The importance of nucleus rotation in determining the largest grains ejected from comets

 

A. Molina^1,2

 

¹ Departamento de Física Aplicada, Universidad de Granada, Facultad de Ciencias, Avenida Severo Ochoa s/n, 18071, Granada, Spain.

² Instituto de Astrofísica de Andalucía, CSIC, Camino Bajo de Huétor 50, 18008, Granada, Spain (amolina@iaa.es).

 

Received 2010 February 18
Accepted 2010 June 16

 

RESUMEN

Se determina el valor máximo del diámetro de las partículas eyectadas de los núcleos cometarios haciendo uso del modelo clásico de expansión radial de los gases de los cometas. Se destaca la importancia de las fuerzas inerciales, principalmente de las debidas a la rotación del cometa. Se muestra una sencilla expresión indicando el valor mínimo que debe tener el periodo de rotación del cometa para que la partícula pueda levantarse de la superficie. Los resultados obtenidos son comparados con los valores determinados a partir de medidas de radar. También se analiza el cometa Churyumov–Gerasimenko, que alcanzará la misión ROSETTA en 2014, proponiendo valores para los diámetros de las mayores partículas que pueden desprenderse del cometa.

 

ABSTRACT

The maximum diameter of large boulders ejected from the cometary nuclei is investigated using the classical model of dust grain as dragged out by radially expanding cometary gases. The importance of the inertial forces, and particularly those due to the rotation of the comet is shown. Although a larger dust grain can be lifted from the nucleus surface if the rotation is faster, the rotation period has to be larger than a certain value. A simple expression for this critical value of rotation period is given. Our results are applied to different comets and a comparison with the maximum radius values obtained by radar measurements is made. Finally, comet Churyumov–Gerasimenko, the target of the ROSETTA mission to arrive on 2014, is going to be analyzed and a range for the maximum diameter of the dust grains that can be lifted is proposed.

Key Words: comets: general — comets: individual (Halley, Wirtanen, Hyakutake, C/2001 A2 LINEAR, IRAS–Araki–Alcock, Churyumov–Gerasimenko) — interplanetary medium — meteoroids.

 

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ACKNOWLEDGMENTS

The author acknowledges the helpful comments of an anonymous referee which resulted in an improved version of this paper. This work was supported by contracts AY2007–6370, ESP2006–02934, and AYA2009–08190.

 

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