Photographs taken might show
evidence of relatively recent water erosion on Mars.
It was thought that all of the planet's water was locked
up in the polar icecaps and in deep permafrost layers
in the soil. However, images from about 120 sites show
us features that may be evidence of recently flowing water.
 |
|
|
| South Polar
Pitted Walls |
|
Nirgal Vallis |
| The features are landforms
that appear to be gullies racing down cliff
walls in canyons and canyons. Each is
composed of a deep channel with a collapsed
region at the top (called an alcove) and at
the other end an area of accumulated debris
(called an apron). The material at the
apron appears to have been transported down
the slope. This may be the result of liquid
water, soil, rock and ice that has cut through
the cliff face. |
| An area
that is near a cliff face (canyon or
crater wall) may experience some initial
seepage (the cause is still unknown).
As the water evaporates, it cools the
ground, freezing the water behind it,
forming an ice barrier. Pressure
then builds up behind the 'ice dam'
and eventually the dam bursts sending
forth floods of water mixed with soil,
ice and rocks forming a landslide. Since
liquid water exposed to the Martian
atmosphere would immediately begin to
boil, scientists think that this boiling
could be explosive and violent.
The sudden outbursts of water and debris
might then be similar to flash floods
on the Earth. |
Gorgonum
Chaos
|
A
different hypothesis is that the sublimation
of ground ice - a change from solid to gas -
loosened the landslide material, which then
moved downslope. This hypothesis does
not include the presence of liquid water, merely
the presence of underground ice deposits. |
| 
Martian
Crater/Earth Volcano |
Interestingly
these features are seen mostly in very cold
areas. They are found in shadowed sides of crater
and canyon walls, the sides that see less sunlight,
and in latitudes higher than 30 degrees.
The reason is because frozen water escaping
on the sunny side would instantly boil
and evaporate into vapor because of the low
atmospheric pressure on Mars, about 100 times
less than it is at sea level on the Earth.
|
| 
Noachis
Crater |
The gullies look similar to gully washes
seen in the American West. The eruptions
all seem to appear at approximately the same depth,
about 100-500 meters down from the surface.
The gullies overlay all other features implying
that they are, geologically speaking, relatively
young. Each flow that came down a gully
may have had a volume of water of approximately
2,500 cubic meters (~90,000 cubic feet) or enough
to supply 100 households for a month! |
The presence
of possible liquid water on Mars today has important
implications for the question "Does Mars have life?"
If life did develop on Mars and has survived into the
present, these landforms may be a good place to look.
In addition, if water is available in substantial amounts
in other areas besides the polar caps then human crews
could access and use it (for drinking, air to breath,
and to create rocket fuel by extracting the oxygen and
hydrogen).
Questions
to think about:
- As an engineer or scientist on Earth, what types
of robotic spacecraft and experiments could you devise
to test out the hypothesis that liquid water was responsible
for these gullies?
- As an explorer on the surface of Mars, what types
of vehicles or equipment would you need to explore
these regions?
- If water does exist on Mars at this depth and is
near the surface in these regions, how would you recommend
extracting it for use by humans?
Next... The Geology
of Mars: Ice Caps (pg. 10 of 13) |
