Letter to the Editor

Thermal desorption of Na in meteoroids

Dependence on perihelion distance of meteor showers

¹ National Astronomical Observatory of the Japan (NAOJ), National Institute of Natural Science, 2–21–1 Osawa, Mitaka, Tokyo 181–8588, Japan e-mail: kasugats@cc.nao.ac.jp
² Institute of Low Temperature Science, Hokkaido University, Kita-19, Nishi-8, Kita-ku, Sapporo, Hokkaido 060–0819, Japan

Received: 31 March 2006
Accepted: 25 April 2006

Abstract

Context.The observed sodium abundance of meteoroids in meteor showers might differ from the original abundance because of processing in interplanetary space after ejections from their parent bodies. Among various processes, thermal alteration of alkali silicate is most likely the major process of Na depletion.

Aims.We clarify at which perihelion distances the thermal desorption alters the Na content of meteoroids that are observed as meteor showers.

Methods.We compile Na abundances of meteoroids in meteor showers at each perihelion distance and compare them to the sublimation temperatures of alkali silicates.

Results.Na abundances of meteoroids do not depend on their perihelion distances at  AU. No Na depletion in these distances constrains the temperature of meteoroids at  AU to be lower than the sublimation temperature of alkali silicates  K.

Conclusions.Meteoroid particles are characterized as large, compact, blackbody- like particles. On orbit with perihelion distances  AU, meteoroids would show evidence of thermal desorption of metals, in particular, Na.