Uranus’ stratospheric HCl upper limit from Herschel/SPIRE

Herschel/SPIRE observations of Uranus are used to search for stratospheric hydrogen chloride (HCl) emission at 41.74 cm$^{-1}$. HCl was not detected and instead 3$\sigma$ upper limits were determined; $<$6.2 ppb ($<$2.0$\times$10$^{14}$ molecules/cm$^{2}$) for a 0.1 mbar step profile and $<$0.40 ppb ($<$1.2$\times$10$^{14}$ molecules/cm$^{2}$) for a 1 mbar step profile. HCl is expected to have an external source and these upper limits are consistent with abundances of other external species (CO, H$_2$O, CO$_2$) and a solar composition source.Comment: 4 pages, 1 figure, accepted for publication in RNAAS 202

Exoplanets with JWST: degeneracy, systematics and how to avoid them

The high sensitivity and broad wavelength coverage of the James Webb Space Telescope will transform the field of exoplanet transit spectroscopy. Transit spectra are inferred from minute, wavelength-dependent variations in the depth of a transit or eclipse as the planet passes in front of or is obscured by its star, and the spectra contain information about the composition, structure and cloudiness of exoplanet atmospheres. Atmospheric retrieval is the preferred technique for extracting information from these spectra, but the process can be confused by astrophysical and instrumental systematic noise. We present results of retrieval tests based on synthetic, noisy JWST spectra, for clear and cloudy planets and active and inactive stars. We find that the ability to correct for stellar activity is likely to be a limiting factor for cloudy planets, as the effects of unocculted star spots may mimic the presence of a scattering slope due to clouds. We discuss the pros and cons of the available JWST instrument combinations for transit spectroscopy, and consider the effect of clouds and aerosols on the spectra. Aerosol high in a planet’s atmosphere obscures molecular absorption features in transmission, reducing the information content of spectra in wavelength regions where the cloud is optically thick. We discuss the usefulness of particular wavelength regions for identifying the presence of cloud, and suggest strategies for solving the highly-degenerate retrieval problem for these objects

Internet as an Instrument to Transmit Theoretical Knowledge

The problem of transmitting theoretical knowledge and the role of the Internet in it require the solution due to the existing modernization of theoretical knowledge transmission process. The objective of this research is to define the role of the Internet in transmitting theoretical knowledge as it is the extremely important resource of the modern society. According to the carried out analysis of the problem and its solution the information technology is not only the mean that accumulates the volumes of knowledge, but also the tool of its social use, forms of social activity by way of social and information technology. As a result, using method of the methodological analysis in combination with competency-based approach we revealed that the Internet as a diachronic way of transmitting knowledge and experience is characterized by a polyagentity and interdisciplinarity

Uranus's and Neptune’s stratospheric water abundance and vertical profile from Herschel-HIFI

Here we present new constraints on Uranus’s and Neptune’s externally sourced stratospheric water abundance using disk-averaged observations of the 557 GHz emission line from Herschel’s Heterodyne Instrument for the Far-Infrared. Derived stratospheric column water abundances are × 1014 cm−2 for Uranus and ×1014 cm−2 for Neptune, consistent with previous determinations using ISO-SWS and Herschel-PACS. For Uranus, excellent observational fits are obtained by scaling photochemical model profiles or with step-type profiles with water vapor limited to ≤0.6 mbar. However, Uranus’s cold stratospheric temperatures imply a ∼0.03 mbar condensation level, which further limits water vapor to pressures ≤0.03 mbar. Neptune’s warmer stratosphere has a deeper ∼1 mbar condensation level, so emission-line pressure broadening can be used to further constrain the water profile. For Neptune, excellent fits are obtained using step-type profiles with cutoffs of ∼0.3–0.6 mbar or by scaling a photochemical model profile. Step-type profiles with cutoffs ≥1.0 mbar or ≤0.1 mbar can be rejected with 4σ significance. Rescaling photochemical model profiles from Moses & Poppe to match our observed column abundances implies similar external water fluxes for both planets: × 104 cm−2 s−1 for Uranus and ×104 cm−2 s−1 for Neptune. This suggests that Neptune’s ∼4 times greater observed water column abundance is primarily caused by its warmer stratosphere preventing loss by condensation, rather than by a significantly more intense external source. To reconcile these water fluxes with other stratospheric oxygen species (CO and CO2) requires either a significant CO component in interplanetary dust particles (Uranus) or contributions from cometary impacts (Uranus, Neptune

