The Astrophysical Journal, 620:1027-1032, 2005 February 20
© 2005. The American Astronomical Society. All rights reserved. Printed in U.S.A.



Sticky Ice Grains Aid Planet Formation: Unusual Properties of Cryogenic Water Ice

H. Wang ,1 R. C. Bell ,2 M. J. Iedema ,3 A. A. Tsekouras ,4 and J. P. Cowin 3
Environmental Molecular Science Laboratory, Pacific Northwest National Lab, Richland, WA 99352

Received 2004 April 9; accepted 2004 October 25


There is limited time for the dust in the nebula around a newborn star to form planetesimals: in a few million years or less the star's stellar winds will disperse most of the unagglomerated dust. It has been difficult to explain the efficiency by which dust grains must have agglomerated to form planetesimals in circumstellar disks. A major obstacle is the fragility of aggregates, leading to collisional fragmentation, which makes it difficult for them to grow to, and beyond, meter-sized bodies. The distinct properties of cryogenic (5–100 K) amorphous water ice, which composes or coats the grains in the cooler parts of the nebulae (≳Jovian distances), may be able to account for the rapid agglomeration. Measurements are presented that show that this ice readily acquires persistent macroscopic electric dipoles, strongly enhancing grain-grain adhesion. In addition, measurements were made showing that vapor-deposited amorphous water ice is also highly mechanically inelastic (≈10% rebound). Together these may explain this efficient net sticking and net growth. Similar properties of higher temperature grains may aid agglomeration in the inner regions of the nebulae.

Subject headings: astrochemistry—dust, extinction—molecular processes

     1 National Center for Nanoscience and Nanotechnology, 21st North Street, Zhongguancun, Beijing 100080, China;
     2 Department of Chemistry, Pennsylvania State University, Altoona, PA 16601-3760;
     3 Pacific Northwest National Lab, K8-88, Box 999 Richland, WA 99352;,
     4 Department of Chemistry, University of Athens, Zografou 15771, Athens, Greece;