Now that
NASA's Phoenix Mars Lander is likely dead, mission scientists have time to
fully examine the treasure trove of data generated in its five months in the
red planet's arctic region, in order to shed more light on the mysteries of
Mars.
Phoenix's confirmation
of water ice below the Martian arctic surface and its surprising
characterization of the Martian dirt are among the findings researchers will be
busy investigating further in the next few months.
The Phoenix mission will also help inform future missions to Mars, including the upcoming MAVEN
orbiter mission and the planned Mars
Science Laboratory rover.
Beginning
to end
Phoenix landed
in the Vastitas Borealis plains of Mars on May 25 to the jubilant cheers of
mission controllers. (Phoenix was in part a replacement for the failed Mars Polar
Lander, so tensions to have a successful landing were running high.)
In the five-plus
months it spent alive at its landing site, the spacecraft dug up samples of
Martian dirt and subsurface water ice and analyzed them for signs of the planet's
past potential habitability.
Yesterday NASA
announced that the
mission, whose final cost was about $475 million, was effectively over.
Dwindling sunlight (caused by the transition from summer to fall at Phoenix's location, which is roughly equivalent to northern Alaska on Earth) and
light-obscuring dust in the atmosphere finally pushed Phoenix below its power
threshold on Nov. 2.
"It's
rather tough living up north above the article circle, so we always knew that
the end would be coming near for us," said Phoenix project manager Barry Goldstein
of NASA's Jet Propulsion Laboratory in Pasadena, Calif.
Phoenix's demise, while expected
to come with diminishing light and plummeting temperatures, occurred a few
weeks sooner than engineers had hoped, largely due to the poor weather at its
landing site. But even with its early death, Phoenix went above and beyond its
primary mission goals, which were achieved by the end of its original
three-month mission in August.
"The
vehicle ... has achieved all of its science goals and then some, and I've think
we have had a huge success," Goldstein said.
Phoenix's findings
The biggest
success of the mission was to confirm the presence of water ice under the
surface of the Martian arctic — which had first been detected by the Mars
Odyssey orbiter in 2002 — though that discovery didn't come right away.
"When
we landed, we looked around, we saw a field of dirt and rocks that was spread
out to the horizon, and we didn't see ice right away, it wasn't until we looked
under
the spacecraft that we found out we were standing on it, and this was quite
a thrill for everybody," said Phoenix principal investigator Peter Smith of
the University of Arizona in Tucson.
Over the
course of the mission, Smith and his team used Phoenix's robotic arm and
analysis instruments to scrape, poke, prod and characterize this rock-hard ice
layer.
"We've
excavated to the ice, we know its depth, we know how it changes over the
surface, we've seen different types of ice," Smith said, adding that the
analysis of the ice isn't over.
In digging
down to the subsurface ice layer, Phoenix also scooped up samples of the
overlying dirt and analyzed them in its microscopes, wet chemistry lab (which
dissolved the samples in water to look for soluble chemicals) and Thermal and
Evolved-Gas Analyzer (TEGA) (which baked the samples and analyzed the vapors
given off). These analyses led to some surprising findings.
Unlike
other landers and rovers that have detected acidic dirt with plenty of sulfates
— indicative of volcanic activity — Phoenix found the dirt at its landing site
was alkaline with lots of carbonates and clay minerals, the later of which
typically form when liquid water is around.
"On
the Earth, we would conclude immediately that there was liquid water in this
soil — for Mars we have to be a little more careful, and we're going to develop
this story as we can, as we interpret our data," Smith said. "But
definitely liquid water has been a part of this soil" in the past.
The dirt
samples also showed evidence of salts and perchlorate.
Perchlorate was "totally unexpected," Smith said, and "has
profound implications for Mars," because it can act as a potential energy
source for microbes.
Life?
"And
that leads to the question, is this a habitable zone? Have we found such a
thing on Mars?" Smith said. The analysis the team will carry out now will
aim to help answer those questions, he said. Such research could set the stage
for future missions that might actually look for biology on the red planet.
Phoenix also took roughly 25,000 pictures
during its tenure on Mars, from complete 360-degree panoramas to close-up peeks
at the ice in trenches it dug.
The lander
also took weather measurements, including pressure, temperature, winds, and humidity.
"We've
got a complete weather record for the entire time we were there," Smith
said, adding that it was "one of the major accomplishments of the mission."
Towards the
end of the mission, the team even saw frost forming on the surface and snow
falling from the sky.
"This
is really unexpected, and I think a first to see it, especially from the
surface," Smith said.
Though
mission team members were disappointed by the lander's premature demise, they
looked forward to the information it would bring them on Mars.
"While
we're losing a spacecraft, it's really an Irish wake rather than a funeral
we're looking forward to here," said Dough McCuistion, director of the
Mars Exploration Program at NASA Headquarters in Washington, D.C. "We
should celebrate what Phoenix has done, what the Phoenix team has done, and
where it's going to take us in the future."
Future
Mars exploration
Up next for
Mars are the planned Mars Science Laboratory mission, currently still slated
for a 2009 launch, and the next member of the Scout mission (of which Phoenix was the first) — the MAVEN orbiter.
MAVEN will
examine the upper and middle atmosphere of Mars to understand how materials,
especially water, escape from the planet's gravitational pull. Understanding
this link of Mars' water cycle will help scientists "to understand what
the history of liquid water on the surface of Mars may have been in the past,"
McCuistion said.
Phoenix's success "has really set a
standard for future Scout missions," he added.
Even with
its success, Phoenix ran into its share of snags. "A lot of lessons [were]
learned in this mission," McCuistion said.
The unexpected
stickiness of the Martian dirt made it difficult to deliver samples to the
lander's instruments, as they would get stuck in openings and to the robotic
arm's scoop.
"We
learned a lot about handling of soils, soil consistency and how difficult it
can be," McCuistion said.
Along those
lines, the team learned "how difficult it is to handle ice when it
sublimes quickly in the atmosphere," he added.
But
overall, NASA was pleased with the Phoenix mission and its accomplishments, as
were the members of the team who planned, built, and operated the lander.
"I'm
just thrilled to death with what we've been able to do here," Smith said.
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