Visualization of SIRTF as it orbits the Sun

(PLANET QUEST) -- Early next year, the field of new planet observations will be extended into space with the launch of the Space Infrared Telescope Facility (SIRTF).

Scheduled to launch in January 2003, SIRTF will obtain images and spectra of various astrophysical targets by detecting the infrared energy, or heat, radiated by objects in space between wavelengths of 3 and 180 microns (1 micron is one-millionth of a meter). Most of this infrared radiation is blocked by the Earth's atmosphere and cannot be observed from the ground.

The observatory will devote considerable time to studies of the circumstellar ("surrounding a star") disks of dust and gas found around nearby stars, providing key information about the formation of extrasolar planetary systems.

Attempting to see the faint disk at visible wavelengths is extremely difficult because of the bright light from the parent star. However, the relative difference is reduced in the infrared, where SIRTF will conduct its measurements.

More the 100 new planetary systems have been discovered within the past decade, but all have been indirectly detected through ground-based observations. SIRTF will be among the first missions to carry on the search from the improved vantage point of space.

Dr. Michelle Thaller, manager of the SIRTF Education and Public Outreach Program, recently discussed the integral role the mission will play in NASA's search for new worlds.

PlanetQuest: How is data gathered by SIRTF important to the search for extrasolar planets?

A close-up near-infrared image of the edge-on protoplanetary disk discovered with adaptive optics on the Gemini North telescope. (Credit: UC-Berkeley/CfA/Gemini Observatory/NOAO/NSF)

Thaller: All kinds of debris gets blown out during star formation -- dust, gas, Kuiper belt objects, and so on. Even though some of this material is quite old, it still has a temperature and will radiate some infrared light. SIRTF sees way out into the infrared, so we should be able to image disks that are the evidence of either planets forming right now, or past planet formation.

One of the more famous examples of these disks is around the star Vega. Infrared radiation around Vega has been widely thought to be evidence of a disk, but SIRTF will give us a better look. It's close enough that we might be able too see a gap in the disk, which would be a good clue that planets are there. We'll also monitor density variations that might suggest the presence of planets.

PlanetQuest: Will SIRTF be able to directly confirm the existence of extrasolar planets?

Thaller: Probably not -- we're looking for that indirect evidence. If we see some very well-defined mass fluctuation in a disk, the only way to explain that would be the existence of planet. It won't tell us details, but we can say we're pretty sure there's a planetary system there.

SIRTF should be able to directly image brown dwarfs (failed stars), but it lacks the angular resolution to image even Jupiter-size planets around other stars. However, it may be able to obtain spectroscopic data for gas giant planets.

PlanetQuest: How will SIRTF improve our understanding of the frequency of extrasolar planetary systems?

Thaller: It will do that quite well. We'll be able to take a pretty good census and get some statistics on the number of stars that have planetary disks. The disks would have to be pretty thin to be missed by SIRTF.

This information will help define the targets for future planet-finding missions such as the Space Interferometry Mission and Terrestrial Planet Finder.

PlanetQuest: When will SIRTF's study of protoplanetary disks begin?

Thaller: Although SIRTF is scheduled to launch in January, it's going to take at least until March before the instruments are cold enough to begin science observations. At that point, protoplanetary disks will probably be among the first objects SIRTF looks at. Find out more:
Space Infrared Telescope Facility home page