The inspiration behind Juice’s Galileo plaque

A commemorative plaque celebrating Galileo’s discovery of Jupiter’s moons was unveiled on ESA’s Jupiter Icy Moons Explorer, Juice, on 20 January 2023. The spacecraft had just completed its final tests before departing Airbus Toulouse, France for Europe’s Spaceport in French Guiana to count down to an April launch.

The plaque features imagery of Galileo Galilei's first observations of Jupiter and its moons from a copy of the Sidereus Nuncius hosted in the library of the Astronomical and Copernican Museum, at the headquarters of the Istituto Nazionale di Astrofisica (INAF) in Rome, Italy. The copy is one of the first 550 ever printed in 1610 in Venice.

This image shows the three photos from a copy of Sidereus Nuncius that inspired the plaque.

The lefthand image shows the title page with the historical signature of the "Museo Copernicano a Roma" (Copernican Museum in Rome) and the name "A Wolynski" – Artur Wolynski, the first owner of the booklet, a Polish scholar who donated his Copernican collection to the former central meteorological office of the Collegium Romanum Observatory in 1882.

The middle and righthand images are photos from pages depicting a series of observations made by Galileo. The open circle represents Jupiter and the ‘stars’ represent the changing locations of the moons as they orbited the planet.

Galileo’s observation that the moons changed position from night to night overturned the long-held idea that everything in the heavens revolved around the Earth. The moons – Io, Europa, Ganymede and Callisto – were to become collectively known as the Galilean satellites in his honour.

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