Baryonic matter in the Universe is almost exclusively a plasma, a gas of charged particles governed by complex interactions with electromagnetic fields. It is for this reason that the Nobelist H. Alfvén coined the term Plasma Universe. Examples of cosmic plasmas include, but are not limited to, planetary and exoplanetary ionospheres and magnetospheres, stellar coronae, interplanetary, interstellar and intergalactic media, supernova remnants, accretion disks and astrophysical jets. 

Understanding how charged particles are energized in plasmas is a fundamental plasma physics problem, which is compelling and of major importance for the worldwide space and astrophysical plasmas communities. Despite the large body of available observations and numerical simulations, we still do not fully understand how plasma energization work. The key missing piece is the understanding of how plasma scales couple with each other, and new multi-scale observations are needed to experimentally solve this problem.

Both in situ and remote observations are essential to advance our understanding of scale coupling in plasma energization, through a synergistic approach. Nevertheless, despite their importance and their growing resolution, current remote observations of distant plasmas can only probe energization indirectly, by measuring radiation from energized particles, and are limited to integrated, often model-dependent, quantities. Direct observations of electromagnetic fields and of particle distribution functions at multiple points and multiple scales are required, to unravel local, scale-coupling physics in 3D. 

The terrestrial Magnetospheric System is a key example where massive plasma energization occur and where energization can be studied under a variety of plasma conditions through high-resolution in situ measurements, that can be made at multiple points and can be transmitted to the ground in large volumes. Existing datasets from multi-point missions, such as Cluster, THEMIS and MMS, however do not have a sufficient number of observation points to resolve scale coupling in 3D. Plasma Observatory will be the first mission having such capability in the Earth’s Magnetospheric System, through measurements at seven points in space covering simultaneously ion and fluid scales in the key science regions where the strongest plasma energization occur: the foreshock, bow shock, magnetosheath, magnetopause, magnetotail current sheet and transition region, which also mimic a number of distant astrophysical environments. 

In this seminar, I will present several key open questions and challenges related to plasma energization in space and astrophysical plasmas, focusing on the role of plasma scale coupling and on the need of new, multi-scale in situ observations. I will present an overview of the science objectives, instrumentation and mission profile of the Plasma Observatory mission, which has been recommended in June 2026 as the future ESA M7 mission, with selection by the Science Programme Committee expected in November 2026. I will also discuss possible synergies with plasma environments other than the terrestrial environment, both in the Heliosphere and beyond, which could allow expanding our understanding of plasma energization over a broader range of plasma conditions and processes.

References

A Retinò et al., Particle energization in space plasmas: towards a multi-point, multi-scale plasma observatory, Experimental Astronomy, 2022, https://doi.org/10.1007/s10686-021-09797-7 
Plasma Observatory ESA Public Presentation https://www.cosmos.esa.int/web/m7-public-presentation