Detectability of Remanent Magnetism in the Crust of Venus

Abstract

Observations of planetary magnetic fields provide fundamental insights into the origin and evolution of terrestrial planets. However, whether Venus ever hosted a dynamo is unknown. Here we show that crustal remanent magnetism is a potentially observable consequence of an ancient Venusian dynamo, in contrast to previous studies that dismissed this possibility. Past spacecraft measurements only exclude crustal magnetization near the Venera 4 landing site and northward of 50° South latitude for >150‐km coherence scales and strong magnetization intensities. Magnetite grains with sizes commonly observed in volcanic rocks can retain thermoremanent magnetism at Venusian conditions for >1 billion years. Depths to the Curie temperature of magnetite are ~5–40 km and typically less than predicted crustal thicknesses at our analyzed localities. Aerial platforms could detect expected magnetizations at horizontal scales similar to the ~50‐km operating altitude. Any detection would validate models of planetary accretion, geologic processes, and climate history.

Magnetic Topology at Venus: New Insights Into the Venus Plasma Environment

“…As illustrated in Figure 4b, these lower altitude fields can be thought of as locally induced, or the result of deeply penetrated, draped IMFs (e.g., Ma et al, 2020) modified by magnetic reconnection and/or plasma flow in the ionosphere. Alternatively, there are ongoing searches for weak global dynamo or localized crustal magnetic fields at Venus (e.g., Luhmann et al, 2015;O'Rourke et al, 2019) suggesting we cannot exclude the possibility that the "open" and "closed" fields in our study are connected back to Venus' surface and interior -or even to a conductive metallic core (e.g., Zharkov, 1983). Furthermore, collisional diffusion must affect the interactions of both external and planetary fields in this region.…”

“…In terms of the magnetic environment, one of the major differences between Mars and Venus is that Mars has localized intense crustal magnetic fields which can connect the solar magnetic field to the planet surface, while Venus has insignificant intrinsic magnetism (e.g., Phillips & Russell, 1987;O'Rourke et al, 2019). As a result, the Venusian atmosphere and ionosphere interact directly with the solar wind and the IMF penetrates into the ionosphere to a degree that varies dynamically with the upstream solar wind dynamic pressure as well as the ionospheric plasma thermal pressure (e.g., Luhmann, 1986;Luhmann & Cravens, 1991;Futaana et al, 2017).…”

Venus: A Thick Basal Magma Ocean May Exist Today

“…Thermal conductivity of the core is no longer a critical uncertainty because the cooling rate of the core is subadiabatic regardless. Crustal remanent magnetism is a potentially observable consequence of an early dynamo in either the core or BMO (O'Rourke et al, ). Alternatively, Venus could have accreted under less energetic conditions where any BMO was short‐lived and chemical stratification precluded convection in the core (Jacobson et al, ), meaning no crustal remanence would exist.…”

Scientific Exploration of Venus with Aerial Platforms

“…The proximity of the aerobot to the surface of Venus enables geophysical measurements with much greater sensitivity and spatial resolution than is possible from an orbiting spacecraft. Detection of remanent magnetization at horizontal scales similar to the ~50-km aerobot altitude, would test hypotheses of a permanent magnetic field existing early in Venus' history [12]. Measurements of changes in the magnetosphere induced by the solar wind enable probing of the planetary core [13].…”