"When Spitzer launched in 2003, the idea that we would use it to study planets in other solar systems was so crazy that no one considered it," said Sean Carey of NASA's Spitzer Space Telescope Science Center at the California Institute of Technology in Pasadena. "But now, finding planets has become our primary scientific mission."
Approaching its 10th anniversary, NASA's Spitzer Space Telescope has been converted from a general astronomical observatory to an observatory for extrasolar planets. This telescope was not designed in advance for this task. While the engineers and scientists who built Spitzer did not think of this goal, the features they gave the spacecraft made it possible to change the spacecraft's purpose. This was mainly made possible thanks to the telescope's extraordinary stability, thanks to which engineers today can give the space telescope observation capabilities that were beyond its original design.
"When Spitzer launched in 2003, the idea that we would use it to study planets in other solar systems was so crazy that no one considered it," said Sean Carey of NASA's Spitzer Space Telescope Science Center at the California Institute of Technology in Pasadena. "But now, finding planets has become our primary scientific mission."
Spitzer perceives the universe in infrared light which is a little less energetic than the light our eyes can see. Infrared light can easily penetrate through concentrations of stray cosmic gas and dust, allowing researchers to peer into stunning dust fountains, galaxy centers and nascent solar systems. This ability of Spitzer in the infrared field is also translated today to the study of planets. When a planet passes in front of its star, it blocks a tiny portion of the star's light. These are subtle defects that allow Spitzer to reveal the size of the alien world.
Planets emit infrared light and therefore Spitzer will be able to study the composition of their atmospheres. As a planet orbits its sun, it shows different areas of its surface to Spitzer's cameras. Changes in total brightness in the infrared range can tell about the climate. A planet's diminution as it passes behind its star can also provide a measurement of the alien world's temperature.
While the study of star formation and the disks of dust from which planets form has always been the cornerstone of Spitzer's science program, the study of the planet was made possible only by reaching an unprecedented level of sensitivity beyond its original design.
The design of the spacecraft was carried out before 1996, that is, before even one planet was discovered using the transit method, and despite the high level of accuracy, the change in brightness necessary to observe the planets passing across their sun was not considered realistic in the infrared field, because no infrared instrument existed at that time Didn't offer anything close to the accuracy required.
However, the systems put on Spitzer allowed for excellent control of temperature changes and contained a system for pointing and focusing on stars, much better than what was considered necessary for the work of the telescope. These two design elements that "saw the future" provided value in achieving the extreme precision required for the study of planets."
The fact that Spitzer can still do scientific work can be attributed to an early stage in the design that involved innovative thinking. Spitzer was initially loaded with enough coolant to keep the three heat-sensitive science instruments operational for at least two and a half years. This "cryo" mission ended up lasting more than five and a half years before running out of coolant.
But Spitzer's engineers had a built-in backup plan: a passive cooling system that kept one set of infrared cameras at an extremely low operating temperature of minus 244 degrees Celsius, or 29 degrees above absolute zero. The infrared cameras continued to operate at full sensitivity, allowing her to persist in an extended "hot" mission, so to speak, although it was still very cold by national standards.
Spitzer is painted black on the side facing away from the sun. This allows the telescope to radiate a maximum amount of heat into space. On the side facing the sun, Spitzer has a glossy coating that reflects as much heat from the sun as possible to the solar panels. This is the first infrared telescope to use such an innovative design and it set the standard for future missions.
Making Spitzer a planet-gazer also required some clever changes to the flight path, long after it had flown beyond the reach of human hands into a towed orbit around Earth. Despite the excellent relative stability for a small oscillating telescope, it remained pointed at the target star, the cameras also exhibited slight oscillations when the star passed a single pixel of the camera. Both of these things make it difficult to meet the delicate task of measuring transits of planets.
In the first step, we reduced the charging time of the heating system and were satisfied with charging that lasted only 30 minutes and produced about 50% of the heat, thus reducing the duration of the fluctuations. Spitzer's engineers and scientists were still not satisfied. In September 2011, they managed to bring the camera used by Spitzer's vote control sensor back to life. This camera was used during the cryo mission and was designed for routine calibration of stars that helped point the telescope in the right direction. The telescope rocked back and forth naturally as it stared at the target star. Given this unavoidable jitter, the ability to be able to control the light passing through the infrared camera is critical to obtaining accurate measurements. The engineers succeeded in this and allowed the astronomers to place stars precisely in the central pixel of the camera.
Since the return of the focusing camera astronomers have taken this process further by carefully mapping the peculiarities of a single pixel within the camera. They actually found the "sweet spot", using which provides the most stable observations. About 90 percent of Spitzer's planet observations are well focused to the sub-pixel level, up to a certain quarter of a pixel." We can use the camera to position ourselves precisely and put the light spot on the best part of the pixel,” said Carey. "So you put the light on the sweet spot and just let Spitzer stare."
These three actions more than doubled Spitzer's stability and focus and provided it with the amazing sensitivity it needed to measure planets outside the solar system.
"Because of these engineering changes, Spitzer became a planet-searching telescope," Carey said. "We expect from Spitzer an abundance of information about planets outside the solar system in the future."
