NASA Astrobiology Institute (NAI)

1. Formation of Planetesimals in a Dynamically Evolving Nebula

   Project Investigators: Nader Haghighipour

   Astrobiology Roadmap Objectives:

   • Objective 1.1: Models of formation and evolution of habitable planets

   Project Progress

   Work on the dynamics of dust grains in the neighborhood of density-enhanced structures in a planet-forming nebula has been continuing. In particular, a new project on the dynamics and coagulations of dust particles in a dynamically evolving nebula has been launched. In such and environment, the physical properties of the nebula, such as its temperature and pressure, constantly vary. This work has shown that such variations will manifest themselves as gas density-enhanced regions and affect the dynamics of small grain in their neighborhood. The presence of pressure gradients on both sides of these structures causes solid objects to undergo inward and outward migrations, and accumulate at the location of maximum gas density. The analysis has been expanded to include the interactions between small dust grains and the background material of the nebula. The results of recent analyses, which will appear in the Monthly Notices of the Royal Astronomical Society, indicate that, in the vicinity of such structures, dust grains grow to a few centimeters by sweeping up smaller objects, and will rapidly accumulate around the location of maximum gas density on the midplane. Recent simulations are allowing for turbulence. It is expected that, once cm-sized particles are accumulated on both sides of the midplane, because of the velocity differences between solids and gas molecules, turbulence will occur and these particles will be removed from the midplane to higher elevations. On the other hand, turbulence will cause particle to collide with one another faster and increases the rates of their coagulation. The results of this project have direct application to the long-lasting issue of planetesimal formation in a solar nebula.

   
   Figure 1. Growth of a 10-micron-sized particle at 2AU (top) and 0.25 AU (bottom) in a nebula with a gas-density maximum at 1 AU. The temperature of the gas is 300 K.

Publications

Haghighipour, N.  (2004).  Dynamical Evolution of a Circumbinary Disk and its Effect on the Growth and Sedimentation of Dust Particles [Abstract].  Second TPF/Darwin International Conference:128.  San Diego, CA.

Haghighipour, N.  (2004).  On the Dynamical Evolution of a Nebula and its Effect on Dust Coagulation and the Formation of Centimeter-sized Objects [Abstract].  Workshop on Chondrites and Protoplanetary Disks.  Lihue, HI.

Haghighipour, N.  (2004).  On the Growth of Dust Particles in a Non Uniform Solar Nebula.  In: S.S. Holt & D. Deming (Eds.).  The Search For Other Worlds. Fourteenth Astrophysics Conference. AIP Conference Proceedings (pp. 119-122).  Melville, NY: American Institute of Physics.

Haghighipour, N.  (In Press, 2005).  Growth and Sedimentation of Dust Particles in the Vicinity of Local Pressure Enhancements in a Solar Nebula.  Monthly Notices of the Royal Astronomical Society.