The Infrared Eye of WISE

By Jonathan McDowell
Sky & Telescope
December 2008

As the Spitzer Space Telescope nears the end of its primary, cryogenic phase, work on NASA’s next infrared observatory is advancing. The telescope for the Wide–field Infrared Survey Explorer (WISE) is having its focus checked at the Space Dynamics Lab in Utah, before being shipped next year to Colorado, where the spacecraft bus is assembled.

Spitzer gave deep, detailed looks at narrow fields. WISE, a much smaller craft, will map the whole infrared sky at several wavelengths. Its telescope will scan the sky continuously as the satellite orbits Earth. To avoid blurring, a small mirror will pivot to counteract spacecraft motion long enough to let WISE make tiled images in 10–second snapshots.

For optimum sensitivity, WISE’s four infrared cameras will be swathed in a block of solid hydrogen at a temperature of 8 kelvins, while the telescope is kept at a comparatively balmy 20 kelvins. Compared to the liquid helium used in most infrared space telescopes, solid hydrogen is much lighter and doesn’t evaporate as easily, making the mission cheaper and longer–lasting.

Launch of WISE is planned for November 2009. The first sky scan should begin the following month and be complete by summer 2010. The resulting celestial maps will be at wavelengths of 3.3, 4.7, 12, and 23 microns, and will reach hundreds of times fainter than the classic IRAS map of the infrared sky from the 1980s. WISE’s near– and mid–infrared data will complement the recent sky survey by Japan’s Akari satellite, which operated in the far infrared (July issue, page15).

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