We found a match
Your institution may have rights to this item. Sign in to continue.
- Title
A Joint Experimental‐Modeling Investigation of the Effect of Light Elements on Dynamos in Small Planets and Moons.
- Authors
Pommier, Anne; Davies, Christopher J.; Zhang, Rong
- Abstract
We present a joint experimental‐modeling investigation of core cooling in small terrestrial bodies. Significant amounts of light elements (S, O, Mg, Si) may compose the metallic cores of terrestrial planets and moons. However, the effect of multiple light elements on transport properties, in particular, electrical resistivity and thermal conductivity, is not well constrained. Electrical experiments were conducted at 10 GPa and up to 1850 K on high‐purity powder mixtures in the Fe‐S‐O(±Mg, ±Si) systems using the multianvil apparatus and the four‐electrode technique. The sample compositions contained 5 wt.% S, up to 3 wt.% O, up to 2 wt.% Mg, and up to 1 wt.% Si. We observe that above the eutectic temperature, electrical resistivity is significantly sensitive to the nature and amount of light elements. For each composition, thermal conductivity‐temperature equations were estimated using the experimental electrical results and a modified Wiedemann‐Franz law. These equations were implemented in a thermochemical core cooling model to study the evolution of the dynamo. Modeling results suggest that bulk chemistry significantly affects the entropy available to power dynamo action during core cooling. In the case of Mars, the presence of oxygen would delay the dynamo cessation by up to 1 Gyr compared to an O‐free, Fe‐S core. Models with 3 wt% O can be reconciled with the inferred cessation time of the Martian dynamo if the core‐mantle boundary heat flow falls from >2 TW to ~0.1 TW in the first 0.5 Gyr following core formation. Plain Language Summary: Different elements (like S, O, Mg, Si) are present in the metallic (Fe) cores of some planets and moons. The effect of these elements on the physical properties of the core is not well understood. Here we performed electrical experiments under pressure and temperature on different core compositions. The samples contain small amounts of S, O, Mg, and Si. Our experimental results show that at high temperature, the electrical response of the sample is significantly sensitive to the nature and amount of added elements. For each composition, we also estimated the ability of the sample to conduct heat. All these results were used as part of core cooling models. Our modeling results suggest that core chemistry significantly changes the energy available to power dynamo action during cooling. Applied to the core of Mars, our model shows a significant effect of oxygen on the activity of the core dynamo. Key Points: The effect of chemistry on the electrical properties of cores is important and should be accounted for as part of core cooling modelsBulk chemistry significantly affects the power available to drive the dynamo during core coolingThermal conductivities can change the dynamo cessation time significantly, by a billion years or more
- Subjects
INNER planets; MASS spectrometry; HOMOGENEITY; IRON alloys; NUCLEATION
- Publication
Journal of Geophysical Research. Planets, 2020, Vol 125, Issue 8, p1
- ISSN
2169-9097
- Publication type
Article
- DOI
10.1029/2020JE006492