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Erika Nesvold: Beta Pictoris is a star about 60 light years from the Earth.
And it's surrounded by this huge disk of chunks of rock and ice
that we call a debris disk. Marc Kuchner: Inside that disk is
a central clearing in the larger planetesimals and inside that central
clearing is a planet more massive than any in our solar system.
Erika Nesvold: We see the Beta Pictoris debris disk edge-on, so we just see the
thin strip of it from the edge. But there's an interesting feature that
we can see just from that edge-on view. Marc Kuchner: When we view Beta Pictoris at
longer wavelengths, people claim that there is a "warp" in the center of the
disk. At shorter wavelengths, it looks more like an "X."
And we haven't really understood until now, how those patterns were related.
But Erika Nesvold and I created a new kind of 
model, which shows us the connection between those patterns. Erika Nesvold: Our model is called
SMACK, which stands for the Super-particle Method Algorithm for 
Collisions in Kuiper Belts. We're creating a virtual solar system
inside the computer, and by tweaking the parameters of the
system, we can control what this virtual debris disk looks like.
Then we can compare our results to the actual images of the debris
disk we see and understand how the planet could be creating these
different shapes in the disk. Marc Kuchner: The model painted one picture of Beta
Pictoris that showed us the origin of the "X" pattern, the origin
of the warp, and also a bunch of other details about the system.
Erika Nesvold: Our simulation is the first model that can capture
the 3D structure of the disk, as well as the collisions that are
occurring between the planetesimals in the disk. And our simulation is the 
first model that can explain these multiple different features that we 
observe when we look at the Beta Pictoris Disk. So if we look at our simulation
results edge-on--the same way that we see the real Beta Pictoris disk--
then we see this warp structure that's created because the planet is
orbiting tilted with respect to the disk. If we look at our
simulation results face-on--which is a way we can't see the real disk--
then this face-on simulation shows this spiral
density structure of the planetesimals. And this spiral is created
because the planet is on an eccentric orbit. It's not a perfect circle, it's an ellipse.
When the spiral created by the eccentricity of the planet
intersects with that vertical wave from the inclination of the 
planet, the collisions are enhanced in some places and 
damped out in others, which creates this clumpy collision structure.
Marc Kuchner: If you look at our model in cross-section, you can see the crests and
troughs of the wave where the collisions are enhanced. Like and ocean
wave, in front of the wave it's calm, but then the crest comes
along and lifts the planetesimals out of the plane. And then there's a trough
and then the wave starts wrapping around tighter and tighter
and then it's almost like foam on the backside of the wave. The planetesimals get all
stirred up and start colliding with one another and breaking into dust.
We've learned so much about Beta Pictoris over the years
but all the little pieces of evidence didn't seem to fit together before.
This model has tied together in a nice, neat
package, the story of Beta Pictoris and its planet.
Erika Nesvold: In the future, we'll be able to use our SMACK models to 
study other debris disk systems and use our observations of
those disks to predict the presence exoplanets that we
otherwise wouldn't be able to detect.
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