Research ArticleGEOPHYSICS

Timing of the martian dynamo: New constraints for a core field 4.5 and 3.7 Ga ago

See allHide authors and affiliations

Science Advances  01 May 2020:
Vol. 6, no. 18, eaba0513
DOI: 10.1126/sciadv.aba0513
  • Fig. 1 Dynamo timing scenarios.

    An early dynamo “[a]” predating Hellas, Isidis, and Argyre (1). The basin age range is shown according to the isochron (cyan) and N(50) (blue) age (47). Early dynamo termination by 4.13 Ga “[b]” is based on magnetic field signatures of a larger basin population (7, 8). The age of magnetization of meteorite ALH84001 [3.9 to 4.1 Ga; (48)] overlaps the early dynamo time frame “[c].” A late dynamo “[d]” postdating the major basins (913). New constraints from MAVEN data (stars) over the BB, around the Utopia basin, and LP that indicate a dynamo at ~4.5 and ~3.7 Ga. The timing of Utopia is uncertain (dotted line). The map displays Mars Observer Laser Altimeter topography (49) with BB, Utopia, and LP marked (stars).

  • Fig. 2 Northern hemisphere observations.

    (A) Magnetic field strength, |B|, from all nighttime MAVEN tracks at altitudes less than 200 km. (B) MOLA topography (49). Polar stereographic projection from 20°S to the North pole, showing the basins Borealis (solid black ellipse), Utopia (U), and Isidis (I) (dashed-dotted circles), and the equator (white-black dashed line). Uncertainties in the magnetic field from measurement error are less than 1 nT (14).

  • Fig. 3 LP observations.

    (A to C) Magnetic field over AP and LP below 200 km altitude. (A) |B| from MAVEN nighttime tracks. (B) |B| and (C) Br along four tracks close to the fresh LP crater. AP and LP are indicated by arrows and dashed black lines, respectively. The magnetic field is shown by the colors along the tracks. The white wiggles show |B| and Br as a function of distance along the track, and the scale bar in (B) denotes the amplitude. (D) Geological map (22) with track for topographic profile shown in (E). (F) A Mars Reconnaissance Orbiter Context Camera (CTX, 6 m/pixel resolution) image of the fresh crater highlighted by the red box in (D) and (E). Unit abbreviations are as follows: eNh, Early Noachian highland; HNt, Hesperian and Noachian transition; eHt, Early Hesperian transition; mNh, Middle Noachian highland; Nve, Noachian volcanic effusive; Hve, Hesperian volcanic effusive.

  • Fig. 4 Magnetization of LP.

    (A and B) The distributions of vertically integrated magnetization spatially associated with the Htu and AHtu units of LP (blue) as well as the HNt (brown) and lAv (yellow) units. The dashed lines represent the median for each distribution (15.7, 31.7, and 47.7 A for lAV, HNt, and LP, respectively). (B) Resulting estimations of the ancient field strength for LP layer thicknesses of 1 and 2 km versus thermoremanent susceptibility, χTRM, after subtraction of the median values of the vertically integrated magnetizations underlying the lAv and HNt from that for LP (dashed and solid lines, respectively). In SI units, χTRM is dimensionless. (C) Compilation of NRM intensity ranges (bottom axis) of terrestrial pyroclastic deposits (see the Supplementary Materials), martian synthetic basalts with mean and median of 1.3 and 7.7 A/m (36), and estimated NRMs derived from 27 martian meteorites (range in red) with a mean and median of 1.7 and 4.4 A/m [table 2 from (30)]. The vertical lines correspond to the lines in (B).

Supplementary Materials

  • Supplementary Materials

    Timing of the martian dynamo: New constraints for a core field 4.5 and 3.7 Ga ago

    A. Mittelholz, C. L. Johnson, J. M. Feinberg, B. Langlais, R. J. Phillips

    Download Supplement

    This PDF file includes:

    • Comparison of the LP magnetization with terrestrial and synthetic martian basalts.
    • Table S1
    • Figs. S1 to S7
    • References

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article