Sketch shows the structures of boundaries upstream of Mars in the top row: solar wind, BS, magnetosheath, magnetopause, and induced magnetosphere. The magnetopause is an MHD discontinuity, either TDor RD. The inner part of magnetosheath is called the PDR, similar to the PDL at Earth, in which the magnetosheath magnetic fields are compressed and piled up, and the plasma is depleted. This PDR with enhanced magnetic field was previously identified as the IMB and the MPB. The magnetopause, that is, the TD or RD transition region, has also been referred to as the ICB, which separates H⁺ ions in the magnetosheath and heavy ions in the induced magnetosphere.