Re: Asteroid may strike Mars in late January 2008

On Dec 21, 10:29 pm, SkySea <Sky...@xxxxxxx> wrote:
"Kickin' Ass and Takin' Names" <PopUlist...@xxxxxxxxxxx> wrote:
A newly discovered hunk of space rock has a 1 in 75 chance of
slamming into the Red Planet on January 30, scientists said Thursday.

I have to confess, I'm not really sure what they mean by 1 in 75
chance. Are there 75 factors to consider, any one which can be altered
to form a hit? Are they saying it has passed Mars by fewer than 75
times, and within the remainder, it will hit?

They mean that they don't know the motions of the asteroid exactly.
There is a certain statistical distribution which applies to its
orbital elements as we know them.

Thus, at the time it passes by Mars, the object's position in relation
to Mars can be thought of as being distributed anywhere in an oval
shape with a certain center. The portion of that distribution
corresponding to it hitting Mars contains about 1.33% of that
distribution.

The probability is therefore applicable only to a single encounter.
Another way of putting it is that if you bet a dollar that it would
hit, winning 75 dollars if it did would make it a fair bet.

John Savard
.

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