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Crustal and time-varying magnetic fields at the InSight landing site on Mars


Magnetic fields provide a window into a planet’s interior structure and evolution, including its atmospheric and space environments. Satellites at Mars have measured crustal magnetic fields indicating an ancient dynamo. These crustal fields interact with the solar wind to generate transient fields and electric currents in Mars’s upper atmosphere. Surface magnetic field data play a key role in understanding these effects and the dynamo. Here we report measurements of magnetic field strength and direction at the InSight (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) landing site on Mars. We find that the field is ten times stronger than predicted by satellite-based models. We infer magnetized rocks beneath the surface, within ~150 km of the landing site, consistent with a past dynamo with Earth-like strength. Geological mapping and InSight seismic data suggest that much or all of the magnetization sources are carried in basement rocks, which are at least 3.9 billion years old and are overlain by between 200 m and ~10 km of lava flows and modified ancient terrain. Daily variations in the magnetic field indicate contributions from ionospheric currents at 120 km to 180 km altitude. Higher-frequency variations are also observed; their origin is unknown, but they probably propagate from even higher altitudes to the surface. We propose that the time-varying fields can be used to investigate the electrical conductivity structure of the martian interior.

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Fig. 1: IFG data for sols 35–106.
Fig. 2: Regional geology and inferred magnetization.
Fig. 3: Time variations–daily signals.
Fig. 4: Pulsations.
Fig. 5: Toward interior electrical conductivity.

Data availability

All IFG data reported in this manuscript are available on the Planetary Data System (PDS) Planetary Plasma Interactions (PPI) node:


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This research was funded through the InSight Project at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration, the InSight Participating Scientist Program, the Canadian Space Agency and the Centre National d’Etudes Spatiales. C.L.J. acknowledges support from the Green Foundation for Earth Sciences during leave at the Institute of Geophysics and Planetary Physics, Scripps Institution of Oceanography (2019–2020). This paper is InSight Contribution Number 106.

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Authors and Affiliations



W.B.B. and S.E.S. lead and co-lead the InSight mission, respectively. P.L. is the PI of the SEIS instrument on InSight; D.B. is the lead for the APSS instrument suite. C.T.R. led the development of the UCLA magnetometer contributed to the InSight mission. C.T.R. also directs the processing and delivery of IFG data by S.J. and X.L. to the team and the Planetary Data System. C.T.R. and C.L.J. are the co-leads of the InSight Magnetics Working Group. A.M. is the lead for weekly Event Request Proposals for IFG data. A.M., Y.Y., C.L.J. and S.N.T. have participated in IFG data processing and product review. C.L.J. led the synthesis of the magnetic field investigations reported here and wrote most of the main text. C.L.J. conducted the crustal magnetization inversion and coordinated the crustal field study together with A.M., B.L., C.T.R., M.A.W. and S.E.S. C.L.J. and A.M. produced all the figures and tables with the exception of Fig. 4 (P.J.C.) and Extended Data Figs. 5 and 6 (S.N.T.). P.J.C. identified the continuous pulsations and contributed the accompanying text. M.O.F. and Y.Y. contributed to the discussion of daily variations in the magnetic field. S.N.T. and A.M. contributed the assessment of lander activities on the magnetic field signals. V.A., M.G., C.M., C.Q.-N., L.P. and P.L. contributed the regional geology and crustal structure discussions to the paper. D.B., A.S. and F.F. contributed to discussions regarding external fields, in particular signals that might be driven by atmospheric phenomena and ionospheric fields. H.F.H. and S.S. reviewed the manuscript and Extended Data materials. All authors read and commented on the manuscript.

Corresponding author

Correspondence to Catherine L. Johnson.

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Extended data

Extended Data Fig. 1 Contributions to the Magnetic Field Measured by the IFG.

Time-varying fields are either of external origin (orange), including the interplanetary magnetic field, ionospheric currents and weather events such as dust devils; they can also be of lander origin (blue), e.g., due to movement of the arm, RISE communications, Solar Array Currents, or martian temperature variations, measured by the temperature sensors on the lander. The martian static crustal field (red) results from crustal magnetization, represented schematically here as subsurface dipoles. A DC field is also associated with the lander itself (green). Inset shows the IFG sensor box and connecting cable.

Extended Data Fig. 2 All IFG data available as of Aug 1, 2019, covering sols 14-299.

