Wednesday, September 26. 2012
The landscape surrounding the very young impact Giordano Bruno gives us a sense for how widespread the effects of even moderate-sized impacts can be on a planetary body. The young age (perhaps <10 million years) of Giordano Bruno offers a marvelous opportunity to inspect some of the more subtle morphologic changes that occur in the extended and discontinuous ejecta blanket during impacts of this size. Eventually, after 10's of millions of years, the action of micrometeorite impacts will rework or "garden" the lunar surface and obscure much of what we see here. Several examples of extended ejecta features are included in this post, all collected from the same Narrow Angle Camera (NAC) image (M146308704R).
The apparent flatness of these crater floors suggest that the debris was behaving very fluid-like when it was emplaced. Determining the difference between impact melt and granular debris flows can be challenging, however. What clues would you look for to find out if the crater floors are truly flat? How would you decide between melt and granular deposits? If impact melt, what does it suggest about the temperature of the liquid and its cooling rate to find it having such a low viscocity this far-removed from its source?
As might be expected, at some point during cooling the viscocity of melt becomes high enough to cause sluggishness, and develop steep-sloped margins. Interesting shapes can then result.
Ejecta can create hummocky patterns when ballistically emplaced, as with these secondary craters. Some of the appearance may also be due to ground-hugging debris that piles up as it encounters resistance from friction with the ground.
How do we know that these features come from Giordano Bruno and not some other crater in the region? The full NAC image can be inspected here for clues. Other information on the Giordano Bruno impact itself can be found in several recent Featured Image posts, including the Very Oblique View of Giordano Bruno, Sunset Over Giordano Bruno, and Giordano Bruno, The Big Picture.