The Bepi-Colombo mission was launched in October 2018, headed for Mercury. This mission is a collaboration between Europe and Japan. It is dedicated to the study of Mercury and its environment. It will be inserted into Mercury orbit in December 2025 after a 7-year long cruise. Probing of Hermean Exosphere By Ultraviolet Spectroscopy (PHEBUS) is an ultraviolet Spectrograph and is one of the 11 instruments on-board the Mercury Planetary Orbiter (MPO). It is dedicated to the study of the exosphere of Mercury, its composition, dynamics and variability and its interface with the surface of the planet and the solar wind. The PHEBUS instrument contains four distinct detectors covering the spectral range from 55 nm up to 315 nm and two additional narrow windows at 404 nm and 422 nm. It also has a one-degree of freedom mechanism that allows observations along a cone with an half angle of 80 •. This paper follows a detailed presentation of the PHEBUS instrument design that was presented by Chassefière et al. (2010). Here we present an update of the science objectives and measurement requirements following the results published by the MErcury Surface, Space

This Letter addresses the first Solar Orbiter (SO)-Parker Solar Probe (PSP) quadrature, occurring on 2021 January 18 to investigate the evolution of solar wind from the extended corona to the inner heliosphere. Assuming ballistic propagation, the same plasma volume observed remotely in the corona at altitudes between 3.5 and 6.3 solar radii above the solar limb with the Metis coronagraph on SO can be tracked to PSP, orbiting at 0.1 au, thus allowing the local properties of the solar wind to be linked to the coronal source region from where it originated. Thanks to the close approach of PSP to the Sun and the simultaneous Metis observation of the solar corona, the flow-aligned magnetic field and the bulk kinetic energy flux density can be empirically inferred along the coronal current sheet with an unprecedented accuracy, allowing in particular estimation of the Alfvén radius at 8.7 solar radii during the time of this event. This is thus the very first study of the same solar wind plasma as it expands from the sub-Alfvénic solar corona to just above the Alfvén surface.

The advent of nanoscale multilayer (ML) technology has led to great breakthroughs in many scientific and technological fields such as nano-manufacturing, bio-imaging, atto-physics, matter physics and solar physics. ML nanostructures are an enabling technology for the development of mirrors and reflective gratings having high efficiency at normal incidence in the extreme ultraviolet (EUV) range, a spectral region where conventional coatings show a negligible reflectance. In solar physics, ML mirrors have proved to be key elements for both imaging and spectroscopy space instruments, as they allow to make observations of EUV solar plasma emissions with spatial and spectral resolutions never reached before. ML-based instruments have been used in many of the major solar satellites and have flown in numerous sounding rocket experiments; moreover, in the last two decades many studies were performed in order to develop ML structures with increasingly better performance for future solar missions. In this paper, a review of the most promising ML nanostructures developed so far and applied to the observation of solar plasma emission lines is presented. After a brief recall of ML theory, a detailed discussion of the most promising material pairs and layer stack structures proposed and applied to past and current space missions will be presented; in particular, the review will focus on the ML structures having high efficiency in the 6 nm-35 nm wavelength range. Finally, the ML stability to low energy ion bombardment will be discussed.