Mercury's scorched, torched surface is an evidence of a nova of the Sun, and of Little Brother's approach very close to our Sun.
Tumultuous tides increase as the inverse of the cube of the distance.
At 15,000,000 miles Little Brother would create 64 x as much internal tidal turmoil as at 60,000,000 miles. At 7,500,000 miles, the turmoil would be 512 times as much, if not more, as at 60,000,000 miles. It's approach was a close enough flyby to create gigantic mutual, reciprocal tides. Otherwise, Mercury's crust would have been melted down completely. And there would have been a partial meltdown of the crusts of Venus and the Earth.