NASA: 2 places on Mars could have been habitable
By Elizabeth Landau, CNN Filed under: Innovation
NASA's twin rovers, Spirit and
Opportunity, have revealed many secrets of the Red Planet since landing
on Mars in January 2004. Spirit stopped communicating in 2010, but
Opportunity is still collecting data. This illustration depicts the
identical look of both rovers.
(CNN) -- Two NASA rovers are about 5,200 miles apart on the surface of Mars and will likely never meet.
Curiosity Rover marks first anniversary
NASA's twin rovers, Spirit and
Opportunity, have revealed many secrets of the Red Planet since landing
on Mars in January 2004. Spirit stopped communicating in 2010, but
Opportunity is still collecting data. This illustration depicts the
identical look of both rovers.
HIDE CAPTION
A decade of discoveries on Mars
STORY HIGHLIGHTS
- The twin Spirit and Opportunity rovers landed on Mars in January 2004
- Spirit lost communication with Earth in 2010, but Opportunity is still sending data
- Studies describe insights about past life-supporting environments
- The Curiosity rover followed in August 2012
But though they roam
alone, Curiosity and Opportunity continue to reveal details about the
Red Planet's former habitable conditions. New studies in the journal Science describe insights from each of those rovers about ancient environments where microorganisms could have once lived.
"These results
demonstrate that early Mars was habitable, but this does not mean that
Mars was inhabited," writes John Grotzinger, lead scientist on the
Curiosity mission, in an introduction to the studies in the journal
Science.
We've been hearing a lot
about how the two-ton, car-sized Curiosity rover has been finding
evidence that Mars may have hosted life at some point. Last year NASA
came out and said that yes, Mars was once habitable.
The new research reinforces that statement from Curiosity's vantage point, and adds the perspective of the Opportunity rover, which has found a different ancient habitable environment on another part of the planet.
Opportunity is smaller --
weighing 384 pounds, and about 5 feet in both length and height -- and
older, having landed January 25, 2004, at a place called Meridiani
Planum. It has driven just under 25 miles in a decade, and is currently
situated in a place called Endeavour Crater.
What Opportunity has found
Opportunity does not have
the tools required to detect carbon or nitrogen -- chemicals required
for life -- directly. But it has been able to find smectite clay
minerals -- which form in the presence of water -- in rocks on the rim
of Endeavour Crater, with supporting evidence from the Mars
Reconnaissance Orbiter orbiting above.
Scientists directed
Opportunity to a place on the crater rim where the orbiter suggested
these clays could be found. There, Opportunity uncovered evidence of
rocks that preexisted the formation of the crater. Scientists believe
the crater's rim formed more than 3.7 billion years ago.
"These are rocks that
were happy on the surface, and along comes the asteroid or the comet
that formed Endeavour, and the rocks were uplifted on the rim, and then
the ejecta was plopped right on top of them," said Raymond Arvidson,
lead study author and planetary scientist with the rover missions.
The ancient rocks are
called the Matijevic formation. They are fine-grained, layered rocks
with dark veneers that are carrying iron clays that suggest water with a
neutral to only slightly acidic pH was once in the area.
Opportunity showed
scientists fractures across these ancient rocks they wanted to explore.
The rover's rock-abrasion tool allowed scientists to uncover an
aluminous clay that could be formed in only mildly acidic, and
non-oxidizing waters.
"Whether or not life got
started and evolved in that particular niche, in this groundwater
percolating through the fractures, remains to be seen," Arvidson said.
Curiosity Rover marks first anniversary
But in a younger rock
formation called the Burns formation, which largely filled in the
crater, the rover found evidence of a more acidic and very oxidizing
environment. This suggests that the environment was less hospitable
after the formation of Endeavour Crater.
Curious findings
Curiosity, on the other
hand, landed in Gale Crater, and helped scientists determine that an
area called Yellowknife Bay was habitable in ancient times. Here, from
the rim of the crater came stream waters that formed "a
lake-stream-groundwater system that might have existed for millions of
years," Grotzinger wrote.
Smectite clay minerals
there indicate there was a moderate to neutral pH, and the lack of
sulfate minerals suggest also that there was not an acidic environment,
Grotzinger wrote.
This ancient habitable
environment seems completely different from what Opportunity found at
the Matijevic formation on Endeavour Crater, Arvidson said. Yellowknife
Bay is probably younger, and definitely a sedimentary environment.
All this suggests three distinct periods in Martian history, Arvidson said.
In the first, in the
early days, lots of water flowed on the surface, with lakes and
groundwater flowing through, as represented by the Matijevic formation
that Opportunity found and the mudstone in Yellowknife Bay that
Curiosity found. One theory is that these warm, wet surface conditions
took place in early times, when the planet's iron-nickel core was still
at least partially molten, Arvidson said. The molten core provided a
magnetic field around it that shielded the atmosphere, scientists
believe.
The Burns formation, as
examined by Opportunity, represents a later period -- likely, a drying
out of Mars -- with more acidic, oxidizing waters. Volcanic activity was
probably dying down, and the magnetic field waning. Lake beds were
turned into sand dunes.
"Then the whole system shut off," Arvidson said. The planet became what we see today: Cold and dry.
Curiosity is equipped to
find organic molecules, but finding them may be difficult. Assuming
such molecules were enriched, and not destroyed when sediment turned
into rock, they would have also needed to survive ionizing radiation. Another new study in Science
describes the radiation environment on Mars, and suggests that, in
theory, organics could have been preserved from millions of years ago --
but the indication of them might be much weaker now.
What's next for the rovers
The Curiosity rover,
representing a $2.5 billion mission, is now on its way to Mount Sharp, a
sedimentary formation that will allow the rover to explore Mars'
history by driving up the peak's slope and exploring rock chemical
composition layer by layer.
NASA is planning to
launch another Curiosity-sized rover in 2020, which could collect
samples that later missions might return to Earth.
Opportunity will
continue exploring Endeavour Crater, moving southward to see if there
are more of these ancient rocks from a more livable time.
But Opportunity's twin, Spirit, isn't going anywhere.
Spirit also landed in January 2004, on the opposite side of the planet, and got stuck in the soft soil of a place called Troy.
That location turned out
to be a scientific gold mine. Spirit showed evidence that water,
possibly in the form of snow melt, had trickled into the subsurface
relatively recently, and continuously.
Spirit has been defunct since it stopped communicating in 2010. The other rovers are too far away from it to pay their respects.
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