Mars 4 Billion Years Ago --"The Water Planet"

                 

"We can now say that the planet was altered on a global scale by liquid water about four billion years ago." 

John Carter of the University of Paris

Minerals in northern Mars craters observed by two NASA orbiters suggested that a phase in Mars' early history with conditions favorable to life occurred globally, not just in the south. Southern and northern Mars differ in many ways, so the extent to which they shared ancient environments has been open to question.

In recent years, the European Space Agency's Mars Express orbiter and NASA's Mars Reconnaissance Orbiter have found clay minerals that are signatures of a wet environment at thousands of sites in the southern highlands of Mars, where rocks on or near the surface are about four billion years old. Until this week, no sites with those minerals had been reported in the northern lowlands, where younger volcanic activity has buried the older surface more deeply.

French and American researchers report that some large craters penetrating younger, overlying rocks in the northern lowlands expose similar mineral clues to ancient wet conditions.
Other types of evidence about liquid water in later epochs on Mars tend to point to shorter durations of wet conditions or water that was more acidic or salty.

The researchers used the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM), an instrument on the Mars Reconnaissance Orbiter, to check 91 craters in the northern lowlands. In at least nine, they found clays and clay-like minerals called phyllosilicates, or other hydrated silicates that form in wet environments on the surface or underground.

Earlier observations with the OMEGA spectrometer on Mars Express had tentatively detected phyllosilicates in a few craters of the northern plains, but the deposits are small, and CRISM can make focused observations on smaller areas than OMEGA.

"We needed the better spatial resolution to confirm the identifications," Carter said. "The two instruments have different strengths, so there is a great advantage to using both."

CRISM Principal Investigator Scott Murchie of Johns Hopkins University Applied Physics Laboratory, said that the findings aid interpretation of when the wet environments on ancient Mars existed relative to some other important steps in the planet's early history.

The prevailing theory for how the northern part of the planet came to have a much lower elevation than the southern highlands is that a giant object slammed obliquely into northern Mars, turning nearly half of the planet's surface into the solar system's largest impact crater. The new findings suggest that the formation of water-related minerals, and thus at least part of the wet period that may have been most favorable to life, occurred between that early giant impact and the later time when younger sediments formed an overlying mantle.

"That large impact would have eliminated any evidence for the surface environment in the north that preceded the impact," Murchie said. "It must have happened well before the end of the wet period."

The Daily Galaxy via NASA/JPL

Comments

[Prizm]

Wasn't John Carter the main character in Edgar Rice Burroughs' 'Gods of Mars' series of novels?

[Greg]

Maybe the Northern part has a much lower elevation because it used to be an ocean? If all the water on Earth suddenly flash evaporated, wouldn't the areas where the oceans currently are be at a much lower elevation than the continents?

[Michael]

That makes sense.

[John]

So Carter has returned again in the guise of a modern-day scientist. Interesting. Still a virile man of 30ish age. ;)

[Jet Brou]

John Carter? Really?

[Marshall Eubanks]

The Northern lowlands are commonly supposed to be old sea-beds. The impact idea concerns how they got to be lowlands.

Remember, as far as we know Mars has never had tectonics (although the alignment of Tharsis has always made me suspicious) so, unlike Earth, old scars never really go away. E. Darwin's old idea that the Pacific Ocean was an impact basin isn't really possible for the Earth, but on Mars the basic global topography may retain the imprint of very early events.