“This is the closest spacecraft to this giant moon in an entire generation,” Scott Bolton, Juno principal investigator at the Southwest Research Institute, said in a statement. “We’ll take our time before drawing any scientific conclusions, but until then we can only marvel at this celestial wonder, the only moon in our solar system larger than Mercury.”
Juno ran across Ganymede at 1:35 p.m. EDT on Monday, passing 645 miles from the moon and capturing a clear view of the cratered world, which is believed to harbor an underground sea beneath an ice crust. In addition to taking new images, Juno’s science instrument cluster has also collected data.
“The Ganymede ice crust has light and dark areas, indicating that some areas may be pure ice while others contain dirty ice,” Bolton said before the flight. “Juno” fournit la première enquête approfondie structure sur la façon dont la composition et la de la glace varient avec la profondeur, ce qui permettra de mieux comprendre la formation de la coquille de glace et les processus en cours qui refont surface de la glace au fil time”.
Juno was launched from Cape Canaveral in 2011 and brakedon July 4, 2016. NASA is still very active at the end of its initial two-year mission, and has now approved two expansions, the most recent of which runs from this summer to mid-2025.
Designed to study Jupiter’s deep interior, atmosphere, magnetic field, and aurora borealis, Juno has made frequent close passes over the planet’s north polar regions, providing breathtaking views of unprecedented polar storms, and discovering signs of a rather diffuse core of the giga-cluster. Bytes of data to better understand the global behavior of the planet.
The polar probe’s 53-day orbit is tuned to slowly move the closest approach northward as the flight progresses. On the other side of the orbit, the spacecraft first crossed the equatorial plane away from Ganymede’s orbit.
But the closest approach moved inland during the mission and the recent expansion provided a golden opportunity for flyovers close to Ganymede, Europe, and Io volcano.
“We are going to cross the orbital plane near Ganymede and as the orbit continues to advance further and further north, the (equatorial) crossing is moving more and more,” Bolton said in a previous interview. “So we cross first near Ganymede, then we continue to go forward and cross near Europe. Finally, we pass near Io, and then we are even inside Io.”
The Ganymede meeting on Monday is set to use the moon’s gravity to bend the path a bit, reducing Juno’s orbital period by about 10 days. This in turn results in one flyby of frozen Europe on September 29, 2022 and two close flights at Io on December 30, 2023 and February 3, 2024.
“We have these near-satellite bridges that will now allow us to point our instruments at the satellites, get the first close-up analysis and look for changes since the days of Galileo and Voyager,” Bolton said.
Juno is not equipped with a telescope for close-up and narrow-angle observations. Instead, his “Junocam” imaging device was primarily intended for wide-angle contextual observations and general awareness, providing stunning hemispherical views of Jupiter’s turbulent atmosphere.
Bolton expects equally stunning views from the overflights of Ganymede, Europa and Io.
“When we’re too far away, we can’t take a high-resolution photo,” he said. “But when we’re close, we get a wide, high-resolution field of view.” That wide field of view makes a big difference when you look at it, he said, saying Do I understand the context?
JunoCam captured almost an entire side of Ganymede during the probe’s flyby on Monday. Shots using different filters will later be combined to provide full color views, resolving surface features as small as six tenths of a mile from view.
Juno’s navigation camera captured a much larger view of the dark side of Ganymede, illuminated by sunlight reflecting off Jupiter. Additional images stored on board the spacecraft will be returned later.