Figure 1
NASA's Spitzer Space Telescope recently captured these infrared images of
six older stars with known planets. The yellow, fuzzy blobs are stars circled by
disks of dust, or "debris disks," like the one that surrounds our own Sun.
Though astronomers had predicted that stars with planets would harbor debris
disks, they could not detect such disks until now.
Spitzer was able to sense these dusty disks via their warm infrared glows.
Specifically, the presence of the disks was inferred from an excess amount
of infrared emission relative to what is emitted from the parent star
alone.
The stars themselves are similar in age and temperature to our Sun. In
astronomical terms, they are stellar main sequence stars, with spectral
types of F, G, or K. These planet-bearing stars have a median age of four
billion years. For reference, our Sun is classified as a G star, with an
age of approximately five billion years.
The disks surrounding these planetary systems are comprised of cool
material, with temperatures less than 100 Kelvin (-173 degrees Celsius).
They are10 times farther away from their parent stars than Earth is from
the Sun, and are thought to be analogues of the comet-filled Kuiper Belt
in our solar system.
The contrast scale is the same for each image. The images are
approximately 2 arcminutes on each side. North is oriented upward and
east is to the left. The pictures were taken with the 70-micron filter of
Spitzer's multiband imaging photometer. The telescope resolution at 70
microns is 17 arcseconds and there is no evidence for any emission
extended beyond the telescope resolution.
