The exact age of formation for Giordano Bruno crater (35.9°N, 102.8°E) is not known. Legend has it forming sometime in the 12th century, and more recent crater counts have this beautiful crater forming up to 10 million years ago. Crater counts must be more accurate than legend, right? Perhaps, but one of the new results from analysis of LROC images is that self-secondaries (sometimes called auto-secondaries) may be more pervasive than previously thought.
A self-secondary crater forms as late stage ejecta lands on top of early ejecta, all from the same impact event. In this case the impact that formed Giordano Bruno crater. So despite the best efforts of the lunar science community, all we know is that this fascinating crater formed no later than 10 million years ago and no earlier than 18 June 1178. How can we get to an unambiguous answer; what is the exact age of formation of Giordano Bruno? The answer is simple, radiometric age dating of rocks that melted during the impact! When a rock is melted and then recrystallizes its radiometric clock is reset, thus all we need to do is collect a sample of the abundant impact melt rocks either from the floor or flanks of Giordano Bruno.
In terms of planetary missions, collecting such a sample is relatively straightforward (although no planetary spacecraft missions are simple): land, scoop, return. First scientists and engineers find the safest landing spot on an impact melt deposit. My favorite is just outside the crater, on the crater's southern rim (visit last week's Featured Image mosaic of Giordano Bruno crater). This large area provides numerous 100 meter size landing spots on now frozen deposit of impact melt. Next, you have to build the sample return spacecraft and land it safely on the Moon. This is no small feat, but keep in mind that the Soviet Union did this successfully three times almost four decades ago. While on the surface, key supporting measurements would be acquired; images, spectral measurements, magnetic properties, and perhaps information about surface radiation exposure to help design safer spacecraft and spacesuits for future astronauts. Finally, after no more than a lunar day on the surface, a sample is scooped up and then returned to Earth. What would we learn? Of course, we'd learn about the age of formation of Giordano Bruno crater, but also much more.
Be sure and check out the amazing details in the full resolution complete oblique mosaic of Giordano Bruno crater.
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