Temperature and Density on the Forsterite Liquid-Vapor Phase Boundary
E J Davies1,2, M S Duncan3, S Root4
1Lawrence Livermore National Laboratory Livermore CA USA.
Journal of Geophysical Research. Planets
|July 5, 2021
Summary
Giant impacts during planet formation can vaporize planetary mantles. New experiments on forsterite reveal past models underestimated this vapor production, impacting planet structure predictions.
Area of Science:
- Planetary Science
- High-Pressure Geophysics
- Materials Science
Background:
- Planet formation involves extreme pressures and temperatures, particularly during giant impacts.
- Accurate thermodynamic paths are crucial for modeling post-impact planetary structures.
- Forsterite (Mg2SiO4) is a key component of rocky planet mantles and a proxy in impact simulations.
Purpose of the Study:
- To experimentally determine the liquid-vapor phase boundary of forsterite under shock conditions.
- To refine equations of state for forsterite used in giant impact models.
- To assess the impact of new data on predictions of vapor production during planetary collisions.
Main Methods:
- Shock experiments were conducted on forsterite using the Sandia Z Machine.
- Density and temperature of the liquid branch of the liquid-vapor phase boundary were measured.
- Data were combined with existing Hugoniot data for forsterite.
Main Results:
- Experimental results show significant discrepancies with existing forsterite equation of state models.
- Past models appear to underestimate entropy production and overestimate temperatures on the Hugoniot.
- The liquid-vapor phase boundary determined experimentally differs substantially from previous models.
Conclusions:
- Giant impacts may produce more vapor than previously estimated.
- Existing models for forsterite may need revision for accurate giant impact simulations.
- These findings support the potential for large portions of rocky planet mantles to become supercritical fluids after impacts.
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