Good things come in threes. As our Juno spacecraft completed its 38th close flyby of Jupiter on November 29, 2021, it captured the swirling storms of the gas giant and two of its largest moons – Callisto and Io. Seen faintly at the bottom of the image, Callisto is the second-largest moon in the Jovian system and third largest in our solar system. Callisto has a thin atmosphere of carbon dioxide, and scientists believe its ice-crusted surface may hide a salty ocean. Only slightly larger than Earth's moon, Jupiter's moon Io is the most volcanically active planetary body in the solar system. Caught between the massive gravitational pull of Jupiter and two of its neighboring moons, Europa and Ganymede, Io is tidally locked – meaning the same side of Io always faces the planet. Now in its extended mission, the spacecraft will continue to study Jupiter and its moons in greater detail, learning about the Jovian system's magnetic fields, atmosphere, and magnetosphere. Image description: ...