Oblique and rippled heliosphere structures from the Interstellar Boundary Explorer

• Published in: Nature astronomy Vol. 6; no. 12; pp. 1398 - 1413
• Main Authors: Zirnstein, Eric J., Shrestha, Bishwas L., McComas, David J., Dayeh, Maher A., Heerikhuisen, Jacob, Reisenfeld, Daniel B., Sokół, Justyna M., Swaczyna, Paweł
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 2022; Nature Publishing Group
• Subjects: 639/33/34/865; 639/33/525; 639/766/1960/1134; 639/766/525/870; Astronomy; Astrophysics and Cosmology; Boundaries; Physics; Physics and Astronomy; Spacecraft; Wind pressure; Solar physics; Interstellar medium; Space physics; Astrophysical plasmas
• ISSN: 2397-3366; 2397-3366
• DOI: 10.1038/s41550-022-01798-6

Past analysis has shown that the heliosphere structure can be deduced from correlations between long-scale solar wind pressure evolution and energetic neutral atom emissions. However, this required spatial and temporal averaging that smoothed out small or dynamic features of the heliosphere. In late 2014, the solar wind dynamic pressure increased by roughly 50% over a period of 6 months, causing a time and directional-dependent rise in around 2–6 keV energetic neutral atom fluxes from the heliosphere observed by the Interstellar Boundary Explorer. Here, we use the 2014 pressure enhancement to provide a simultaneous derivation of the three-dimensional heliospheric termination shock (HTS) and heliopause (HP) distances at high resolution from Interstellar Boundary Explorer measurements. The analysis reveals rippled HTS and HP surfaces that are oblique with respect to the local interstellar medium upwind direction, with significant asymmetries in the heliosphere structure compared to steady-state heliosphere models. We estimate that the heliosphere boundaries contain roughly ten astronomical unit-sized spatial variations, with slightly larger variations on the HTS surface than the HP and a large-scale, southwards-directed obliquity of the surfaces in the meridional plane. Comparisons of the derived HTS and HP distances with Voyager observations indicate substantial differences in the heliosphere boundaries in the northern versus southern hemispheres and their motion over time. Energetic neutral atom fluxes measured at 1 au by the IBEX spacecraft between 2014 and 2019 are used as proxy to map the heliosphere at high resolution. Persistent ripples that corrugate the heliospheric boundary and induce variations by up to ~10 au are observed, with marked north–south asymmetry.