Craters on the "dark side". Don't see "craters"? Read on. Credit:NASA/Goddard Space Flight Center/Arizona State University.

Here is an image from the Lunar Reconnaissance Orbiter. The image shows secondary craters.  Secondary craters are  those craters formed not by an foreign body hitting the moon, rather they are formed by the stuff blown out from a crater forming impact.

The NASA caption for the image is below, but before you get there, I know there are some of you taking issue with the title…Dark Side indeed. The dark side of the moon exists maybe in some of the areas around the poles and in Pink Floyd songs…the reality is there is no dark side. Yes I know that, interestingly enough the LRO site titled the page “Craters on the dark side of the moon” (linked below).

Now how many of you don’t see craters and instead you see “lumps”?  It’s a trick your eyes are playing on you, click  here and you will see the very same image just rotated 180^o. The image opens in a new window so you can move it around and get the two side by side (you may need to resize the new window).  Did you do it? Pretty cool eh?

Ok here’s the caption from the LRO site:

When people envision a “moonscape” it probably looks something like this — craters, craters everywhere.

There are two types of impact craters on the Moon: primary and secondary. Primary craters form as the result of an asteroid or comet (or spacecraft) impacting the Moon. Secondary impact craters formed from the impact of ejecta expelled during primary crater formation. Secondary impact craters dominate this scene, possibly from the relatively recent impact that created nearby Jackson crater (43.5 miles across), located 42 miles to the west.

Geologists use small secondary craters to help unravel the stratigraphy of the lunar surface. These secondary craters reside on the floor of a 8.7 mile wilde crater. What is the age of this host crater? If these secondary craters originated from the Jackson event, then it is a fair bet the Jackson impact was more recent. If you look at the bottom of this NAC frame in the LROC Image Gallery at ASU, you can see that this crater also has a very subdued rim, in contrast to Jackson’s well-defined rim, providing more evidence of it’s age.