Comparison Between Equatorial Ionospheric and Surface Level Magnetic Fields at Mars Matthew Fillingim¹ ([email protected]), Catherine Johnson²⸴³, Anna Mittelholz⁴, Benoit Langlais⁵, Steve Joy⁶, Peter Chi⁶, Robert Lillis¹, Jared Espley⁷, Heidi Haviland⁸, Sue Smrekar⁹, Bruce Banerdt⁹, & Bruce Jakosky¹⁰ ¹UC Berkeley, ²U British Columbia, ³Planetary Science Institute, ⁴ETH Zürich, ⁵U Nantes, ⁶UCLA, ⁷NASA GSFC, ⁸NASA MSFC, ⁹JPL/Caltech, ¹⁰CU Boulder InSight/IFG MAVEN Overflights Altitude Dependence Local Time Dependence The Interior Exploration using Seismic Since September 2014, the Mars We compare the residual IFG magnetic field There is evidence of local time dependence in Investigations, Geodesy, and Heat Transport Atmosphere and Volatile Evolution (static field subtracted) to the residual the magnitude of the residual magnetic fields (InSight) mission landed on Elysium Planitia (MAVEN) mission has been measuring the MAVEN field (model* field subtracted): (4.5 N, 135.6 E) in November 2018 carrying upper atmosphere and plasma environment  compare surface ΔB to ionospheric ΔB. the InSight FluxGate magnetometer (IFG), the around Mars. (*crustal field model of Langlais et al., 2019) first magnetometer on the surface of Mars. Due to orbital precession, MAVEN periapsis IFG is sensitive to equatorial* ionospheric (~ 150 km) passes over the latitude of currents which change over the course of a InSight every 5 to 6 months. Magnitude of the ionospheric (left) and day and over the course of weeks During overflights MAVEN measures the surface (middle) residual fields as a function (see Johnson et al., Nat. Geosci. [2020] and ionospheric magnetic field (very nearly) of local time color coded by magnitude; Mittelholz, this conference). Color-coded by MAVEN altitude: directly overhead InSight while InSight altitude of the ionospheric observations as brown shades < 200 km (in the ionospheric (Granted, “equatorial” doesn't have quite the simultaneously measures the function of local time (right) colored coded by surface level dynamo region; blue shades > 200 km same connotation at Mars due to the lack of magnitude of the residual ionospheric field. magnetic field. (above the dynamo); white ~ 200 km. a global dipole field. However, the magnetic Comparing ionospheric and surface level Largest residual fields at MAVEN (left) and field is predominantly horizontal [at least in If ΔB due to ionospheric currents, then ΔB at magnetic fields gives us information about InSight (middle) occur near local noon. the unmagnetized northern hemisphere on the surface should be 180o in azimuth away the ionospheric currents flowing between [But not at the same time; the “red” interval the dayside] such as near the magnetic from ΔB above the ionosphere (blues); the measurement points. in the left and middle panels is not the same] equator at magnetized planets.) expect points to fall along dashed lines in We analyze 36 overflights over 4 seasons the middle panel. The right panel shows that the strongest when MAVEN was below 300 km and within residual ionospheric fields occur in the But no clear correlations are seen between o (~ 300 km) of InSight and data are daytime (LT < 18) at altitudes below 200 km. +/- 5 the residual surface field and residual available from both spacecraft: ionospheric field magnitude, azimuth angle, This is in agreement with expectations; https://bit.ly/3pb5KGN. or dip angle. May indicate that currents are strongest ionospheric currents (hence ΔB) weak, small scale, and/or time varying. should occur on the dayside (where *Granted, “equatorial” doesn't have quite the same connotation at Mars due to the lack of a global dipole field. However, the magnetic ionospheric densities are largest) in the field is predominantly horizontal (at least on the dayside) such as near the magnetic equator at magnetized planets. dynamo region (where currents are driven).