Page 48 - (DK) Eyewitness - Mars

Water on Mars

Scientists believe water once flowed on Mars, forming rivers
and lakes, even causing floods. As the planet cooled billions of
years ago, the water evaporated, froze, or sank beneath the
surface. Instruments on orbiting spacecraft, such as Odyssey
and Mars Express, have detected hydrogen in the Martian soil.
This suggests water ice is near the surface. Hydrogen-rich soil
is especially common in volcanic regions, in the canyons of
Valles Marineris, and at the poles. Some northern polar soils are
estimated to be 50 percent water. This means a pound of soil
would yield half a pound of water if heated. Farther underground,
where temperatures are warmer, liquid water might exist. Also,
A WATERY PLANET IN NOACHIAN TIMES
This painting shows how Mars might subsurface mineral salts could dissolve in underground water
have appeared 3.5 billion years ago,
partially covered with water. At and keep it from freezing.
bottom left is submerged Hellas
Planitia. The northerly Utopia Planitia,
and Isidis Planitia at left, are part of a
great sea. Near its shores stand the
Elysium volcanoes; top to bottom:
Hecates Tholus, Elysium Mons,
and Albur Tholus.

Impact craters

TEARDROP MESA
Landforms on Mars take strange and
interesting shapes. This image from the
European Space Agency's Mars Express
orbiter shows a teardrop-shaped mesa—
a high, flat-topped formation. Found in
Chryse Planitia, it likely was an island,
with water flowing past. The double
impact craters were caused by later
meteorite strikes.

FORMING CLIFF GULLIES THUNDERING THROUGH A CANYON
Under the Martian surface, near a crater or In this painting, water gushes down from cliffs, breaking through ravines
canyon wall, water might be present along and filling a valley. This normally dry Martian terrain foams with water that
with ice, rock, and soil in a “semi-permeable” has burst from underground reservoirs and is surging away. Such long-ago
layer. If a barrier plug of ice melted and floods would have happened in warmer weather, when ice plugs
turned to vapor, the water would rush disappeared and briefly unblocked pools of subsurface water.
downhill, creating gullies.

HIGHLAND GULLIES
Ice barrier Many gully systems are
Steam clouds found high on Martian
ridges. Some systems seem
recent, with sharply cut
Semi-permeable features that cross older,
water layer wind-scoured erosion. These
recent systems could have
been made by meltwater
Channel erosion running under a protective
covering of snow or by water
Rock/debris field that burst from underground
channels in periods of
warmer weather.

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