The Gaseous Envelope and Dense Core of Sub-Neptune GJ 160 b

Positioned within the orbit of its host M-dwarf star, GJ 160 b stands as a prime example of the elusive sub-Neptune class—planets that bridge the gap between terrestrial worlds and gas giants. With a mass approximately 8 times that of Earth and a radius roughly 2.5 times larger, GJ 160 b defies simple classification. It is a world defined by a high-pressure, volatile-rich envelope and a deep, potentially rocky or high-pressure ice interior, representing a distinct transition zone in planetary formation models.
The Gaseous Envelope and Dense Core of Sub-Neptune GJ 160 b - Section 1 overview

Atmospheric Composition and Thermal Profile

The atmosphere of GJ 160 b is dominated by a substantial hydrogen and helium envelope, likely enriched with heavier molecular species. Infrared spectroscopic analysis suggests the presence of methane and carbon monoxide, which participate in complex photochemical cycles at the upper reaches of the atmosphere. Because the planet orbits in close proximity to its parent star, it experiences intense stellar irradiation. This heat creates a stratified atmosphere where temperature gradients drive global circulation, forcing warm air from the dayside toward the perpetual twilight of the terminator zone.

The Gaseous Envelope and Dense Core of Sub-Neptune GJ 160 b - Section 2 overview

Interior Structure and Geophysical Dynamics

Beneath the convective outer atmosphere, GJ 160 b hosts an interior characterized by extreme states of matter. At depths where the atmospheric pressure exceeds several thousand atmospheres, the hydrogen-rich gases transition into a supercritical fluid. Further inward, the internal structure may transition into a pressurized mantle of water ice in exotic phases—such as Ice VII or Ice X—or a silicate-rich rocky core, depending on the planet's bulk metallic and silicate fractions. The lack of a strong magnetosphere suggests that internal convective motions are dampened or absent, preventing the generation of a global magnetic dipole.


Orbit and Orbital Dynamics

GJ 160 b exists in a tightly constrained orbital path, leading to synchronous rotation or at least significant tidal locking. This proximity subjects the planet to consistent stellar tides, which influence its internal heating rates. As the planet moves through its orbit, it faces constant stellar radiation on one hemisphere, creating a permanent dayside-nightside heat imbalance. This thermal gradient is the engine for the planet's atmospheric weather, where massive, persistent wind systems circulate kinetic energy across the planetary scale, ensuring that no region remains at a static temperature.

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