Developing a self‐consistent description of Titan's upper atmosphere without hydrodynamic escape

In this study, we develop a best fit description of Titan's upper atmosphere between 500 km and 1500 km, using a one‐dimensional (1‐D) version of the three‐dimensional (3‐D) Titan Global Ionosphere‐Thermosphere Model. For this modeling, we use constraints from several lower atmospheric Cassini‐Huygens investigations and validate our simulation results against in situ Cassini Ion‐Neutral Mass Spectrometer (INMS) measurements of N 2 , CH 4 , H 2 , 40 Ar, HCN, and the major stable isotopic ratios of 14 N/ 15 N in N 2 . We focus our investigation on aspects of Titan's upper atmosphere that determine the amount of atmospheric escape required to match the INMS measurements: the amount of turbulence, the inclusion of chemistry, and the effects of including a self‐consistent thermal balance. We systematically examine both hydrodynamic escape scenarios for methane and scenarios with significantly reduced atmospheric escape. Our results show that the optimum configuration of Titan's upper atmosphere is one with a methane homopause near 1000 km and atmospheric escape rates of 1.41–1.47 ×10 11 CH 4  m −2 s −1 and 1.08 ×10 14  H 2  m −2 s −1 (scaled relative to the surface). We also demonstrate that simulations consistent with hydrodynamic escape of methane systematically produce inferior fits to the multiple validation points presented here. Key Points The methane homopause is most likely near 1000 km altitude Hydrodynamic escape of methane is not required to match INMS Molecular hydrogen is best fit with a methane homopause of 1000 kmPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108005/1/jgra51076.pd

Science Overview of the Europa Clipper Mission

The goal of NASA’s Europa Clipper mission is to assess the habitability of Jupiter’s moon Europa. After entering Jupiter orbit in 2030, the flight system will collect science data while flying past Europa 49 times at typical closest approach distances of 25–100 km. The mission’s objectives are to investigate Europa’s interior (ice shell and ocean), composition, and geology; the mission will also search for and characterize any current activity including possible plumes. The science objectives will be accomplished with a payload consisting of remote sensing and in-situ instruments. Remote sensing investigations cover the ultraviolet, visible, near infrared, and thermal infrared wavelength ranges of the electromagnetic spectrum, as well as an ice-penetrating radar. In-situ investigations measure the magnetic field, dust grains, neutral gas, and plasma surrounding Europa. Gravity science will be achieved using the telecommunication system, and a radiation monitoring engineering subsystem will provide complementary science data. The flight system is designed to enable all science instruments to operate and gather data simultaneously. Mission planning and operations are guided by scientific requirements and observation strategies, while appropriate updates to the plan will be made tactically as the instruments and Europa are characterized and discoveries emerge. Following collection and validation, all science data will be archived in NASA’s Planetary Data System. Communication, data sharing, and publication policies promote visibility, collaboration, and mutual interdependence across the full Europa Clipper science team, to best achieve the interdisciplinary science necessary to understand Europa

MagneToRE: Mapping the 3-D Magnetic Structure of the Solar Wind Using a Large Constellation of Nanosatellites

Unlike the vast majority of astrophysical plasmas, the solar wind is accessible to spacecraft, which for decades have carried in-situ instruments for directly measuring its particles and fields. Though such measurements provide precise and detailed information, a single spacecraft on its own cannot disentangle spatial and temporal fluctuations. Even a modest constellation of in-situ spacecraft, though capable of characterizing fluctuations at one or more scales, cannot fully determine the plasma’s 3-D structure. We describe here a concept for a new mission, the Magnetic Topology Reconstruction Explorer (MagneToRE), that would comprise a large constellation of in-situ spacecraft and would, for the first time, enable 3-D maps to be reconstructed of the solar wind’s dynamic magnetic structure. Each of these nanosatellites would be based on the CubeSat form-factor and carry a compact fluxgate magnetometer. A larger spacecraft would deploy these smaller ones and also serve as their telemetry link to the ground and as a host for ancillary scientific instruments. Such an ambitious mission would be feasible under typical funding constraints thanks to advances in the miniaturization of spacecraft and instruments and breakthroughs in data science and machine learning

Recommendations for Addressing Priority Io Science in the Next Decade

Io is a priority destination for solar system exploration. The scope and importance of science questions at Io necessitates a broad portfolio of research and analysis, telescopic observations, and planetary missions - including a dedicated New Frontiers class Io mission

