Oceans are back on Mars

Since spacecraft sent back the first close-up images of Mars more than 30 years ago, some experts have insisted that oceans once existed on the now dry, cold planet. Critics have maintained for decades that such an idea is the product of unrestrained imaginations. Now, a study published in the June 14 issue of the British journal Nature reports new evidence that our neighbor in space once boasted an ocean or oceans as big, relative to planet size, as the Atlantic on Earth.  "We were able to lay to rest one of the main objections to the idea that there once were oceans on Mars," says Taylor Perron, a postdoctoral fellow in Harvard's Department of Earth and Planetary Sciences.

To those looking for life on other planets, that conclusion is a wave in the right direction. "Follow the water," is the mantra chanted by the National Aeronautics and Space Administration in its search for extraterrestrial life, because wherever there's water on Earth, there's life.

When geologists started making maps of Mars, using data broadcast by spacecraft that landed there in the 1970s, they were struck by the sight of a huge basin covering a third of the planet. Located in the northern plains, the flat, sediment-covered area reminded them of the ocean floors on Earth.

The basin is bordered by shorelines, which are cut by the downstream ends of huge channels eroded into the face of Mars. It is easy to imagine these channels as places where water flowed from the higher southern regions into the basin.

Two shorelines run continuously for thousands of miles. Planetary scientists named them Arabia and Deuteronilus, and they estimate their ages at between 2 billion and 4 billion years.