damages with a threshold at 2 °C. We run the model for a broad set of scenarios accounting for the diversity of “worldviews” in the climate debate. For a significant share of scenarios we observe that it is considered optimal to exceed the threshold. Among those “non-compliers” we discriminate ”involuntary non-compliers” who cannot avoid the exceedance due to physical constraint from ”deliberate compliers” for whom the exceedance results from a deliberate costs-benefit analysis. A second result is that the later mitigation efforts begin, the more difficult it becomes to prevent the exceedance. In particular, the number of ”deliberate non-compliers” dramatically increases if mitigation efforts do not start by 2020, and the influx of involuntary non-compliers become overwhelming f efforts are delayed to 2040. In light of these results we argue that the window of opportunity for reaching the 2 °C objective with a credible chance of success is rapidly closing during the present decade. Further delay in finding a climate agreement critically undermines the credibility of the objective.     

Performance analysis of multi-GNSS static and RTK techniques in estimating height differences

ABSTRACT

Establishing reliable elevation differences is imperative for most geoscience and engineering applications. This work has traditionally been accomplished through spirit leveling techniques; however, surveyors have been utilizing satellite positioning systems in measuring height differences for more than a decade. Yet the quality of these heights needs to be evaluated in order to adopt them in different applications. In this article, we present the outcome of an accuracy assessment of height differences obtained with static and RTK surveys. Twenty control points with an average baseline length of 1?km were occupied with dual-frequency GNSS receivers for different time periods. Collected signals were processed using open-source software and verified with an online processing tool. Heights were estimated by processing the GPS and the GLONASS data individually, and combined (i.e. GNSS). Height differences were determined and compared with those measured by spirit levels and corrected through geoid models. Best results were achieved by combining GPS and GLONASS solutions for both static and RTK surveys. Solutions with either GPS or GLONASS satellites were comparable, but in most cases, the GPS solutions performed better. For the static surveys, longer occupation provided much accurate height differences. Inconsistencies among 10 different RTK surveys were minimum for the GPS?+?GLONASS solutions and worst for the GLONASS solutions. The ANOVA, LSD, F, and χ² statistical tests confirmed our findings at the 95% confidence level.     

Acoustic Events in the Solar Atmosphere from <Emphasis Type="Italic">Hinode</Emphasis>/SOT NFI Observations

We investigate the properties of acoustic events (AEs), defined as spatially concentrated and short duration energy flux, in the quiet Sun, using observations of a 2D field of view (FOV) with high spatial and temporal resolution provided by the Solar Optical Telescope (SOT) onboard Hinode. Line profiles of Fe i 557.6 nm were recorded by the Narrow-band Filter Imager (NFI) on a 82″×82″ FOV during 75 min with a time step of 28.75 s and 0.08″ pixel size. Vertical velocities were computed at three atmospheric levels (80, 130, and 180 km) using the bisector technique, allowing the determination of energy flux to be made in the range 3 – 10 mHz using two complementary methods (Hilbert transform and Fourier power spectrum). Horizontal velocities were computed using local correlation tracking (LCT) of continuum intensities providing divergences. We found that the net energy flux is upward. In the range 3 – 10 mHz, a full FOV space and time averaged flux of 2700 W m⁻² (lower layer 80 – 130 km) and 2000 W m⁻² (upper layer 130 – 180 km) is concentrated in less than 1 % of the solar surface in the form of narrow (0.3″) AE. Their total duration (including rise and decay) is of the order of 10³ s. Inside each AE, the mean flux is 1.6×10⁵ W m⁻² (lower layer) and 1.2×10⁵ W m⁻² (upper). Each event carries an average energy (flux integrated over space and time) of 2.5×10¹⁹ J (lower layer) to 1.9×10¹⁹ J (upper). More than 10⁶ events could exist permanently on the Sun, with a birth and decay rate of 3500 s⁻¹. Most events occur in intergranular lanes, downward velocity regions, and areas of converging motions.     

Radiative habitable zones in martian polar environments

The biologically damaging solar ultraviolet (UV) radiation (quantified by the DNA-weighted dose) reaches the martian surface in extremely high levels. Searching for potentially habitable UV-protected environments on Mars, we considered the polar ice caps that consist of a seasonally varying CO2 ice cover and a permanent H2O ice layer. It was found that, though the CO2 ice is insufficient by itself to screen the UV radiation, at approximately 1 m depth within the perennial H2O ice the DNA-weighted dose is reduced to terrestrial levels. This depth depends strongly on the optical properties of the H2O ice layers (for instance snow-like layers). The Earth-like DNA-weighted dose and Photosynthetically Active Radiation (PAR) requirements were used to define the upper and lower limits of the northern and southern polar Radiative Habitable Zone (RHZ) for which a temporal and spatial mapping was performed. Based on these studies we conclude that photosynthetic life might be possible within the ice layers of the polar regions. The thickness varies along each martian polar spring and summer between approximately 1.5 and 2.4 m for H2O ice-like layers, and a few centimeters for snow-like covers. These martian Earth-like radiative habitable environments may be primary targets for future martian astrobiological missions. Special attention should be paid to planetary protection, since the polar RHZ may also be subject to terrestrial contamination by probes.     

Enhanced seamount location database for the western and central Pacific Ocean: Screening and cross-checking of 20 existing datasets

Seamounts are habitats of considerable interest in terms of conservation and biodiversity, and in terms of fisheries for bentho-pelagic and pelagic species. Twenty previously compiled datasets including seamount/underwater feature lists, bathymetric maps and emerged feature maps from different sources (ship-derived and satellite altimetry-derived) at different spatial scales (from individual cruise to worldwide satellite data) were gathered in order to compile an enhanced list of underwater features for parts of the western and central Pacific Ocean (WCPO). The KL04 dataset [Kitchingman, A., and Lai, S., 2004. Inferences on potential seamount locations from mid-resolution bathymetric data. Fisheries Centre Research Reports 12 (5), 7–12], listing seamount positions and depths as calculated from satellite altimetry-derived bathymetry, provided the baseline data for this study as it covered the entire region of interest and included summit depth information. All KL04 potential seamounts were cross-checked with other datasets to remove any atolls and islands that had been incorrectly classified as seamounts, to add seamounts undetected by KL04, to update the overall database (geolocation, depth, elevation, and name) and to compile a 12-class typology of the different types of underwater features. Of the 4626 potential seamounts identified in KL04, 719 were multiple identifications of the same large underwater features and 373 (10%) were actually emerged banks, atolls and islands, leaving 3534 actual underwater features. Conversely, 487 underwater features were documented in other datasets but not registered by KL04. The screening of all the potential WCPO seamounts produced a final list of 4021 underwater features with agreed upon position and information. This enhanced list should have many applications in oceanography, biodiversity conservation and studies of the influence of seamounts on pelagic ecosystems and fisheries.     

Formation and dynamics of vegetated fluvial landforms follow the biogeomorphological succession model in a channelized river

Feedback between hydrogeomorphological processes and riparian plants drives landscape dynamics and vegetation succession in river corridors. We describe the consequences of biogeomorphological feedback on the formation and dynamics of vegetated fluvial landforms based on observations from the channelized Isère River in France. The channel was laterally confined with embankments and mostly straightened. From the beginning of the 1970s to the end of the 1990s, alternate bars were progressively but heavily colonized by vegetation. This context presented an exceptional opportunity to analyse temporal adjustments between fluvial landforms and vegetation succession from bare gravel bars to mature upland forest as the consequence of biogeomorphological interactions. Based on a GIS analysis of aerial photographs (between 1948 and 1996), we show that the spatiotemporal organization of vegetated bars within the river channel observed in 1996 resulted from a bioconstruction and biostabilization effect of vegetation and interactions between bars of varying age, size and mobility. Field measurements in 1996 reflected how a strong positive feedback between sedimentary dynamics and riparian vegetation succession resulted in the construction of the vegetated bars. A highly significant statistical association of geomorphological and vegetation variables (RV of co-inertia analysis = 0.41, p < 0.001) explained 95% of the variability in just one axis, supporting the existence of very strong feedback between geomorphological changes (i.e. the transformation of small bare alternate bars to fluvial landforms covered by mature upland forest, and vegetation succession). Such dynamics reflect the fluvial biogeomorphological successions model, as described by the authors earlier. © 2020 John Wiley & Sons, Ltd.     

