I've seen lots of others do this concept. They usually spend hours brushing huge displays of fire. I chose to make it more subtle... As if you are viewing the initial impact between the planets. The bright flash of the hydrogen in the atmoshpheres igniting apon first contact.

It really isn't supposed to be Earth and Mars... It just so happens that if an inhabitable planet ever crashes into another, it wont be crashing into an ice planet... I originally had it a tan/brown color. But I thought red fit it better.