Investigation of Venus' thermal history, crustal evolution, and core dynamics with a coupled interior-lithosphere-atmosphere model

Technical Deep Dive: Venus' Thermal History, Crustal Evolution, and Core Dynamics

Overview

This technical deep dive summarizes research that used a coupled one-dimensional solar-atmosphere-lithosphere-mantle-core model to investigate Venus' thermal history, crustal evolution, and core dynamics. The study identified four distinct evolutionary pathways that simultaneously match key constraints on Venus' atmospheric composition and lack of a core dynamo.

Problem & Context

• Venus is broadly similar to Earth in bulk properties, but has vastly different surface and atmospheric characteristics:
  • Venus lacks surface liquid water, has a 92 bar CO2 atmosphere, and no detectable core dynamo
  • Earth has a 1 bar N2/O2 atmosphere and an active core dynamo
• Reconstructing Venus' history is challenging due to limited observational data on its interior
• Previous models have struggled to reproduce key constraints like atmospheric composition and lack of magnetic field

Methodology

• Developed a 1D "whole planet" model tracking Venus' geodynamo, thermal evolution, geochemistry, surface, and atmosphere over 4.5 Gyr
• Assumed Venus operated in a stagnant lid tectonic mode throughout its history
• Varied 15 parameters related to initial conditions and physical assumptions across reasonable ranges
• Identified 808 simulations (0.35% of total) that matched modern Venus constraints on atmospheric CO2, H2O, and lack of magnetic field

Results

• Simulations produced four distinct evolutionary scenarios:
  1. Type I (Conventional): Smooth, monotonic cooling of mantle and core
  2. Type II (Low Melt): Loss of mantle water leads to stiffening, shutdown of melting and outgassing
  3. Type III (Smaller Inner Core): Core evolves with small or no inner core
  4. Type IV (Oscillatory): Damped oscillations in mantle properties
• Key drivers of the evolutionary types:
  • Type II behavior linked to high initial mantle water and strong water-viscosity coupling
  • Type III behavior linked to core liquidus depression and lower mantle viscosity
• Across all scenarios:
  • Venus retains at least 1 Earth ocean's worth of water in mantle
  • Venus remains volcanically active today, contrary to "dead planet" scenarios
  • Most simulations show evidence of past magnetic field

Interpretation

• The diversity of evolutionary pathways highlights the complexity of Venus' history
• Water cycling, volatile outgassing, and core heat flow are critical for understanding the evolution
• Venus may have operated in multiple tectonic regimes over its history, not just stagnant lid
• Many plausible histories show transient magnetic fields, suggesting future missions may detect remnant magnetism

Limitations & Uncertainties

• One-dimensional model cannot capture all complexities of a 3D mantle and core
• Some parameters like potassium content and core thermal conductivity are poorly constrained
• The role of early impacts, non-thermal atmospheric escape, and changes in tectonic mode over time are not fully explored

What Comes Next

• Further constrain model parameters using new data from upcoming Venus missions (DAVINCI, VERITAS, EnVision)
• Extend analysis to exoplanets to predict their properties based on this Venus study
• Investigate the potential for remnant magnetism and implications for past magnetic field history