Sunset Over Giordano Bruno

Giordano Bruno oblique 13 July 2011
Slump terrace in the northern half of Giordano Bruno crater seen at sunset, from an altitude of 54 km. Terrace is 4800 meters wide, NAC M165190579LR [NASA/GSFC/ Arizona State University].

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.

Preview of Giordano Bruno oblique
Subsampled version of NAC oblique view of Giordano Bruno crater (21 km diameter) [NASA/GSFC/ Arizona State University].

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.

Impact melt
Impact melt deposit on south flank of Giordano Bruno crater, arrow indicates center of landing site shown at full resolution below [NASA/GSFC/Arizona State University].

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.

Giordano Bruno landing site
Example landing spot (250 m diameter circle) on now frozen impact melt [NASA/GSFC/Arizona State University].
This new knowledge will help crater counting experts understand the importance of self-secondary craters on very young craters. A new calibration for these youngest craters could be obtained, thus making age estimates for all other young craters on the Moon more reliable. Additionally this part of the Moon is far from the Imbrium basin and the KREEPy region from where all the Apollo and Luna samples were returned. So this precious sample would be our first look at unsampled highlands terrain, the oldest portion of the Moon's crust. All-in-all, this site is a prime candidate for an automated precursor sample return - lets go!

Be sure and check out the amazing details in the full resolution complete oblique mosaic of Giordano Bruno crater.

Previous LROC Giordano Bruno Featured Images

The Big Picture

Outside of Giordano Bruno

Fragmented Impact Melt

Delicate Patterns in Giordano Bruno Ejecta

Impact Melt Flows on Giordano Bruno


Posted by Mark Robinson on July 25, 2012 10:07.