- 1University of Bern, Physics Institute, Space Research and Planetary Science, Bern, Switzerland (andre.galli@unibe.ch)
- 2Space Research Centre PAS (CBK PAN), Warsaw, Poland
- 3University of New Hampshire, Durham, USA
- 4Southwest Research Institute, San Antonio, USA
- 5University of Texas at San Antonio, San Antonio, USA
- 6Department of Mathematics and Statistics, University of Waikato, Hamilton, New Zealand
- 7Department of Astrophysical Sciences, Princeton University, Princeton, USA
Our heliosphere is surrounded by the Local Interstellar Medium. Their interactions lead to a range of observable phenomena such as energetic neutral atoms from the outer regions of the heliosphere and the influx of some interstellar neutrals into the inner solar system. Hydrogen is the dominant neutral species in the Local Interstellar Medium, but due to ionization and radiation pressure only a fraction of the interstellar neutral hydrogen atoms reach the inner solar system. Observing this signal therefore offers a reality check for our assumptions on the Local Interstellar Medium and on solar-activity dependent loss processes inside the heliosphere. So far, the IBEX-Lo instrument onboard the Interstellar Boundary Explorer in Earth orbit has been the only instrument to directly measure interstellar neutral hydrogen atoms.
This presentation shows the maps of 15 years of IBEX-Lo observations of the interstellar neutral hydrogen signal, covering more than one solar cycle and including two solar minima where the signal in IBEX-Lo is strongest. Despite the very intense interstellar neutral helium signal, the hydrogen signal can be retrieved with appropriate knowledge of the instrument, choice of optimum observation season, and supporting modeling. As expected, the retrieved interstellar neutral hydrogen signal is anti-correlated with solar activity. On the other hand, the discrepancy, known from earlier studies, between observed and predicted energy of the interstellar hydrogen atoms persists.
How to cite: Galli, A., Swaczyna, P., Bzowski, M., Kubiak, M. A., Kowalska-Leszczynska, I., Wurz, P., Rahmanifard, F., Schwadron, N. A., Möbius, E., Fuselier, S. A., Sokol, J. M., Gasser, J., Heerikhuisen, J., and McComas, D. J.: 15 years of interstellar neutral hydrogen observed with the Interstellar Boundary Explorer, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3201, https://doi.org/10.5194/egusphere-egu25-3201, 2025.
