A New Way to Find Planets Around Stars: Dusty Rings Are Signposts of Recent Planet Formation

Young stars are surrounded by a thin, swirling cloud
of gas and dust that may be the birthplace of planets. New computer
calculations reveal that a newborn planet signals its presence by a clear,
sharp ring of cold dust. Such rings are seen around many nearby stars.

Physicist Ben Bromley of the University of Utah and astronomer Scott
Kenyon of the Smithsonian Astrophysical Observatory obtained these
findings using a parallel supercomputer at the National Aeronautics and
Space Administration’s Jet Propulsion Laboratory in Pasadena, Calif.

The computer simulations included a high level of realism, and showed
how rings of dust around stars appear, grow and then fade, depending on
size and number of planets. The findings will be published in the Sept. 20
issue of The Astrophysical Journal.

Existing methods of searching for planets around other stars are
capable of finding only Jupiter-sized planets, although a variety of
proposed Earth-orbiting telescopes promise to detect planets the size of
Earth.

The new method – looking for planets within dusty rings encircling
other stars – “really is the only technique we have of finding something
as small as Pluto,” says Bromley, an assistant professor of physics at the
University of Utah.

Kenyon, a staff scientist at the Smithsonian Astrophysical Observatory
in Cambridge, Mass., adds: “For people who are looking for planets, these
dusty rings provide a way to locate where an object – ranging in size from
Pluto up to the moon and larger – would be in a circumstellar disk.”

The rings of dust come about because of the way planets are assembled.
The dust and gas around a new star condense – like drops of water in rain
clouds – to form “planetesimals,” small bodies of ice and rock ranging in
diameter from meters to kilometers. These bodies are the seeds of planets
like the Earth. As planetesimals grow in size by colliding with each
other, the larger ones stir up the smaller bodies to high speeds. When the
smaller planetesimals strike each other, they shatter into the dust that
is seen in rings.

The scientists produced animations to demonstrate how rings develop
and persist as a result of planets forming under a variety of conditions.
The animations and text describing the research are on the web at:

http://cfa-www.harvard.edu/~kenyon/pf/sp/index.html

Evidence is mounting that many stars have planets, similar to those
in our own solar system. Massive, Jupiter-sized planets tug on their
parent star causing the star to have a small, but detectable, wobble.
Dozens of stars reveal their Jupiter-like planets in this way. But small
planets like the Earth are harder to find. The calculations reported by
Kenyon and Bromley show that dusty rings can reveal the orbital paths of
the more elusive small planets.

Kenyon emphasized computer simulations so far have shown only that
dusty rings are produced when planets the size of Pluto to about Earth
form at Pluto-like distances from the central star. He and Bromley have
not yet simulated formation of Earth-sized planets at Earth-like distances
from a star.

But “the point is that our computer calculations produce objects like
the mass of the moon, Mercury and larger, and they produce a detectable
signature, namely, these dusty rings,” Kenyon says. “The planets are so
dim you would never see them.”

Computational aspects of the research will be highlighted by the
JPL/Caltech Supercomputer and High Definition Systems Group in a poster
display during the Nov. 16-22 SC2002 supercomputing conference in
Baltimore, Md.

Kenyon will discuss the study during a lecture sponsored by the
University of Utah High Energy Astrophysics Institute. The lecture is
scheduled for 10:30 a.m. MDT Thurs. Sept. 26 in Room 110 of the
Intermountain Network and Scientific Computation Center (INSCC) Building
on the University of Utah campus.

Reporters who would like a copy of The Astrophysical Journal study should
contact Lee Siegel or Ben Bromley at the e-mail addresses or phone numbers
listed atop this release.