Could a direct hit by comet Siding Spring make Mars more hospitable for life? (Earth, moon)

[wrcousert]

From 'http://cosmiclog.nbcnews.com/_news/2013/03/08/17241258-marsageddon-comet-scenario-adds-to-concerns-about-space-threats' comet scenario adds to concerns about space threats

A direct hit on Mars' backside wouldn't tear the planet apart, but it would produce an explosion that Bad Astronomy's Phil Plait estimates at somewhere around a billion megatons of TNT. That would create a huge crater, blast tons of debris into space and perhaps set off a flood reminiscent of the one that washed over Marte Vallis millions of years ago.

We could have liquid water flooding the planet and possibly a denser atmosphere as the impact heats up dry ice in the soil. What more would we need? How long would these conditions last?

[Glitch]

First, the comet is not going to hit Mars. It will come within 210,000 miles (340,000 km) of Mars. Almost the same distance our moon is from Earth.

Second, they estimate the size of the comet's nucleus is somewhere between 1.8 and 31 miles across (3 to 50 km). If a 1.8 mile icy body object traveling at 56 km/s impacts Mars at a 45 degree angle, it will generate 5.3 million megatons of energy and create a crater 18.1 miles wide and 6.4 miles deep. If a 31 mile diameter icy body object traveling at 56 km/s were to impact Mars at a 45 degree angle it will generate 24.5 billion megatons of energy and create a crater 163 miles wide and 57.5 miles deep.

Third, even if the comet did impact Mars, it would be a spectacular event to watch, but it would not have a noticable long term effect on the planet overall. There would be no liquid water resulting from the impact because Mars' atmospheric pressure is 87 times less than Earth. Liquid water sublimates directly into a gas at that low pressure.