Pre-mission InSights on the Interior of Mars

Abstract The Interior exploration using Seismic Investigations, Geodesy, and Heat Trans- port (InSight) Mission will focus on Mars’ interior structure and evolution. The basic structure of crust, mantle, and core form soon after accretion. Understanding the early differentiation process on Mars and how it relates to bulk composition is key to improving our understanding of this process on rocky bodies in our solar system, as well as in other solar systems. Current knowledge of differentiation derives largely from the layers observed via seismology on the Moon. However, the Moon’s much smaller diameter make it a poor analog with respect to interior pressure and phase changes. In this paper we review the current knowledge of the thickness of the crust, the diameter and state of the core, seismic attenuation, heat flow, and interior composition. InSight will conduct the first seismic and heat flow measurements of Mars, as well as more precise geodesy. These data reduce uncertainty in crustal thickness, core size and state, heat flow, seismic activity and meteorite impact rates by a factor of 3–10× relative to previous estimates. Based on modeling of seismic wave propagation, we can further constrain interior temperature, composition, and the location of phase changes. By combining heat flow and a well constrained value of crustal thickness, we can estimate the distribution of heat producing elements between the crust and mantle. All of these quantities are key inputs to models of interior convection and thermal evolution that predict the processes that control subsurface temperature, rates of volcanism, plume distribution and stability, and convective state. Collectively these factors offer strong controls on the overall evolution of the geology and habitability of Mars

Initial results from the InSight mission on Mars

NASA’s InSight (Interior exploration using Seismic Investigations, Geodesy and Heat Transport) mission landed in Elysium Planitia on Mars on 26 November 2018. It aims to determine the interior structure, composition and thermal state of Mars, as well as constrain present-day seismicity and impact cratering rates. Such information is key to understanding the differentiation and subsequent thermal evolution of Mars, and thus the forces that shape the planet’s surface geology and volatile processes. Here we report an overview of the first ten months of geophysical observations by InSight. As of 30 September 2019, 174 seismic events have been recorded by the lander’s seismometer, including over 20 events of moment magnitude Mw = 3–4. The detections thus far are consistent with tectonic origins, with no impact-induced seismicity yet observed, and indi- cate a seismically active planet. An assessment of these detections suggests that the frequency of global seismic events below approximately Mw = 3 is similar to that of terrestrial intraplate seismic activity, but there are fewer larger quakes; no quakes exceeding Mw = 4 have been observed. The lander’s other instruments—two cameras, atmospheric pressure, temperature and wind sensors, a magnetometer and a radiometer—have yielded much more than the intended supporting data for seismometer noise characterization: magnetic field measurements indicate a local magnetic field that is ten-times stronger than orbital estimates and meteorological measurements reveal a more dynamic atmosphere than expected, hosting baroclinic and gravity waves and convective vortices. With the mission due to last for an entire Martian year or longer, these results will be built on by further measurements by the InSight lander

Mittelholz et al., 2022

This contains the data files to produce figure 8. The data is derived from the Mars climate data base (http://www-mars.lmd.jussieu.fr/mars/access.html)</p

Mars’ external and internal magnetic fields from orbital observations

Magnetic fields play a big role in the evolution of a planet and can be used as a tool to understand the interior of it. Orbital spacecraft missions, Mars Global Surveyor (MGS) and Mars Atmosphere and Volatile EvolutioN (MAVEN), have acquired magnetic field data, collectively providing full global coverage at different altitudes. Those data carry information about fields of internal origin, specifically the crustal field, and of external origin, fields generated by the Sun and in the ionized upper atmosphere. Time variable external fields induce electric currents in the subsurface, providing information about the electrical conductivity structure and thus, material properties of the martian interior. The locally strong static crustal field of Mars provides evidence for an ancient global dynamo field. I first explore the global structure of external fields and what we can learn from this, in particular about the contribution of the ionosphere to large-scale magnetic fields. I then investigate how we can extract magnetically quiet orbits, e.g., orbits during which the external field is minimal, from MAVEN data to use in crustal field models. Such models are essential for predicting the field at the surface of the planet and the magnetization responsible for it; this is important for mission planning and we show predictions for the landing sites of Mars 2020 and InSight. Furthermore, such predictions in combination with satellite data provide insight into ancient Mars. I specifically address the timing of the ancient dynamo, and the distribution of magnetization in Mars’ crust. Thus, in this thesis I explore internal and external aspects of the field, contributing to the understanding of past and on-going processes of Mars.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat

