chongo's Journal: Comments on potential impact path information

From time to time I will present potential impact tables for paths where Earth is within the 5-sigma or less target range. Rather than repeat this same text each time, I will simply refer to this journal entry from now on.

Here is a typical example:

2035-09-19.13 3.07 +/- 2.55 (Earth inside 2-sigma path)

The following provides a more detail about such tables:

1. date (YYYY-MM-DD.DD)
   
   The .00 start of a day is with respect to midnight UTC (think GMT +0 hrs, +5 hrs EST, +8 hrs PST).
2. close approach distance (in 6420 km units)
   
   The distance will be given in Earth target size units of 6420 km (slightly larger to account for the thickness of the atmosphere). So a distance of 6.78 means 6420*6.78 = 43527.6 km.
3. +/- error term (in 6420 km units)
   
   The +/- error is also given in the 6420 km Earth target size. The error represents a ~68.3% (1 sigma) certainty. So a +/-2.47 means that there is a ~68.3% chance that the asteroid will be within 2.47 * 6420 = 15857.4 km of the 6420*6.78 = 43527.6 km center close approach distance.

NOTE: Even if the Earth is within the ~68.3% (1 sigma) path certainty, the odds of the path impacting the Earth will be less (and almost always FAR LESS) than ~68.3%. This is because one has to take into account the chance that the asteroid will actually follow that given path.