Detection of Dust around Mars and its Implications

Abstract

Recent observations of MAVEN find dust to be present at altitudes from ~150 to 1000 km from the Mars surface. It is expected that it could be interplanetary in nature, based on assumption of particle velocity. Existence of dust at orbital altitudes on Mars could be mainly due to two plausible sources, viz. interplanetary dust and Phobos/Deimos-originated dust. Dust devils prevailing near the surface can lift the dust to a few tens of kilometres and at present, no physical process can explain dust transport to high altitudes (>50 km) from the dust devils. Another possible source of dust around Mars could be interstellar in nature; however, its possibility is rare. Dust originating from Phobos/Deimos could be either due to secondary ejecta created by continuous bombardment of micrometeorites or due to grain levitation. Though dust levitation on the Moon is yet to be confirmed by in-situ measurements, it is expected that it should occur on the airless bodies. The velocity of secondary ejecta and that of levitated dust can exceed the escape velocity of Phobos/Deimos and cause the dust to escape into outer space. Such escaping particles can form dust ring/torus around Phobos/Deimos and therefore also around Mars. The dust ring/torus is yet to be studied and fully understood. Observations of dust, whether originating from Phobos/Demos or interplanetary dust particles, are necessary for finding its origin, abundance and distribution around Mars. This article discusses the existence of high-altitude (>100 km) dust around Mars, and techniques for the detection of these dust particles using an impact ionization detector in a future Mars orbiter mission.