ANCIENT HORIZONS
In 2003 a rover found evidence that water once flowed on
Mars, but early climatic conditions on the red planet are still
up for debate. Models suggest two extremes that would have
allowed some liquid to exist on the surface, illustrated here;
scientists suspect Mars may have cycled between both states.MANUEL CANALES AND MSOURCES: ASHLEY PALUMATTHEW W. CHWBO, BROWASTYK, NGMN UNIVERSITY; ROBIN W STAFF; ALEXANDER STEGMORDSWORTH, HARVARD UNIVERSITY; NASAAIER. ART: ANTOINE COLLIGNON