Shouldn't two spheres colliding either make one whole sphere or just two spheres that are connected at their side?
Check your math professor, if you still have one, or find someone educated in mathematics.
In mathematics, two perfect spheres colliding can only be represented as a circle.
its really not that hard. imagine two bubbles, both only defined by their outline.
Now the bubbles drift together and merge.
What do these two bubbles share together as boundry territory?
What marks the edge of their union?
Only a circle, and only a circle fits.
If you disagree, please go back to 7yr old math and start over.