Photochemistry-emission coupled model for Europa and Ganymede

Abstract

In the frame of the JUICE mission, preliminary studies of the Jupiter's icy moons, such as Ganymede and Europa, are mandatory. The present paper aims at characterizing the impact of the solar UV flux and its variability on their atmospheres. The solar UV radiation is responsible for the photoionization, photodissociation, and photoexcitation processes within planetary atmospheres. A 1-D photoabsorption model has been developed for different observational geometries, on the basis of a neutral atmospheric model. Considering various production and loss mechanisms but also the transport of oxygen atoms, we estimate the red and green line emissions from photo impact-induced excitation only. These dayglow emissions can represent few percent of the global airglow emission, mainly dominated by electron-induced excitation in auroral regions. For limb viewing conditions, red line emission is bright enough to be detected from actual spectrometers, from 338 R to 408 R according to the solar activity. This is also the case for the green line with 8 R at limb viewing. Considering a different neutral atmosphere model, with an O 2 column density 50% more important, leads to a 14% increase in the red line emissions for limb viewing close to the surface. This difference could be important enough to infer which neutral model is the most likely. However, uncertainties on the solar UV flux might also prevent to constrain the O 2 column density when using ground-based observations in the visible only. The impact of solar flares on the red line emissions for Europa has also been investigated within a planetary space weather context.

Solar irradiance observations with PREMOS filter radiometers on the PICARD mission: In-flight performance and data release

“…Both TSI and SSI measurements are of primary interest for space weather and space climate studies. The planetary climate response to the solar irradiance is sensitive to the 11-year cycle, when considering the Earth (Egorova et al 2004;Ermolli et al 2013) as well as planetary objects such as the jovian icy moons (Cessateur et al 2016). The 27-day solar modulation also has a strong impact on mesospheric neutral species such as hydroxyl (e.g.…”

Reactivity of Cyanide at Water-Ice Interfaces: Implications for the Search for Organics on Icy Worlds

“…UV radiation using Hg lamps has been considered in only a few studies that considered the production of organics from HCN/cyanide as main reactant (Abelson, 1966;Mizutani et al, 1975;Hartig and Getoff, 1980;Ritson and Sutherland, 2012;Ruiz-Bermejo et al, 2013a). The amount and type of UV radiation that arrives at a predetermined planetary zone depend on several factors (the dispersion, transmittance, and albedo of the environment), and it is an important constraint to take in consideration in the astro/exobiological exploration of the icy objects of solar systems (Cessateur et al, 2016). Ice is a highly dispersive environment and reflects UV radiation; thus, the presence of an icy layer notably reduces the UV radiation incident on the liquid water of the ocean, and it has been demonstrated that sea ice acts as a photochemical microreactor, where 85% of the reactions are produced in the upper zone of the icewater column (King et al, 2005).…”