Harvard-Smithsonian Center for Astrophysics
Contact Information:
Dr. Scott Kenyon, 617-495-7235, skenyon@cfa.harvard.edu
Dr. Kenny Wood, 617-495-7301, kwood@cfa.harvard.edu
Harvard-Smithsonian Center for Astrophysics
60 Garden Street
Cambridge, MA 02138
Dr. Barbara Whitney, 608-221-3938, bwhitney@execpc.com
Dr. Michael Wolff, 303-492-3774, wolff@colorado.edu
Space Science Institute
1540 30th Street
Suite 23
Boulder, CO 80303
For Release: Wednesday, October 20, 1999
A Dusty Ring May Be the Tell-Tale Mark of an Emerging Planetary System
CAMBRIDGE, MA -- The popular image of nascent planetary systems as thin,
spinning pancakes of cosmic dust and debris may be changed by a new
computer model that shows how that disk of debris is transformed into a
very distinct ring once Pluto-like bodies start to form.
By analyzing Hubble Space Telescope images of a suspected young planetary
system recently discovered around the star HR 4796A, Scott Kenyon and
Kenny Wood of the Harvard-Smithsonian Center for Astrophysics and Barbara
Whitney and Michael Wolff of the Space Science Institute have produced a
computer model that suggests the ring around that object probably is a
common feature of all planetary systems. Indeed, the well-known Kuiper
Belt of asteroids in our own Solar System may even be the residual remains
of such a ring.
Most theories of planetary formation predict that planets like Earth,
Mars, and Jupiter, grow from the coalescence of much smaller bodies,
so-called planetesimals embedded in a very thin disk-like nebula of dust
and gas rotating around a hot young star. The planetesimals, ranging in
size from one meter to one kilometer in diameter, are in constant
collision, careening off each other like pinballs in an arcade game.
Eventually, however, enough of the colliding bodies stick together to
create either rocky planets like Earth and Mars, or icy ones like Pluto. The
long, slow growth process has been compared to the proverbial snowball
that grows larger and larger as it rolls down a snowy slope.
As the larger objects grow even larger, they stir up and accelerate
smaller bodies in the nebula. The grinding, shattering effect of constant
high-speed collisions produces untold millions of micrometer-sized
particles that reflect light from the central star, which is seen through
telescopes -- especially those sensitive to infrared radiation -- as a dusty
disk.
When Kenyon and his colleagues simulated this process on the computer,
the shining dust first appeared once planets like Pluto began to form.
Moreover, the dust formed in a distinct and compacted ring, rather than
in a diffuse and flattened disk. In fact, the presence of a ring may be the
signature of an emerging planetary system, with the ring itself serving as
a clear demarcation line between inner and outer regions. Inside a ring,
new planets serenely circle the central star; outside, the cosmic
construction project continues.
The scientists feel our own Solar System probably had just such a dust
ring during the first 10 to 100 million years of its life. Today, a
reminder of that evolutionary feature can be seen in the Kuiper Belt,
which contains a host of massive bodies that never coalesced into larger
planets, analogous to the scraps of building materials left over at a
construction site. Indeed, they argue, the Kuiper Belt may contain several
primordial "Plutos" still waiting to be discovered.
The paper "Forming the Dusty Ring in HR 4796A" by Kenyon, Wood, Whitney,
and Wolff will appear in the 20 October 1999 issue of "Astrophysical
Journal Letters." An abstract is available at
http://cfa-www.harvard.edu/~kenyon/hr4796/info.html
An image and caption can be found at
http://cfa-www.harvard.edu/~kenyon/hr4796/pict.html
