Mars’ magnetic field has been measured at large scale by orbiting spacecraft and at very small scale via Martian meteorites. Here we report on a ground magnetic survey on metre to kilometre scales. The Zhurong rover made vector measurements at 16 sites along a 1,089 m track in the Utopia Basin on Mars. It recorded an extremely weak magnetic field, with an order of the average intensity less than that inferred from orbit, in contrast to the large magnetic field in Elysium Planitia measured by InSight. A spacecraft measurement samples an area with radius comparable to its altitude, while a ground measurement samples an area with radius comparable to the depth of the magnetized body. The weak magnetic field measured by Zhurong indicates no magnetization anomalies for a depth of many kilometres around and below the rover’s traverse. We suggest two possible explanations for the weak magnetic field: the entire Utopia Basin may have remained unmagnetized since its formation about 4 billion years ago or that the 5-km-radius ghost crater where Zhurong landed may have been been demagnetized by impact.

Dipolarization front (DF)—a sharp boundary separating hot tenuous plasmas from cold dense plasmas—is followed by a strong B_z region, which is termed flux pileup region (FPR) or dipolarizing flux bundle (DFB). Using 9‐year (2001–2009) Cluster data, we show that the FPR hosts whistler waves because of the pancake distribution of electrons, whereas the DF boundary hosts lower hybrid drift waves due to the strong density and magnetic gradients statistically. Different from statistical results, we report an unexpected case: whistler waves are generated at the DF boundary rather than inside the FPR. Using Cluster data, we observed strong whistler waves at DF boundaries but no whistlers inside FPRs, although flux tubes inside the FPRs are significantly compressed and suprathermal electrons there are perpendicularly anisotropic. We calculate wave growth rates and successfully explain the generation/damping of these whistlers. We find that 1–4 keV electrons are responsible for generation/damping of these whistlers.

Geomagnetic vector field is always measured by a strapdown triaxial magnetometer on a vehicle. The magnetometer measurements are polluted by the magnetometer inherent errors, misalignment error, and vehicle-generated magnetic inferences. With the aid of absolute attitude information from the gyro, the calibration accuracy has been proved to be greatly improved, especially for vector measurements. However, the performance of calibration methods is greatly affected by the gyro bias, which causes error accumulated over time in the absolute attitude information. In this work, we propose an improved calibration method robust to gyro bias based on relative attitude information from the gyro. Simulation results indicated that the proposed method can estimate the calibration parameters more accurately and stably than the traditional method when the gyro bias exists. The influence on the calibration accuracy of the different parts of the gyro bias is also analyzed by simulation. Experiment using a low-cost gyro proved that the proposed method can effectively improve the estimation accuracy of the calibration parameters, as the influence on the traditional method of the gyro bias is 2-3 orders of magnitude higher than that on the proposed method.

Magnetic reconnection between neighboring magnetic field loops, the so-called interloop reconnection, is a common process to drive flares in the solar atmosphere. However, there is no direct evidence that a similar but less explosive process can take place on planets. The strong crustal fields on Mars generate plenty of magnetic loops in the near-Mars regions, providing a unique environment to research the interloop reconnection on a planet. Here, we report magnetic reconnection events between crustal field loops in the Martian ionosphere observed by Mars Atmosphere and Volatile EvolutioN (MAVEN) for the first time. During the current layer crossing, MAVEN recorded the characteristic signals of collisionless magnetic reconnection, including the Hall magnetic field, Alfvénic outflow, and electron energization. This finding implies that the interloop reconnection in the Martian ionosphere could contribute to the localized energy deposition and particle energization, which provides the seed source for aurora in the Martian atmosphere.

• In-flight calibration of the fluxgate magnetometer (FGM) was performed using scalar magnetic field data from the CDSM onboard Macau Science Satellite-1. • Euler angles were estimated through two approaches for a low-inclination satellite: using the CHAOS-7 geomagnetic field model and simultaneous estimation together with spherical harmonic coefficients. • Calibrated FGM data are found suitable for advancing geomagnetic field scientific research.