Solar to Interstellar B-fields and Interactions

Scientific Investigation 2: Identify and advance understanding of processes related to the interactions of the magnetic field of the Sun and the local interstellar medium. 

IBEX Ribbon

IBEX Ribbon

IMAP resolves the temporal and spatial evolution of the enigmatic “Ribbon” of enhanced energetic neutral atoms (ENAs) discovered by the Interstellar Boundary Explorer (IBEX), the higher energy “Belt” discovered by Cassini/INCA, and the interstellar boundary regions. IMAP will measure complete ENA energy spectra from distinct regions (e.g., nose, tail, flanks, poles, Ribbon, Belt) to define the morphology and evolution of heliosheath populations from the plasma core, to suprathermal and energetic particles. Observations that span this complete energy range are critical for establishing not only the origin of the Ribbon but also its relationship to the Belt. 

IMAP’s 6 month resolution of global maps represents a significant enhancement over IBEX, which only resolved changes in spatial structures over 2–4 years. IMAP will probe evolution on even shorter scales to test for the existence of instabilities near the nose and heliopause, and possible rapid evolution of the Ribbon and Belt. IMAP provides improvements in average collection power for Lo, Hi, Ultra compared to IBEX and INCA to statistically resolve spatial evolution. 

Fine Structure

Prime motivation for IMAP is the resolution of possible fine structure to discover the origin of the Ribbon, and its connection to the Belt. (A) All-sky ENA map showing the IBEX Ribbon at 1.1 keV, including locations of the Nose and Voyager. (B) Detail of a segment showing apparent fine structure [McComas et al., 2009].

A necessary test of each Ribbon origin hypothesis is for a model to reproduce key observables, such as the global spatial geometry, global spectral properties, location relative to the Sun’s motion through the LISM, and variability of the ENA emission intensity over space and time. In particular, for hypotheses in which the ENAs originate from the solar wind (SW), the time variation of ENA flux and its association with SW is emerging as a definitive test. 

Giacalone and Jokipii, 2015

Predicted double-peaked ribbon structure [Giacalone and Jokipii, 2015].

A recent model predicts that the Ribbon is double-peaked due to particle–wave interactions, which may be related to fine structure in the Ribbon. The existence of Ribbon fine structure (or a double-peak) is unconfirmed. IMAP’s improved spatial resolution is sufficient to discover fine structure associated with instabilities in Ribbon and Belt formation, and potentially other heliosphere structures.