Giant impacts, core stratification, and failure of the Martian dynamo
Bibliographic record
Abstract
The close timing of the giant impacts and the cessation of the core dynamo of Mars at around 4 Ga suggest a possible causal relationship between these two events. We study the shock heating of the Martian interior caused by the impact that created Utopia basin, the largest of the 20 giant impact basins formed on Mars around 4 Ga. Using empirical scaling laws connecting the diameters of the basin and the projectile, we calculate the shock pressure distribution in Mars on the basis of Pierazzo et al.'s (1997) formula, which is then used to estimate the impact‐induced temperature increase in the Martian mantle and core, adopting the “ordinary” and “foundering” shock heating mechanisms proposed by Watters et al. (2009) and impact velocities of 10 and 15 km/s. It is shown that the reduction of the heat flux out of the core due to impact heating of the overlying mantle is on the order of 0.03%–0.3% of the preimpact heat flux of the core (15 mW/m 2 ), indicating that the impact heating of the mantle has insignificant effect on the thermal convection of the core. However, the shock waves that penetrate into the core directly and differentially heat the core in only a few minutes, which causes stable thermal stratification of the core within about a few years and diminishes the core convection and the thermally driven core dynamo within a few thousand years. Exhaustion of the impact heat and removal of the stratification is necessary to reestablish a superadiabatic temperature gradient and reactivate convection in the core. As the impact heat becomes concentrated in the upper parts of the core, the stratified part of the core first cools by conduction to the mantle and then later with a contribution from penetrative convection below the core‐mantle boundary and by conduction into the deeper parts of the core. Depending on the impact velocity and the shock heating mechanisms, tens of millions of years may be needed to fully exhaust the core heat to the mantle, during which time global core convection is suppressed and a thermally driven core dynamo is problematic.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".