116-5 Melting the Moon: First High-Temperature Calorimetry of Apollo Soils

Session: Lunar Science and Exploration in the Artemis Era (Posters)

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Understanding the high-temperature heat capacity of lunar regolith is essential for in situ resource utilization (ISRU), sintering, melt-processing, and thermal conductivity modeling. However, prior studies have been limited to low-temperature (<100 °C), non-destructive measurements. Here, we present the first high-temperature differential scanning calorimetry (DSC) data on six Apollo soils (30°C/min to 1620°C): one mare (Apollo 11 10084,2095) and five highland (Apollo 16: 64501,16; 64801,189; 65701,159; 67711,14; 68841,133).

All Apollo 16 soils exhibit similar thermodynamic properties with reproducible bimodal melting behavior. Stone Mountain soils show a prominent anorthosite peak near ~1405°C, while others have a stronger norite melting peak around ~1259°C. The Apollo 16 average enthalpy of fusion is 553 ± 74 J/g (2σ) and liquidus 1545 ± 8°C (2σ). 10084 is lower at 427 ± 78 J/g (2σ) and 1350 ± 98°C (2σ). The average liquid heat capacity of all bulk Apollo 16 melts is 1.50 ± 0.17 J/g (2σ).

After melting and holding at 1620°C for 25 minutes, 10084 crystallized spherulites on cooling (1085–850°C, peak 991°C), while all Apollo 16 melts quenched to glass. On reheating, all Apollo 16 showed similar glass transition peaks at 790 ± 28°C (2σ), followed by crystallization troughs, melting peaks at ~1180°C and ~1320°C, and liquidus near ~1307 ± 23°C (2σ). Notably, 67711 and 64501 recrystallized ~5x more strongly than others, releasing -201 ± 62 J/g (2σ).

All soils show evidence of glass and space weathering, including two exothermic crystallization events: a low-temperature event (~360–600°C) and a post-glass transition event (~785-960°C). We attribute the low-temperature crystallization to extreme instability of irradiated, space-weathered glasses, particularly vapor-deposited rims. These findings indicate lunar soils are highly metastable and amorphous, with average total Apollo 16 crystallization enthalpy of -72 ± 17 J/g (2σ). Total glass content estimation is complicated by multiple crystallization steps, but enthalpy-based methods suggest >20 wt.% glass in Apollo soils.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8468

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