New supercomputer simulations tracking the interactions of thousands of
dust grains show what the solar system might look like to alien
astronomers searching for planets...
New supercomputer simulations tracking the interactions of thousands of
dust grains show what the solar system might look like to alien
astronomers searching for planets. The models also provide a glimpse of
how this view might have changed as our planetary system matured.
"The planets may be too dim to detect directly, but aliens studying the
solar system could easily determine the presence of Neptune -- its
gravity carves a little gap in the dust," said Marc Kuchner, an
astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md.
who led the study. "We're hoping our models will help us spot
Neptune-sized worlds around other stars."
The dust originates in the Kuiper Belt, a cold-storage zone beyond
Neptune where millions of icy bodies -- including Pluto -- orbit the
sun. Scientists believe the region is an older, leaner version of the
debris disks they've seen around stars like Vega and Fomalhaut.
"Our new simulations also allow us to see how dust from the Kuiper Belt
might have looked when the solar system was much younger," said
Christopher Stark, who worked with Kuchner at NASA Goddard and is now
at the Carnegie Institution for Science in Washington, D.C. "In effect,
we can go back in time and see how the distant view of the solar system
may have changed."
Kuiper Belt objects occasionally crash into each other, and this
relentless bump-and-grind produces a flurry of icy grains. But tracking
how this dust travels through the solar system isn't easy because small
particles are subject to a variety of forces in addition to the
gravitational pull of the sun and planets.
The grains are affected by the solar wind, which works to bring dust
closer to the sun, and sunlight, which can either pull dust inward or
push it outward. Exactly what happens depends on the size of the grain.
The particles also run into each other, and these collisions can
destroy the fragile grains. A paper on the new models, which are the
first to include collisions among grains, appeared in the Sept. 7
edition of The Astronomical Journal.
"People felt that the collision calculation couldn't be done because
there are just too many of these tiny grains too keep track of,"
Kuchner said. "We found a way to do it, and that has opened up a whole
new landscape."
With the help of NASA's Discover supercomputer, the researchers kept
tabs on 75,000 dust particles as they interacted with the outer
planets, sunlight, the solar wind -- and each other.
The size of the model dust ranged from about the width of a needle's
eye (0.05 inch or 1.2 millimeters) to more than a thousand times
smaller, similar in size to the particles in smoke. During the
simulation, the grains were placed into one of three types of orbits
found in today's Kuiper Belt at a rate based on current ideas of how
quickly dust is produced.
From the resulting data, the researchers created synthetic images
representing infrared views of the solar system seen from afar.
Through gravitational effects called resonances, Neptune wrangles
nearby particles into preferred orbits. This is what creates the clear
zone near the planet as well as dust enhancements that precede and
follow it around the sun.
"One thing we've learned is that, even in the present-day solar system,
collisions play an important role in the Kuiper Belt's structure,"
Stark explained. That's because collisions tend to destroy large
particles before they can drift too far from where they're made. This
results in a relatively dense dust ring that straddles Neptune's orbit.
To get a sense of what younger, heftier versions of the Kuiper Belt
might have looked like, the team sped up the dust production rate. In
the past, the Kuiper Belt contained many more objects that crashed
together more frequently, generating dust at a faster pace. With more
dust particles came more frequent grain collisions.
Using separate models that employed progressively higher collision
rates, the team produced images roughly corresponding to dust
generation that was 10, 100 and 1,000 times more intense than in the
original model. The scientists estimate the increased dust reflects
conditions when the Kuiper Belt was, respectively, 700 million, 100
million and 15 million years old.
"We were just astounded by what we saw," Kuchner said.
As collisions become increasingly important, the likelihood that large
dust grains will survive to drift out of the Kuiper Belt drops sharply.
Stepping back through time, today's broad dusty disk collapses into a
dense, bright ring that bears more than a passing resemblance to rings
seen around other stars, especially Fomalhaut.
"The amazing thing is that we've already seen these narrow rings around
other stars," Stark said. "One of our next steps will be to simulate
the debris disks around Fomalhaut and other stars to see what the dust
distribution tells us about the presence of planets."
The researchers also plan to develop a more complete picture of the
solar system's dusty disk by modeling additional sources closer to the
sun, including the main asteroid belt and the thousands of so-called
Trojan asteroids corralled by Jupiter's gravity.
Related Links:
› Geeked on Goddard: Bodies in motion
› NASA Supercomputer Shows How Dust Rings Point to Exo-Earths
› Twin Keck Telescopes Probe Dual Dust Disks
› Warped Debris Disks around Stars are Blowin’ in the Wind