SERENA Science

Search for Exospheric Refilling and Emitted Natural Abundances (SERENA) is an instrument package on board the BepiColombo/Mercury Planetary Orbiter (MPO). It will investigate Mercury's complex particle environment.

Mercury’s environment is subjected to strong interaction with the solar wind and the interplanetary medium. The interaction between energetic particles, solar radiation and micrometeorites with the Hermean surface gives rise to both thermal and energetic neutral populations in the near-planet space. Such populations will be recorded by the SERENA neutral particle analyzers, namely Emitted Low Energy Neutral Atoms (ELENA) sensor and Start from a Rotating FIeld mass spectrometer (STROFIO).
The photoionized or charged component of the surface release processes as well as the precipitating and circulating ions in the Hermean magnetosphere will be recorded by the SERENA Ion Spectrometers, namely Planetary Ion Camera (PICAM) and Miniature Ion Precipitation Analyzer (MIPA).

In particular, ELENA will observe the energetic neutral atoms back-scattered from the surface after ion impact, investigating the plasma precipitation and the related involved processes; STROFIO will provide the thermal exospheric gas composition; PICAM will observe the planetary ion distribution, composition, and the close-to-planet dynamics; MIPA will detect the plasma precipitation toward the surface and ions energized and transported throughout the environment of Mercury.
In summary, the 4 sensors of the SERENA package can provide information on the whole surface-exosphere-magnetosphere coupled system and the processes involved, plus the interactions between energetic particles, the solar wind, micrometeorites and the interplanetary medium.

Schematic representation of Mercury’s (Hermean) environment. The four SERENA sensors are color-coded to indicate their individual measurement domains and their complementary roles in probing the various components of the system.

In this perspective, the major SERENA scientific objectives may be listed as in the following:

Primary Objectives:

Chemical and elemental composition of the exosphere
Neutral gas density profiles and asymmetries
Exo-ionosphere composition
Exo-ionosphere spatial and energy distribution
Ion precipitation rate
Surface emission rate and release processes (both neutrals and ions)
Particle loss rate from Mercury's environment

Further Objectives:

Remote sensing of the surface composition
Magnetosphere structure and dynamics
Planetary response to solar wind variations
ENA imaging applications for comparative solar-planetary relationship
Heavy ion sputtering products

The SERENA experiment deals with some of the main scientific objectives of the BepiColombo mission: composition, origin and dynamics of Mercury's exosphere and polar deposits; and structure and dynamics of Mercury's magnetosphere.
In order to successfully perform the observations, the SERENA units are based on novel concepts for particle instrumentation, potentially interesting for future planetary missions beyond BepiColombo.

SERENA constitutes the only package on board the BepiColombo-MPO for the investigation of the particles’ environment of Mercury. For this reason it is the crucial experiment that will link the ESA MPO to the JAXA MMO satellite (the spinning polar-orbiting satellite essentially devoted to the study of the Hermean Magnetosphere).

The SERENA measurements will also complement other payload elements on board MPO devoted to environmental studies, like MAG (magnetic field), SIXS (solar radiation and energetic particles), and PHEBUS (UV exospheric emission).

In addition, it will provide complementary information to the surface instruments (like SIMBIO-SYS, MIXS and MERTIS) to constrain how the erosion of the surface (via micrometeorites impacts and subsequent sublimation) contributes to the generation of the planetary exosphere and how external agents produce space weathering of the Hermean regolith.