Spitzer’s Cold Look at Space

To get a clear view of infrared emissions from celestial objects, the Spitzer Space Telescope has been cryogenically cooled—and what sights it has seen

Michael Werner

The Warm Spitzer Mission

With the exhaustion of its liquid helium, Spitzer’s radiative-cooling sytem and its heliocentric orbit—which carries it far from the heat of the Earth—has allowed the telescope and its instruments to remain at a stable temperature below 30 kelvins. Two of Spitzer’s arrays, which cover the shortest wavelength bands at 3.6 and 4.5 micrometers, have the same high sensitivity as before. The Warm Spitzer Mission, using these arrays, will operate for at least two additional years, through mid-2011, with the possibility of an extension for two or three years beyond that before Spitzer drifts out of easy communication range.

Much of the time available for observations during the first two years of the warm mission has been awarded competitively to scientific teams that will carry out large programs of broad general interest. Some of the topics covered will be familiar: galactic structure, clusters of galaxies and the distant universe. In these areas, Warm Spitzer will extend the results of the cryogenic mission.

In the dynamic area of exoplanet research, Warm Spitzer provides a much-needed capability to follow up on the additional discoveries that will undoubtedly be announced in the coming months, including those from the Kepler Mission, which will employ the first NASA spacecraft devoted to exoplanet studies.

Some totally new programs will also take place, such as monitoring the variability of young and forming stars as a means of studying both the stars and their planet-forming disks, and measurements of hundreds of Near Earth Objects (asteroids and extinct comets) to determine their sizes and to help in the assessment of the hazards these populations might pose to Earth. There will also be a re-examination of the local distance scale to provide an improved value for Hubble’s constant, which relates the recession velocity of a galaxy to its actual distance. In addition to these and other observational advances using Warm Spitzer, the next two years should see a continuing flow of results from Spitzer’s cryogenic mission due to vigorous exploitation of Spitzer’s rich data archive.

Other missions in addition to Warm Spitzer will be supporting the infrared exploration of the universe in the coming years. In May 2009 the European Space Agency and NASA successfully launched the Herschel Space Observatory. Herschel will extend the work of Spitzer to longer wavelengths, looking at cooler and perhaps more distant objects. Its spectrometers will study interstellar atoms and molecules with unprecedented precision. The WISE mission mentioned earlier will launch in late 2009 to carry out a highly sensitive survey of the entire sky at infrared wavelengths. A few years later, the SOFIA airborne observatory will start to carry instruments above most of the Earth’s atmosphere to provide access to much of the infrared spectrum. As an airborne observatory, SOFIA will also support the development and deployment of novel instruments as preludes to their use in space. Finally in the middle of the next decade the James Webb Space Telescope, with 50 times the telescope area of Spitzer, will extend the work of its predecessors to unprecedented depths.

Thus as Spitzer’s rich scientific legacy continues to grow during the coming years, we expect to look back on the depletion of its helium not only with a tinge of sadness but also as the start of an exciting era of new scientific challenges, opportunities and discoveries.

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Werner, M., G. Fazio, G. Rieke, T. L. Roellig and D. M. Watson. 2006. First fruits of the Spitzer Space Telescope: Galactic and solar system studies. Annual Review of Astronomy and Astrophysics 44:269–321.