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Regional Processes Led to Huge Martian Floods

By David Reneke

Regional processes led to huge Martian floods, and interstellar seeds could have created oases of life throughout the universe.

Gigantic groundwater outbursts created the largest flood channels in the solar system on Mars 3.2 billion years ago. For many years it was thought that this was caused by the release of water from a global water table, but research carried out by the Planetary Science Institute reveals that the source was regional deposits of sediment and ice set in place 450 million years earlier.

“The flooding is due to regional processes, not global processes,” said J. Alexis P. Rodriguez, who was lead author of the research published in Scientific Reports (http://tinyurl.com/pbgoy5v).

The evidence is intriguing. Deposition of sediment from rivers and glacial melt filled giant canyons beneath a primordial ocean contained within the planet’s northern lowlands. It was the water preserved in these canyon sediments that was later released as great floods, the effects of which can be seen today.

The canyons filled, the Martian ocean disappeared and the surface froze for approximately 450 million years. Then, about 3.2 billion years ago, lava beneath the canyons heated the soil, melted the icy materials and produced vast systems of sub­terranean rivers extending hundreds of kilometres. This water erupted onto the now-dry surface in giant floods.

“Our investigation suggests that early Mars sedimentation could have buried and trapped enormous volumes of surface water, perhaps triggering the transition into the frozen world that Mars has been during most of its history,” Rodriguez said. “Evidence for ancient environments capable of sustaining Earth-like life forms could be present in subsurface materials that are now exposed.”

Because the process of deposition, freezing, heating and eruption were regional, there may be vast reservoirs of water ice still trapped beneath the Martian surface. They would most probably lie along the boundaries of its ancient northern ocean as well as within the subsurface of other regions of the planet where contemporaneous seas and lakes formed.

This could be critical to the future of human activity on Mars. Everywhere we find life on Earth, including desert regions, we find water.

Interstellar Seeds Could Create Oases

We only have one example of a planet with life, and that’s Earth. But within the next generation it should become possible to detect signs of life on planets orbiting distant stars.

If we find alien life, new questions will arise. Did it arise spontaneously, or could it have spread from elsewhere? If life crossed the vast gulf of interstellar space long ago, how would we tell?

Harvard astrophysicists have reported that if life can travel between the stars, a process called “panspermia”, it would spread in a characteristic pattern that we could potentially identify (http://arxiv.org/abs/

1507.05614). “In our theory, clusters of life form, grow and overlap like bubbles in a pot of boiling water,” said Henry Lin of the Harvard-Smithsonian Centre for Astrophysics.

There are two basic ways for life to spread beyond its host star. The first would be via natural processes such as gravitational sling-shotting of asteroids or comets. The second would be for intelligent life to deliberately travel outward. The study doesn’t deal with how panspermia occurs, it simply asks whether we could we detect it if it does occur. In principle, the answer is yes.

The model assumes that seeds from one living planet spread outward in all directions. If a seed reaches a habitable planet orbiting a neighbouring star, it can take root. Over time, the result of this process would be a series of life-bearing oases dotting the galactic landscape.

“Life could spread from host star to host star in a pattern similar to the outbreak of an epidemic. In a sense, the Milky Way galaxy would become infected with pockets of life,” explains the paper’s other co-author, Avi Loeb.

If researchers detect signs of life in the atmospheres of alien worlds, the next step will be to look for a pattern. For example, in an ideal case where the Earth is on the edge of a “bubble” of life, all the nearby life-hosting worlds we find will be in one half of the sky while the other half will be barren.

Lin and Loeb caution that a pattern will only be discernible if life spreads somewhat rapidly. Since stars in the Milky Way drift relative to each other, stars that are neighbours now won’t be neighbours in a few million years. In other words, stellar drift would smear out the bubbles.

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio. Subscribe to David’s free Astro-Space newsletter at www.davidreneke.com