"The core of the comet will be moving 56 kilometers per sec when it smashes into Mars. The explosion it creates will be equal to*40 BILLION 500kt nuclear bombs(avg US and Russ arsenal weapon) going off at once, or 20 billion megatons of TNT, or 1.33 trillion Hiroshima bombs, or 1.3 billion Castle Bravo explosions. Its enough to kill all life on the planet if any were living there.*Astronomers predict a large-scale disaster on the Red Planet in October 2014, when a comet may ram into Mars, creating a 500-kilometer crater, the website of the Russian observatory ISON-NM said. [link to english.pravda.ru]*"
A 500km crater
All of usa and russias nukes going off at the same time and 1.333 trillion hiroshima bombs are equivalents.
Expect to hear more mainstream news on it when more data is in..supposedly they havent tracked the comet very long so they still are adjusting calculation..but most all calculations are pointing to direct impact with mars or a slight miss.