Any alien astronomers searching for life-supporting exoplanets could be in for a disappointment if they look at our solar system - the massive amount of dust in the outer solar system could make all the planets except Neptune effectively invisible.
Although we tend to think of our solar system as the Sun plus the eight (or, for traditionalists, nine) planets, there's also the vast expanse beyond Neptune that's full of millions of icy bodies. Known as the Kuiper Belt, this second asteroid belt is nearly twice as far from the Sun as Neptune is, and it's 20 times as wide and as much as 200 times as massive as the more familiar asteroid belt between Mars and Jupiter.
The Kuiper Belt also creates a massive dust disk, and that dust may be shrouding most of our inner solar system in a veil of secrecy, as NASA astrophysicist Marc Kuchner explains:
"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. We're hoping our models will help us spot Neptune-sized worlds around other stars."
The dust is generated as Kuiper Belt objects smash into and pulverize each other, releasing countless icy particles that build into a massive dust cloud. The dust then travels throughout the Solar System, although it's unclear precisely how, because the dust is governed by some difficult to predict push-and-pull effects from solar wind and sunlight.
Kuchner and his team have now done what some thought was impossible by simulating the movement of these dust grains. Using a NASA supercomputer, they simulated the movement of about 75,000 particles ranging in size from a grain of sand to the particles in smoke. They then used these simulations to build infrared views of how our Solar System would look to outside observers. You can see the dust cloud at several different points in our Solar System's history in the image above.
These simulations reveal that collisions have shaped the Kuiper Belt into the broad, fuzzy disk we see today, but that isn't always how it looked. It was once a sleeker, denser ring that was considerably brighter - and nearly identical to similar debris disks we've spotted around other stars. The team hopes to run similar simulations for the disks around other stars, which may help us understand what role these disks play in the formation of planets.