COMPLETE: a mission concept for comprehensive 3D understanding of coronal magnetic energy storage and release

Despite many decades of research, it is still poorly understood exactly how magnetic energy is stored and impulsively released to power plasma heating, particle acceleration, and bulk flows in impulsive solar eruptions (flares, coronal mass ejections) and more gradual energetic processes (coronal heating in active regions, solar wind outflows). Breakthroughs have been hindered by two critical limitations: lack of knowledge of the 3D coronal magnetic field and its evolution, and a similar lack of insight into how localized energy release manifests and propagates within 3D coronal structures. Transformative progress to close these gaps requires systematic observations from multiple viewpoints, in a variety of wavelengths, and including coronal magnetometry. Recent and ongoing technological advancements allow us to realize these goals within a decadal timescale.

To that end, we present the COMPLETE mission concept, currently under study for the upcoming Heliophysics Decadal Survey. COMPLETE’s highly co-optimized and complementary instrument suite include spectroscopic imagers for X-rays, gamma-rays, and energetic neutral atoms; high-resolution wide-field EUV filtergram imagers; photospheric Doppler vector mangetographs; and Hanle-effect UV (Lyman-α) coronal magnetographs. Distributed across three spacecraft at the L₁, L₄, and L₅ Earth-Sun Lagrange points, COMPLETE would provide the first comprehensive measurements of the 3D low- and middle-coronal magnetic field and simultaneous 3D energy-release diagnostics from large eruptions down to small-scale processes.

COMPLETE’s instrument suite is deliberately complementary across its individual spacecraft, and each spacecraft suite is optimized for the measurements from that vantage point and for the mission as a whole. Data from all instruments will be processed to enable systems-level analysis from the entire observatory. Overlapping fields of view and optimized capabilities provide a zone of ideal coverage near the west limb as viewed from Earth. Within this region, COMPLETE provides comprehensive observations of 3D structures, photospheric and coronal magnetic fields, and signatures of impulsive energy release within integrated data products. COMPLETE represents a strategic shift from the nearly ubiquitous current practices of siloed study in isolated subdisciplines towards a comprehensive, unified systems approach to solar, coronal, and heliospheric physics, to enable us to finally close decades-old questions of how the Sun’s magnetic field and impulsive energy release are interrelated, from local to global scales.