Astronomers have just begun imaging planets
around other stars the technique isn't very
advanced yet, and it can't see any planets
as small as those in our own solar system.
But let's suppose for a moment that alien
astronomers are looking at our planetary system.
Could they find any evidence that planets
exist around the sun, even if they couldn't
see the planets themselves? The answer is
probably yes. That's because at least one
world in our solar system would make its presence
known by its effects on a huge cloud of dust
at the fringes of the solar system in a place
called the Kuiper Belt.
The Kuiper Belt is a kind of cold storage
zone out beyond Neptune, occupied by millions
of icy bodies, including Pluto. The icy objects
in the Kuiper Belt release dust that from
afar, could appear as a hazy disk at infrared
wavelengths. New computer models created by
NASA scientists, shown here, reveal what dust
in the Kuiper Belt might look like to an alien
astronomer. Neptune creates the intricate
The massive planet's gravity tugs on the clouds
dust grains, nudging them in their orbits.
Neptune creates a ring structure in the dust
cloud which features a gap where the planet
itself resides. And this gap should make it
fairly easy to tell where Neptune is from
afar, even at distances where the planet is
too dim to detect directly. The supercomputer
simulations that Marc Kuchner and I performed
also allow us to see what the dust in the
solar system may have looked like when the
solar system was much younger.
In effect, we can go back in time and see
how the distant view of the solar system may
In its youth, the Kuiper Belt contained many
more objects and, consequently, lots more
dust. In fact, the dust was so thick that
the particles themselves often collided.
When we included collisions between dust particles,
we were really amazed by what we saw.
Successively younger models of the Kuiper
dust cloud show progressively simpler structure,
eventually leading to a single narrow ring
beyond Neptune's orbit.
Dust collisions change Neptune's gravitational
imprint. The gap in the ring disappears. The
amazing thing is, we've already seen ring
structures like this around other younger
stars, like Fomalhaut. In terms of dust, we
now know that these other systems may look
similar to our young solar system.
Dust around other stars can tell us a lot
about possible planets, just as in our own
solar system, it could reveal Neptune.