Spitzer Hunting For Exoplanets
September 25, 2013

Spitzer Gets A New Mission – Hunting For Exoplanets

Brett Smith for redOrbit.com - Your Universe Online

After 10 years of orbiting the sun, the Spitzer Space Telescope is now playing a completely different role than it was a decade ago – hunting for exoplanets outside the solar system.

"When Spitzer launched back in 2003, the idea that we would use it to study exoplanets was so crazy that no one considered it," said Sean Carey of NASA's Spitzer Science Center  in a statement. "But now the exoplanet science work has become a cornerstone of what we do with the telescope."

NASA scientists use Spitzer’s capacity for seeing the universe in the infrared spectrum to scan the cosmos for exoplanets, or planets that orbit a star other than our Sun. When an exoplanet passes in front of its star in a process known as transiting, it obstructs a fraction of starlight reaching the telescope. These tiny eclipses can be used to reveal the size of an alien planet.

Thanks to some innovative thinking during the design stage, Spitzer has been able to continue operating far beyond its initial mission. The telescope was outfitted with enough coolant to maintain its three temperature-sensitive instruments for at least two-and-a-half years, however, the coolant actually ended up lasting over five years.

In addition to extending the life of its coolant, Spitzer also has a passive cooling system built in that kept one set of infrared cameras operational at a super-low operational temperature of minus 407 degrees Fahrenheit - just 29 degrees above absolute zero.

To transition the telescope into an exoplanet spotter demanded some in-flight adjustments, however. Despite the telescope's stability as it orbits the sun, a small "wobbling" was occurring as it pointed at target stars. The cameras also showed small brightness changes when a star drifted slightly across one of the camera’s individual pixels. These two issues combined to make the sensitive task of recording accurate exoplanet transits that much more difficult.

To solve these problems, NASA engineers first had to find the source of the wobble – and they did: a heater that kicks on to keep Spitzer’s battery at a certain temperature. In October 2010, the engineers decided that the heater did not need to be cycled through its full hour and temperature range, cutting the telescope's wobble in half.

In September 2011, the NASA engineers then solved their pixel problem by repurposing Spitzer's Pointing Control Reference Sensor "Peak-Up" camera. This camera was used to collect infrared light precisely into a spectrometer and to calibrate the telescope's star-trackers, which help direct the observatory. Knowing it would allow for the placement of observed stars precisely on the center of a camera pixel, the NASA engineers applied the Peak-Up to the infrared camera observations.

The scientists took their use of the Peak-Up camera a step further by carefully "mapping" the idiosyncrasies of a single pixel within the camera. They were eventually able to finely target 90 percent Spitzer's exoplanet observations down to a particular quarter of a pixel.

"We can use the Peak-Up camera to position ourselves very precisely on the camera and put light right on the best part of a pixel," said Carey. "So you put the light on the sweet spot and just let Spitzer stare." These three in-flight tweaks have more than doubled the telescope's steadiness and targeting, giving Spitzer superb sensitivity when it comes to capturing exoplanet measurements.

"Because of these engineering modifications, Spitzer has been transformed into an exoplanet-studying telescope," said Carey. "We expect plenty of great exoplanetary science to come from Spitzer in the future."