The Science Case for Io Exploration

Io is a priority destination for solar system exploration, as it is the best natural laboratory to study the intertwined processes of tidal heating, extreme volcanism, and atmosphere-magnetosphere interactions. Io exploration is relevant to understanding terrestrial worlds (including the early Earth), ocean worlds, and exoplanets across the cosmos

Evaluation of a real-time virtual intervention to empower persons living with HIV to use therapy self-management: study protocol for an online randomized controlled trial

Background: Living with HIV makes considerable demands on a person in terms of self-management, especially as regards adherence to treatment and coping with adverse side-effects. The online HIV Treatment, Virtual Nursing Assistance and Education (Virus de I'immunodeficience Humaine-Traitement Assistance Virtuelle Infirmiere et Enseignement; VIH-TAVIE (TM)) intervention was developed to provide persons living with HIV (PLHIV) with personalized follow-up and real-time support in managing their medication intake on a daily basis. An online randomized controlled trial (RCT) will be conducted to evaluate the efficacy of this intervention primarily in optimizing adherence to combination anti-retroviral therapy (ART) among PLHIV.Methods/design: A convenience sample of 232 PLHIV will be split evenly and randomly between an experimental group that will use the web application, and a control group that will be handed a list of websites of interest. Participants must be aged 18 years or older, have been on ART for at least 6 months, and have internet access. The intervention is composed of four interactive computer sessions of 20 to 30 minutes hosted by a virtual nurse who engages the PLHIV in a skills-learning process aimed at improving self-management of medication intake. Adherence constitutes the principal outcome, and is defined as the intake of at least 95% of the prescribed tablets. The following intermediary measures will be assessed: self-efficacy and attitude towards antiretroviral medication, symptom-related discomfort, and emotional support. There will be three measurement times: baseline (T0), after 3 months (T3) and 6 months (T6) of baseline measurement. The principal analyses will focus on comparing the two groups in terms of treatment adherence at the end of follow-up at T6. An intention-to-treat (ITT) analysis will be carried out to evaluate the true value of the intervention in a real context.Discussion: Carrying out this online RCT poses various challenges in terms of recruitment, ethics, and data collection, including participant follow-up over an extended period. Collaboration between researchers from clinical disciplines (nursing, medicine), and experts in behavioral sciences information technology and media will be crucial to the development of innovative solutions to supplying and delivering health services

Molecular Nitrogen And Methane Density Retrievals From Cassini Uvis Dayglow Observations Of Titan\u27S Upper Atmosphere

We retrieve number densities of molecular nitrogen (N2) and methane (CH4) from Titan\u27s upper atmosphere using the UV dayglow. We use Cassini Ultraviolet Imaging Spectrograph (UVIS) limb observations from 800 to 1300km of the N I 1493Å and N II 1085Å multiplets, both produced directly from photofragmentation of N2. UVIS N2 and CH4 densities are in agreement with measurements from Cassini\u27s Ion Neutral Mass Spectrometer (INMS) from the same flyby if INMS densities are scaled up by a factor of 3.0 as reported in previous studies. Analysis of three Cassini flybys of Titan shows that (1) the CH4 homopause on Titan is between 900 and 1100km, (2) upper atmospheric temperatures vary by less than 10K over 6h at the same geographic location and (3) from 1100 to 1700 local solar time temperatures also vary by less than 10K. The capability of retrieving the global-scale composition from these data complements existing techniques and significantly advances the study of upper atmospheric variability at Titan and for any other atmosphere with a detectable UV dayglow

The Coupling Problem at Titan: Where are the Magnetospheric Influences to Titan’s Complex Ionosphere?

Since the arrival of Cassini to the Saturn system in 2004 the suite of in-situ and remote sensing instruments onboard have sampled Titan nearly 100 times. Even with this large number of samples the coverage in the multitude of geospatial, magnetospheric, solar, and seasonal configurations is rather sparse resulting in an incomplete understanding of the coupling (if present) between the complex ionosphere of Titan and Saturn’s corotational magnetospheric plasma. Studies by the in-situ CAPS, INMS, and LP data have shown a clear ionospheric dependence on solar parameters, however several flybys show unique properties implying some magnetospheric influence manifest in rather abrupt heating events in the thermosphere. In this talk we review the Cassini observations from multiple instruments at Titan and attempt to piece together a cohesive picture of the Saturn magnetosphere-Titan ionosphere-Titan thermosphere interaction

The 12C/13C ratio on Titan from Cassini INMS measurements and implications for the evolution of methane

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