16-May-2008, 10:54 PM
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Senior Member
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Join Date: Mar 2004
Posts: 10,775
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Phoenix more probably will land outside the 1-sigma ellipse.
Again, Planetary Society Weblog: Landing ellipses:
Quote:
"The probability that Phoenix will land inside that 1-sigma ellipse happens to be only 39%. In order to find a shape on the surface that has a high probability of containing the true landing site, we typically choose three standard deviations for our landing ellipse or '3-sigma'. Our 3-sigma ellipse is centered on our target point (like the 1-sigma ellipse) and is also oriented in the same direction. However, it is three times bigger, (17 x 2 x 3 or about 100) kilometers long by (3 x 2 x 3, about 20) kilometers wide. The probability that Phoenix will land inside its 3-sigma ellipse is 98.8%. Very high.
[...]
"For the math fans out there, the probability that Phoenix will land inside "k" standard deviations (or k-sigma) is exactly:
1 - e^(-k^2 /2)
[...]
"So when you see a Mars landing ellipse, you now know that the center of that ellipse is much more likely than near its edges! Now we simply have to get ready, set, aim!
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In between, inside the 2-sigma ellipse: 86.5%.
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