Collisional Growth of Dust

It is widely believed that in protoplanetary disks, dust consisting of submicron-sized particles accumulates to form planets through repeated collisions and coalescences. This collisional growth process is, however, still unclear. It is one of the big remaining problems in the planetary formation theory. Here we introduce a movie of dust collisions based on numerical simulations.

In the early stages, small dust particles with a radius of about 0.1 micron circulate around the Sun (central star) together with gas in a protoplanetary disks. These dust particles grow through repeated collisions. One particle collides with and sticks to another particle, making a larger dust particle. Then, such newly formed dust collides with and sticks to other dust, over and over.
The dust grows into structures consisting of many particles, called “aggregates.”
As a result of this multiplicative growth process, dust aggregates are very fluffy. If they continued to grow like this without any change, the bulk density could be as low as 10-4 g/cm3, lighter than the air!
In the early growth stage, dust aggregates grow through collisions without any restructuring. They start to be compressed during the collisions when their collision energy (or velocity) becomes large. Even though they develop a more compact structure, they are still fluffy.
When they collide at higher velocities (> 10 m/s), the dust aggregates are disrupted, scattering fragments. In this case, we simulate collisions of dust aggregates having a realistic size distribution for their constituent particles, ranging from 0.025 to 0.4 micron.
Dust aggregates are catastrophically disrupted in collisions at higher velocities (> 100 m/s). It looks as if they were blown to smithereens, but the largest remaining fragment is larger than the original pre-collision dust aggregates, indicating that collisional growth is continuing.
Oblique collisions are the norm for dust aggregates. It is thought that by repeating collisional growth, with occasional disruptive collisions as well, dust aggregates can grow up to become km-sized seeds of planets, so-called planetesimals. These planetsimals are then expected to ultimately grow in planets. This is a potent theory for dust growth, but so far it is limited to icy dust aggregates. In the present understanding, rocky dust aggregates could not survive high velocity collisions.

Details of Numerical Simulation

PurposeTo reveal the collisional growth (or disruption) process of dust.
Calculation MethodParticle calculation method with up to several tens-of-thousands of particles, considering realistic mechanical interactions between particles.
Computergeneral-purpose calculating machines
Time Scale< ~1 µsec
Spatial Scale< ~100 µm
ReserchersKoji Wada (Chiba Institute of Technology), Toru Suyama (Nagano City Museum), Hidekazu Tanaka (Tohoku University)
References Wada, K., Tanaka, H., Okuzumi, S., Kobayashi, H., Suyama, T., Kimura, H., and Yamamoto, T., 2013, Growth efficiency of dust aggregates through collisions with high mass ratios, Astron. Astrophys., 559, A62 (pp.8).
Suyama, T., Wada, K., Tanaka, H., and Okuzumi, S., 2012, Geometrical cross sections of dust aggregates and a compression model for aggregate collisions. Astrophys. J. 753, 115 (10pp).
Wada, K., Tanaka, H., Suyama, T., Kimura, H., and Yamamoto, T., 2009, Collisional Growth Conditions for Dust Aggregates. Astrophys. J., 702, 1490-1501.
Wada, K., Tanaka, H., Suyama, T., Kimura, H., and Yamamoto, T., 2008, Numerical Simulation of Dust Aggregate Collisions. II. Compression and Disruption of Three-Dimensional Aggregates in Head-on Collisions. Astrophys. J., 667, 1296-1308.

Details of Visualization

This simulation video was made using particles smaller than the wavelength of visible light. Therefore, the “color” of the particles is a meaningless concept, but for this simulation they have been colored to look like ice. In the scenes in the second half where dust scatters, in order to achieve a stereoscopic feel, I created images where you seem to float in the particles. Because this video was created with stereoscopic images in all directions, it can also be viewed on a head mounted display (HMD).

YouTube for VR

Web Browsers: You can aim the movie point-of-view in any direction you prefer by dragging the mouse over the YouTube screen.
Smartphones and Tablets: Using the YouTube App (iOS, Android), all directions can be seen by facing your device in the chosen direction. With VR viewers like Google Cardboard, you can enjoy the full effect of stereoscopic vision in all directions.
※Please note that there are some cases in which this video cannot be watched depending on your environment.


  • Simulation: Koji Wada, Toru Suyama, Hidekazu Tanaka
  • Visualization: Satoki Hasegawa
  • Four-Dimensional Digital Universe Project, NAOJ

360p (.mov, zip file : 231.3 MB) (.wmv, zip file : 121.2 MB)

720p (.mov, zip file : 507.5 MB) (.wmv, zip file : 179.7 MB)

1080p (.mov, zip file : 812.9 MB) (.wmv, zip file : 178.5 MB)

Side-by-Side Stereovision, 1080p (.mov, zip file : 1.13 GB) (.wmv, zip file : 179.2 MB)

Panoramic Video for VR (Stereovision with Side-by-Side, .mp4, zip file : 459.1 MB) (Stereovision with Top-and-Bottom,.mp4, zip file : 642.2 MB) (Non-Stereo, .wmv, zip file : 321.3 MB)

Other file formats

  • 1080p Stereovision (files for right and left eyes, .wmv, .mov)
  • 4096x4096 Stereo/Non-Stereo Dome Master (.mp4, .png sequence files)
If you want to use these file formats, please contact us.


  • 2018.12 Version 1.0 was released.