Well, we initially start with the "growing shadow" idea as someone suggested but soon we came across an issue.
Managing the overlapping of two objects on the ground: we have the chicken shadow at its height, let's say X. Being consistent with the 2D space and perspective, the meteor shadow was at the same height X, because the meteor is above the chicken, on the same 2D plane.
The effect caused by the overlapping and the growing was not good, to our eyes.
Thank for your reply!