Image lunaire du jour 

Un tunnel à travers la Lune ?

Messier and Pickering (or Messier A as nomenclatural "reformers" renamed Pickering) are perhaps the most perplexing craters on the Moon. Their shapes are not standard round ones, their rays are parallel mysteries, and their obviously related origins have been controversial. Do the parallel rays imply an intelligent construction of a railroad? Did a meteor smash into the ground creating one crater, tunnel thru and come up, forming the other? The most ridiculous ideas are the most fun, but we must remember they were offered by observers who were completely flummoxed by this supremely odd crater pair. The truth, it turns out, is also pretty amazing. The answer was figured out by Don Gault, a NASA engineer and scientist, and his colleagues who used a vertical gun to shoot small projectiles into targets at hypervelocities of several kilometers per hour. Their goal was to study the physics of impact cratering. After they had successfully done that they experimented with oblique impacts, discovering that craters stayed relatively circular until the impacting projectile was less than 45 degrees above the surface. They were able to reproduce the non-circular shapes and strange ray patterns of Messier and Pickering with nearly grazing impacts of less than 5 degrees. The projectile came in low over eastern Mare Fecunditatis and excavated Messier - notice its faint rays just at right angles to the crater's long axis. Part of the projectile ricocheted forward and formed at lower velocity Pickering and its parallel downrange rays. Weirder than fiction!

— Chuck Wood

Détails techniques:
Le 12 octobre 2003. Télescope Newton 10" (25 cm) f/6 + barlow x5 et webcam Philips Touacm pro; 250 vues empilées. Notez que la rainure au Nord de Messier se termine en une série de puits effondrés. Encore plus de volcanisme est indiqué le long du côté gauche de l'image par le halo sombre entourant une version miniature de la Tête de Cobra. Et est ce que la formation linéaire immédiatement à l'Est de la rainure est aussi une rainure ou une faille ?

Liens en relation (En anglais)
K.C. Pau

L'ILUJ de demain: Des cratères volcaniques sur la Lune