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 B_X, B_Y, B_Z in the spacecraft frame, with the 2 Hz data shown in color (red = B_X, green = B_Y, blue = B_Z) 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.