资源环境科技发展态势分析平台

The identification of magnetically quiet or noisy observations is important for data selection in a wide range of studies, including crustal field modeling and investigations of the ionosphere. However this remains a challenge when studying the magnetic field of Mars, as no continuous magnetic activity index is available. Such indices are widely used for studies of Earth's magnetic field, and they are largely based on data from ground observatories. We suggest a martian magnetic activity proxy based on satellite data, from the Mars Atmosphere and Volatile EvolutioN spacecraft (MAVEN). MAVEN has been in orbit since November 2014, providing measurements of the magnetic field that extend those from the Mars Global Surveyor mission. The proxy uses the magnitude of the interplanetary magnetic field upstream of the bow shock and is motivated by the correlation of the interplanetary magnetic field amplitude with the nightside magnetic field at 150- to 600-km altitude, measured on the same MAVEN orbit. We demonstrate the utility of the proxy, by producing a model of the surface crustal field in a previously mapped low-amplitude region in the vicinity of the InSight landing site. The proposed proxy successfully separates quiet and noisy data and will facilitate MAVEN data selection for higher-resolution crustal field models. Other applications include data selection for magnetic sounding studies using the InSight magnetometer, or studies of the ionosphere. The deployment of a ground-based magnetometer by InSight will also allow the refinement of the proxy, using simultaneous satellite and surface magnetic field measurements.

Plain Language Summary The ability to distinguish between magnetically quiet and noisy data measured at or above the surface of a planet is important for a wide range of studies. For example, high fidelity models of the crustal magnetic field require data that contain minimal signals from other sourcesi.e., that are quiet. At Earth, such data selection uses estimates of magnetic activity (so-called activity indices or proxies) derived from ground-based magnetic observatories. We propose a proxy for magnetic field activity at Mars, where no ground-based measurements are yet available, that uses magnetic data from the MAVEN spacecraft. The proxy is based on the correlation of the magnetic field measured in the solar wind and that measured closer to the planet, out of the solar wind, on the nightside. We show an application of the proxy by developing an updated crustal field model in the vicinity of the InSight landing site. The InSight mission will provide the first surface magnetic field measurements at Mars, and the opportunity to refine the proposed proxy.