Evidence of hydrogen-helium immiscibility at Jupiter-interior conditions

Area of Science:

• Planetary Science
• Materials Science under extreme conditions
• Computational Physics

Background:

• The phase behavior of hydrogen-helium (H-He) mixtures is crucial for understanding the internal structure and evolution of gas giants like Jupiter and Saturn.
• Previous studies of H-He phase behavior under planetary conditions were limited due to experimental and computational challenges.

Purpose of the Study:

• To experimentally probe the phase behavior of H-He mixtures under conditions simulating the interiors of Jupiter and Saturn.
• To constrain the H-He miscibility gap relevant to planetary evolution models.

Main Methods:

• Utilized laser-driven shock compression of pre-compressed H2-He samples in diamond-anvil cells.
• Probed sample properties, including reflectivity, at extreme temperatures and pressures (up to 150 GPa and 10,200 K).

Main Results:

• Identified a region of immiscibility in H-He mixtures along the Hugoniot curve.
• Observed discontinuous reflectivity changes indicating the boundaries of the immiscibility region at specific pressure-temperature points.
• Constrained the H-He phase separation to occur above 150 GPa at 10,200 K and above 93 GPa at 4,700 K.

Conclusions:

• Experimental constraints on H-He immiscibility support models of a layered interior for Jupiter.
• Phase separation of H-He is estimated to affect approximately 15% of Jupiter's radius.
• Findings provide microphysical support for explaining observations from the Juno and Galileo missions.