Spatial heterogeneity in the radiogenic activity of the lunar interior: Inferences from CHACE and LLRI on Chandrayaan-1

TL;DR

This study uses data from Chandrayaan-1's CHACE and LLRI instruments to investigate spatial variations in lunar radiogenic activity, revealing heterogeneity in the Moon's interior and surface antiquity through high-resolution measurements.

Contribution

It provides the first high spatial resolution analysis of lunar radiogenic activity heterogeneity using combined in-situ noble gas isotope data and topography measurements.

Findings

Detected spatial heterogeneity in 40Ar/36Ar ratios across the lunar surface.

Corroborated radiogenic activity variations with topography data.

Indicated potential links between lunar interior processes and surface features.

Abstract

In the past, clues on the potential radiogenic activity of the lunar interior have been obtained from the isotopic composition of noble gases like Argon. Excess Argon (40) relative to Argon (36), as compared to the solar wind composition, is generally ascribed to the radiogenic activity of the lunar interior. Almost all the previous estimates were based on, 'on-the-spot' measurements from the landing sites. Relative concentration of the isotopes of 40Ar and 36Ar along a meridian by the Chandra's Altitudinal Composition Explorer (CHACE) experiment, on the Moon Impact Probe (MIP) of India's first mission to Moon, has independently yielded clues on the possible spatial heterogeneity in the radiogenic activity of the lunar interior in addition to providing indicative 'antiquity' of the lunar surface along the ground track over the near side of the moon. These results are shown to broadly corroborate the independent topography measurements by the Lunar Laser Ranging Instrument (LLRI) in the main orbiter Chandrayaan-1. The unique combination of these experiments provided high spatial resolution data while indicating the possible close linkages between the lunar interior and the lunar ambience.