2.5-D retrieval of atmospheric properties from exoplanet phase curves: Application to WASP-43b observations

We present a novel retrieval technique that attempts to model phase curve observations of exoplanets more realistically and reliably, which we call the 2.5-dimensional (2.5D) approach. In our 2.5D approach we retrieve the vertical temperature profile and mean gaseous abundance of a planet at all longitudes and latitudes simultaneously, assuming that the temperature or composition, x, at a particular longitude and latitude (Λ, Φ) is given by x(Λ,Φ)=x¯+(x(Λ,0)−x¯)cosnΦ⁠, where x¯ is the mean of the morning and evening terminator values of x(Λ, 0), and n is an assumed coefficient. We compare our new 2.5D scheme with the more traditional 1D approach, which assumes the same temperature profile and gaseous abundances at all points on the visible disc of a planet for each individual phase observation, using a set of synthetic phase curves generated from a GCM-based simulation. We find that our 2.5D model fits these data more realistically than the 1D approach, confining the hotter regions of the planet more closely to the dayside. We then apply both models to WASP-43b phase curve observations of HST/WFC3 and Spitzer/IRAC. We find that the dayside of WASP-43b is apparently much hotter than the nightside and show that this could be explained by the presence of a thick cloud on the nightside with a cloud top at pressure <0.2 bar. We further show that while the mole fraction of water vapour is reasonably well constrained to (1–10) × 10−4, the abundance of CO is very difficult to constrain with these data since it is degenerate with temperature and prone to possible systematic radiometric differences between the HST/WFC3 and Spitzer/IRAC observations. Hence, it is difficult to reliably constrain C/O

Hazy Blue Worlds:A Holistic Aerosol Model for Uranus and Neptune, Including Dark Spots

We present a reanalysis (using the Minnaert limb-darkening approximation) of visible/near-infrared (0.3 - 2.5 micron) observations of Uranus and Neptune made by several instruments. We find a common model of the vertical aerosol distribution that is consistent with the observed reflectivity spectra of both planets, consisting of: 1) a deep aerosol layer with a base pressure > 5-7 bar, assumed to be composed of a mixture of H2S ice and photochemical haze; 2) a layer of photochemical haze/ice, coincident with a layer of high static stability at the methane condensation level at 1-2 bar; and 3) an extended layer of photochemical haze, likely mostly of the same composition as the 1-2-bar layer, extending from this level up through to the stratosphere, where the photochemical haze particles are thought to be produced. For Neptune, we find that we also need to add a thin layer of micron-sized methane ice particles at ~0.2 bar to explain the enhanced reflection at longer methane-absorbing wavelengths. We suggest that methane condensing onto the haze particles at the base of the 1-2-bar aerosol layer forms ice/haze particles that grow very quickly to large size and immediately 'snow out' (as predicted by Carlson et al. 1988), re-evaporating at deeper levels to release their core haze particles to act as condensation nuclei for H2S ice formation. In addition, we find that the spectral characteristics of 'dark spots', such as the Voyager-2/ISS Great Dark Spot and the HST/WFC3 NDS-2018, are well modelled by a darkening or possibly clearing of the deep aerosol layer only.Comment: 58 pages, 23 figures, 4 table

Hazy Blue Worlds:A Holistic Aerosol Model for Uranus and Neptune, Including Dark Spots

