Energy spectra of the average energetic neutral hydrogen flux. (a) Measured spectrum of the flux from the surface (black dots) compared to the instrument response to the model (grey diamonds), using data from the time interval of 11 January 2019 to 22 October 2020. Vertical error bars indicate a 90% confidence interval of the flux. Horizontal error bars represent the full width half maximum of the corresponding energy bin. The dotted line is a 90% confidence sensitivity limit (Feldman & Cousins 1998), below which the signal cannot be distinguished from zero due to the significant background that was subtracted. (b) Fitted model of energetic neutral hydrogen flux with sputtered and backscattered components separated.