Mars started out relatively wet and temperate, underwent a major
climate shift, and evolved into a cold, dry place strewn with acidic
rock – less than ideal conditions for supporting life.
This is the finding of an international team of scientists who have
created the most comprehensive mineral history of Mars, a history
closely linked to the presence of liquid water on the planet. According
to the mineral record, created with Mars Express mission data and
detailed in Science, Mars would only have been hospitable to life in
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 John Mustard, a Brown University geologist
and a primary author of the Science paper.
If any living organisms had formed on Mars, that evidence would
likely be found in clay-rich rocks and soil north of the Syrtis Major
volcanic plateau, in Nili Fossae and in the Marwth Vallis Regions, the
These areas make compelling targets for future lander missions,
according to Mustard, a co-investigator on the Mars Express and Mars
Reconnaissance Orbiter missions. In the meantime, the Compact
Reconnaissance Imaging Spectrometer for Mars, or CRISM, aboard the Mars
Reconnaissance Orbiter, will in September begin beaming mineralogical
data on these clay-rich regions. The images will be 20 times more
precise compared with those captured by Mars Express.
“I’m eager to get the CRISM data and explore the deposits found by
OMEGA, as well as discover new sites and minerals,” Mustard said.
“OMEGA shows that some of the most interesting sites are small – and
CRISM is designed to find and characterize small deposits.”
Jean-Pierre Bibring, an astrophysicist from the University of Paris,
led the team of scientists from France, Italy, Russia, Germany and the
United States. The investigators pieced together the mineral history
using data from Mars Express, a mission launched by the European Space
Agency. An instrument aboard the spacecraft dubbed OMEGA – short for
Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité –
determines mineral composition from visible and infrared light
reflected from the Red Planet’s surface. The team used two years worth
of data from OMEGA, which has mapped more than 90 percent of the
The team found three distinct geological eras on Mars:
- The first era lasted from the birth of Mars, about 4.6
billion years ago, until about 4 billion years ago. The oldest rock –
exposed by erosion, impact or faulting – shows the presence of clay
minerals. These minerals, such as chamosite and nontronite, need
abundant water, moderate temperatures and low acidity to form.
second era lasted from between 4 and 3.5 billion years ago. Minerals
made during this era, such as gypsum and grey hematite, were found in
Meridiani and in Valles Marineris. These rocks, traced by sulfates,
mark a dramatic shift from a moist and alkaline environment to a dry,
acidic one. The shift, the team concludes, was likely caused by massive
volcanic eruptions that spewed sulfur into the atmosphere, which then
rained back down on the planet’s surface.
- The third era
began between 3.2 billion and 3.5 billion years ago and continues to
the present. Minerals during this period were not formed with, or
altered by, liquid water. These iron-rich minerals, dominated by ferric
oxides, were found across most of the planet and reflect the cold, dry
conditions that persist on Mars.
The team’s analysis led them to draw an intriguing conclusion:
Liquid water didn’t make the Red Planet red. Instead, the team states,
Mars most likely gets its glow from tiny grains of red hematite or
possibly maghemite, both riddled with iron.
The Centre National d’Etudes Spatiales, Agenzia Spatiale Italiana
and the Russian Space Agency funded the OMEGA instrument. In the United
States, NASA supported OMEGA data analysis.
Source : Brown University