Some asteroids that have comet-like orbits may actually be comets that have lost gases and other easily vaporized substances, according to a NASA research team.

The team will present its findings at the American Astronomical Society's Division for Planetary Sciences annual meeting in Cambridge, England, on Sept. 5.

"Several objects classified as asteroids have orbits that are dynamically similar to those of comets," said Dale Cruikshank, an astronomer at NASA Ames Research Center in California's Silicon Valley and a member of the research team. These asteroids may be comets that have lost gases and other materials by repeated passages through the inner solar system, according to Cruikshank.

The team studied infrared light from 55 asteroids using NASA's Spitzer Space Telescope to "better understand possible links between asteroids and comets," according to the authors. In addition to co-author Cruikshank, Joshua Emery who also works at NASA Ames and is an employee of the SETI Institute, Mountain View, Calif. is the principal author; and Jeffrey Van Cleve of Ball Aerospace, Boulder, Colo., is the other co-author.

"The suggestion that some asteroids originated as comets has been made before, but the new Spitzer Space Telescope observations provide the first chance to really test this suggestion," Emery noted. "Most of the objects observed in our program appear to be typical asteroids, but a few have surface compositions and textures that are more similar to comets," Emery added.

"The infrared light we are studying gives us information about the composition and surface textures of solid bodies in the solar system." Cruikshank said.

The research team reports that some of the asteroids have very fine-grained surfaces. "We think this fine-graininess is a characteristic of comets," Cruikshank explained.

The Jet Propulsion Laboratory in Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA.

For information on the Spitzer Space Telescope visit:

http://www.spitzer.caltech.edu/spitzer/

For high-resolution images of comets, please visit:

http://www.nasa.gov/centers/am es/multimedia/images/2005/comets1.html