Towards a Longitude Network of Io Torus Observatories

The Io Plasma Torus (IPT) plays a key role in the workings of the Jupiter System at large. It is a complex system driven by Io’s volcanism and surface-atmosphere that interacts with numerous Jupiter System objects. Despite significant and varied modelling efforts, the description of its spatial structure and temporal variability remains challenging, especially because of insufficient data coverage.

In this EGU Poster, we analyze the IPT's spectral emissions and spatio-temporal dynamics to establish the optical specifications for a future ground-based observation system. Our main conclusions are as follows:

1- Temporal variability: the large diversity of objects in the Jupiter System with which the IPT interacts, and the complex, highly non-linear nature of these interactions, contribute to the strong observed temporal variability of the IPT, which displays a broad range of time scales, from hourly to multi-decadal. Capturing all timescales requires hourly, intercalibrated observations, necessitating dedicated space platforms and/or a longitudinal ground network.

2- Spatial scales: the Io system includes interconnected objects of very different spatial extensions, from tens of km with Io’s volcanoes and plumes, to more than 1000 Rj with the nebula(e). Hence, an observation system covering the Io system in a comprehensive way will need to combine observations with very diverse spatial coverages, from sharp AO observations (e.g. 0.02’’ achieved with the LBT) to 5.5°.

3- Spectral extension: electromagnetic emissions generated by the Io system cover a very large part of the electromagnetic spectrum, and the different components of the system emit to a large part in different wavelength ranges and in the different spectral lines corresponding to different neutral and ionized species. Hence, a combined set of telescopes covering this system in a comprehensive way will have to optimally combine observations of different spectral lines in different spectral ranges. 

4- Complementary observations: beyond the body of UV / EUV observations from space, ground-based observations over the last 50 years have also borne very valuable fruit. Indeed, instrumentation necessary to image the IPT does not necessarily need to be expensive: simple designs using smart "amateur-class" equipment already allow for the observation of the brightest lines. As spaceborne and ground-based observations offer complementary advantages and limitations, a future comprehensive observation system for the IPT will likely have to combine both.

Given stringent time resolution constraints, and aiming at an affordable budget envelope, the development of a longitudinal network of telescopes appears as particularly cost-effective and promising. It could build on the successful IPT telescopes that already exist in different longitude sectors and complement them with one or several ones at key locations, including the European and African sectors. In France, such an effort will be coordinated at the national level, allowing one to take full advantage of synergies between radio observations at Nançay and new optical observations. In this poster, we outline design guidelines for a smart, multi-site, multi-spectral system capturing the IPT's spatiotemporal dynamics and coupling processes that will address the choice of telescope as well as of the spatial (coronagraph) and spectral (color filters) filtering systems.