Comet-like mineralogy of olivine crystals in an extrasolar proto-Kuiper belt
8 October 2012
B. L. de Vries and co-authors, including M. J. Barlow
Some planetary systems harbour debris disks containing planetesimals such as asteroids and comets. Collisions between such bodies produce small dust particles, the spectral features of which reveal their composition and, hence, that of their parent bodies.
Using data from the Herschel satellite, researchers have been studying the 69-micrometre-wavelength band of olivine crystals in the spectrum of the debris disc around the main sequence star Beta Pictoris. As a result of the disk being optically thin, it has been possible to associate the crystals with an extrasolar proto-Kuiper belt at a distance of 15-45 astronomical units from the star (one astronomical unit is the Sun-Earth distance). Additionally their magnesium-rich composition has been determined and shows that they make up 3.6+-1.0 per cent of the total dust mass. These values are strikingly similar to the dust emitted by the most primitive comets in the Solar System, even though Beta Pictoris is significantly larger, luminous and has a different planetary system architecture.
a) Resolved surface brightness map of the Beta Pictoris debris disk at 70 microns wavelength, taken with the Herschel Space Observatory's Photodetector Array Camera and Spectrometer (PACS). The disk is barely resolved with PACS, which has a point-spread function with a full-width at half-maximum of 8.2 arcsec (hatched circle).
b) Spitzer Space Telescope infrared spectrograph spectrum showing prominent olivine features (solid grey). The white solid line is our best model fit and the grey dashed line is the continuum. The uncertainties (1-σ) in the Spitzer data are indicated in the figure.
c) The flux-corrected Herschel PACS spectrum with error bars (1-sigma) showing the 69-micron band of crystalline olivine (solid grey; 12sigma detection). The white solid line shows the model fit to the 69-micron band of crystalline olivine and the dashed grey line shows the underlying dust continuum. The best model contains crystalline olivine (Mg2−2xFe2xSiO4) with x = 0.01 ± 0.001 (1-σ) and a temperature of 85 ± 6 K (1-σ).