NASA’s Juno Mission Extended

NASA’s Juno spacecraft, currently orbiting Jupiter, has had its mission extended for the next four years.

Leicester planetary scientists were delighted to receive the news that NASA has authorised a mission extension, so that Juno – which has been orbiting Jupiter since 2016 – can continue to deliver new insights into the giant planet.

NASA’s most distant planetary orbiter will now continue its investigation of the solar system’s largest planet through September 2025, or until the spacecraft’s end of life. This extension tasks Juno with becoming an explorer of the full Jovian system – Jupiter and its rings and moons – with multiple rendezvous planned for three of Jupiter’s most intriguing Galilean moons: Ganymede, Europa, and Io. The extended mission’s science campaigns will expand on discoveries Juno has already made about Jupiter’s interior structure, internal magnetic field, atmosphere (including polar cyclones, deep atmosphere, and aurora), and magnetosphere.

Proposed in 2003 and launched in 2011, Juno arrived at Jupiter on July 4, 2016. The prime mission will be completed in July 2021. The extended mission involves 42 additional orbits, including close passes of Jupiter’s north polar cyclones; flybys of Ganymede, Europa, and Io; as well as the first extensive exploration of the faint rings encircling the planet.

Juno will also fly through the Europa and Io tori – ring-shaped clouds of ions – on multiple occasions, characterizing the radiation environment near these satellites to better prepare the Europa Clipper and JUICE missions for optimizing observation strategies and planning, science priorities, and mission design. The extended mission also adds planetary geology and ring dynamics to Juno’s extensive list of science investigations.

The natural evolution of Juno’s orbit around the gas giant provides the wealth of new science opportunities that the extended mission capitalises on. Every science pass sends the solar-powered spacecraft zooming low over Jupiter’s cloud tops, collecting data from a unique vantage point no other spacecraft has enjoyed.

The point during each orbit where Juno comes closest to the planet is called perijove (or PJ). Over the course of the mission, Juno’s perijoves have migrated northward, dramatically improving resolution over the northern hemisphere. The design of the extended mission takes advantage of the continued northward migration of these perijoves to sharpen its view of the multiple cyclones encircling the north pole while incorporating ring and Galilean moon flybys.

The satellite encounters begin with a low-altitude flyby of Ganymede on June 7, 2021 (PJ34), which reduces the orbital period from about 53 days to 43 days. That flyby sets up a close flyby of Europa on Sept. 29, 2022 (PJ45), reducing the orbital period further to 38 days. A pair of close Io flybys, on Dec. 30, 2023 (PJ57), and Feb. 3, 2024 (PJ58), combine to reduce the orbital period to 33 days.