Magnetic field components Bx, By, Bz in the local lander level (LL) frame from 11 December, 2019 until 29 September, 2019. Data gaps occur due to safing at times of APSS anomalies. The average field ± 1 std for the entire period is [BX, BY, BZ] = [-1353 ± 6, 1168 ± 5, -925 ± 6] nT. As nighttime data are less contaminated by external fields (ionospheric currents and the draped interplanetary magnetic field, IMF) we report the average field computed between local times of 8pm and 4am in the main paper. This is indistinguishable from that computed for all local times. The uncertainty in the crustal field is dominated by the uncertainty in the spacecraft field as described in the main text. Corrections for temperature and solar array currents are described in detail in the IFG Software Interface Specification (SIS) document available on the PDS (

Extended Data Fig. 3 Predictions for the surface magnetic field strength from satellite-based models.

Surface magnetic field strength, B, in the vicinity of the InSight landing site (asterisk) predicted by two recent magnetic field models that use MAVEN and MGS data. a, The regional model of12 predicts B = 236 nT at the InSight landing site. b, The global model of13 predicts B = 314 nT at the InSight landing site. Within about 60 km to the northwest of the landing site there are locally stronger fields, reaching 324 nT in12 and 400 nT in13. Both models use the same equivalent source dipole modeling approach and use MAVEN and MGS data. Adapted from14.

Extended Data Fig. 4 Time variable signals.

Expected and/or observed periodicities in the magnetic field, together with their causes and any challenges associated with observing them in IFG data to date. IMF refers to Interplanetary Magnetic Field. A ‘Yes’ in the last column means that these signals have been unambiguously detected in IFG data a ‘No’ means they have not yet been identified. Time variations for which there are hints in current data but that require a longer time series or better statistics for confident detection are marked with a question mark.

Extended Data Fig. 5 Magnetic field signatures of various lander activities.

IFG data contain many transient signals that are of spacecraft origin, shown in this example of data from sols (a) 182 and (b) 189 (1 June 2019 and 8 June 2019, respectively). Time series are plotted in Local Mean Solar Time (LMST). From ~0700 LMST on sol 182 onwards the continuous IFG data have been available at 2 Hz, c.f. 0.2 Hz prior to this and during periods such as solar conjunction (August 2019). For each sol, the top 3 panels show BX, BY, BZ in the spacecraft frame, with the 2 Hz data shown in color (red = BX, green = BY, blue = BZ) and data down-sampled to 0.2 Hz data shown in gray. The bottom panel shows the actual (red dots) total solar array current (SACT; channel G_0036) and the model current (blue) used to estimate and subtract the effect of the solar array current in the IFG data. Also shown are four spacecraft activities that have associated transients in the IFG data. For each activity, the start and end times are shown by vertical dashed and dotted lines respectively. The activities include: (1) the lander transitions from ON to OFF or vice versa (yellow); (2) RISE communications (cyan); (3) lander communications (brown); and (4) arm operations (magenta). Lander-on times are typically followed by spikes in all 3 magnetic field components. Jumps or drops are associate with lander and RISE communications, and a sawtooth signal is often seen in association with arm movements. Furthermore, the 2 Hz data (and 20 Hz event data) show substantial noise typically between about 10:00 and 16:00 LMST. Examination of multiple sols of data indicate that the onset of this IFG noise above 0.2 Hz occurs in association with times of increased scatter in the solar array current data. Similarly, the termination of the noise correlates with a transition to solar array currents that are more smoothly-varying in time. Although important to diagnose, none of the transients or noise characteristics shown here impact the results discussed in the main text. They are, however, important for understanding whether small, short time-duration signals such as those discussed in Extended Data Fig. 6 can be reliably interpreted to be of martian rather than spacecraft origin.

Extended Data Fig. 6 Magnetic field signals during vortices.

A few vortices show a very small (<1 nT) magnetic signal, typically in the North and East components. One example is shown here for sol 15 (11 December, 2018). 20 Hz IFG data are routinely requested in a 6-minute interval around a pressure drop identified by the Mars Weather Service team. (a) BX, (b) BY in the LL frame for 20 Hz IFG data (gray dots), and for these data down-sampled via FIR-filtering to 1 Hz and 0.2 Hz (the cadence of the continuous data on sol 15), and (c) pressure. Time of the pressure drop (> 1Pa) indicated by vertical dashed line.

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Johnson, C.L., Mittelholz, A., Langlais, B. et al. Crustal and time-varying magnetic fields at the InSight landing site on Mars. Nat. Geosci. 13, 199–204 (2020).

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