This artist's conception shows a young, hypothetical planet around a cool star. Observations from NASA's Spitzer Space Telescope show that planet-forming gas and dust disks around cool stars have a different chemistry than disks of sun-like stars. Planets that arise from those disks could have a different chemistry, too. (NASA/JPL-Caltech)
If planets exist around cool, low mass stars, they could be chemically different from planets in our solar system, astronomers conclude from observations made with NASA's Spitzer Space Telescope.
University of Arizona astronomer Michael Meyer was part of the team that used Spitzer's infrared spectrograph to detect gas molecules in dusty planet-forming disks around young, nearby stars in the Milky Way.
In research led by Ilaria Pascucci of Johns Hopkins University, Meyer and colleagues compared the abundances of the two most prominent molecules in the spectra, acetylene and hydrogen cyanide, in planet-forming disks around 17 cool, low mass stars and 44 sun-like stars.
They discovered that planet-forming disks around both types of stars contain acetylene, but only disks around sun-like stars contain hydrogen cyanide. Pascucci is first author on the study, which will be published in the April 10 issue of the Astrophysical Journal.
"The chemistry that is going on in the disks of these two types of stars appears to be different," Meyer said. "This suggests that the composition of planets forming in those disks could be very different.
"This is an exciting new line of research that is ripe for further exploration using both ground- and space-based telescopes," Meyer said. "How is it that the molecules of gas and grains of dust in the disks around sun-like stars are different from the material in disks around low-mass stars? And how could that influence the kinds of planets that form within them?"
One possible explanation for the presence of hydrogen cyanide in disks around sun-like stars but not in disks around cool, low mass stars is ultraviolet radiation, Pascucci and her co-authors suggest.
Young sun-like stars and their inner disks radiate much more ultraviolet light than do cool stars plus disk systems. Stronger ultraviolet light would break up more molecular nitrogen, freeing nitrogen atoms to form hydrogen cyanide.
The theory needs further testing, Meyer said, "but if it holds up, it could tell us something important about how the ultraviolet activity of young stars changes the chemistry in such a way that it might change the kinds of rocky planets that could form."
Pascucci and her colleagues also speculate on the implications this might have for the complex organic chemistry that leads to the emergence of life.
Other authors include Daniel Apai of the Space Telescope Science Institute, Baltimore, Md.; Kevin Luhman of Pennsylvania State University; Thomas Henning and Jeroen Bouwman of Germany's Max Planck Institute for Astronomy; Fred Lahuis of the SRON Netherlands Institute for Space Research; and Antonella Natta of Italy's Arcetri Astrophysical Observatory.
NASA's Jet Propulsion Laboratory, 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.
Michael Meyer
520-626-9199
mmeyer@as.arizona.edu