Melting the Moon: First High-Temperature Calorimetry of Apollo Soils
Year: 2025
Type: article
Abstract: High-T regolith heat capacity underpins in situ resource utilization (ISRU), sintering, melt-processing, thermal-conductivity models, and impact melt behavior. However, prior studies were confined to low-temperature (<100°C), non-destructive Cp measurements, qualitative DTA, EGA-focused analysis, or simulant-based, until now. We present the first high-T differential scanning calorimetry (DSC) on six Apollo soils (30°C/min, 1625°C), to our knowledge, the first complete melting of Apollo 16 regolith. 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 539± 86J/g (2σ) and liquidus 1545 ± 14°C (2σ). 10084 is lower at 432 ± 146 J/g (2σ) and 1314 ± 1°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 1625°C for 25 minutes, 10084 crystallized spherulites on cooling (1125-800°C, peak 986°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 Apollo soils are significantly glassy and space-weathered, exhibiting two exothermic crystallization events below 1000°C: a low-T interval (~350-650°C) we attribute to extremely metastable, irradiated and vapor-deposited rims (contributing roughly one-third of the released energy), and a post-Tg interval (~780-980 °C) from impact-melt glass. These data indicate lunar soils are highly metastable and amorphous, with Apollo 16 averaging a total crystallization enthalpy of -75 ± 16 J/g (1σ). Total glass content estimation is complicated by multiple crystallization steps, but enthalpy-based methods with our data currently suggest >20 wt.% glass in Apollo soils. Sintering-relevant melt onsets further differentiate the soils: Apollo 16 shows bimodal melting at ~1259°C (noritic onset) and ~1404°C (An melts), whereas Apollo 11 10084 exhibits a single melting peak at ~1144°C.NOTE: Abstract updated from the original GSA submission as additional data were gathered and integrated into this poster.
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Award: G5112584870
OpenAlex ID: W7092198402
FWCI:
Cites:
Cited by:
Related to: