The video in the post above, which represents the current "scholarly consensus" most closely, suggests that the northern hemisphere was hit and
sheared away by a single huge object about 4 billion years ago. This is certainly possible, but alternative theories exist.
Another possibility, expounded most popularly in the book The Mars
by Graham Hancock, points to the large craters in the south
as the entry-points of two or three extremely large objects. Under
this "minority view" (endorsed by some academic scientists as well as popular speculative writers like Hancock), Mars was hit in rapid succession in
the south by two or three giagantic objects, as well as "buckshot-style" explosions that account for the many smaller craters in the southern
hemisphere. The shockwaves from this impact would have rippled across the surface of the planet, colliding on the opposite side and shearing off much
of the crust across the northern hemisphere. So this is an alternative impact therory, but here the hit takes place starting from the opposite
One interesting thing about the southern impact theory is that it could more closely fit with the breakup of a now-destroyed possible planet tenth
planet (called "Astra" in the theories of scientists Donald Patten and Samuel Windsor). In this scheme, "Astra" would have been located between
Jupiter and Mars, and its remains are the cosmic rubble that now forms the asteroid belt. The destruction of "Astra" also may have taken place much
more recently than 4 billion years ago (the date for an impact proposed in the "northern impact" theory of the video above).
Some scientists suggest it might have taken place as recently as 20,000 years ago, at the end of the last ice age on Earth! Could this have been
connected with the end of the ice age on earth in some causal or related way? The jury is still out. We just don't know. But it would be an
interesting coincidence if the Mars impact and a massive change on earth just happened to occur at the same time. Could both be results of the
destruction of a tenth planet ("Astra")? Or could the change in Mars's shape and orbit somehow have altered the earth's climate? Proposed models
along these and other lines have been put forth.
Whatever the case, the current scholarly consensus (endorsed by NASA among others) is that Mars once contained flowing water. This means it probably
had a thicker atmosphere and was a warmer, wetter world. Considering a southern-hemisphere multiple concussion scenario, the water in the south would
have flowed rapidly from its higher elevation down to the new, lower elevation in the northern hemisphere. There, it would either have been lost to
space or locked in the now-frozen polar Martian ice-cap. The Martian ice-cap also contains frozen CO2, suggesting a thicker, more Earth-like
atmosphere that was blasted away one way or another.
Additionally, patterns on Mars's surface point to massive south-to-north flows of water that cut deeply into the crust. The rate of flow would have
been astounding: millions of cubic meters of water per second. It would have been a catestrophic flooding beyond anything imaginable thus far on
Earth. An example of a surface pattern suggesting the rapid release of water and south-to-north flooding is the so-called "teardrop" pattern seen
The teardrop-shaped "islands" in the image above would be the preserved space, with the areas surround them violently washed away in gigantic, rapid
mega-flows of gushing water.
It's all still very much up in the air, but whether from the north or the south, whether 4 billion or only 20,000 years ago, evidence is coalescing
that a huge impact blasted the planet and utterly changed it in a dramatic and perhaps horrific way. A warmer, wetter pre-impact Mars (perhaps able to
support life?) was blown to smithereens almost instantly, most of the northern hemisphere's crust was sheared off, most of it's thicker, wetter,
life-friendlier atmosphere hissed out into space, and the planet was changed forever.
I toss this info out there for your general consideration, ATS. If anyone has opinions on the pre-impact nature of Mars, the south-versus-north
controversy, the presence and flows of water, the time in which the event took place, or other related matters, by all means please share with the
[edit on 5/3/10 by silent thunder]