"An Impact Basin as Deep as Mount Everest" --Was Mars' Magnetic Field Destroyed by a Colossal Asteroid?
An impact basin deep enough to swallow Mount Everest and surprising slopes in Valles Marineris highlight what might be the results of a ancient asteroid collision with the Red Planet. Magnetic analysis of Martian sites by Berkeley researchers show that the red planet's protective field was switched off half a billion years ago, and NASA scientists say they know why.
"The most curious aspect of the topographic map is the striking difference between the planets low, smooth Northern Hemisphere and the heavily cratered Southern Hemisphere," which sits, on average, about three miles (five kilometers) higher than the north, Smith added. The MOLA data show that the Northern Hemisphere depression is distinctly not circular, and suggest that it was shaped by internal geologic processes during the earliest stages of martian evolution.
The massive Hellas impact basin in the Southern Hemisphere is another striking feature of the map. Nearly six miles (nine kilometers) deep and 1,300 miles (2,100 kilometers) across, the basin is surrounded by a ring of material that rises 1.25 miles (about two kilometers) above the surroundings and stretches out to 2,500 miles (4,000 kilometers) from the basin center.
This ring of material, likely thrown out of the basin during the impact of an asteroid, has a volume equivalent to a two-mile (3.5-kilometer) thick layer spread over the continental United States, and it contributes significantly to the high topography in the Southern Hemisphere.
The difference in elevation between the hemispheres results in a slope from the South Pole to North Pole that was the major influence on the global-scale flow of water early in martian history. Scientific models of watersheds using the new elevation map show that the Northern Hemisphere lowlands would have drained three-quarters of the martian surface.
If you've seen The Core then you that the only thing between us and instant space-death is a magnetic field. You also know that's the only thing that's even heard of real science in the entire movie, but it's a pretty important one - and could explain why the otherwise eminently habitable Mars is such a barren wasteland.
Scientists think the Martian magnetic field might have been hammered into submission by strikes from space. A flowing current creates a magnetic field, even when the current is massive volumes of charged liquid metal moving under the influence of temperature gradients (convection) - in fact, especially then.
John Hopkins University scientists calculated that a period of massive asteroid impacts, known to have happened around the same time, could not only have massively impacted on the surface Deep Impact-style (with all the atmospheric alteration and great-big-crater-making that entails) but added enough energy to the planet to heat up the outer layers of the planet.
Without the huge temperature difference between the core and mantle, the mega-magnetic dynamo convection currents would be switched off - and unable to start up again when things cooled down. Remember, planetary core behavior is still carrying on from when the planets first formed - as far as they're concerned the whole "crust" thing and all life as we know it is just a cooling scum on the surface. If you break something from back then you just don't have the juice to start it up again.
Without the magnetic field Mars is defenseless against the radiation that constantly pours in from space (never mind the Fantastic Four, the only superpower cosmic rays'll give you is decomposition). Earth is thought to have survived the same space-bombing because of our superior size, with our dynamo maybe stuttering a little but - very importantly - not stopping. As you can maybe tell by the fact you exist.
Image credit: With thanks to http://jules.unavco.org/Voyager/Docs/ImageGallery