u (Top) The ANTS zones correspond to deep lava dikes in this GRAIL gravity map. G R AIL M A P: N ASA / GSFC / A RIZON A STATE UNIV ERSIT Y / VA L A N TIN AS & SCHULT Z CREDIT RIDG E M A P: N ASA / GSFC / A RIZON A STATE UNIV ERSIT Y / M. COLLINS u (Bottom) ANTS tend to be located along mare ridges. This map highlights all the mare ridges visible on the lunar nearside. speculate that the reactivation is associated with adjustments from an oblique impact origin for the South Pole-Aitken basin, thought to have formed roughly 4.3 billion years ago. You can engage in your own examination of ANTS by tracing the ridges that contain them, to see where recent activity is apparently occurring. An easy place to start is Mare Imbrium. The Valantinas and Schultz map reveals that most boulder concentrations occur on the wrinkle ridges that define the inner ring of the Imbrium impact basin. The boulder ridges start near Promontorium Laplace and pass near Montes Recti and Montes Teneriffe, and then skip to the ridge west of Montes Spitzbergen and to Dorsum Grabau west of Archimedes. The Serenitatis and Humorum impact basins are rich in ANTS boulders, which occur atop wrinkle wridges near the mare edges. And the radial wrinkle ridges that define Lamont in western Mare Tranquilitatis are all ANTS sites (though the concentric ridges aren't), renewing questions about the origin of Lamont (S&T: Apr. 2019, p. 52) and raising speculations about whether and how Lamont is still tectonically active. Someday, when there's a network of seismometers on the Moon, it'll be exciting to see if current moonquakes occur along these ANTS ridges. Not mentioned here is the discovery of other small scarps all around the Moon that reinforce the likelihood that the Moon is still seismically and tectonically active. Just as the Moon is not as dry as once thought, we're now learning that it may not be as geologically dead as we thought - it could still be adjusting to events from its earliest history in ways not yet understood. ¢ Contributing Editor CHUCK WOOD keeps one eye on the latest lunar research to share with S&T readers. s k y a n dstkeyl easncdotpe el e.cs o cm o p e*. o rDg E*CDEE M C EBMEBRE R220022 0 53http://www.skyandtelescope.org