Credit: G. Di Achille
The Martian (Water) Chronicles
June 28, 2012 --
Scientists believe that more than 3 billion years ago, Mars' northern plains were covered by an ocean that spread across more than one-third of the planet's surface. Now, new analysis of two Martian meteorites suggests the inside of Mars is wet as well. The rocks came from a partly melted area of Mars' mantle, located just under the crust, and crystallized just below and on the surface. An impact blasted the rock into space and it landed on Earth some 2.5 million years ago. The research indicates Mars' mantle contained between 70 and 300 parts per million of water. That's more water than what is found in Earth’s upper mantle, which is 50 to 300 parts per million. Scientists guess that volcanic eruptions may have been the primary mechanism for getting water to the surface. This artist's rendering, based on elevation data from an instrument on NASA’s now-defunct Mars Global Surveyor spacecraft, shows a Martian coastline as it may have looked 3.5 billion years ago.
Credit: Lowell Observatory
Canals on Mars? It wasn't too long ago that our best idea of Mars looked like this drawing made by astronomer Percival Lowell, who believed that the lines etched into the planet's face were irrigation canals built by an extraterrestrial civilization. The notion was dismissed as optical illusion by the early 20th century, but it wasn't until 1965 when NASA's Mariner 4 spacecraft flew by Mars that scientists were able to get their first close-up pictures of Mars' barren, cratered surface -- quite the opposite view to what Lowell had imagined.
Search for Life By the 1970s, scientists rallied around the idea that Mars harbored microbial life and set up an elaborate, ambitious mission to get the proof. Two Viking orbiters and two Viking landers arrived at Mars in 1976 to take pictures, analyze the atmosphere and surface and search for evidence for life. They didn't find it and the United States put its Mars exploration plans on the shelf for the next 20 years.
Fossilized Martian Mystery In 1996, two NASA scientists published an analysis of a Martian meteorite recovered from Allan Hills, Antarctica, that they said contained evidence microscopic fossils of Martian bacteria. Based on dates derived from naturally occurring radioactive material in the rock, scientists believe it formed early Mars' history, when the planet was warmer and wet. The key evidence for life were organic molecules in the meteorite and embedded chain-like features that resemble fossils of nano-sized bacteria. Follow-up studies however showed similar structures could be created by non-biological processes, but these also have been contested.
Etchings in Mars' Surface Along with an energy source, like the sun, and carbon, life as we know it needs water. Some of the strongest evidence that water once flowed on Mars is etched in the planet's now-dry and sandy face. Gullies were first found in high-resolution pictures taken by NASA's Mars Global Surveyor. Similar channels on Earth are made by flowing water. Mars is too cold for liquid surface water today, but some scientists think water may well up from the ground and stay liquid long enough to erode the surface. Another idea is that they were carved by frozen carbon dioxide, the main component of the thin Martian atmosphere.
Ground Truth More than eight years ago, two robotic geologists -- Mars Exploration Rovers Spirit and Opportunity -- arrived on Mars to hunt for signs of past water. Among their finds: a vein of what appears to be gypsum, which on Earth is deposited by water. "This tells a slam-dunk story that water flowed through underground fractures in the rock," lead scientist Steve Squyres, with Cornell University, said when the discovery was announced in December 2011.
Water Runs Deep Through analysis of observations made by ESA's Mars Express and NASA's Mars Reconnaissance Orbiter, there is evidence that large quantities of water existed deep below the surface of Mars for long periods during the first billion years of the planet's existence. By zooming-in on impact craters, the chemistry of rocks embedded in the crater walls could be analyzed. "The large range of crater sizes studied, from less than 1 km to 84 km wide, indicates that these hydrated silicates were excavated from depths of tens of meters to kilometers," says Damien Loizeau, lead author of the study. "The composition of the rocks is such that underground water must have been present here for a long period of time in order to have altered their chemistry."
Credit: NASA/JPL/Malin Space Science Systems
Next Step With firm evidence that Mars once had water, NASA is zeroing in on the more challenging search for organic material. That quest begins in earnest this summer following the arrival of a car-sized rover, named Curiosity. The Mars Science Laboratory mission will unfold in a 96-mile-wide crater near the planet’s equator called Gale Crater (pictured here). Rising from the floor of the pit is a 3-mile-high mound of what appears to be layers of sediment. Landing is scheduled for 1:31 a.m. EDT Aug. 6.
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