Io: Tier 4. Jupiter's moon. Alot of Volcanoes leaking lava over the tops. Mercury: Tier 4. Closest planet to the sun. No atmosphere. Massive sun. Freezing at night. Hot at day. Ariel: Uranus's moon. Tier 6. Has alot of ice. Very cold. Titan: Saturn's Moon: Tier 5. Alot of oil. Pale orange atmosphere.