A hot flow anomaly at Mars

摘要: One of the most important modes planet/solar wind interaction are “foreshock transients” such as hot flow anomalies (HFAs). Here we present early observations by NASA Mars Atmosphere and Volatile EvolutioN spacecraft, confirming their presence at for first time an unmagnetized planet revealing underlying ion perturbations that drive phenomenon, finding them to be weaker than magnetized planets. Analysis revealed HFA virtually microscopic: smallest on record ∼2200 km across commensurate with local proton gyroradius, resulting in a much stronger perturbation solar protons alpha particles. As Venus, despite being physically diminutive, is still large (0.66 RM) when compared relative size induced magnetosphere. Given associated order magnitude decrease dynamic pressure (411 pPa  ⇒ 70 pPa), find HFAs have potential directly impact topside ionosphere. We thus hypothesize loss planetary magnetic dynamo left far more vulnerable pulses from related foreshock transients.