Time for your close-up, Ganymede.
On Monday, NASA’s Juno spacecraft passed Ganymede, the largest of Jupiter’s 79 known moons and, in fact, the largest moon in the entire solar system, within 645 miles. It was the first close examination of Ganymede since a previous NASA probe, Galileo, came by in December 2000.
NASA released two images of the flyby on Tuesday, showing in remarkable detail craters, possible tectonic faults and distinct light and dark terrain.
A picture from the main JunoCam captured most of the day of Ganymede. At the moment the picture is in black and white. However, when additional versions of the same view, captured through red and blue filters, are returned from the spacecraft, the images can be combined into a color portrait.
The second image was taken by a navigational camera called the Stellar Reference Unit, which can operate in low light and had a clear view of the night side of Ganymede as Juno flew by.
“It will be fun to see what the two teams can put together,” said Heidi Becker, head of radiation monitoring for the Juno mission.
The spacecraft will continue to send back its observations in the coming days.
Juno, who reached Jupiter on July 4, 2016, is just finishing her primary mission to examine the deep interior of the largest planet orbiting the sun. It has found that storms like the Great Red Spot penetrate deep into the giant planet’s gaseous atmosphere and that Jupiter’s core is larger and more diffuse than expected.
But instead of ending the mission by sending Juno on a death dive to Jupiter, NASA extended the mission to 2025. Juno will now make 42 additional orbits of Jupiter and some of those orbits will be close flybys of Ganymede and two of Jupiter’s other major orbits including Moons, Io, and Europa.
“We are very fortunate that the spacecraft is healthy,” said Scott Bolton, chief investigator for the mission, “and has been able to produce such great scientific knowledge and results and incredible images over the years.”
Larger than the planet Mercury, at over 3,200 miles wide, Ganymede is the only moon large enough to create its own magnetosphere – a bubble of magnetic fields that traps charged particles and deflects them away from the sun.
“We are well equipped, probably better equipped, to measure the Ganymede magnetosphere and its interaction with the Jupiter magnetosphere than any other spacecraft ever,” said Dr. Bolton.
The data Juno collects will help with some future missions. Next year, the European Space Agency will launch JUICE – the Jupiter Icy Moons Explorer – which will make multiple flybys of three major moons – Ganymede, Europa, and Callisto – before entering orbit around Ganymede in 2032.
Another NASA mission, Europa Clipper, is slated to launch later this decade and will focus on Europe, one of the most fascinating worlds for planetary scientists looking for life elsewhere in the solar system. Europe has a deep ocean beneath its ice-encrusted surface, with the heat from the core of the moon potentially providing enough energy for organisms to live in the waters.
“We’ll fill in the blank a little,” said Dr. Bolton.
The immense gravitational pull of Jupiter is steadily tilting Juno’s orbit so it is now closest to Jupiter in the northern hemisphere. That wasn’t ideal for some of the observations made during the primary mission, but now it will allow planetary scientists to get a better look at Jupiter’s North Pole and the region’s enigmatic storms.