Heliosphere Responds to a Large Solar Wind Intensification: Decisive Observations from IBEX

D. J. McComas, M. A. Dayeh, H. O. Funsten, J. Heerikhuisen, P. H. Janzen, D. B. Reisenfeld, N. A. Schwadron, J. R. Szalay, E. J. Zirnstein

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Our heliosphere - the bubble in the local interstellar medium produced by the Sun's outflowing solar wind - has finally responded to a large increase in solar wind output and pressure in the second half of 2014. NASA's Interstellar Boundary Explorer (IBEX) mission remotely monitors the outer heliosphere by observing energetic neutral atoms (ENAs) returning from the heliosheath, the region between the termination shock and heliopause. IBEX observed a significant enhancement in higher energy ENAs starting in late 2016. While IBEX observations over the previous decade reflected a general reduction of ENA intensities, indicative of a deflating heliosphere, new observations show that the large (∼50%), persistent increase in the solar wind dynamic pressure has modified the heliosheath, producing enhanced ENA emissions. The combination of these new observations with simulation results indicate that this pressure is re-expanding our heliosphere, with the termination shock and heliopause already driven outward in the locations closest to the Sun. The timing between the IBEX observations, a large transient pressure enhancement seen by Voyager 2, and the simulations indicates that the pressure increase propagated through the heliosheath, reflected off the heliopause, and the enhanced density of the solar wind filled the heliosheath behind it before generating significantly enhanced ENA emissions. The coming years should see significant changes in anomalous cosmic rays, galactic cosmic radiation, and the filtration of interstellar neutral atoms into the inner heliosphere.

Original languageEnglish
Article numberL10
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Mar 20 2018


Data used in this study have been validated using procedures developed by the IBEX team (McComas et al. 2012, 2014a, 2017), and are available to the community. This work was funded by the IBEX mission as a part of the NASA Explorer Program (NNG17FC93C; NNX17AB04G). We acknowledge solar wind ram pressure data at 1 au from missions such as ACE and Wind, collected in the OMNI database:ftp://spdf.gsfc. nasa.gov/pub/data/omni.

FundersFunder number
National Aeronautics and Space AdministrationNNX17AB04G, NNG17FC93C


    • Sun: activity
    • Sun: heliosphere
    • Sun: magnetic fields
    • local interstellar matter
    • solar wind


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