Lunar Crater Ina: Analysis of the Morphology of Intracrater Landforms

Abstract

We present the results of geological and morphological analysis of LROC NAC images of a small volcanic crater Ina, D-shaped in plan view (2.9 × 1.9 km), and its immediate surroundings. This crater is located at the top of a very gently sloping shield volcano, the slopes of which, judging by the density of superimposed small craters, were formed ~3.5 Ga ago. Inside the crater there is a region with uneven relief and low hills, the density of small craters on which corresponds to an age of <100 Ma. In a number of works, the formations inside the Ina crater are considered to be manifestations of very young volcanism, while in other works, hills with an apparent age of <100 Ma are considered to be composed of “magmatic foam” such as massive pumice, which could affect the formation of small craters on them, reducing their diameters and thereby underestimating their measured spatial density. Accordingly, the Ina crater may be ancient and have the same age as the slopes of the shield volcano. In this paper, we studied the degree of morphological “freshness” of formations inside the Ina structure and compared the morphology of small craters superimposed on the hills inside Ina and on the slopes of the shield volcano adjacent to the Ina structure. In addition, model calculations of the thickness of the regolith layer for the cases of a “normal” target and a target consisting of “magmatic foam” have been performed. It is shown that the morphological freshness of the formations inside the Ina crater does not agree with the assumption about the ancientry of this crater, and morphologically “fresh” small craters on the hills inside Ina barely differ from those on the slopes of the shield volcano. These observations appear to contradict the “magmatic foam” hypothesis and support the conclusion that Ina’s structure is young.