The
most comprehensive study ever conducted of minerals on Mars' surface reveals
the planet has undergone three distinct geological eras throughout its history,
with water playing a progressively lesser role in each.
If life as
we know it here on Earth ever existed on the red planet, it could only have
survived in the planet's infancy, during the earliest era, the study concludes.
"Starting
about 3.5 billion years ago, conditions on Mars became increasingly dry and acidic--not a pleasant place for any form of life,
even a microbe," said study team member John Mustard, a geologist from Brown University.
The
mineral maps were created using data from OMEGA, the major spectrometer aboard
the Mars
Express, as well as related observations collected by other Mars orbiters
and the two rovers.
The study,
led by Jean-Pierre Bibring from the University of Paris, is detailed in the
March 21 issue of the journal Science.
The three faces of Mars
Based on their analyses,
the team divided Mars' geological history into three distinct eras:
The first era, which lasted
from about 4.6 billion years ago to 4 billion years ago, was a relatively wet
one. The oldest rock--exposed by erosion, impact or faulting--showed the presence
of clay minerals, such as chamosite and nontronite, that require abundant
water, moderate temperatures and low acidity to form.
The next era was
drastically different. Massive volcanic eruptions spewed sulfur into the atmosphere,
turning the planet's moist and alkaline environment to a dry, acidic one. This
period lasted form about 4 and 3.5 billion years and is evidenced by minerals
such as gypsum and grey hematite, which were found in Meridiani and in Valles
Marineris.
Minerals from the most
recent era, which began about 3.5 billion years ago and continues to the present,
show no evidence of forming with, or being altered by, liquid water. These
iron-rich minerals, mostly ferric oxides, were found across most of the planet
and reflect the cold, dry conditions that persist on Mars to this day.
The new study also revealed
what is responsible for Mar's reddish hue: most likely, the researchers say,
the red planet gets its color from tiny grains of red hematite or possibly
maghemite, two minerals that are riddled with iron.
A target for future
mission
If Martian life ever did
exist, it could probably have only survived during the first era, the team
reports. And evidence for that life is most likely to be found in the Syrtis
Major volcanic plateau, in Nili Fossae and in the Marwth Vallis Regions, two
regions rich in the clay minerals abundant during Mars' youth. The researchers
added that these areas would make compelling targets for future lander missions.
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