Phase C, hardware fabrication; launch October 2006

THEMIS answers fundamental outstanding questions regarding the magnetospheric substorm instability, a dominant mechanism of transport and explosive release of solar wind energy within geospace. THEMIS will elucidate which magnetotail process is responsible for substorm onset at the region where substorm auroras map (~10 R_e): (1) a local disruption of the plasma sheet current or (2) that current’s interaction with the rapid influx of plasma emanating from lobe flux annihilation at ~25 R_e. Correlative observations from long-baseline (2 to 25 R_e) probe conjunctions will delineate the causal relationship and macroscale interaction between the substorm components. THEMIS’s five identical probes will measure particles and fields on orbits that optimize tail-aligned conjunctions over North America. Ground observatories time auroral breakup onset. Three inner probes at ~10 R_e monitor current disruption onset, while two outer probes, at 20 and 30 R_e, respectively, remotely monitor plasma acceleration due to lobe flux dissipation. In addition to addressing its primary objective, THEMIS will answer critical questions in radiation belt physics and solar wind-magnetosphere energy coupling. THEMIS’s probes use flight-proven instruments and subsystems, yet demonstrate spacecraft design strategies ideal for constellation class missions. THEMIS is complementary to MMS and a science and a technology pathfinder for future STP missions.

• Establish when and where substorms start,

• Determine how the individual substorm components interact macroscopically,

• Determine how substorms power the aurora, and

• Identify how the substorm instability couples dynamically to local current disruption modes.

THEMIS addresses two of NASA’s primary SEC themes: How does our planet respond to solar variations? and, How does solar variability affect society? THEMIS will play a key role in understanding Earth’s space environment and a prerequisite to understanding space weather. Specifically, the coupling of energy from the magnetosphere to the ionosphere is dominated by substorms, and if the time and place of substorm initiation can be predicted accurately, then better predictions of the resulting effects on the upper atmosphere and ionosphere can be made.

THEMIS is a macroscale mission, with objectives and orbits complementary to those of the micro- and mesoscale mission MMS.

Front Matter (R1-R12)

Executive Summary (1-4)

1 Introduction (5-11)

2 Enabling Exploration of the Sun-Heliosphere-Planetary System (12-24)

3 Implementation Strategy and Recommendations (25-30)

Appendix A: Statement of Task (31-34)

Appendix B: Sun-Earth Connection Missions and Exploration (35-51)

Appendix C: A National Science Research Agenda (52-53)

Appendix D: Biographies of Committee Members (54-57)

Appendix E: Acronyms (58-60)