November 14, 2016

Sampling the Atmosphere of Europa can provide insight into the composition of ocean beneath the miles of ice and signs of potential life if it exists

A spacecraft flying past Europa may be able to sample its colossal watery plumes – even if they stopped erupting weeks earlier. A new analysis suggests that jets spewing from Jupiter’s icy moon could produce complex, constantly shifting chemical patterns in its atmosphere, which we could use to figure out what is on, and even below, the surface.

Europa has an ocean underneath miles of ice. This ocean could be one of the best place to look for life in the solar system.

Both NASA and the European Space Agency have missions in the works, targeted for launch in the early 2020s, that will fly past Europa.

Europa’s gravity may pull material from the plumes back to the surface, creating a layer of frost. Later, some of those particles would be propelled back off the surface, either by evaporating or by being thrown upwards when charged particles from Jupiter’s magnetosphere hit the surface, much like the splash when a pebble drops into a pond.

These particles feed Europa’s atmosphere, and could provide clues about the composition of the surface and the plumes – even if the plumes have already stopped. We could reconstruct a timeline of days or even weeks of previous activity, Teolis says. By calculating where the particles came from, we could begin to draw a map of fresh features on the moon’s surface.

Icarus - Plume and surface feature structure and compositional effects on Europa's global exosphere: Preliminary Europa mission predictions

Highlights
• 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



Abstract
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.




SOURCES- Icarus, New Scientist

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