The two Viking missions, Mars Phoenix and the Mars Science Laboratory rover Curiosity count the sol on which each lander touched down as "Sol 0"; Mars Pathfinder and the two Mars Exploration Rovers instead defined touchdown as "Sol 1".

NASA scientists who recently tried to access material on the 1976 Viking mission to Mars discovered that 20 percent of it has simply vanished and that the rest is going fast.

The concept of canals with flowing water was later proved erroneous by more accurate observation of the planet, and later landings by Russian and American probes such as the two Viking missions which found a lifeless world too cold for water to exist in its liquid state.

The theory of an inhabited planet with flowing water was disproved by data provided by Russian and American probes such as the two Viking missions which found a dead, frozen world where water could not exist in a fluid state.

Scientists report that complexity analysis studies of the Labeled Release experiments of the 1976 Viking mission to Mars may suggest the detection of "extant microbial life on Mars."

The ideas of canals with flowing water and an inhabited, if dying world, were later disproved by more accurate observation of the planet, and fly bys and landings by Russian and American probes such as the two Viking missions which found a dead, frozen world where water could not exist in a liquid state.

This is far more images than any other mission; in fact, it is nearly twice the number returned by the two Viking missions in the late 1970's.

It was the kind of experience that put him in line to be the chief project scientist for the two Viking missions.

For all the triumph of NASA's 1976 Viking mission, which put two unmanned spacecraft on Mars, there was one major disappointment: The landers failed to find carbon-based molecules that could serve as the building blocks of life.

Almost since the time of the two Viking missions in 1976, planetary scientists have focused attention on the region of Antarctica known as the dry valleys - a network of glacial gorges and valleys transecting the Royal Society mountain range and leading to the west coast of the Ross Sea.