early in the Solar System's formation. However, a moon-moon collisional origin is still plausible if the number of retrograde irregular moons around Jupiter was much more numerous in the past.

On the other hand, the Himalia group is unlikely to have formed from an impact with a passing planetesimal, it probably formed from a moon-moon collision instead. The parent body split into much more massive fragments proportionally; the largest fragment comprises only 78% of the mass of the parent body. Combined