We present a reanalysis (using the Minnaert limb-darkening approximation) of visible/near-infrared (0.3 - 2.5 micron) observations of Uranus and Neptune made by several instruments. We find a common model of the vertical aerosol distribution that is consistent with the observed reflectivity spectra of both planets, consisting of: 1) a deep aerosol layer with a base pressure > 5-7 bar, assumed to be composed of a mixture of H2S ice and photochemical haze; 2) a layer of photochemical haze/ice, coincident with a layer of high static stability at the methane condensation level at 1-2 bar; and 3) an extended layer of photochemical haze, likely mostly of the same composition as the 1-2-bar layer, extending from this level up through to the stratosphere, where the photochemical haze particles are thought to be produced. For Neptune, we find that we also need to add a thin layer of micron-sized methane ice particles at ~0.2 bar to explain the enhanced reflection at longer methane-absorbing wavelengths. We suggest that methane condensing onto the haze particles at the base of the 1-2-bar aerosol layer forms ice/haze particles that grow very quickly to large size and immediately 'snow out' (as predicted by Carlson et al. 1988), re-evaporating at deeper levels to release their core haze particles to act as condensation nuclei for H2S ice formation. In addition, we find that the spectral characteristics of 'dark spots', such as the Voyager-2/ISS Great Dark Spot and the HST/WFC3 NDS-2018, are well modelled by a darkening or possibly clearing of the deep aerosol layer only.Comment: 58 pages, 23 figures, 4 table

The Origin of Titan’s External Oxygen:Further Constraints from ALMA Upper Limits on CS and CH₂NH

Titan's atmospheric inventory of oxygen compounds (H2O, CO2, CO) are thought to result from photochemistry acting on externally supplied oxygen species (O+, OH, H2O). These species potentially originate from two main sources: (1) cryogenic plumes from the active moon Enceladus and (2) micrometeoroid ablation. Enceladus is already suspected to be the major O+ source, which is required for CO creation. However, photochemical models also require H2O and OH influx to reproduce observed quantities of CO2 and H2O. Here, we exploit sulphur as a tracer to investigate the oxygen source because it has very different relative abundances in micrometeorites (S/O ~ 10−2) and Enceladus' plumes (S/O ~ 10−5). Photochemical models predict most sulphur is converted to CS in the upper atmosphere, so we use Atacama Large Millimeter/submillimeter Array (ALMA) observations at ~340 GHz to search for CS emission. We determined stringent CS 3σ stratospheric upper limits of 0.0074 ppb (uniform above 100 km) and 0.0256 ppb (uniform above 200 km). These upper limits are not quite stringent enough to distinguish between Enceladus and micrometeorite sources at the 3σ level and a contribution from micrometeorites cannot be ruled out, especially if external flux is toward the lower end of current estimates. Only the high-flux micrometeorite source model of Hickson et al. can be rejected at 3σ. We determined a 3σ stratospheric upper limit for CH2NH of 0.35 ppb, which suggests cosmic rays may have a smaller influence in the lower stratosphere than predicted by some photochemical models. Disk-averaged C3H4 and C2H5CN profiles were determined and are consistent with previous ALMA and Cassini/CIRS measurements

HCN ice in Titan's high-altitude southern polar cloud

Titan's middle atmosphere is currently experiencing a rapid change of season after northern spring arrived in 2009. A large cloud was observed for the first time above Titan's southern pole in May 2012, at an altitude of 300 km. This altitude previously showed a temperature maximum and condensation was not expected for any of Titan's atmospheric gases. Here we show that this cloud is composed of micron-sized hydrogen cyanide (HCN) ice particles. The presence of HCN particles at this altitude, together with new temperature determinations from mid-infrared observations, indicate a very dramatic cooling of Titan's atmosphere inside the winter polar vortex in early 2012. Such a cooling is completely contrary to previously measured high-altitude warming in the polar vortex, and temperatures are a hundred degrees colder than predicted by circulation models. Besides elucidating the nature of Titan's mysterious polar cloud, these results thus show that post-equinox cooling at the winter pole is much more efficient than previously thought.Comment: Published in Nature on 2 October 2014. This is the author version, before final editing by Natur