Analogous to the case of Venus, electron dissociative recombination of the ionospheric O2+ ions can be an important source of suprathermal atomic oxygen in the exosphere of Mars. Because of the weaker surface gravitational attraction on Mars as compared to that on Venus, a hot oxygen corona so formed could be denser than the corresponding corona on Venus at altitudes >2000 km in spite of the lower ionospheric content of Mars. Modification to the solar wind interaction via ionization pickup of the exospheric oxygen ions may be detectable by ion mass spectrometer experiment on a Mars orbiter mission. If an extended oxygen corona exists, collisional interaction with the Martian satellite, Phobos, would lead to the formation of an oxygen gas torus of average number density of only 〈n〉 ≈ 1-2 cm-3 along the orbit of Phobos. In comparison, intrinsic gas emission from Phobos, if total gas production rate is ≈1023 H2O molecules sec-1, would contribute to a gas torus with 〈n〉 ≈ 103 oxygen atoms cm-3 exceeding the ambient value of 100-200 cm-3 as estimated for the hot oxygen corona.