In 1995, the spacecraft Galileo released a probe towards Jupiter was to become the first Earth emissary ever to penetrate the atmosphere of any of the outer gas giants (Dec 1995). The mission's scientific objectives included measurement of the temperature and pressure structure of Jupiter's atmosphere and the chemical composition of Jupiter. Also, it studied the cloud layers and cloud particle size and density. Measurement were made of the amount of helium relative to hydrogen on Jupiter, winds in the atmosphere, how sunlight and energy coming from the deep interior are distributed in Jupiter's atmosphere. The probe could also detect lightning and energetic protons and electrons trapped in Jupiter's magnetic field.