Water on Mars any point in the year but would be ideal for solid carbon dioxide. The carbon dioxide melting in the warmer summer would yield liquid carbon dioxide which would then form the gullies. Even if gullies are carved by flowing water at the surface, the exact source of the water and the mechanisms behind its motion are not understood. The dry gullies are deep grooves etched into the slopes that are there year-round. There are many other features on Mars, and some of them change seasonally. In August 2011, NASA announced the discovery by undergraduate student Lujendra Ojha of current seasonal
Crewed Mars rover rovers, because they need to know at least roughly where they are and where they are going to get to a destination. Dead reckoning was the method used by the Mars Pathfinder rover "Sojourner" for navigation. A GPS satellite network for Mars would mean a constellation of satellites in Mars orbit, but one alternative would be a surface based pseudo-satellites array. These devices would have to be emplaced with high precision, unless they were self-calibrating. An example of criteria for humaned Mars surface rover was expressed by NASA in the surface variant of the aforementioned SEV, in development in during