The Enigmas on Mars 65
Rock Hounding on Mars
Point to Wetter
A Nasa space probe has discovered a new category of minerals spread across large regions of Mars. The find suggests liquid water remained on Mars' surface a billion years later than scientists had previously thought. The US Mars Reconnaissance Orbiter (MRO) spacecraft found evidence of hydrated silica, better known as opal.
The discovery adds to the growing body of evidence that water played a crucial role in shaping the Martian landscape and - possibly - in sustaining life. Hydrated, or water-containing, minerals are telltale signs of when and where water was present on ancient Mars.
Researchers made the discovery using the Compact Reconnaissance Imaging Spectrometer (CRISM) instrument on MRO. The $720m (£449m; 565m euro) MRO robotic probe reached the Red Planet in 2006; its objectives are to study Mars' geology, climate and atmosphere from orbit, as well as to search for signs of water.
Details of the latest findings appear in the November issue of the academic journal Geology. The minerals were recently found at Gusev Crater on Mars by the Spirit rover. This study reveals that they are widespread and occur in relatively young terrains.
Gem of a find
"This is an exciting discovery because it extends the time range for liquid water on Mars, and the places where it might have supported life," said Scott Murchie, from Johns Hopkins University Applied Physics Laboratory in Maryland.
Dr Murchie, who is chief scientist on the CRISM team, added: "The identification of opaline silica tells us that water may have existed as recently as two billion years ago." CRISM works by "reading" over 500 colours in reflected sunlight to detect particular minerals on the Martian surface - including those that formed in the presence of water.
Until now, only two major groups of hydrated minerals, phyllosilicates and hydrated sulfates, had been observed by spacecraft orbiting Mars.
Clay-like phyllosilicates formed more than three-and-a-half billion years ago where igneous rock came into long-term contact with water. During the next several hundred million years, until about three billion years ago, hydrated sulfates formed from the evaporation of salty and sometimes acidic water.
The newly discovered "opaline silicates" are the youngest of the three types of hydrated minerals. They formed where liquid water altered materials created by volcanic activity or meteorite impacts on Mars' surface. One such location is the large Martian canyon system known as Valles Marineris.
"We see numerous outcrops of opal-like minerals, commonly in thin layers extending for very long distances around the rim of Valles Marineris and sometimes within the canyon system itself," said Ralph Milliken of Nasa's Jet Propulsion Laboratory (JPL) in Pasadena, California.
In some locations, CRISM observed opaline silica with iron sulfate minerals, either in or around dry river channels. This suggests the acidic water remained on the Martian surface for an extended period of time. Dr Milliken and his colleagues think that in these areas, low-temperature acidic water was involved in forming the opal. However, in areas where there is no clear evidence that the water was acidic, deposits may have formed under a wide range of conditions.
"What's important is that the longer liquid water existed on Mars, the longer the window during which Mars may have supported life," said Ralph Milliken.
"The opaline silica deposits would be good places to explore to assess the potential for habitability on Mars, especially in these younger terrains."
Nasa is due to send a robotic rover, Mars Science Laboratory (MSL), to the planet in 2009 to look for signs of past or present life. The European Space Agency (Esa) also plans to send a rover to investigate Mars' habitability. This mission, called ExoMars, is now scheduled to launch in 2016.
'missing' Mars mineral
Nasa's Mars Reconnaissance Orbiter has finally spotted rocks on the Red Planet that bear carbonate minerals. The ingredients needed to make the rocks are very evident, so their absence had been a major puzzle. One theory to explain the omission is the idea that water on Mars has been too acidic to allow carbonates.
The rocks' identification now shows these harsh waters have not dominated all parts of Mars - and that is good news for the search for life. "You want to get an environment that is basically as clement as possible, that's not difficult to live in," explained Bethany Ehlmann from Brown University in Providence, Rhode Island. "It's difficult to live in a highly acidic environment; it's difficult to live in a very salty environment. If you have neutral waters then that presents a less difficult environment for microbial life," she told BBC News.
Ehlmann and colleagues have been detailing the discovery here at the American Geophysical Union's (AGU) Fall Meeting 2008. A paper explaining their findings is also being published in the journal Science.
“ That means there are some places we can go and look for evidence for past life - if it ever existed ”The carbonate minerals were detected in a mid-latitude region called Nili Fossae, on the western edge of the Isidis impact basin. The landscape viewed by the Mars Reconnaissance Orbiter (MRO) is believed to have formed more than 3.6 billion years ago. Carbonates are produced in the weathering process that sees water with dissolved carbon dioxide re-fashion the original chemistry of rocks. The carbonates - in this case, magnesium carbonate - precipitate out of solution. On Earth, carbonates are usually associated with great marine sediments like limestone and chalk; although the scientists here stressed the Martian carbonates would look nothing like that.
Previous data from orbiting spacecraft and from the robot rovers on the surface of Mars has revealed salt-rich, acidic waters affected much of the planet in more modern times. Given that carbonates dissolve quickly in low pH solutions, it is possible that many large carbonate formations created on early Mars may simply have disappeared; and this could explain why it has taken so long to find a carbonate signature.
But the MRO discovery shows that some areas of the Red Planet must have been untouched by these harsher conditions. That makes Nili Fossae an interesting place for future Mars missions to explore. "If you preserve carbonates on the surface then you know carbon-bearing compounds can survive in some environments on the planet," said Richard Zurek, the project scientist on MRO. "That means there are some places we can go and look for evidence for past life - if it ever existed."
Interestingly, Nili Fossae lost out in the site selection contest to choose the landing location of the next Nasa rover, called the Mars Science Laboratory (MSL). The vehicle's launch recently slipped from 2009 to 2011 and the scientists at AGU said it was possible the contest outcome could now be reviewed. However, they also said there would be other opportunities to visit Nili Fossae. "MSL is not the last lander that we intend to send to the planet. With this diversity of environments, there are many places to explore," said Dr Zurek.
Story from BBC NEWS: Nasa finds 'missing' Mars mineral
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