Origins of perturbations in dayside equatorial ground magnetograms

To determine the cause(s) of perturbations seen in dayside equatorial ground magnetograms, we conducted a systematic survey of simultaneous ground-based and geosynchronous satellite-based observations during the 90-day period from December 1, 2020 to February 28, 2021. We examined Huancayo ground magnetometer observations from 14:00:00 to 20:00:00 UT each day, during which Huancayo passed through local noon. From those data we chose perturbation events selected on the basis of large (>20 nT) event amplitude and classified the selected events as responding primarily to solar wind pressure, or to variations in the north/south component of the interplanetary magnetic field (IMF Bz), or perhaps in part to both. The results show that an equivalent number of events were identified for each model during this 90-day period. Variations in the lagged solar wind dynamic pressure routinely correspond to nearly simultaneous sudden impulses recorded at both geosynchronous orbit and on the ground. Variations in IMF Bz produce erosion signatures at geosynchronous orbit and can correspond to ground events if lag times for reconnection to enhance convection in the magnetosphere are taken into account

Successful Kinetic Impact into an Asteroid for Planetary Defense.

While no known asteroid poses a threat to Earth for at least the next century, the catalog of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation1,2. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid1-3. A test of kinetic impact technology was identified as the highest priority space mission related to asteroid mitigation1. NASA's Double Asteroid Redirection Test (DART) mission is the first full-scale test of kinetic impact technology. The mission's target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by DART's impact4. While past missions have utilized impactors to investigate the properties of small bodies5,6, those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft's autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in Dimorphos's orbit7 demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary