Who Would win in a fight and why?
Both can not only fly into a star, but also get stronger by doing so.
Superman's Powers and abilities(Modern Age):
Solar energy absorption
Superhuman strength
Invulnerability
Superhuman speed
Flight
Healing-factor
Super-stamina, endurance, durability, agility and reflexes
Super-senses
Super-intelligence
Super-memory
Multilingualism
Tactile telekinesis
Longevity
Captain Planet's Powers and abilities:
Weather and climate manipulation
Ability to generate and control earth, fire, wind, water, lightning, magma, and magnetism
Near invincibility
Invisibility
Telepathy
Empathy
Flight
Superhuman strength
Superman's known weaknesses:
Kryptonite, red star radiation and magic.
Captain Planet's known weaknesses:
Pollutants, radiation, smog, etc.