Triple impact on Moon

Please consider donating to Behind the Black, by giving either a one-time contribution or a regular subscription, as outlined in the tip jar below. Your support will allow me to continue covering science and culture as I have for the past twenty years, independent and free from any outside influence.


Regular readers can support Behind The Black with a contribution via paypal:

Or with a subscription with regular donations from your Paypal or credit card account:


If Paypal doesn't work for you, you can support Behind The Black directly by sending your donation by check, payable to Robert Zimmerman, to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652

Impact craters Messier and Messier A on the Moon

Cool image time! A new image release from Lunar Reconnaissance Orbiter (LRO) takes a look at the impact process that created the crater Messier and its neighbor crater Messier A. The photo to the right, cropped to post here, shows both craters.

Take a close look at Messier A. It is actually a double crater itself. From the release:

Messier A crater, located in Mare Fecunditatis, presents an interesting puzzle. The main crater is beautifully preserved, with a solidified pond of impact melt resting in its floor. But there is another impact crater beneath and just to the west of Messier A. This more subdued and degraded impact crater clearly formed first.

Did these three craters happen as separate events. According to the data, it appears no. Instead, they might have all been part of a single rain of asteroids, all occurring in seconds.

Messier crater is extremely elongated, which is an indication that it formed when an impactor struck the surface at a very shallow angle (less than 15° from the surface). Its high-reflectance rays stretch to the north and south, caused by ejecta that was emplaced asymmetrically, another sign of a low-angle impact. Messier crater’s presence suggests that each of these impact craters may be related, forming when an impactor broke up, and struck the surface as three pieces instead of just one.

…Another theory (the “decapitated” impactor scenario) suggests that the impactor could have actually split apart after hitting the surface at the Messier impact site, with a portion of the impactor continuing downrange to form Messier A crater.

Try to imagine the event that created these 9-mile-wide craters, especially the second scenario, where the asteroid zooms in at a low angle, hits the ground, its top half breaking off into two pieces that smash into the ground, bam-bam, just to the west.



  • Lee S

    Excellent cool image Bob! How cool it would be to be a bystander ( at a safe distance!)

  • Patrick Underwood

    Carolina Bays!!

  • pzatchok

    I was under the impression that all impact craters are round no matter the angle of impact. It has to do with the shock-wave rebounding off of the larger body blowing out material in a circle.

    That said why is that one crater (b) oblong? Could it also be a simultaneous double impact of nearly identical objects?

Leave a Reply

Your email address will not be published. Required fields are marked *