A
Mars-orbiting satellite recently
spotted seven dark spots near
the planet's equator that
scientists think could be
entrances to underground caves.
The
football-field sized holes were
observed by Mars Odyssey's
Thermal Emission Imaging System
(THEMIS) and have been dubbed
the
seven sisters --Dena, Chloe,
Wendy, Annie, Abbey, Nikki and
Jeanne--after loved ones of the
researchers who found them. The
potential caves were spotted
near a massive Martian volcano,
Arisa Mons. Their openings range
from about 330 to 820 feet (100
to 250 meters) wide, and one of
them, Dena, is thought to extend
nearly 430 feet (130 meters)
beneath the planet's surface.
The
researchers hope the discovery
will lead to more focused
spelunking on Mars.
"Caves on
Mars could become habitats for
future explorers or could be the
only structures that preserve
evidence of past or present
microbial life ," said Glenn
Cushing of Northern Arizona
University, who first spotted
the black areas in the
photographs.
A project
here on Earth aims to refine the
visual and infrared techniques
THEMIS used to find the
Martian caves and to also
develop robots that can one day
enter the caverns and explore
them.
Practicing on Earth
Called the
Earth-Mars Cave Detection
Program, the project is
preparing to enter phase 2,
during which scientists will
test their approach in "Mars
analogue" sites, terrestrial
environments with similarities
to Martian landscapes. These
sites will include dry,
blistering deserts, such as the
Mojave in California and the
Atacama in Chile, as well as
frigid environments like Iceland
and Antarctica.
During the
first phase of the project, the
researchers acquired the thermal
signatures of a dozen caves in
Arizona and New Mexico using an
experimental infrared detector
flown aboard an airplane, called
the Quantum Well Infrared
Photodetector (QWIP), as well as
data collected on the ground
using a handheld thermal camera.
Cave
detection using QWIP works by
spotting regions in the
landscape where temperatures are
different from the surroundings.
Inside a cave, temperatures are
nearly constant due to lack of
sunlight. Outside, temperatures
fluctuate with the rising and
setting of the Sun. At a cave
entrance, these two temperature
regimes mix together to create a
unique thermal signature that,
depending on the time of day,
can be either warmer or cooler
than the surrounding
environment.
"The caves
show up as hotspots in a sea of
cold, or as cold spots in a sea
of warmth," said study team
member Murzy Jhabvala, chief
engineer of the Instrument
Systems and Technology Center at
NASA's Goddard Space Flight
Center.
The data,
still being analyzed, look
promising. In one series of
images, the researchers snapped
thermal images of Xenolith Cave
in New Mexico over a 24-hour
period. The cave opening can be
seen clearly in some of the
images.
"It
jumps out at you," said Jut
Wynne, a biospeleologist (cave
biologist) with the U.S.
Geological Survey and Northern
Arizona University. "It lights
up like a Christmas tree in the
predawn and in the late-night
shots. It's a bit more ephemeral
during the day shots."
In Phase 2,
the researchers will tweak their
technique to figure out the best
wavelengths to use and optimal
times during the day for cave
hunting. "In so doing, we're
going to take these applications
and then apply them to an
orbiter platform for Mars," said
Wynne, who is also the
Earth-Mars Cave Detection
Program project leader.
Robotic cave explorers
The project
team also aims to design robots
that can explore caves on Mars
after they have been spotted.
Natalie Cabrol, a planetary
geologist with NASA Ames and the
SETI Institute, will be integral
to this part of the project.
Cabrol is a
Mars robot veteran. Before
Spirit and Opportunity were sent
to Mars, she helped engineers
perfect their designs by
field-testing the robotic rovers
in the Atacama Desert in Chile.
The
researchers may have to design
more than one type of robotic
cave explorer. "There are many
types of caves," Cabrol said in
a telephone interview. "It may
be that we come up with one very
versatile design ... or we might
end up with several designs."
If the caves
have a relatively simple
structure--like lava tubes,
which are caves carved by
flowing magma and are relatively
simple and straight--a
rover-type robot might work,
Cabrol said. "I would doubt that
a rover, equipped as they are
now, would do a good job in a
cave" with a more complicated
geometry, she said.
Open
to ideas
The
researchers are also considering
other robotic design
possibilities, including the
deployment of several miniature
robots together into a cave.
"You could
throw out an array of
microbots in a birdshot
approach over an area where you
think there is a cave," Wynne
told SPACE.com . The
microbots could then use sonar
or some other method to confirm
the presence of a cave and
pinpoint its location.
Whatever form
the team's robotic explorer
ultimately takes, it will have
to be agile, have some basic
sense of self-awareness, sport
excellent night vision and have
the ability to communicate with
one other in some innovative
way, since conventional radio
communication might not work
well in caves, Cabrol said.
"We are very
much on the starting line on
this," she added. "This is very
exciting. This is really the
time when ideas are flitting all
over the place."
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