High-resolution science cameras on the JUICE spacecraft, which will eventually head to Jupiter, have been busy taking images of lunar craters and clouds in Earth's atmosphere as the spacecraft flies by Earth to use Earth's gravity to redirect its course to the next destination on its eight-year journey to the Jovian system.
JUICE (Jupiter Icy Moons Explorer) is a European Space Agency mission to explore the gas giant planets, launched in April 2023. However, the probe's route to Jupiter is circuitous, first visiting Earth and Venus. These visits are intended to enable a gravity assist that will help JUICE escape the inner solar system with minimal fuel and gain enough speed to land on Jupiter in July 2031.
The first flyby of Earth will take place on August 20, with JUICE having come close to the Moon the day before. Images taken by JUICE's surveillance and navigation cameras during the flyby have already been released, but now ESA scientists have released the first images from the spacecraft's science camera, JANUS.
JANUS is an acronym for the Latin phrase Jovis, Amorum ac Natorum Undique Scrutator, which translates to “Watcher of Jupiter and all his lovers and offspring.” Jupiter's Galilean moons Io, Europa, Ganymede, and Callisto are all named after lovers of Zeus (Jupiter to the Romans) in Greek mythology.
Related: Jupiter-bound JUICE spacecraft passes by Earth on its way to Venus (photos)
Indeed, once JUICE reaches the Jovian system, it will study Jupiter and its moons in detail, so the flyby of Earth and the Moon was an important test of JANUS' capabilities.
The airless surface of the moon, for example, was a challenging target not much different from the airless surfaces of Europa, Ganymede, and Callisto, where JANUS was designed to create a comprehensive map of the surface. (Io isn't on the menu because it's a volcanic moon, not an icy ocean moon, and its close proximity to Jupiter makes navigation to the volcanic moon difficult; however, JUICE's long-range instruments will monitor Io's erupting volcanoes.)
The cratered lunar surface photographed by JANUS during JUICE's lunar flyby on August 19. (Image credit: ESA/JUICE/JANUS)
When JUICE enters orbit around Ganymede in 2033, JANUS will be able to image the moon's icy surface with a resolution of 2.4 meters (7.87 feet) per pixel — a much higher resolution than any camera ever sent into the Jovian system. It'll be like literally mapping a new world. For comparison, Ganymede is 5,268 kilometers (3,270 miles) in diameter, bigger than the planet Mercury.
Earth's atmosphere, meanwhile, provided a good test of JANUS's cloud-imaging capabilities: Pointed at Jupiter's atmosphere, JANUS could see vibrant cloud bands in detail down to 10 kilometers (6.2 miles) per pixel.
The bright highlands of the Moon as seen by JUICE's JANUS camera (Image credit: ESA/JUICE/JANUS)
Plus, the imaging team didn't make it easy for JANUS to capture its Earth-Moon flyby. A good photographer takes the time to capture the perfect scene, but taking images remotely from a spacecraft 741 to 968 million kilometers (460 to 601 million miles) away from Earth in orbit around Jupiter is a different story, and the images aren't always perfect. So the imaging team intentionally blurred parts of the Earth and Moon images to see how well the camera's resolution recovery algorithms performed at “unblurring” the images.
For other images, the team partially saturated the exposure to test how saturation affected the unsaturated parts of the image. They also experimented with different camera settings and exposure times, and overall thoroughly tested JANUS' performance. As you can see from these images, the camera and spacecraft passed the tests with flying colors.
Footage from the JANUS camera on Luzon Island in the Philippines taken during JUICE's Earth flyby on August 20. (Image credit: ESA/JUICE/JANUS)
A close-up of clouds over the Philippines taken by the JANUS camera on the JUICE spacecraft. (Image credit: ESA/JUICE/JANUS)
This photo taken by JUICE's science camera, JANUS, shows swirling clouds (dark areas on the left) over Hawaii. (Image credit: ESA/JUICE/JANUS)
Full version of the header image, a high-contrast close-up of the lunar surface. (Image credit: ESA/JUICE/JANUS)
Now JUICE is ready for the next stage of its long journey to Jupiter. The close approach of Earth has altered JUICE's orbit, effectively slowing it down by a total of 5.7 kilometers (3.5 miles) per second and bending its course 100 degrees toward Venus, where gravitational acceleration is scheduled for August 2025. This approach will send JUICE hurtling toward Earth again, for two more close approaches in September 2026 and January 2029, for its final acceleration to Jupiter.
