Bow shock protons in the lunar environment

Protons from the Earth's bow shock are observed by the Suprathemal Ion detector Experiment (SIDE) in two regions of the lunar orbit. The dawn region begins at the dawn side bow shock crossing and ends approximately 5 days later and the dusk region begins at approximately 2 days prior to entering the dusk side magnetosheath and ends at the inbound bow shock crossing. Dusk and dawn refer to a terrestrial coordinate system. The dominant contribution to the ion spectra observed by the SIDE in these regions is from particles with energies between approximately 750eV q-1 and 3500eV a-1 is the upper limit of the energy range of the detector. Analysis of simultaneous data from the Explorer 35 magnetometer and the SIDE indicates that the observability of bow shock protons at the lunar distance is dependent on the configuration of the interplanetary magnetic field