Goddard Camera Debuts on New Space Telescope

An infrared camera developed by Goddard gave its first performance on board the Space Infrared Telescope Facility (SIRTF) mission, launched August 25 from Cape Canaveral, Fla.

Image of data from the Space Infrared Telescope Facility.

The images were taken as part of an operational test of the camera, called the infrared array camera (IRAC). It will take about a month to fully focus and fine-tune the telescope and cool it to optimal operating temperature, so these early images will not be as sharp or polished as future pictures.

IRAC is a general-purpose camera that can be used for a wide variety of astronomical observations. It makes images from the infrared light emitted by celestial objects. Infrared light is invisible to the human eye, but some types are generated by and perceived as heat. The camera is one of three instruments installed on SIRTF.

IRAC is endowed with a number of advances over previous infrared instruments. The camera has four infrared array detectors, each sensitive to a different kind of infrared light (wavelengths of 3.6, 4.5, 5.8, and 8.0 microns). This gives the instrument the ability to see the many diverse objects that glow in different types of infrared light. Each of the four infrared detectors are 256 by 256 pixel arrays, a size that gives the camera the ability to view a large area of the sky (5.12 by 5.12 arcminutes). This permits quick and efficient observations. The detectors also generate extremely low noise, which will give the science team confidence that very faint sources are indeed real and not just an artifact of the instrument noise.

The four infrared types observed by IRAC will be used to explore many objects and phenomena in space. The two array detectors sensitive to wavelengths of 3.6 and 4.5 microns will observe objects emitting near-infrared light. These include small, dim, cool stars called red dwarfs, and even colder objects, called brown dwarfs, that lacked sufficient mass to form a star. Also, dust is transparent to this kind of light. Since the cores of many galaxies are shrouded in dust, observing them in these wavelengths will reveal their hidden interiors. They are of interest because some galactic cores harbor supermassive black holes, which are believed to be the engines powering active galactic nuclei, which can outshine a trillion suns.

The two detectors sensitive to infrared at 5.8 and 8 microns will observe objects that glow in the mid-infrared range. Warm interstellar dust shines brightly in mid-infrared, so these detectors will be used to observe the dust disks that sometimes surround young stars. These disks are called protoplanetary disks because astronomers believe planets eventually form from their material, so studying them may reveal secrets regarding how planets are born.

Finally, IRAC can be used as a time machine to study the early Universe. Because light takes time to traverse the immense distances of the cosmos, looking farther into space is equivalent to gazing back into time. For example, we see the Sun as it existed about eight minutes ago, because that's how long it takes the Sun's light to travel roughly 93 million miles to Earth. The closest star appears at it was over four years ago, because light takes that long to bridge the more than 24 trillion miles that separate us, and the closest large galaxy is seen as it existed around two million years ago. If astronomers look far enough, they can observe the Universe as it appeared when it was newborn. One of IRAC's principal objectives will be to understand how galaxies first formed and how they evolved.

The telescope's dust cover was ejected on Aug. 29, and its aperture door opened on Aug. 30. The spacecraft is operating in normal mode, and all systems are operating nominally. "The team is very pleased with the rapid progress of the observatory and all of its onboard systems," said Project Manager David Gallagher of JPL.

In addition to the infrared array camera, the multi-band imaging photometer instrument was also switched on for the first time in a successful engineering test. The spacecraft's pointing calibration and reference sensor detected light from a star cluster. The third instrument, the infrared spectrograph, will be turned on later this month.

These operations are part of the mission's two-month in-orbit checkout, which will be followed by a one-month science verification phase. After that, the science mission will begin a quest to study galaxies, stars and other celestial objects, and to look for possible planetary construction zones in dusty discs around other stars.

Goddard, built Cambridge, Mass., IRAC with management and scientific leadership by the Smithsonian Astrophysical Observatory, under principal investigator Dr. Giovanni Fazio.

JPL, a division of the California Institute of Technology in Pasadena, manages the Space Infrared Telescope Facility for NASA's Office of Space Science, Washington.

The most striking image is available on the Internet at: http://www.nasa.gov/vision/universe/starsgalaxies/sirtf_alive.html

For more information about the Space Infrared Telescope Facility, visit: http://sirtf.caltech.edu/