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Almost 30 years ago, in 1992, the Galileo probe captured the Moon on its way to Jupiter. While our satellite is obviously approaching gray tones, the onboard instruments made it possible to make this color-saturated image.

<!–[if IE 9]><!–[if IE 9]> La partie colorée de la Lune correspond à l'hémisphère nord. © NASA / JPL

The colored part of the Moon is the northern hemisphere © NASA / JPL


Although billionaire Jeff Bezos, the conquest of Mars and astronaut Thomas Pesquet are in the news today, space exploration is not new. NASA likes to take us back three decades, 29 years ago to be precise. It was on December 8, 1992, that the Galileo probe, then on its way to Jupiter, captured our Moon. It was precisely these images that made it possible to create this coloured, or rather, coloured Moon from scratch.

29 years separate us from this image

Obviously, the Moon was not photographed like this. Moreover, the U.S. Space Agency leaves no doubt on this point and does not hesitate to call the photo“false color image of the Moon” when it shares it on Instagram. To achieve such a result, 53 images captured with three different filters had to be combined.

If you’re unfamiliar with the technique, remember that many of the color photos we see were actually originally captured in black and white. An excellent video from Vox explained this technique using images from the Hubble Space Telescope as an example.

A creation from 53 photos

Here, the colored area of the Moon corresponds to the northern hemisphere of the satellite. On the left side of the image is the part visible from the ground. The bright pink shades correspond to mountainous regions like the one around the basaltic lava-filled Sea of Crises, which can be seen at the bottom of the image.

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<!–[if IE 9]><!–[if IE 9]> En bas, la mer des Crises avec sur sa gauche, en bleu, la mer de la Tranquillité. © NASA JPL

Below, the Sea of Crises with the Sea of Tranquility on its left in blue.

NASA JPL

The blue to orange shades indicate volcanic lava flows. Completely to the left of theIn the image, the large dark blue area represents the Sea of Tranquility. The mineral-rich soils recently struck by meteorites form craters that are easily distinguished by their light blue colour. This difference is caused by the relatively thin thickness of this mineral layer.

Spectroscopy to the rescue

If the aesthetic aspect of these images appeals to us, the scope of these images is nonetheless scientifically useful. Thanks to the instruments and these saturated colours, it is possible to determine the composition of the surface of our natural satellite. The blue colour indicates a soil rich in titanium, while the orange tones indicate a weaker presence of this metal. Normally black pyroclastic rocks are purple while red denotes the presence of iron.

<!–[if IE 9]><!–[if IE 9]> Cette deuxième image composite est différente de la première. Elle a été réalisée grâce à trois photos capturées à l'aide de différents filtres. La sonde est à 425 000 km de la Lune. En bas de l'image, on observe le cratère Tycho de 85 km de diamètre. © NASA / JPL

This second composite image is different from the first. It was made using three photos captured with different filters. The probe is 425,000 km from the Moon. At the bottom of the image, we can see the 85 km diameter Tycho crater.

NASA / JPL

15 years of good and loyal service

Galileo’s primary mission was to study the Jupiter system. The probe was placed in orbit around the largest planet in our solar system in December 1997. The nearly 2-tonne probe needed the assistance of the Earth’s gravity and then that of Venus to reach its destination after a six-year journey. Since its launch on December 18, 1989, and throughout its mission, which ended in 2003, Galileo has captured 14,000 images.

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