Spitzer reborn

BY DR EMILY BALDWIN

ASTRONOMY NOW

Posted: 7 May, 2009

After five and a half years of probing the Universe at infrared wavelengths, NASA’s Spitzer Space Telescope will run out of coolant, marking a new era of “warm” observations.

For a telescope to detect infrared light – essentially heat – from
cool cosmic objects, it must have very little heat output of its own. By the end of the month, however, the liquid helium used to cool some of Spitzer’s instruments to less than three degrees above absolute zero will run out. But this is by no means the end of the mission, just the mission as we currently know it, and with two channels of one instrument still working at full capacity, Spitzer will remain at the forefront of cosmic exploration for a little while longer.

Spitzer seen against an infrared sky. Image: NASA/JPL-Caltech.

“We like to think of Spitzer as being reborn,” says Robert Wilson, Spitzer project manager at NASA’s Jet Propulsion Laboratory. “Spitzer led an amazing life, performing above and beyond its call of duty. Its primary mission might be over, but it will tackle new scientific pursuits, and more breakthroughs are sure to come.”

The mission has already exceeded expectations, since the cryogen was only projected to last two and a half years, but careful operations and an efficient design allowed it to last more than twice that, resulting in data from the telescope being cited in more than 1,500 scientific papers. Perhaps one of the most revolutionary Spitzer discoveries to date is direct observations of exoplanets and their atmospheres and weather.

“Nobody had any idea Spitzer would be able to directly study
exoplanets when we designed it,” says Spitzer Project Scientist Michael Werner of JPL, who has been working on Spitzer for more than 30 years. “When astronomers planned the first observations, we had no idea if they would work. To our amazement and delight, they did.”

Spitzer discovered that the closest known planetary system to our own, Epsilon Eridani hosts two asteroid belts, in addition to planets an outer comet ring. Image: NASA/JPL-Caltech.

Although the new mission phase has been dubbed as ‘warm’, in fact the telescope will still operate at a rather chilly -242 degrees Celsius. While the longer wavelength multi-band imaging photometer and its infrared spectrograph will no longer be cold enough to detect cool objects, the telescope’s two shortest-wavelength detectors in its infrared array camera will continue to function normally, taking in everything from asteroids in our Solar System to distant dusty stars, planet-forming discs and galaxies, as well as continuing to add to the gas giant exoplanet inventory.

“We will do exciting and important science with these two infrared channels,” says Werner. “Our new science program takes advantage of what these channels do best. We’re focusing on aspects of the cosmos that we still have much to learn about.”

Specific tasks on Spitzer’s new work list include refining estimates for the rate at which the Universe is expanding, that is, Hubble’s constant; searching for galaxies at the edge of the Universe; measuring the size distribution of asteroids to assess how often potentially hazardous asteroids might impact Earth; and characterising the atmospheres of gas giant planets that Kepler is predicted to discover.