EGU2020-2238
https://doi.org/10.5194/egusphere-egu2020-2238
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Evidence for a Wet Martian Interior from Magnetic Sounding with the InSight Magnetometer

Yanan Yu1, Christopher Russell1, Matthew Fillingim2, and William Banerdt3
Yanan Yu et al.
  • 1University of California,Los Angeles, Institute of geophysics, Earth and Space Science, Los Angeles, United States of America (ctrussel@igpp.ucla.edu)
  • 2Space Sciences Laboratory, University of California, Berkeley, CA 94720, USA
  • 3Jet Propulsion Laboratory, NASA, Pasadena, CA, USA

The martian magnetic field oscillates at frequencies from once per day to periods of only 100s of seconds. The interior of Mars is electrically conducting, and the time-varying magnetic fields create induced currents in the electrically conducting subsurface of Mars. The diurnal periods are little affected by the interior conductivity, but at periods shorter than about 1000 sec, the reflection of the magnetic wave energy is strong, and the vertical component of the oscillating magnetic field approaches zero as the frequency increases. Electromagnetic waves at the shorter (<1000s) periods are produced by the nighttime currents such as those flowing on and within the Mars magnetotail. These fluctuations are weak in the vertical component of the waves associated with the restriction of the currents to flow horizontally as the wave period grows shorter. This phenomenon is also seen on Earth and has been well characterized there. The measure of the attenuation of the vertical component is referred to as the skin depth. The attenuation observed at the InSight landing site is consistent with a skin depth of 3.4 km for the expected conductivity of terrestrial seawater. We have not seen any variation of this skin depth with season. These observations are consistent with the many manifestations of the occasional presence of water on or near the surface of Mars and strengthen the case for permanent water in the soil only several kilometers beneath the surface.

How to cite: Yu, Y., Russell, C., Fillingim, M., and Banerdt, W.: Evidence for a Wet Martian Interior from Magnetic Sounding with the InSight Magnetometer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2238, https://doi.org/10.5194/egusphere-egu2020-2238, 2020

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Display material version 1 – uploaded on 04 May 2020
  • CC1: Comment on EGU2020-2238, Gunther Kletetschka, 04 May 2020

    When looking at your data and after the calibration of the electronics, temperature and so on, ..., how do you account for possible inducing magnetic properties of the crustal rock under the InSight?

    • AC1: Reply to CC1, Christopher Russell, 04 May 2020

      We are sensitive only to conductivity. However, the amount of water of the conductivity expected for 

      planetary water is very reasonable and the nature of the signal looks like a very broad conducting  surface and not a small conducting region. We welcome any other constraints other investiations could add.  C T Russell

      • CC2: Reply to AC1, Gunther Kletetschka, 05 May 2020

        Thank you for your comment. Sensitivity to crustal conductivity would be proportional to ionospheric magnetic field change, therefore, the largest effect would be when magnetic field changes. However, sensitivity to induced magnetization would be proportional to the magnetic fields generated by the ionospheric currents Given the remanence magnetization results in ~2000 nT, One can estimate the effect of the induced magnetization. The remanent source has already induced compoent that is stregthening the original magnetic remanence. In general one can assume koenisberger ratio to be close to 10 in Mars condition at InSight location. This would point to 200 nT induced be magnetic remanent source. Magnetic susceptibility of the crustal rock would then give proportion of your magnetometer signature. In your data, where do you see the effect of large magnetic field change followed by change due to crustal conductivity?

        • AC2: Reply to CC2, Christopher Russell, 06 May 2020

          The effect that we see is that the vertical component of the AC field disappears with increasing frequency.

          This implies a certain integrated conductivity. So about 4 km of seawater could provide the induced current to cancel the sounding signal produced in the ionosphere. We know the external AC field as we measure it in the horizontal components. It disappears in the vertical. The simplest explanation is that 

          a spherical conductor was responsible. Other physically reasonable explanations are welcome.