Sunday, 24 February 2013

The Spectacular Giordano Bruno crater on the Moon

The other day, a friend and colleague from Russia asked me to send him an image of the crater Giordano Bruno from a popular science article I had written last year. The image I had didn't show the detail that he needed, so I made a better one for him from original data. And in doing so, I was reminded of all the spectacular features that this crater displays.

Giordano Bruno crater, Moon
Giordano Bruno crater on the eastern far side limb of the Moon (35.9° N, 102.8° E) as revealed by the Lunar
Reconnaissance Orbiter Camera. The annotated image on the right shows the locations of the following images.
Image credit: NASA/GSFC/Arizona State University
Giordano Bruno Slump Block
This Slump Block in the upper right part of the crater slid
down the crater wall well after the crater was formed.
Image credit: NASA/GSFC/Arizona State University
Giordano Bruno is located on the far side of the Moon, just beyond the eastern limb. It's a relatively small crater as lunar crater go, only about 22 km in diameter. But at this size, it is large enough to exhibit some of the interesting features that show up in impact craters as they get bigger.

Many of these features are being revealed for the first time by very high resolution imagery from the Lunar Reconnaissance Orbiter's Narrow Angle Camera (LROC NAC). These NAC images have resolutions of about half a meter per pixel. This means that something the size of a chair (or you!) would take up one pixel, and your desk or kitchen table would show up as a 2 by 3 pixel rectangle. With those kinds of resolutions, there are some spectacular things to be seen.

Giordano Bruno Chaotic Melt
Chaotic Impact Melts line the floor of Giordano Bruno, showing complex
structures that tell us of entrained boulders and folding chill crusts.
Image credit: NASA/GSFC/Arizona State University

For starters, there is a very interesting slump feature, located in the upper right part of the crater. It looks as if a whole block of the crater side slid down the crater wall in one piece. Such slumps are common in large impact craters, which tend to collapse at the end of their formation process. But, studies by Dr. Yuriy Shkuratov (from the Astronomical Institute of Kharkov in Ukraine) and his colleagues suggest that the slumping of this block occurred at a later time and so was not related to the crater formation process. Before this, it was thought that such big changes to craters only happened during their formation.

Giordano Bruno Ejected Melts
Ejected Melts beyond the crater rim can show channels
and rivulets where the hot melt flowed downhill from the crater rim crest.
Image credit: NASA/GSFC/Arizona State University

Next, the floor of Giordano Bruno crater is covered with chaotic impact melts. During the impact that formed this crater, temperatures got high enough to melt a lot of the crustal rock and this melt flowed down to the bottom of the crater, where it solidified. Now, high-resolution LROC NAC images are showing us that these melt are much more complex than had been previously believed. The melts entrained a lot of boulders and solid rock chunks, which can be seen poking above the melt surface. Ropy textures (that look like bunched up material) tell us that the top of the melts cooled quickly, forming what is called a chill crust, but the material underneath remained molten and mobile for some time, dragging the chill crust along and folding it as obstacles were encountered. Such images can help us learn how much melt formed and what happened to it during the crater-forming process

Not all melts end up on the crater floors. Some melt material gets ejected outside the crater. Again, high-resolution NAC images are showing us this process in amazing detail. Dark smooth patches show where melts were emplaced beyond the crater rim. In some cases, rivulets and channels were left behind as the hot melt flowed from the peak of the crater rim down the outside flanks of the crater.

Solid materials are also ejected beyond the crater rim. Many large boulders, ranging in size from 1 to 30 meters, can be seen at the edges of Giordano Bruno crater in this NAC image. To understand the scale of these boulders, consider that a meter-sized boulder is about as big as a desk, while a 30 meter-sized boulder is roughly equal to 9 houses bunched together. Sometimes, these boulders can roll down the slopes of the crater, either outside or inside the crater rim

Giordano Bruno Boulder Tracks
Boulder Tracks on the slopes of the crater show how house-sized boulders on or
near the rim can roll down the crater walls.
Image credit: NASA/GSFC/Arizona State University

Lots of other spectacular features can be found in and around this interesting crater. Feel free to explore more of Giordano Bruno crater on your own at the ACT-REACT QuickMap on line LROC image atlas tool. A simple guide for using the ACT-REACT QuickMap can be found here.

References: Shkuratov et al., The lunar crater Giordano Bruno as seen with optical roughness imagery, Icarus 218, 525-533, doi:10.1016/j.icarus/2011.12.023, 2012.


  1. Thanks for your post!
    I have wondered that can we know when did the impact happen just from those pictures? or any other methods?

    1. Thanks for the comment Siaosing.
      It's hard to tell exactly when an imapact happened. From this kind of image, though, we can tell that the crater is relatively young. The rim is crisp and undegraded, the melt surfaces are still smooth, and there are very few small craters, all of which tells us that the crater is young in comparison to most craters on the Moon. We could count all the small craters that have been emplaced on top of this crater and use that to estimate the age of the crater, but that is a tricky process - and probably should be the topic of a future post.