... Comet NEAT Passes an Erupting Sun . ... Just as the comet swooped inside the orbit of Mercury and developed a long and flowing tail of gas and dust, the Sun emitted a huge Coronal Mass Ejection (CME). ... But Mars is too cold and its atmosphere too thin for liquid water to exist on the surface. ... First imaged by the Mariner 9 spacecraft, Valles Marineris, the grand canyon of Mars, is a system of enormous depressions called chasmata that stretch some 4,000 kilometers along the Martian equator. ...