How did asteroid Ida end up with a companion moonlet?
The companion asteroid called Dactyl is a small scrap of rock only a few dozen
meters across or so. It must have been captured by Ida under some very unique
orbital circumstances since the escape velocity from Ida is measured in meters
per second.
Ida's orbit may have intersected that of Dactyl which was
traveling on a very similar orbit with a very small relative velocity less
that Dactyl's escape velocity. Dactyl could not have been a fragment of Ida
that got blasted into space during an impact between Ida and another body
since the average relative velocity of such an impact would have been far
larger than Ida's escape velocity and all of the fragments would have escaped
Ida.
Copyright 1997 Dr. Sten Odenwald
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