The velocity distribution of periodic comets and the meteor shower on Mars

Abstract

Abstract. ThecollisionvelocitieswithMarsof theknown periodic cometswithperiheliondistances lessthantheorbital radiusof Mars 1.52 au are calculated and statisticallyanalyzed. The velocity distribution shows that short-period comets usually havesmaller collision velocities than the long-period comets whether they are numbered or unnumbered. For comets with period P ≤270 y, most collision velocities with Mars are less than 30 km s −1 . These velocities are smaller than the correspondingcollisionvelocities withEarth.Basedonthesimilarityofthevelocitydistributionsof thecomets andmeteoroidstreams, meteorshowers on Mars are discussed briefly. Key words. celestial mechanics – comets: general – meteors, meteoroids 1. Introduction It is well known that comets, as they near the perihelion oftheir orbits, release large numbers of dust grains (Kirkwood1861) due to the normal process of gas ejection. These parti-cles, namely meteoroids, leave the cometary nucleus at speedswhich are significantly less than the orbital velocity of thecomet(Whipple1951).Inconsequence,thesemeteoroidsmoveon almost the same orbitsas the parentcomets,graduallydrift-ingaheadandbehindthecometbecauseof smalldifferencesinorbital period. After a time interval of a few tens of cometaryperiods, the meteoroids will have spread all the way aroundthe cometary orbit (Steel 1994; Williams 1996). At this stage,meteors(whichareproducedbytheimpactofthestreammete-oroidswiththeatmosphereoftheEarth)canbeobservedwhen-ever the Earthpasses throughthe cometarynodes.In principle,there could also be meteor showers on Mars or any other plan-ets with an atmosphere whenever the planet encounters a me-teoroid streams.MeteoroidsstriketheEarthwitha velocitythatis similar tothe orbital velocity, that is, several tens of kilometers per sec-ond. At such velocities, dust impacts can affect all phases ofspacecraft operation (Beech et al. 1995, 1997; McBride 1997;McBride & McDonnell 1999). For example, the