NASA's
Phoenix Mars Lander may have found water ice on the red planet, but it still
has a lot of work left to do to answer the question that has been on scientists'
minds for decades: Has Mars ever been capable of harboring life?
Phoenix scientists announced yesterday that
the mission finally confirmed
the presence of subsurface water ice in the north polar regions of Mars —
first detected by NASA's Mars Odyssey orbiter in 2002 — about two months after
touching down on the Martian surface on May 25.
The lander
is now analyzing the ice to see if it was ever a liquid and if it contains organic
materials, the building blocks of life.
The ice,
collected from below the surface at the lander's site in the Martian arctic,
could have acted
like a freezer, protecting any organics that may have formed there.
"We
have an environment where organics could be preserved," said mission
scientist William Boynton of the University of Arizona.
The
detection of organics on Mars would not necessarily mean there is life. It
would just mean that carbon and other molecules that make up life as we know it
were present.
"Organics
would be the home run or the grand slam of the mission," said Bruce
Jakosky, a geologist at the University of Colorado who is not affiliated with
the mission. However, if they don't find organics, "that doesn't mean that
there wasn't life on Mars," Jakosky said. Other missions, planned and
unplanned, will keep the search alive.
Liquid
water
The
confirmation of the Odyssey ice observations was a key goal of the $420 million
Phoenix mission, but only the first of several steps in characterizing the
dirt and ice layer of Mars' Vastitas Borealis region to determine whether it
may once have been habitable at some point in the planet's past.
'I see this
as a step along the way of Phoenix getting to its major science results," Jakosky
said. "By itself, that's not a major result."
One of
those steps is determining whether the water ice ever existed in a liquid form,
said Phoenix robotic arm co-investigator Ray Arvidson of Washington University
in St. Louis — liquid water being a key resource for life as we know it.
Phoenix will
look for signs of ancient liquid water by heating up samples of the icy
dirt mixture in the tiny ovens of its Thermal and Evolved-Gas Analyzer (TEGA),
which can analyze the vapors given off by the heated samples to analyze their
composition.
TEGA has
already begun heating up the sample that confirmed that the rock-hard layer
beneath the surface dirt was indeed water ice — when ice begins to melt, it
takes more heat to raise the temperature of the sample. Over the course of the
next week, TEGA will gradually heat the sample all the way up to 1,832 degrees Fahrenheit
(1,000 degrees Celsius).
As the
sample is heated, any hydrated minerals, or those that likely formed in the
presence of liquid water, show themselves as they break apart and the signature
of their water is detected by the instrument, explained Boynton, a TEGA
co-investigator.
Finding
hydrated minerals, such as carbonates, sulfates or clays, would indicate that
liquid water once permeated the Martian regolith where Phoenix now sits,
Arvidson said in a telephone interview last night.
This water
would not have flowed as rivers or streams, as it once likely did closer to
Mars' equator, where hydrated salts have already been found by NASA orbiters
and rovers, but would have percolated through the dirt layer as Mars' orbital
motions tipped the northern parts of the planet toward the sun, warming them
up, Arvidson added.
The
stuff of life
The other
big signature Phoenix will look for as the mission continues and the probe's
ovens heat up dirt samples will be organic molecules, the building blocks of
life.
"Finding
organics would really change our way of thinking," Boynton said.
But so far,
organic molecules haven't shown up on Mars. When the Viking landers heated up
dirt samples in the 1970s, "there were really no organic molecules at
all," Boynton said.
But dirt
near the Martian equator faces strong oxidizing pressures, which can destroy
organics, Boynton added, which is why Phoenix is looking for them farther north.
Organics
have proven elusive to Phoenix
so far; the first dirt sample analyzed by TEGA, taken from the surface, found
no sign of them. But this wasn't much of a surprise to mission scientists.
"We
didn't really expect to find them in the surface soils," because the
surface is subjected to the same oxidizing pressure as the equatorial regions,
Boynton told SPACE.com.
TEGA will
keep looking for signs of organics in subsequent samples taken closer to the
ice layer, he added.
If Phoenix doesn't find organics, the mission won't be a flop, Jakosky said, because it still
gives scientists valuable information about the northern region. "Whatever
they find is exciting," he said.
If it does
detect organics though, mission scientists will be cautious about interpreting
the findings, Boynton said. They would assume first that any organics could be contamination
brought with the spacecraft from Earth. Mission scientists will check with a
"blank" brought from Earth to determine whether or not any organics
discovered are terrestrial stowaways.
Even if the
blank shows that the organics came from the Martian soil, they still may not be
native, Boynton said, since the same organic-bearing meteorites that strike
Earth strike Mars as well. Determining the ultimate origin of any organics
would likely take bringing back a sample to Earth, a project that both NASA and
the European Space Agency are working toward.
And
organics don't on their own equal life. "Just because there are organic
compounds, doesn't mean that that's life," said Kim Seelos, a postdoctoral
researcher at Johns Hopkins University.
Future
missions
Whether or
not Phoenix finds signs of organics, it won't be the last time that NASA looks
for them on Mars. NASA's Mars
Science Laboratory (MSL), set to launch in 2009, will pick up where the
1970s Viking missions left off, exploring the regions closer to the equator for
signs of them.
MSL will be
better equipped than Viking, and even Phoenix, to detect organics in dirt
samples, with more powerful and sensitive equipment, as well as the ability to
roam around.
While
"life is teeming on Earth," Arvidson said, it may not have been so
dense on Mars — if it ever existed — perhaps only forming in small pockets.
Since Phoenix, as a lander, stays put by definition, it can only explore the
patch of ground in its immediate vicinity.
However,
any organics detected by MSL would have formed in a much more ancient period of
Mars' history because the landscape near Mars' equator formed billions of years
ago. The surface that Phoenix is exploring is much younger, only tens of millions
of years old.
For now, Phoenix is the only chance of finding organics on this region of Mars, since no future
missions in the works now are planned to return to the frozen northern reaches.
To get another mission back there to look the region in greater detail,
"it would probably take finding organics," Boynton said.
But "Phoenix isn't the last gasp, or MSL isn't the last gasp" to answering the question of
whether life ever existed on Mars, Jakosky said.
The
evidence available to scientists now suggests that Mars could have harbored
life, it's just a matter of finding a spot that preserves the signs of it, he
added. And Phoenix's landing site, or even MSL's, may not be the ideal spot to
go and look for those signs, whether by sending another rover or staging a
mission to return a sample to Earth.
There are
plenty of other environments on Mars where Jakosky would like to look for signs
of life. While he can't point to a particular spot, there is evidence that Mars
once had features that could have supported life, including ancient lake beds,
ancient highlands where evidence suggests that water existed for long periods
of time, and hot springs — "places like Yellowstone," as Jakosky
describes them.
Some
scientists, such as Seelos, doubt that clear evidence of Martian life itself
will ever be found because any life would have likely been microbial, which is
not easily preserved as fossils. But Jakosky sees this as an
"unnecessarily pessimistic" view, because ancient microbes have been
preserved in some places on Earth.
But it
could be awhile before scientists ever answer the question of life on Earth
because they currently understand so little about the history and geology of
Mars, Jakosky said.
"We
don't know the answer and I don't even know how to put odds on "when and
whether they will find the answer," Jakosky said.
His advice
is to keep using missions like Phoenix, MSL, and eventually a sample return
mission to build our knowledge of Mars, as we have built the knowledge of our
own planet's past.
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