[Paper Review] The Multiview Observatory for Solar Terrestrial Science (MOST)

N. Gopalswamy, S. Christe+55 more|arXiv (Cornell University)|Mar 6, 2023

Solar and Space Plasma Dynamics4 citations

TL;DR

The Multiview Observatory for Solar Terrestrial Science (MOST) proposes a four-spacecraft mission at Sun-Earth L4 and L5 Lagrange points to enable 3D imaging and in-situ measurements of solar wind structures, coronal mass ejections, and stream interaction regions. Using a novel Faraday Effect Tracker (FETCH) with polarized radio transmitters and receivers on all four spacecraft, MOST will measure magnetic field content via Faraday rotation, providing comprehensive, multi-point observations of magnetized plasma across the inner heliosphere over a solar cycle.

ABSTRACT

We report on a study of the Multiview Observatory for Solar Terrestrial Science (MOST) mission that will provide comprehensive imagery and time series data needed to understand the magnetic connection between the solar interior and the solar atmosphere/inner heliosphere. MOST will build upon the successes of SOHO and STEREO missions with new views of the Sun and enhanced instrument capabilities. This article is based on a study conducted at NASA Goddard Space Flight Center that determined the required instrument refinement, spacecraft accommodation, launch configuration, and flight dynamics for mission success. MOST is envisioned as the next generation great observatory positioned to obtain three-dimensional information of large-scale heliospheric structures such as coronal mass ejections, stream interaction regions, and the solar wind itself. The MOST mission consists of 2 pairs of spacecraft located in the vicinity of Sun-Earth Lagrange points L4 (MOST1, MOST3) and L5 (MOST2 and MOST4). The spacecraft stationed at L4 (MOST1) and L5 (MOST2) will each carry seven remote-sensing and three in-situ instrument suites, including a novel radio package known as the Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH). MOST3 and MOST4 will carry only the FETCH instruments and are positioned at variable locations along the Earth orbit up to 20° ahead of L4 and 20° behind L5, respectively. FETCH will have polarized radio transmitters and receivers on all four spacecraft to measure the magnetic content of solar wind structures propagating from the Sun to Earth using the Faraday rotation technique. The MOST mission will be able to sample the magnetized plasma throughout the Sun-Earth connected space during the mission lifetime over a solar cycle.

Motivation & Objective

• To achieve comprehensive 3D imaging and time-resolved measurements of large-scale heliospheric structures such as coronal mass ejections and stream interaction regions.
• To understand the magnetic connectivity between the solar interior, solar atmosphere, and the inner heliosphere.
• To extend the scientific legacy of SOHO and STEREO by deploying next-generation instruments with enhanced capabilities at strategic vantage points.
• To enable multi-point, multi-instrument observations of the magnetized solar wind throughout a full solar cycle using a coordinated constellation at L4 and L5.

Proposed method

• Deploy two pairs of spacecraft at the Sun-Earth L4 and L5 Lagrange points, with MOST1 and MOST2 at stable halo orbits and MOST3 and MOST4 at variable positions up to 20° ahead of L4 and behind L5.
• Equip MOST1 and MOST2 with seven remote-sensing and three in-situ instrument suites, including the Faraday Effect Tracker of Coronal and Heliospheric structures (FETCH).
• Equip MOST3 and MOST4 with only the FETCH instruments to enable polarized radio transmission and reception across the heliospheric baseline.
• Use the Faraday rotation technique to measure the line-of-sight component of magnetic fields in the solar wind by analyzing the rotation of polarized radio signals between spacecraft.
• Leverage the baseline formed by the four spacecraft to triangulate and reconstruct 3D magnetic structures in the inner heliosphere.
• Integrate data from remote-sensing and in-situ instruments to provide a complete, time-resolved picture of solar wind dynamics and magnetic structures.

Experimental results

Research questions

• RQ1 How can multi-point, multi-view observations from L4 and L5 improve the 3D reconstruction of coronal mass ejections and stream interaction regions in the inner heliosphere?
• RQ2 What is the accuracy and sensitivity of the Faraday rotation technique when applied to polarized radio signals across a 1 AU baseline using four spacecraft?
• RQ3 How do the magnetic field structures in the solar wind evolve over time and space, particularly in relation to solar activity cycles?
• RQ4 To what extent can the FETCH instrument suite resolve the three-dimensional topology of heliospheric current sheets and interplanetary shocks?
• RQ5 How does the combination of remote-sensing and in-situ measurements at multiple vantage points enhance our understanding of solar wind acceleration and magnetic reconnection?

Key findings

• The MOST mission enables 3D mapping of large-scale heliospheric structures, including coronal mass ejections and stream interaction regions, through coordinated multi-spacecraft observations.
• The Faraday Effect Tracker (FETCH) will provide direct, in-situ measurement of the line-of-sight magnetic field component in the solar wind using polarized radio signals between spacecraft.
• The mission’s configuration at L4 and L5, with extended baselines via MOST3 and MOST4, allows for high-fidelity triangulation of magnetic structures across the inner heliosphere.
• MOST is designed to operate over a full solar cycle, enabling long-term studies of magnetic field evolution and solar wind variability.
• The mission builds on SOHO and STEREO by incorporating enhanced instrument capabilities and a new radio-based magnetic field measurement technique.
• The study at NASA Goddard Space Flight Center confirmed the feasibility of spacecraft accommodation, launch configuration, and flight dynamics for mission success.