Geoscience Reference
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The Viking program data indicate that oxidants on Mars may vary with latitude,
noting that Viking 2 saw fewer oxidants than Viking 1 in its more northerly position.
Phoenix landed further north still. Phoenix's preliminary data revealed that Mars
soil contains perchlorate and thus may not be as life-friendly as thought earlier. The
pH and salinity level were viewed as benign from the standpoint of biology. The
analyzers also indicated the presence of bound water and CO
2
.
The Phoenix lander also confirmed the existence of large amounts of water ice
in the northern region of Mars. This finding was predicted by previous orbital data
and theory and was measured from orbit by the Mars Odyssey instruments. Phoenix
lander's camera showed subsurface water ice exposed by the landing retrorockets, in
an unexpected technique called “diffusive gas explosive erosion,” which uncovered
18 cm of Martian soil. On June 19, 2008, NASA announced that dice-sized clumps
of bright material in the “Dodo-Goldilocks” trench, dug by the robotic arm, had
vaporized over the course of four days, strongly implying that the bright clumps
were composed of water ice which sublimes following exposure. Even though CO
2
(dry ice) also sublimes under the conditions present, it would do so at a rate much
faster than observed. On July 31, 2008, NASA announced that Phoenix confirmed
the presence of water ice at its landing site. During the initial heating cycle of a
sample, the mass spectrometer detected water vapor when the sample temperature
reached 0
ı
C. Liquid water cannot exist on the surface of Mars with its present
low atmospheric pressure and temperature, except at the lowest elevations for short
periods.
Perchlorate (ClO
4
), a strong oxidizer, was confirmed to be in the soil. The
chemical, when mixed with water, can lower the water freezing point in a manner
similar to how salt is applied to roads to melt ice. It has been hypothesized that
perchlorate may be allowing small amounts of liquid water to form on Mars today
and may have formed visible gullies by eroding soil on steep slopes.
Additionally, during 2008 and early 2009, a debate emerged within NASA over
the presence of “blobs” which appeared on photos of the vehicle's landing struts,
which have been variously described as being either water droplets or “clumps of
frost.”
For about as far as the camera can see, the landing site is flat but shaped into
polygons between 2 and 3 m in diameter and is bounded by troughs that are
20-50 cm deep. These shapes are due to ice in the soil expanding and contracting
due to major temperature changes. The microscope showed that the soil on top of
the polygons is composed of rounded particles and flat particles, probably a type of
clay. Ice is present a few inches below the surface in the middle of the polygons, and
along its edges, the ice is at least 3 cm deep. When the ice is exposed to the Martian
atmosphere, it slowly sublimes.
Snow was observed to fall from cirrus clouds. The clouds formed at a level in the
atmosphere that was around
65
ı
C, so the clouds would have to be composed of
water ice, rather than carbon dioxide ice (CO
2
or dry ice) because the temperature
for forming carbon dioxide ice is much lower than
120
ı
C. As a result of mission
observations, it is now suspected that water ice (snow) would have accumulated later
in the year at this location. The highest temperature measured during the mission,
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