The Global Conductivity Structure of the Lunar Upper and Midmantle

Magnetic sounding is a powerful tool to explore the interior of planetary bodies through the electrical conductivity structure. The electrical conductivity structure of the lunar mantle has previously been derived from surface magnetic field measurements as part of the Apollo 12 mission and concurrent magnetometer data acquired from orbit through the Explorer 35 satellite. Here, we derive the first global conductivity structure of the upper and midmantle using only satellite magnetometer data collected by the recent Lunar Prospector and Kaguya Selene satellite missions. We show that the field in the geomagnetic tail exhibits a simple geometrical structure and can be well described by a single spherical harmonic of degree and order one. Employing this information about the inducing field geometry and assuming a potential representation of the field in the geomagnetic tail, we derive a frequency-dependent transfer function and invert it for a one-dimensional (1-D) electrical conductivity profile of the lunar upper and midmantle. Our global transfer function shows striking similarity with the local one obtained from joint analysis of Apollo 12 and Explorer 35 magnetometer data. This indicates the lack of local variations at the Apollo 12 landing site compared to the globally averaged upper to midmantle electrical conductivity structure.ISSN:0148-0227ISSN:2169-909

An Ancient Martian Dynamo Driven by Hemispheric Heating: Effect of Thermal Boundary Conditions

Magnetic field observations from the MGS, MAVEN, and InSight missions reveal that a dynamo was active in Mars’s early history. One unique feature of Mars’s magnetic crustal field is its hemispheric dichotomy, where magnetic fields in the southern hemisphere are much stronger than those in the northern hemisphere. Here we use numerical dynamo simulations to investigate the potential hemispheric nature of Mars’s ancient dynamo. Previous studies show that a hemispheric heat flux perturbation at the core–mantle boundary could result in either a stable hemispherical magnetic field or a constantly reversing field, depending on choices of parameters used in those models. These two scenarios lead to different implications for the origin of crustal fields. Here we test the dynamo sensitivity to varying hemispheric heat flux perturbations at the core–mantle boundary in a broader parameter regime to understand whether a hemispheric dynamo is likely for early Mars. We find that features of the dynamo change from stable, hemispheric magnetic fields to reversing, hemispheric fields, with increasing hemispheric heat flux perturbations at the core–mantle boundary. We also find that magnetic fields powered by bottom heating are more stable and transition from a nonreversing, hemispheric magnetic field to a multipolar field at higher hemispheric heat flux perturbations, while the transition happens at a much lower heat flux perturbation for magnetic fields powered by internal heating

Magnetic Field Signatures of Craters on Mars

Craters on Mars are a window into Mars' past and the time they were emplaced. Because the crust is heated and shocked during impact, craters can demagnetize or magnetize the crust depending on the presence or absence of a dynamo field at the time of impact. This concept has been used to constrain dynamo timing. Here, we investigate magnetic anomalies associated with craters larger than 150 km. We find that most of those craters, independent of age, exhibit demagnetization signatures in the form of a central magnetic low. We demonstrate a statistically significant association between such signatures and craters, and hypothesize that the excavation of strongly magnetic crustal material may be an important contribution to the dominance of demagnetized craters. This finding implies that the simple presence or absence of crater demagnetization signatures is not a reliable indicator for the activity of the Martian dynamo during or after crater formation.ISSN:0094-8276ISSN:1944-800

Space Weather Observations With InSight

Solar activity, in the form of coronal mass ejections and corotating interaction regions, results in changes in the solar wind that propagate out through the solar system and interact with the magnetic field environments of planets. Such phenomena have been observed to affect the magnetic field and plasma around Mars as seen from orbit. However, no surface observations have previously been possible because of the absence of ground-based instrumentation. Here, for the first time, we observe the effects of increased solar activity with the magnetometer on the InSight mission in December 2020. We find several days of increased activity including magnetic field fluctuations at periods of minutes to hours. Although only the flanks of this relatively weak coronal mass ejection hit Mars, the observed effects provide insight into how solar activity alters magnetic fields at the surface.ISSN:0094-8276ISSN:1944-800

Dataset of Mars Hemispheric Magnetic Field From A Full Sphere Dynamo

Dataset for reproducing the figures of Mars Hemispheric Magnetic Field From A Full Sphere Dynamo</p