Rick Nybakken, Juno project manager, holds a model of the Juno spacecraft while talking about the solar panels and the orbit it will take around Jupiter during a briefing. [Photo/IC]

In the weeks leading up to the encounter, Juno snapped pictures of the giant planet and its four inner moons. Scientists were surprised to see Jupiter's second-largest moon, Callisto, appearing dimmer than expected.

The spacecraft's camera and other instruments were switched off for arrival, so there weren't any pictures at that key moment. Scientists have promised close-up views of the planet when Juno skims the cloud tops during the 20-month, $1.1 billion mission managed by NASA's Jet Propulsion Laboratory in Pasadena, California.

The fifth planet from the sun and the heftiest in the solar system, Jupiter is known as a gas giant－a ball of hydrogen and helium－unlike rocky Earth and Mars.