NASA's next
spacecraft to visit Mars has changed course to zero in on its red planet
landing site.
The Phoenix
Mars Lander fired its thrusters for 35 seconds Thursday to fine-tune its
heading for a planned May 25 landing near the Martian north pole.
"This is
our first trajectory maneuver targeting a specific location in the northern
polar region of Mars," said Brian Portock, chief of NASA's Phoenix navigation
team at the Jet Propulsion Laboratory in Pasadena, Calif., in a statement.
Phoenix's targeted
drop zone is an area that mission scientists have dubbed "Green Valley."
The region is a broad, flat valley where mission planners plan to land Phoenix
somewhere within a 62-mile by 12-mile (100-km by 20-km) ellipse.
"Our
landing area has the largest concentration of ice on Mars outside of the polar
caps," said Phoenix principal investigator Peter Smith of the University of
Arizona, Tucson. "If you want to search for a habitable zone in the arctic
permafrost, then this is the place to go."
Ray
Arvidson, chair of the Phoenix landing site working group and veteran Mars
scientist, told
SPACE.com that the lander's target zone offers smooth terrain with a
few scattered rocks. It is also home to so-called "polygonal" plains that are
expected to harbor dirty water ice beneath their surface, added Arvidson, who
is a co-investigator for Phoenix's robotic arm at Washington University in St.
Louis, Mo.
Some five
million rocks have been mapped in the region by spacecraft orbiting Mars,
mission managers said.
"We
have never before had so much information about a Mars site prior to
landing," Arvidson said in a statement.
NASA
launched the $420-million Phoenix last August on a mission to the martian
arctic, where it is expected to use a robotic arm-mounted scoop to dig into the
red planet's surface to study Mars water ice and soil.
Researchers
hope the probe's onboard ovens, wet chemistry lab and other instruments will
determine if its landing site may have once been habitable
for microbial life. Phoenix is also designed to double as a Mars arctic
weather and atmosphere-monitoring station.
But first,
the probe has to reach Mars.
Thursday's
thruster firing was the second of five trajectory tweaks planned during
Phoenix's 422 million-mile (679 million-km) trek to Mars. The spacecraft first
changed course just after its August launch, with three more maneuvers planned
between now and landing day.
Unlike
NASA's Mars
rovers Spirit and Opportunity, which used airbags to make a bouncy landing
on the red planet in 2004, Phoenix's touchdown will rely on a set of rocket
thrusters that will fire in pulses to slow the craft. They rockets are designed
to begin firing just 3,000 feet (914 meters) above the Martian surface and slow
Phoenix to about 5 mph (8 kph) before its three metal legs touch down.
Similar
powered landing approaches were used for NASA's successful Viking landers in
the 1970s, as well as the ill-fated Mars Polar Lander, which was lost just
before landing near the martian south pole in 1999.
"Landing
on Mars is extremely challenging. In fact, not since the 1970s have we had a
successful powered landing on this unforgiving planet," said Doug McCuistion,
director of NASA's Mars exploration program. "There's no guarantee of success,
but we are doing everything we can to mitigate the risks."
SPACE.com
special correspondent Leonard David contributed to this report from Boulder,
Colo. Editor's note: This story has been corrected to reflect the proper
intended landing site of the lost Mars Polar Lander.
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