Page 40 - (DK) Eyewitness - Mars

Craters on Mars

Over billions of years, comets,
asteroids, and meteorites have crashed by
the thousands onto the Martian surface.
From space, the planet looks pocked and
scarred. Unlike Earth, Mars does not have
the thick, protective atmosphere that
burns up most space rocks. They blaze
down and blast the Martian surface,
creating “impact craters” that range from a
few yards to hundreds of miles across. Impact
craters have a circular ridge formed partly by debris
BIRTH OF A CRATER
This illustration by a space thrown out in the explosion. As ages pass, craters are
scientist shows the power of an
asteroid hitting Mars at 6 miles worn down by the work of weather. They are scoured by wind,
(10 km) a second. The massive filled with dust, and perhaps eroded by water. Some impact
explosion ejects debris into the air,
blanketing the surroundings with craters, such as Hellas Planitia, the planet’s largest, could have
rock and soil. This “ejecta” become lakes filled with water. Even if a crater is eroded off the
sometimes crashes down to make
secondary impact craters. surface, the scar of the impact remains below ground.

Debris ejected Path of colliding Impact pushes
by the explosion asteroid surface up CRATER FORMATION
or meteorite into a rim It is not just the mechanical force of the impact that hurls debris
in all directions when an asteroid or meteorite strikes. The space
rock hits Mars faster than the speed of sound, so the impact
creates enormous explosive energy, a fireball. This energy bursts
out as a shock wave of heat, pressure, and mechanical force. This
ejects, or throws out, debris that forms a blanketing layer around
the crater. This layer is termed an “ejecta blanket.”

Ejecta falls all Secondary craters
around from larger ejecta

Bowl-shaped impact crater, Cracks in
with a rim of rock subsurface bedrock

Secondary craters are blasted Debris from
out in various dimensions, slumping of
depending on the size of the ejecta crater wall

Floor of crater slowly rebounds, Ejecta can fall in rays “Ejecta blanket”
forming rings of ridges leading from crater covers area around
the crater

TIME-WORN CRATER
The rim of this impact crater is worn jagged
by wind and weather. Surrounded by smaller,
secondary-impact craters, it has rays formed
from debris that was ejected by the explosion
at first impact. Part of the crater floor has
“bounced back” as circular high ground.

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