Craters
Mars is a
planet of great geological difference. The north has a fiery volcanic past
and the south has a cratered scared past. One of the greatest features on
Mars is its impact basins in the south. A number of impact basins hold huge
craters, some of which may have caused catastrophic effects on the whole
ecosystem. One of the biggest impact basins on Mars is Hellas Planatia.
 From
orbit it seems to be just an enormous dark spot but new mapping techniques
have discovered it is actually an ancient crater. It is possible that this
asteroid may have kicked up enough dust to blanket the planet's atmosphere
and kill whatever lived there. Was this Mars' rocky ending? This image on
the left is a computer generated image of a small section of the Hellas
Basin. It shows the diversity of the landscape. In some areas there are
flat planes for miles and in others there are sharp cliffs jutting into
the sky. |
Wet Craters |
Most old Martian craters (unlike our lunar ones) are eroded
and have features resembling mudflows occurring around almost every large
young crater on Mars. Such frozen mud ejecta probably represents the frozen
remnants of a cataclysmic moment in the past when an asteroid or comet collided
with the Martian surface, melting a patch of icy permafrost and excavating
a large hole. In
|
Grazing Impacts |
Grazing Impacts produce craters that have a distinctive
elongated shape and pattern of ejected  debris
that resemble the wings of a butterfly. On Mars many of these craters probably
resulted from impacts of satellites whose orbits had decayed. Such satellites
would have been orbiting in the plane of the Martian equator, and so the
location of a grazing impact crater should provide a good indication of
where the Martian equator and poles were when the satellite struck. Recent
craters tend to have trajectories oriented on the east-west direction, whereas
ancient craters tend to be oriented in a north-south direction. The polar
points that can be inferred from grazing-impact craters are in close agreement
with those inferred from other data, such as the buildup of thick, layered
deposits and the measurement of glacial deposits near the equator. |
Dry Craters |
 The southern hemisphere of Mars is much
like our moon. It has no volcanic activity just like our moon. You are probably
wondering what that has to do with craters? Well, quite a bit actually.
Every time a volcano erupts, it distributes its lava and rocks all over
the nearby surface, literally renewing the surface and giving it a makeover.
If no eruptions occur in a certain area and many meteorites fall to the
surface, then the surface will remain heavily cratered |
the picture to the left, you can see that all of the land around these craters
remains undisturbed and non eroded. This is because that soil has been strongly
compacted and it is harder to be carried away by flowing water. These craters
and the ones in the upper right hand side are pretty good examples of wet
craters. They are called wet craters or splash craters because when they
land and spew out moist ejecta. Wet soil acts differently than dry soil.This
can be demonstrated by throwing a rock in mud, you will get a splash effect
where the rim of the crater is not a crisp ring it is more a soft and it
would have globs around the outside. 
To the right is another example of a wet
crater. This crater was found near a lava flow in an area in the northern
hemisphere called Chryse Planatia. Looking for "wet craters" can
give clues to scientists about a surface's current or past geological make-up.
Inferring from this event would lead one to believe that during the time
that this meteorite fell to the surface of the planet was geologically active,
and the atmosphere was not thick enough to burn up the meteorite on entry.
So how old is this crater, using that same process of elimination, a time
range can be produced for the impact of this crater.