IMPs: Young Lunar Volcanism?

Small patches of rough terrain in Sosigenes Crater
Irregular Mare Patch located inside Sosigenes Crater (8.7° N, 17.5° E), approximately 17 km across. NAC controlled mosaic containing images M1264703188L/R, M1264710221L/R, and M1264717254L/R [NASA/GSFC/Arizona State University].

IMPs on the Moon, you say? Do small, mischievous demons live on the Moon?! No, not those kinds of IMPs! IMPs or “Irregular Mare Patches” are thought to be volcanic deposits (typically 100–1000 m across). Their general lack of superposed impact craters greater than 20 meters in diameter suggest that they are some of the youngest volcanic deposits on the Moon, perhaps less then 100 million years young. An alternative hypothesis suggests that IMPs might be ancient, but formed from a low density magma – an extreme form of pumice.  To learn about the history of IMP discovery and LROC’s part in finding new ones, check this out!


Below, see some of the other fantastic controlled mosaics of IMPs composed from LROC NAC images!


Rough terrain on the lunar surface known as Lone IMP
A lone IMP located near Manilius Crater (14.8° N, 6.4° E).  NAC controlled mosaic containing images M1264780654L/R, M1264787687L/R, and M1264794721L/R [NASA/GSFC/Arizona State University].

IMPs typically have two distinct morphological features: smooth deposits and uneven deposits, with an abrupt change in slope where the two meet.  Smooth deposits are generally higher in elevation and sometimes appear to superimpose rough deposits.  See if you can spot the different textures with these high-resolution controlled mosaics!

Rough terrain on the lunar surface known as Cauchy IMP
IMP located southwest of Cauchy Crater (7.2° N, 37.6° E).  NAC controlled mosaic containing images M1264717254L/R, M1264710221L/R, and M1264703188L/R [NASA/GSFC/Arizona State University].
Rough terrain on the lunar surface known as Ina IMP
The largest and most well known IMP is Ina, or Ina-D ( ~18.65° N, 5.30° E). NAC controlled mosaic containing images M1184803184L/R, M1184796081L/R, M1184788979L/R, and M1184781877L/R [NASA/GSFC/Arizona State University].

Ina has been studied as far back as the Apollo era. Originally, it was thought to have been a collapsed caldera associated with a shield volcano.  That hypothesis is still valid, however we really do not know the origin of these enigmatic feature.

Rough terrain on the lunar surface known as Maskelyne IMP
Maskelyne Crater IMP (4.3° N, 33.7° E).  NAC controlled mosaic containing images M1264611690L/R and M1264597624L/R [NASA/GSFC/Arizona State University].

IMPs have only been found within nearside maria, where 70 have been identified to date. Lunar scientists would expect to find at least three IMPs larger than 100 meters in diameter within the farside maria, but none have been found – yet!


Zoom in and out of the Sosigenes IMP below!



Learn more about the places near these IMPs:

Sosigenes:  What's Next for LRO? 

Cauchy:  Watch That First Step! 

Ina: Another Lunar Enigma

Maskelyne:  Eroding Craters Walls


Do you want to download these images yourself?

Sosigenes IMP

Lone IMP

Cauchy IMP


Maskelyne IMP


Interested in learning more about controlled mosaics? Check out  Feature Mosaics: Behind the Seams

Published by Jessica Walsh on 24 February 2021