(a) Energy spectrum during peak of ion flux enhancement in the CIR event on 2015 June 8 detected by ACE at ∼1 au. The power laws fitted with the observations are also shown. The observations by ACE are extrapolated to 30 MeV, to show that at both 10 MeV and at 30 MeV, the expected flux levels are below the detection limits (Rodriguez et al. 2014) of GOES. (b) The energy spectrum obtained from MAVEN. The integration time is ∼1 hr in both energy spectra.