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Warmer role for NASA's Spitzer Space Telescope

By / August 5, 2009

Not bad for a shakedown shot. Since May, when the Spitzer Space Telescope ran out of coolant for its infrared detectors, the orbiting observatory's engineers have been reconfiguring the telescope to operate at warmer temperatures. This shot of a star-forming region in the constellation Cygnus was taken July 21, during the telescope's recommissioning phase. It suggests the observatory still has plenty of science to undertake as it winds down its first six years in space.

NASA/JPL-Caltech

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After taking a time-out for a minor make-over, the Spitz is back -- and we're not talking Olympic swimmers.

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NASA's Spitzer Space Telescope has moved into a new phase of its operation. Astronomers will focus much of its observing time on studying planets around other stars. And they will peer back in time to observe galaxies when the universe was only 800 million years old or younger.

Each of these has resulted from observations during the observatory's first six years of operation that few, if any, scientists anticipated that Spitzer could deliver.

Spitzer returned to service July 27 after a couple of months of tweaking and testing to ensure it will still crank out top-tier observations after its superchilled coolant ran out.

The coolant, superfluid (meaning really, really cold) helium, was used to keep the telescope's three science instruments sensitive to infrared radiation from some of the universe's oldest and coldest features. Essentially, the helium allowed the observatory to operate free of the confounding effects of heat the observatory itself generates and radiates into space.

With all the planning and testing that the design, launch, and operation of a space observatory endures, you'd think scientists already would know how well the telescope could operate minus the deep chill.

But they never were allowed to test the equipment on orbit at warmer temperatures, according to Giovanni Fazio,  an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and the lead scientists on one of the two major projects a warmed-up Spitzer will undertake.

After all, the telescope was to operate at the colder temperature during the initial phase of its mission. So all researchers had to go on for an idea of how the warmer observatory might perform was lab simulation.

They now have seen the real deal, and they like what they see. The test image shown above is one of three the program released today.

"I was quite surprised" at the high quality of the images, Dr. Fazio acknowledges.

Spitzer operates at infrared wavelengths -- the region of the electromagnetic spectrum where dust clouds hiding newborn stars in effect become transparent. It's also a set of wavelengths at which some of the universe's coldest features -- also dust -- appear. And at great distances, the telescope can spot objects whose light has been stretched by the universe's expansion from ultraviolet and visible light to longer, infrared wavelengths.

Initially, the orbiting telescope's three instruments were chilled to 1.4 degrees above absolute zero.

In wavelength-speak, the observatory could pick out infrared radiation ranging from 3 to 180 microns, or 3 to 180 millionths of an inch; the larger the number, the colder the object emitting the radiation.

Among Spitzer's observations at such cold temperatures: the disks of dust around other stars -- the building blocks for solar systems.

But with no capacity for an inflight recharge of the fridge, the liquid helium used to cool the instruments ran out in May. So instead of operating at 1.4 degrees above absolute zero, the remaining instruments will now operate at a balmy 30 degrees above absolute zero. For us civilians, that translates to about 406 degrees below zero Fahrenheit.

And that means the instruments that can do so will operate at between 3.6 and 4.5 microns, Dr. Fazio says.

The trade-offs? The telescope no longer will enable astronomers to observe solar-system formation at as early a stage as they could before.

But it will still play a key role in writing the story of how galaxies have evolved. Dr. Fazio explains that one of two major observing projects over the next two years will focus on galaxies that formed when the universe was only 800 million years old or younger.  One of Spitzer's unanticipated results, he says, was the discovery of galaxies at this early stage in the universe's 13.6-billion year (and counting) evolution.

The other major project: Spitzer will play a key role in making follow-up studies of planets that NASA's Kepler mission discovers. Here, too, Spitzer amazed its handlers when it allowed them to spot so-called exoplanets and analyze the planets' atmospheres.

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