NASA’s Juno spacecraft successfully conducted the closest flyby of Jupiter’s volcanic moon Io in over 20 years on December 30, 2023. Coming within just under 1000 km of Io’s surface, Juno captured high-resolution images and data that will help reveal mysteries about the most volcanically active body in the solar system.
Lead Up to the Flyby
Juno was launched in 2011 with the primary goal of studying Jupiter’s atmosphere, magnetosphere and interior structure. However, mission controllers extended Juno’s mission to include several close flybys of Jupiter’s moons as the spacecraft orbits the gas giant.
In July 2021, Juno made close approaches of two other major moons, Ganymede and Europa, yielding valuable science about their makeup and interactions with Jupiter. The Io flyby has been long anticipated as an opportunity to gain insights into Io’s extreme volcanism. Over 400 active volcanoes cover Io’s surface, spewing sulfur dioxide gas and silicate ash.
Juno’s unique polar orbit allows it to pass very close to the poles of Jupiter’s moons for optimal imaging and data collection. Extensive planning by mission control ensured Juno would pass less than 1000 km from Io’s north polar region during the flyby.
Table showing key facts about the Io flyby:
Closest Approach Distance: 950 km
Date: December 30, 2023
Imaging Targets: Volcanic plumes, surface changes, polar region
Focus Science Goals: Io's interior structure, magnetic field, plasma interactions with Jupiter
Key Instruments Used: JunoCam, Stellar Reference Unit, Jovian Infrared Auroral Mapper
Flyby Events and Images
At 11:15 pm EST on December 29, Juno began taking images and readings of Io from around 90,000 km away using its suite of eight science instruments. Over the next 15 hours, the distance rapidly decreased as Juno approached at over 68,000 km per hour.
Stunning images released by NASA reveal changes on Io’s surface since the last close pass by Galileo in 2000. One image shows a massive new lava flow over 250 km long near the volcano Marduk. Additionally, JunoCam photographed two volatile sulfur dioxide plumes extending 190 km over Io’s surface.
Just two hours before the moment of closest approach, Juno switched on its star-tracking navigation camera to precisely measure Io’s orbit and determine how Jupiter’s immense gravity affects its motion. other instruments like the microwave radiometer and gravity science subsystem collected unique data about Io’s molten interior composition.
Analysis teams are excited over the results, which should clarify many puzzles about how Io formed and exactly why it experiences such extreme widespread volcanism. Further study may reveal how future volcanoes eruptions modify Io’s orbit and if an underground magma ocean exists.
Image Highlights from the Flyby:
- 20 km tall plume near volcano Tvashtar
- 250 km long new Marduk flow obscured by ash
- Changes in color patterns across surface
- Crisp view of north polar mountain ridges
What Comes Next
It will take months for scientists to download, process and analyze the wealth of information captured during the historic Io flyby. This data will fuel new research and models on Jupiter/Io interactions and the exotic geology allowing Io’s intense heat and volcanism.
Meanwhile, Juno continues along its extended flight path through July 2025, making additional close passes by Europa, Ganymede and Io. The next flyby occurs in March 2024 when Juno dips to within just 300 km of Europa’s icy surface. Controllers may also approve special maneuvers lowering Juno near interesting volcanoes like Loki Patera or Amirani.
Juno’s montage of spectacular Io images and groundbreaking datasets guarantees new discoveries about this unique volcanic world for decades. The intrepid spacecraft has once again demonstrated how nimble orbital missions can adapt to capture rare science at outer solar system bodies. Even as Juno nears retirement, its legacy inspires ideas for future dedicated mapping and landing missions to Io and other promising Jovian moons.
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