The solar wind emitted from the solar corona carves out a cavity separating the solar and interstellar plasmas called the heliosphere. The global models of the heliosphere predict vastly different structures of the heliosphere. The heliosphere’s structure undergoes significant evolution in response to the solar cycle and secular changes in the solar wind. The direct observations of the plasma in the outer heliosphere are currently only available from New Horizons. Moreover, global imaging is enabled by energetic neutral atoms (ENAs) created in the heliosheath from energetic ions that are neutralized by charge exchange with interstellar neutral atoms. The most important population of energetic ions is pickup ions (PUIs) created by ionizing interstellar neutral atoms penetrating the heliosphere.

In the proposed project, we plan to study the global structure of the heliosphere. We will use the ENA observations from the Interstellar Boundary Explorer (IBEX) and Interstellar Mapping and Acceleration Probe (IMAP) missions. Using spherical harmonics, we will further develop and implement the separation technique of the globally distributed flux and IBEX ribbon components of the ENA signal. The new implementation will use the data from individual orientations of the spacecraft rather than the IBEX maps. We anticipate that this implementation will allow us to conduct more precise studies of the ribbon position. The evolution of the GDF compared with the solar wind changes will allow us to understand better the processes operating in the inner heliosheath. On the other hand, the ribbon evolution reflects the distance to the source, which informs about the distance to the heliopause. Furthermore, we plan to investigate observations of heavy ENAs from the IMAP-Hi instrument. The two sensors of this instrument, unlike IBEX-Hi, are equipped with time-of-flight detectors, allowing for species identification. Helium ENAs would be critical in understanding the heliosphere’s shape if successfully detected. Moreover, they may allow for the observation of extraheliospheric ENA sources. Finally, we will also investigate the energization source of PUIs in the heliosheath using observations from New Horizons. The energization of PUIs is observed, but systematic observational effects must be addressed for full analysis.

The proposed project will investigate the ENA and PUI observations from existing (IBEX, New Horizons) and soon launching (IMAP) missions. We will investigate the processes governing the heliosphere’s global structure and seek a possible source of extraheliospheric helium ENAs. These studies are crucial to understanding the global structure of the heliosphere and its evolution in response to the solar cycle and secular evolutions of the solar wind.