Illustration of the JUICE spacecraft at Jupiter. The Jupiter Icy Moons Explorer (Juice) equipped with the JANUS camera, recently conducted a flyby of the Moon and Earth to test the high-resolution capabilities designed to study Jupiter and its moons. Credit: ESA

JANUS, a camera on the Jupiter Icy Moons Explorer, recently captured test images of the Moon and Earth as part of its mission to study Jupiter and its largest moons.

Since ESA’s Jupiter Icy Moons Explorer (Juice) flew by the Moon and Earth earlier last week, we’ve seen images from its monitoring cameras and we’ve seen images from its navigation camera. Now, the European Space Agency has revealed the first images from its scientific camera, JANUS, designed to take detailed, high-resolution photos of Jupiter and its icy moons.

JANUS will study global, regional, and local features and processes on the moons, as well as map the clouds of Jupiter. It will have a resolution of up to 2.4 m per pixel on Ganymede and about 10 km per pixel at Jupiter.

This image of our own Moon was taken during Juice’s lunar-Earth flyby on August 19, 2024. The main aim of JANUS’s observations during the lunar-Earth flyby was to evaluate how well the instrument is performing, not to make scientific measurements. Credit: ESA/Juice/JANUS

Testing and Calibration of JANUS

The main aim of JANUS’s observations during the lunar-Earth flyby was to evaluate how well the instrument is performing, not to make scientific measurements. For this reason, JANUS took images with various camera settings and time intervals – a bit like if you’re going out to test a DSLR camera for the first time.

In some cases, researchers intentionally ‘blurred’ the images so that they can test out resolution recovery algorithms. In other cases, they partially saturated the image to study the effects induced on the unsaturated areas.

Mythological Significance and Mission Goals

The name JANUS comes from the Latin phrase ‘Jovis, Amorum ac Natorum Undique Scrutator’, or roughly ‘Scrutiniser of Jupiter, and all his loves and descendants’. Jupiter’s four largest moons – the main focus of Juice’s mission – are named after protagonists in the ‘love affairs’ of Zeus, the equivalent of Jupiter in Greek mythology.

This image of planet Earth was taken during Juice’s lunar-Earth flyby. It was taken at dawn on August 20, 2024, and shows the island of Luzon, the largest and most populous island in the Philippines. Credit: ESA/Juice/JANUS

JANUS will transform our knowledge of Jupiter’s icy moons, by capturing them with a resolution and coverage 50 times greater than previous cameras sent to the Jovian system. The camera is equipped with an onboard computer that manages all instrument functions, processes commands, and sends data back to Earth.

This image of planet Earth was taken during Juice’s lunar-Earth flyby at dawn on August 20, 2024. It shows the island of Hawai’i (the dark patch on the left). Credit: ESA/Juice/JANUS

Technical Aspects and Collaboration

In imaging our own Moon, with no atmosphere, JANUS could test out how it will function at Ganymede, Callisto and Europa. In contrast, Jupiter itself has a huge, turbulent atmosphere; JANUS’s images of Earth can better simulate imaging the different layers and components of Jupiter’s atmosphere.

Note: These images are preliminary and have not been processed to use for science

JANUS was developed by an industrial consortium led by Leonardo SpA, under the supervision of the Italian Space Agency (ASI) and in collaboration with the Italian National Institute for Astrophysics (INAF), which is responsible for instrument science, the German Aerospace Center (DLR), CSIC-IAA in Granada (Spain) and CEI-Open University in Milton Keynes (UK).