Interplanetary mesoscale observatory (InterMeso): A mission to untangle dynamic mesoscale structures throughout the heliosphere

Abstract

Mesoscale dynamics are a fundamental process in space physics, but fall within an observational gap of current and planned missions. Particularly in the solar wind, measurements at the mesoscales (100s RE to a few degrees heliographic longitude at 1 au) are crucial for understanding the connection between the corona and an observer anywhere within the heliosphere. Mesoscale dynamics may also be key to revealing the currently unresolved physics regulating particle acceleration and transport, magnetic field topology, and the causes of variability in the composition and acceleration of solar wind plasma. Studies using single-point observations do not allow for investigations into mesoscale solar wind dynamics and plasma variability, nor do they allow for the exploration of the sub-structuring of large-scale solar wind structures like coronal mass ejections (CMEs), co-rotating/stream interaction regions (CIR/SIRs), and the heliospheric plasma sheet. To address this fundamental gap in our knowledge of the heliosphere at these scales, the Interplanetary Mesoscale Observatory (InterMeso) concept employs a multi-point approach using four identical spacecraft in Earth-trailing orbits near 1 au. Varying drift speeds of the InterMeso spacecraft enable the mission to span a range of mesoscale separations in the solar wind, achieving significant and innovative science return. Simultaneous, longitudinally-separated measurements of structures co-rotating over the spacecraft also allow for disambiguation of spatiotemporal variability, tracking of the evolution of solar wind structures, and determination of how the transport of energetic particles is impacted by these variabilities.

On the Mesoscale Structure of Coronal Mass Ejections at Mercury’s Orbit: BepiColombo and Parker Solar Probe Observations

“…Even more so, the work reported here shows that the results of Lugaz et al (2018) and Ala-Lahti et al (2020) apply even at shorter heliocentric distances than 1 au, despite the generally smaller number of evolutionary processes such as interactions and deformations that are expected to have taken place. Fortunately, the importance of investigating mesoscales in the solar wind has been gaining more traction in recent years (e.g., Viall et al 2021), and novel missions are being proposed to investigate variations and variability of solar transient events (e.g., Allen et al 2022;Lugaz et al 2023;Nykyri et al 2023). The potential benefits of a constellation of spacecraft designed to explore the mesoscale region would be invaluable for improving upon our knowledge not only of the fundamental physics of CMEs but also of other transient phenomena such as stream interaction regions and solar energetic particles.…”

The Width of Magnetic Ejecta Measured near 1 au: Lessons from STEREO-A Measurements in 2021–2022

“…Numerous multi-spacecraft in situ mission concepts have been recently proposed to investigate CMEs, shocks, and solar energetic particles (SEPs; e.g., see white papers submitted to the 2023 Decadal Survey (Allen et al 2022;Akhavan-Tafti et al 2023;Lugaz et al 2023;Nykyri et al 2023), some of them based on earlier concepts (St. Cyr et al 2000a;Szabo 2005). The inter-spacecraft separations have been proposed to vary between 60°and 90°for the HELIX mission concept and less than 1°for the SWIFT concept of Akhavan-Tafti et al (2023).…”

A Mosaic of the Inner Heliosphere: Three Carrington Rotations During the Whole Heliosphere and Planetary Interactions Interval

“…However, the coherency began to break down with increased interspacecraft separations in GSE Y, suggesting mesoscale variability in the solar wind was beginning to increasingly affect comparisons between the L1‐orbiting spacecraft, consistent with investigations of mesoscale variability in CME sheaths (Ala‐Lahti et al., 2020). The current constellations of assets do not allow for robust investigations into this structuring across scales, but these findings are in line with calls for dedicated missions to investigate the nature of the mesoscale solar wind (e.g., Allen et al., 2022; Maruca et al., 2021) and consistent with previous studies attempting to elucidate mesoscale structures in the solar wind (e.g., Ala‐Lahti et al., 2020; Neugebauer et al., 2006; Neugebauer & Giacalone, 2005; Owens et al., 2017) and potential effects on the geospace system (e.g., Ala‐Lahti et al., 2021).…”