Asteroid impact on Mars said less likely

PASADENA, Calif. - Scientists tracking an asteroid approaching Mars say that an impact with the Red Planet has become less likely. Refined estimates of the asteroid's orbit were made using new observations from a telescope at the Calar Alto Observatory in Spain, according to the Near-Earth Object Program at NASA's Jet Propulsion Laboratory.

The impact probability fell to 2.5 percent, the NEO office said in Jan. 8 update posted on the NEO Web site. The miss distance was holding steady at about 30,000 kilometers, or 18,600 miles.

The asteroid, dubbed 2007 WD5, was discovered in late November by the NASA-funded Catalina Sky Survey in Arizona.

Odds of an impact had risen to about 4 percent by late December and scientists were excited about the possibility of observing a cosmic collision on Jan. 30.

The size of a football field, the asteroid could blast a half-mile-wide crater into the Martian surface.

The NEO program looks for and tracks asteroids and comets that could potentially be a hazard to Earth.

The path is as calculated, the error radius decreasing with each passing day. The asteroid will miss, which is disappointing since much would be learned about Mars from a fresh crater 1000 feet deep.

With optics the impact would have been seen from earth if it struck on the earth side of the planet..Orbiting spacecraft would have had box seats...Impact would have been followed by a massive dust cloud..

I was really hoping for a massive impact.

There’s a paradox here. Model this like a dart game with Mars about 8.8 Martian radii away from the bulls eye. Suppose the “dart” has an expected Gaussian distribution along two axes in the plane of the dart board ( The plane normal to the path of the asteroid which contains Mars )

Working in units of Martian radii, Mars covers an area of pi on the board, so the probability of hitting Mars is just pi times N(sigma,8.8), where N is the 2-d Normal Distribution as a function of r, the distance from the bulls eye. Note that N(sigma,r) gives the probability per unit area of hitting at a distance r.

So, using my handy dandy homemade yacc implemented calculator in cygwin, I evaluate pi*N(sigma,8.8) for different values of sigma, and find that sigma = 6.8 gives a value of 0.025 for the probability of hitting Mars. The paradox is ( if I’m doing it right ) that the asteroid has only about a 50% chance of passing within 8.8 Martian radii of the target point. That is, within the circle around the bullseye drawn at the distance of Mars. Intuitively, you would tend to think that this would mean a much higher chance of hitting Mars than 2.5% .

Another way of putting it is that the Normal probability distribution centered at 8.8 Martian radii which gives a probability of 0.025 for hitting Mars is much more diffuse than you would expect.

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