Subsolar standoff distance (r₀) identified with different determination methods. The black circles, red inverted triangles, blue squares, and green regular triangles stand for the distances identified by the method of the gradient of the plasma thermal pressure, the gradient of the magnetic field magnitude, the ratio of , and the ratioof (P_th + P_d)∕P_B, respectively. Here , , and are the number densities of the predominantly planetary heavy ions of the oxygen atom, the oxygen molecule, and the solar wind protons, respectively. P_th, P_d, and P_B represent the plasma thermal pressure, the dynamic pressure, and the magnetic pressure, respectively. The solid yellow, red, and blue squares stand for the locations of r₀ from the empirical MPB models of Edberg et al. (2008), Vignes et al. (2000), and Trotignon et al. (2006), respectively. As these empirical models represent the Martian MPB location under the average solar wind condition, these three solid squares are fixed at the same position of the X-axis where P_d = 1 nPa.