End‐Member Venusian Core Scenarios: Does Venus Have an Inner Core?. Issue 17 (7th September 2021)

• Record Type: Journal Article
• Authors: O'Neill, Craig
• Is Part Of: Geophysical research letters. Volume 48:Issue 17(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-09-07
• Subjects: Venus -- inner core -- density structure; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2021GL095499
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Venus's lack of a magnetic field suggests it may not have an inner core; however, evidence of Venus's internal density structure has historically been limited by its slow rotation. New moment of inertia (MoI) estimates allow us to constrain its internal density and thermal structure. Here, we use a mineral‐physics solver, and incorporate equations of state for silicate mantle minerals and core phases, to calculate radial density profiles for variable core and mantle compositions, and estimate the MoI and planetary mass, and optimal outer and inner core radii. For Earth‐like core compositions, our best fit radius for Venus's core is 3, 147.1 ± 16.8 km, with no inner core—implying the liquid core has not cooled sufficiently to start crystallizing. However, for enriched light‐element concentrations in the core (>∼11 wt%), solutions fit large, light cores (∼4, 000 km), and large inner cores (>∼2, 000 km), underpinning the need for tighter cosmochemical/geophysical constraints on these endmembers. Plain Language Summary: Venus has no magnetic field, and it has been suggested that this could be due to both its core freezing out, or not having started to freeze at all. Often the density structure of a planet, which tells us about the core can be determined by a planet's rotation. But this is hard for Venus, as its rotation is very slow. However, new measurements have allowed us to calculate the internal properties of Venus, and work out the optimal core size that fits its rotation data, and mass. We find two end‐member scenarios that fit the rotational data. If Venus has an Earth‐like core, we have determined the core radius to be ∼3, 147 km, and also that Venus has no inner core. But, if the core is enriched in light elements, like Mercury, then the permissible models include very large core radii (>4, 000 km), and large inner cores (>2, 000 km). If the core has not started to freeze, it must have been cooling slowly, implying from plate tectonics has not operated on Venus; however, these scenarios require tighter cosmochemical or geophysical constraints on Venus's core composition. Key Points: Venus density structure calculated from new moment of inertia results Updated mineral physics solvers allow us to constrain temperature and compositional effects, and find optimal core size Earth‐like core compositions suggest no inner core on Venus, and core radius of 3, 147 km; light elements permit large inner core sizes