How the Spitzer Space Telescope Sees the Infrared Universe

infrared astronomy
The "Spider and Fly" Nebula, an object studied by the Spitzer Space Telescope. It's a star-forming region and Spitzer's infrared view shows structures in the cloud affected by a cluster of newborn stars. Spitzer Space Telescope/NASA

Some of the most fascinating objects in the universe emit a form of radiation that we know as infrared light. To "see" those celestial sights in all their infrared glory, astronomers need telescopes that operate beyond our atmosphere, which absorbs much of that light before they can detect it. The Spitzer Space Telescope, in orbit since 2003, is one of our most important windows on the infrared universe and continues to deliver stunning views of everything from distant galaxies to nearby worlds. It has already accomplished one major mission and is now working on its second life.

Spitzer's History

The Spitzer Space Telescope actually started out as an observatory that could be built for use aboard the space shuttle. It was called the Shuttle Infrared Space Facility (or SIRTF). The idea would be to attach a telescope to the shuttle and observe objects as it circled Earth. Eventually, after the successful launch of a free-orbiting observatory called IRAS, for Infrared Astronomical Satellite, NASA decided to make SIRTF an orbiting telescope. The name changed to Space Infrared Telescope Facility. It was eventually renamed the Spitzer Space Telescope after Lyman Spitzer, Jr., an astronomer and major proponent for the Hubble Space Telescope, its sister observatory in space.

Since the telescope was built to study infrared light, its detectors had to be free of any glimmering of heat that would interfere with the incoming emissions. So, builders put in a system to cool those detectors down to five degrees above absolute zero. That's about -268 degrees Celsius or -450 degrees F. Away from the detectors, however, other electronics needed warmth in order to operate. So, the telescope contains two compartments: the cryogenic assembly with the detectors and scientific instruments and the spacecraft (which contains the warmth-loving instruments). The cryogenics unit was kept cold by a vat of liquid helium, and the whole thing was housed in aluminum that reflects sunlight from one side and painted black on the other to radiate heat away. It was a perfect mix of technology that has allowed Spitzer to do its work.

One Telescope, Two Missions

Spitzer Space Telescope functioned for nearly five and half years on what was called its "cool" mission. At the end of that time, when the helium coolant had run out, the telescope switched to its "warm" mission. During the "cool" period, the telescope could focus on wavelengths of infrared light ranging from 3.6 to 100 microns (depending on which instrument was doing the looking). After the coolant ran out, the detectors warmed up to 28 K (28 degrees above absolute zero), which limited the wavelengths to 3.6 and 4.5 microns. This is the state that Spitzer finds itself in today, orbiting in the same path as Earth around the Sun, but far enough away from our planet to avoid any heat it emits.

What Has Spitzer Observed?

During its years on orbit, the Spitzer Space Telescope peered (and continues to study) such objects as icy comets and chunks of space rock called asteroids orbiting in our solar system all the way out to the most distant galaxies in the observable universe. Nearly everything in the universe emits infrared, so it's a crucial window to help astronomers understand how and why objects behave the way they do.

For example, the formation of stars and planets takes place inside thick clouds of gas and dust. As a protostar is created, it warms up the surrounding material, which then gives off infrared wavelengths of light. If you looked at that cloud in visible light, you'd just see a cloud. However, Spitzer and other infrared-sensitive observatories can see the infrared not just from the cloud, but also from regions inside the cloud, right down to the baby star. That's giving astronomers a LOT more information about the process of star formation. In addition, any planets that form in the cloud also give off the same wavelengths, so they can be found, too.

From the Solar System to the Distant Universe

In the more distant universe, the first stars and galaxies were forming just a few hundred million years after the Big Bang. Hot young stars give off ultraviolet light, which streams out across the universe. As it does, that light is stretched by the expansion of the universe, and we "see" that radiation shifted to infrared if the stars lie far enough away. So, Spitzer gives a peek at the earliest objects to form, and what they might have looked like way back then. The list of study targets is vast: stars, dying stars, dwarfs and low-mass stars, planets, distant galaxies, and giant molecular clouds. They all give off infrared radiation. In the years it has been on orbit, Spitzer Space Telescope has not only widened the window on the universe begun by IRAS but has widened it and extended our view back to almost the beginning of time.

Spitzer's Future

Sometime in the next five or so years, Spitzer Space Telescope will cease operation, ending its "Warm" Mission mode. For a telescope built to last for only half a decade, it has been more than worth the more than $700 million it cost to build, launch, and operate since 2003. The return on investment is measured in knowledge gained about our always-fascinating universe.