The app creator made the right decision when he defaulted to a false scale. Scale is not the only important thing to convey, one also wants to show relationships and have a model of the whole that fits in a monkey brain.

Also, in this interface, the planets serve as big "buttons" to navigate to a celestial body of interest. So they have to be larger.

The thing would be unusable, and boring, if it showed specks of dust orbiting a mustard seed.