domingo, 6 de noviembre de 2011
Space Exploration - Did a Colossal Asteroid Impact Deep Enough to Swallow Mount Everest Erase Mar's Magnetic Field?
The image above generated by the Mars Orbiter Laser Altimeter, an instrument aboard NASA's Mars Global Surveyor, shows an impact basin deep enough to swallow Mount Everest and surprising slopes in Valles Marineris. The high-resolution map that has influenced scientific understanding of the red planet for years, represents 27 million elevation measurements.
If you remember seeing the disaster movie, The Core, then you that the only thing between us and instant space-death is a magnetic field (most likely Jupiters). 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. Planetary magnetic fields are created by massive molten metal currents within the planet's core. 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. But magnetic analysis of Martian sites by Berkeley researchers has shown that the red planet's protective field was switched off half a billion years ago.
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. 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.
Astronomers have been puzzled for decades about the huge impact crater shown above -- the largest known crater in the solar system -- and new evidence last month suggests it was caused by the impact of an asteroid the size of the moon. The crater, measuring 5,300 miles across, is so big that it has left half the planet at a lower elevation.
NASA's Mars Reconnaissance Orbiter and Mars Global Surveyor have provided detailed information about the elevations and gravity of the Red Planet's northern and southern hemispheres. A new study using this information may solve one of the biggest remaining mysteries in the solar system: Why does Mars have two strikingly different kinds of terrain in its northern and southern hemispheres? The huge crater is creating intense scientific interest.
The mystery of the two-faced nature of Mars has perplexed scientists since the first comprehensive images of the surface were beamed home by NASA spacecraft in the 1970s.
A giant northern basin that covers about 40 percent of Mars' surface, sometimes called the Borealis basin, is the remains of a colossal impact early in the solar system's formation, the new analysis suggests. At 8,500 kilometers (5,300 miles) across, it is about four times wider than the next-biggest impact basin known, the Hellas basin on southern Mars.
A report calculates that the impacting object that produced the Borealis basin must have been about 2,000 kilometers (1,200 miles) across. That's larger than Pluto. It appears to have held an ocean in crater the size of the combined areas of Asia, Europe and Australia,the early days of the planet, before Mars lost so much of its atmosphere and the water either sublimated away or froze beneath the surface.
Source: The Daily Galaxy