Extreme Nd isotope homogeneity in a large rhyolitic province: the Estérel massif, southeast France

 Previous detailed studies of large rhyolite bodies propose that their elemental and isotopic characteristics were largely acquired in shallow crustal magma chambers. This model explains the common chemical and isotopic zonations of large volumes of rhyolites as well as the less common chemical and isotopic homogeneity of such bodies. We report an intermediate situation (the Estérel massif, southeast France) in which chemical variations contrast with Nd-isotope homogeneity. We thus infer that, in this case, large volumes of rhyolite resided for enough time in shallow magma chambers to develop chemical zonations through differentiation, but this process was not accompanied by crustal assimilation. The subordinate amount of mafic rocks cropping out in the Estérel probably evolved from basalt to trachyte through assimilation and fractional crystallization. The relatively radiogenic Nd-isotope signatures of the rhyolite compared with the Hercynian crust show that it cannot have been generated by partial melting of exposed basement rocks. Several geological similarities with large rhyolitic provinces could suggest that the rhyolite was purely mantle derived or, alternatively, generated by partial melting of an ad hoc crustal component. However, mineralogical, geochemical, and geodynamic connections between the Estérel rhyolite and the hypersolvus anorogenic granites of Corsica, as well as the extreme Nd-isotope homogeneity of the rhyolite, lead us to propose that the rhyolite was generated by mixing between mantle-derived magmas and a mafic lower crust. This scenario accounts for the relatively radiogenic Nd-isotope signatures of the rhyolite compared with the Hercynian crust. The good Nd-isotope homogeneity observed in the rhyolite implies that the mixing process, which occurred in the deep crust, was complete and provided a shallow magma chamber with isotopically and probably chemically homogeneous magmas. Received: 5 December 1997 / Accepted: 16 June 1998     

An interpretation of the nitrogen deficiency in comets

We propose an interpretation of the composition of volatiles observed in comets based on their trapping in the form of clathrate hydrates in the solar nebula. The formation of clathrates is calculated from the statistical thermodynamics of Lunine and Stevenson (1985, Astrophys. J. Suppl. 58, 493-531), and occurs in an evolutionary turbulent solar nebula described by the model of Hersant et al. (2001, Astrophys. J. 554, 391-407). It is assumed that clathrate hydrates were incorporated into the icy grains that formed cometesimals. The strong depletion of the N₂ molecule with respect to CO observed in some comets is explained by the fact that CO forms clathrate hydrates much more easily than does N₂. The efficiency of this depletion, as well as the amount of trapped CO, depends upon the amount of water ice available in the region where the clathration took place. This might explain the diversity of CO abundances observed in comets. The same theory, applied to the trapping of volatiles around 5 AU, explains the enrichments in Ar, Kr, Xe, C, and N with respect to the solar abundance measured in the deep troposphere of Jupiter [Gautier et al 2001a] and [Gautier et al 2001b].     

Oldest description of a caldera-forming eruption in Southeast Asia unveiled in forgotten written sources

GeoJournal - As one of the most powerful volcanic events of the Holocene era with a Volcanic Explosivity Index of seven, the 1257 CE eruption of Samalas volcano in the Rinjani Volcanic Complex had...