The idea that an ancient ocean covered up to one-third of the Martian surface is tempting, but other planetary scientists are challenging the basis for the theory. [right, possible extent of early ocean on Mars. Credit, Univ. of Colorado]
Planetary geologist Rossman Irwin at Tucson-based Planetary Science Institute in Tucson, is quoted as arguing that some of the deltas and valley networks that lie well below the proposed Martian sea level, which contradicts the ocean interpretation.