^{Notes. (a)}Deniau et al. (2022) reported no evidence of backscattered solar wind H+ from Phobos. An upper limit of the differential directional energy flux is given as 10⁶ eV cm⁻²s⁻¹ sr⁻¹ eV⁻¹. Similarly, Futaana et al. (2021) reported observations from two Mars Express flybys (out of more than a dozen) of H⁺ potentially coming from Phobos’ surface. However, the sporadic nature of the observations remains unexplained.