Computational Astrophysics

In the field of computational astrophysics, I am most interested in the classical N-body gravitational problem, with an emphasis on collisional physics. Applications range from planet formation to granular dynamics. I mostly use the computer code pkdgrav for my simulations, which one day soon we hope to make public!

Planetary Science

I started my career in astronomy being involved with the search for extrasolar planets, but gradually turned to planet formation and other planetary science fields where I could apply my interest in computational astrophysics. My present focus is on the dynamics and evolution of small solar system bodies, especially asteroids.


Pkdgrav is a parallel N-body tree code originally designed for cosmology simulations at the N-body Shop, part of the Department of Astronomy at the University of Washington. I added collisional physics to the code so it could be applied to problems in planetary science. This includes adding a large set of initial condition, analysis, and visualization tools. The most recent development, starting with my former graduate student Steve Schwartz's graduate work, was to add a soft-sphere discrete element method to the code for more realistic treatment of particle contact physics suitable for high-resolution granular dynamics simulations. Until a public release is available, interested potential collaborators are welcome to contact me.


Recently I've been lucky enough to get involved in some exciting space missions. Currently I am a Co-Investigator and Lead of the Dynamics Working Group for the DART mission to test kinetic impactor technology on the satellite of the Didymos binary asteroid system. I am also a Collaborator on the OSIRIS-REx sample-return mission to asteroid Bennu and the New Horizons mission to Pluto and beyond.

My Papers

You can browse my publications here. My full CV with a comprehensive list of publications is here (PDF).

The following are probably my most influential papers so far as lead or co-author, in time order:

  1. Lin, D.N.C., Bodenheimer, P., Richardson, D.C. 1996. Orbital migration of the planetary companion of 51 Pegasi to its present location. Nature 380, 606-607—Appearing shortly after the discovery of the first extrasolar planet orbiting a normal star, this paper continues to be cited for our proposed explanations for why the planet is so close to its host star.
  2. Richardson, D.C., Bottke Jr., W.F., Love, S.G. 1998. Tidal distortion and disruption of Earth-crossing asteroids. Icarus 134, 47-76—This paper laid much of the groundwork for the idea that asteroids are fragile gravitational aggregates that can be disrupted by relatively weak forces.
  3. Richardson, D.C., Quinn, T., Stadel, J., Lake, G. 2000. Direct large-scale N-body simulations of planetesimal dynamics. Icarus 143, 45-59—The paper that first introduced pkdgrav as a tool for studying planetesimal dynamics.
  4. Michel, P., Benz, W., Tanga, P., Richardson, D.C. 2001. Collisions and gravitational reaccumulation: Forming asteroid families and satellites. Science 294, 1696-1700—The first in a series of papers (including one in Nature) that demonstrates asteroids form families by gravitational reaccumulation of debris following catastrophic impacts.
  5. Leinhardt, Z.M., Richardson, D.C. 2005. Planetesimals to protoplanets. I. Effect of fragmentation on terrestrial planet formation. Astrophys. J. 625, 427-440—The first implementation of a self-consistent model of planetesimal fragmentation in a planet-formation code, based on earlier simulations of collisions between planetesimals represented as gravitational aggregates [see here], and followed later by studies of the effect of dynamical friction from the debris.
  6. Walsh, K.J., Richardson, D.C., Michel, P. 2008. Rotational breakup as the origin of small binary asteroids. Nature 454, 188-191—This explanation for the formation of small binary asteroids generated a lot of media attention. It was also ranked as one of the top 10 astronomy stories of 2008 by Astronomy magazine!

Other Stuff

Former Ph.D. Students

(For Alice and Carrie, I was Academic Advisor.)

  • Dr. Zoë M. Leinhardt, "Planetesimal Evolution and the Formation of Terrestrial Planets" (2005)
  • Dr. Kevin J. Walsh, "Forming Binary Near-Earth Asteroids from Tidal Disruptions" (2006)
  • Dr. Randall P. Perrine, "N-body Simulations with Cohesion in Dense Planetary Rings" (2011)
  • Dr. Stephen R. Schwartz, "The Development and Implementation of Numerical Tools for Investigation into the Granular Dynamics of Solid Solar System Bodies" (2013)
  • Dr. Ronald-Louis G. Ballouz, "Numerical Simulations of Granular Physics in the Solar System" (2017)
  • Dr. Alice R. Olmstead, "An Assessment of Professional Development for Astronomy and Physics Faculty: Expanding Our Vision of How to Support Faculty‚Äôs Learning About Teaching" (2016)
  • Dr. Harrison Agrusa, "On the Dynamics of Binary Asteroids Applied to DART Mission Target (65803) Didymos" (2022)
  • Dr. Carrie Holt, "A Song of Fire & Ice: Evolutionary Properties of Hot & Cold Small Bodies" (2023)

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