The Infrared Spectrograph (IRS)

The Infrared Spectrograph is one of Spitzer's three science instruments. It provides both high- and low-resolution spectroscopy at mid-infrared wavelengths (from 5 - 40 microns).

Like a prism breaking up light into a rainbow, the spectrograph takes the incoming infrared light from a distant object and breaks it up into a spectrum. Each chemical element in the universe has its own light signature in the spectrum, like a unique fingerprint. By studying the spectrum of light from a distant object, astronomers can tell what elements and molecules the object is made of . Spitzer observers have recently used this method to find water on a planet orbiting another star.

The IRS has four different modules: a low-resolution, short-wavelength module detecting light with wavelengths from 5.3 - 14 microns; a low-resolution, long-wavelength module for observations between 14 - 40 microns; a high-resolution, short-wavelength module covering 10 - 19.5 microns in high detail; and a high-resolution, long-wavelength module for detailed observations between 19 - 37 microns. Each module has its own entry slit to let the infrared light into the spectrograph.

The detectors arrays are 128 x 128 pixels in size. The short-wavelength detectors are treated with arsenic, and the longer-wavelength silicon detectors are treated with antimony. The IRS has no moving parts.

Caption: This plot shows data captured by Spitzer's IRS instrument, which indicates a strong signature of water vapor in the disk of gas and dust surrounding a young star.