Within about a week of May 12, the telescope is expected to run out of the liquid helium needed to chill some of its instruments to operating temperatures. The end of the coolant will begin a new era for Spitzer. The telescope will start its “warm” mission with two channels of one instrument still working at full capacity. Some of the science explored by a warm Spitzer will be the same, and some will be entirely new. Spitzer is the last of NASA‘s Great Observatories, a suite of telescopes designed to see the visible and invisible colors of the universe. The suite also includes NASA‘s Hubble and Chandra space telescopes. Spitzer has explored, with unprecedented sensitivity, the infrared side of the cosmos, where dark, dusty and distant objects hide.
For a telescope to detect infrared light — essentially heat — from cool cosmic objects, it must have very little heat of its own. During the past five years, liquid helium has run through Spitzer’s “veins,” keeping its three instruments chilled to -456 degrees Fahrenheit (-271 Celsius), or less than 3 degrees above absolute zero, the coldest temperature theoretically attainable. The cryogen was projected to last as little as two and a half years, but Spitzer’s efficient design and careful operations enabled it to last more than five and a half years. Spitzer’s new “warm” temperature is still quite chilly at -404 degrees Fahrenheit (-242 Celsius), much colder than a winter day in Antarctica when temperatures sometimes reach -75 degrees Fahrenheit (-59 Celsius). This temperature rise means two of Spitzer’s instruments — its longer wavelength multiband imaging photometer and its infrared spectrograph — will no longer be cold enough to detect cool objects in space. However, the telescope’s two shortest-wavelength detectors in its infrared array camera will continue to function perfectly. They will still pick up the glow from a range of objects: asteroids in our solar system, dusty stars, planet-forming disks, gas-giant planets and distant galaxies. In addition, Spitzer still will be able to see through the dust that permeates our galaxy and blocks visible-light views. Some of Spitzer’s new pursuits include refining estimates of Hubble‘s constant, or the rate at which our universe is stretching apart; searching for galaxies at the edge of the universe; assessing how often potentially hazardous asteroids might impact Earth by measuring the sizes of asteroids; and characterizing the atmospheres of gas-giant planets expected to be discovered soon by NASA’s Kepler mission. As was true during the cold Spitzer mission, these and the other programs are selected through a competition in which scientists from around the world are invited to participate.
