context1: Spectrally Nereid appears grey in colour and water ice has been detected on its surface. Its spectrum appears to be intermediate between Uranus's <strong>moons</strong> Titania and Umbriel, which suggests that Nereid's surface is composed of a mixture of water ice and some spectrally neutral material. The spectrum is markedly different from the outer solar system minor <strong>planets</strong> Pholus, Chiron and Chariklo, suggesting that Nereid formed around Neptune rather than being a captured body.
context2: Water on Mars is found in its polar ice caps, and newly carved gullies recently observed on Mars suggest that liquid water may exist, at least transiently, on the <strong>planet</strong>'s surface, and possibly in subsurface environments such as hydrothermal springs as well. At the Martian low temperatures and low pressure, liquid water is likely to be highly saline. As for Europa, liquid water likely exists beneath the <strong>moon</strong>'s icy outer crust.