A New Way to Find Planets Around Stars: Dusty Rings Are Sign

by University of Utah. Contact: Ben Bromley, assistant professor of physics, University of Utah, bromley@physics.utah.edu

September 17, 2002 -- 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.