Two documents have begun to flesh out the plans for the 2016 ESA-NASA Mars mission. This mission will send an ESA orbiter with ESA and NASA instruments to Mars in 2016. An ESA lander will prove technologies for delivering a mid-sized payload to Mars.
From 2016 to 2018, the orbiter will focus on it's science mission to measure trace gases in the atmosphere, study Martian climatology, and image the surface at high resolution. From 2018, the orbiter's prime mission will be to relay data from ESA and NASA's rovers on the surface, although science activities will presumably continue.
ESA's Entry, Descent and Landing Demonstrator Module (EDM) will be a technology demonstration. "The EDM is expected to survive on the surface of Mars for a short time (about 8 sols) by using the excess energy capacity of its batteries. The science possibilities of the EDM are limited by the absence of long term power and the fixed amount of space and resources that can be accommodated within the module; however a set of scientific sensors will be included to perform limited surface science."
A Joint Instrument Definition Team has recommended a reference suite of instruments (final instruments will be selected through a competitive announcement of opportunity). The straw man list has:
"Solar occultation measurements: This technique provides the best means of surveying atmospheric composition with high sensitivity as it measures absorption of a bright source (sunlight) passing through a large atmospheric path (along the tangent occultation path) with very high spectral resolution to reduce effects of line mixing, etc. A Solar Occultation Fourier Transform IR Spectrometer (SFTIR) can cover a wide spectral interval enabling detection of a broad suite of trace gases. "
"Thermal emission measurements: Sub-millimeter (Sub-mm) and thermal infrared (TIR) spectrometers can be used to look at atmospheric thermal emission when viewing nadir or at the atmospheric limb. These characterize the atmospheric state by providing vertical profiles of temperature and profiles or column abundances of key source gases such as water vapor."
"Visual monitoring of atmospheric phenomena: Wide-angle cameras (WAC) can provide daily monitoring of the global atmosphere and its regional atmospheric phenomena: clouds, storm systems, aerosol layers, dust storms and boundary layer phenomena such as dust devils and wind streaks."
"High-resolution surface imaging/mapping: Very high spatial resolution imaging or mapping instruments (e.g., cameras and multi-beam active lasers) can provide geological context and location of small-area sources should they exist (e.g., a volcanic vent, rift or crater)."
The ESA-NASA ExoMars Programme Orbiter and EDL Demonstrator, 2016
Final Report of the 2016 Mars Orbiter Bus Joint Instrument Definition Team