Smithsonian Astrophysical Observatory

COLLISIONAL CASCADES IN PLANETARY DEBRIS DISKS

I. STELLAR FLYBYS

Scott Kenyon (SAO) & Benjamin Bromley

 

 

The montage below shows model images for the time evolution of a protoplanetary disk after the close passage of a star. The calculation begins at t = 0 with 10 Earth masses of solid material in orbit around a 3 solar mass star. The 64 annuli in the model grid initially have small planetesimals with radii of 10 cm to 10 m. The planetesimals have large orbital eccentricities (e = 0.01) relative to a circular orbit around the central star. The disk extends from 30 AU at its inner edge to 150 AU at its outer edge. The position of the star is shown as a bright point at the center of the disk.

 

Credit for all images: S Kenyon (SAO) and B Bromley (Univ of Utah). The calculations were performed on `Alhena,' an SGI Origin-2000 supercomputer at the Jet Propulsion Laboratory.

 

At the start of the calculation, high velocity collisions between small planetesimals produce microscopic dust grains which absorb and re-radiate light from the central star. These dust grains produce the bright ring at the inner edge of the disk.

As the calculation proceeds, collisions damp particle velocities. Lower velocity collisions produce less dust. The brightness of the disk thus fades with time. The disk dims a hundredfold over 50 million years (50 Myr).

As the brightness of the disk fades, the planetesimals collide and merge to form larger and larger objects. After only 1 Myr, the largest objects are 40 m across; the objects grow to 100 m after 10 Myr, and are almost 20 km across at 50 Myr.

As these objects continue to grow, they eventually reach sizes of 1000 km (the size of Pluto) or larger.

 

Click here to see an animation of the calculation.
Click here to see a more complete description of the calculation.
Click here to read a paper describing the calculation.
 

 

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