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Old 26-02-2013, 09:33 PM
Scopie (Brad)
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Scopie is offline
Join Date: Feb 2012
Location: Perth, SOR
Posts: 55
Its interesting though- the other orbital sims I have seen show the comet not traveling in the ecliptic plane but coming up from beneath it- perhaps its just a trick of perspective.

That doesn't make sense when some of the articles talk of a "head on" collision with the velocities of Mars and the comet combining to make the impact velocity of 55km/s. You know what these things are like- the media rarely gets it right, and space is large. Still if it did hit- what a show! Here's hoping Mars is on our nightside IF that happens- (goes to look up starry night for Oct 19th 2014)....

I also did some calcs looking at a potential Phobos impact. Real back of the envelop stuff considering we have no real idea how big the comet is. I put it at 2km diameter and mass equivalent of solid ice (Halley and Shoemaker-Levy (prior to break-up) are/were supposedly around 10-11km)- impacting on Phobos which is 11km dia and almost twice as dense as solid ice. Phobos is already supposed to have been weakened by the massive impact that formed Stickney crater. I feel fairly confident Phobos wouldn't survive a 55km/s impact with C/2013 A1. I'd love to hear from someone else who can do the arithmetic better though! If you do it as an inelastic collision, C/2013 A1 won't impart a whole lot of delta-v to Phobos, but Phobos as shrapnel would be another story entirely. We would get rings around Mars a whole lot sooner than the current forecast!

If we did get a collision I wonder if covering that big-a$$ sky would get a lot more funding. Diverting something with that much mass traveling that fast would be pretty hard to achieve in 18 months- that's 18 months INCLUDING the time taken for your equipment to be built and sent there. We've already seen some more money tipped in to detection following the pebble that blew up over Siberia last week.

As a footnote, Purdue university has a neat calc webpage (I've seen a better one somewhere else but the venerable Ron Baalke contributed to this one) that will tell you the effects of an impact on the Earth depending on how far you are from it and what it hits (crystalline or sedimentary rock, ocean strike etc.) For a 2km comet traveling that fast it's pretty interesting! You'd want to be more than 500km away and more than 100m above sea level.

Last edited by Scopie; 26-02-2013 at 09:58 PM.
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