Water Flowed on Mars Longer than Thought

Parts of ancient Mars may have been wet for a billion years longer than scientists previously thought, a new study of images of the red planet's surface suggests.

Along with Earth and the other inner planets of our solar system, Mars formed about 4.5 billion years ago. Scientists have long known that flowing water formed many of the features seen on Mars today, but previous studies suggested that water runoff from precipitation had ceased after the first billion years of Mars' history, called the Noachian Epoch.

But one team of scientists thinks these rains and floods persisted into more recent—geologically speaking—periods in Mars' history.

Catherine Weitz, a senior scientist with Planetary Science Institute in Tucson, Ariz., and her colleagues examined close-up images of the plains surrounding the huge Valles Marineris canyon system taken by the HiRISE instrument aboard NASA's Mars Reconnaissance Orbiter (currently still circling the planet). HiRISE can resolve features as small as 3 feet (1 meter) in diameter.

Weitz and her team noticed that light-toned layered deposits in the plains around Valles Marineris had different features from those inside the canyon; these features suggested that water continued to flow on a large scale in these plans after the Noachian, into the Hesperian epoch of Mars, until about 3.7 billion to 3 billion years ago. Phenomena associated with flowing water are called fluvial processes.

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