The European Jupiter probe JUICE flew past the moon on Monday (August 19) for a “gravity assist” and took some photos to commemorate the historic encounter.
JUICE (short for Jupiter Icy Moons Explorer) came within 750 kilometers of the lunar surface on Monday evening on the first leg of an unprecedented gravity-assisted dual flight. The second leg will follow on Tuesday evening when the probe flies past Earth.
JUICE documented Monday’s lunar encounter with some images it captured with its two onboard surveillance cameras. And the European Space Agency (ESA) shared those photos with the world when they touched down on Earth, via a live webcast that included commentary from some JUICE team members. (The images aren’t spectacularly sharp, but that wasn’t expected; the surveillance cameras were designed to confirm the deployment of the probe’s solar arrays and scientific instruments, not to study celestial objects.)
JUICE launched in April 2023 with the goal of studying Jupiter and three of its four large Galilean moons – Ganymede, Callisto and Europa. All three are thought to have oceans of liquid water beneath their icy shells, and Europa’s moon is likely in contact with a rocky seafloor, allowing for a variety of fascinating chemical reactions. (Ganymede and Callisto’s seas could be trapped between layers of ice.)
This week’s flybys of the Moon and Earth are historic; according to ESA, no other mission has ever performed a dual gravity assist. The two maneuvers will put the probe on course for a similar encounter with Venus in August 2025, which will hurl JUICE toward the giant planet.
“In fact, this flyby is a braking manoeuvre, so we are not accelerating JUICE in the sense of gaining speed relative to the Sun,” said Ignacio Tanco, JUICE spacecraft operations manager, during the ESA lunar flyby webcast.
“We found that by sequencing Earth first and then Venus, we can save about half a year of travel time and reach Jupiter in July 2031,” Tanco added. “This kind of counterintuitive approach of braking first actually ends up leading to the shortest possible travel phase.”
To achieve the same change in velocity through engine firings as in this week’s two flybys, the JUICE team would have had to use up virtually all of the fuel in the probe’s tanks, Tanco said.
During its flyby of Earth on Tuesday, JUICE will come as close as 4,200 miles (6,840 km) to Earth. If all goes according to plan, closest approach will occur at 5:57 p.m. EDT (9:57 p.m. GMT) over the North Pacific Ocean.
Amateur astronomers could theoretically observe the probe through a telescope during the encounter, JUICE team members said, provided they are in or near Alaska or another location in the North Pacific.
However, there will be no further webcast with photos from Tuesday’s flyby. ESA’s telemetry receiving stations for the Pacific region are all in the southern hemisphere, so the JUICE team will not be able to communicate with the probe during the encounter, team members said on Monday.
