Astronomy on the Wing

More than meets the eye: The constellation Orion
in visible light (left) and infrared (right)
Visible light image: Akira Fujii;
Infrared image: Infrared Astronomical SatelliteSome months ago my blog, "SOFIA: Fly By Night," talked about the up-and-coming astronomy ace of the night skies, SOFIA: the Stratospheric Observatory for Infrared Astronomy--a 2.5 meter infrared telescope built into a Boeing 747 airplane.

SOFIA's been flying, and is gearing up to begin its first science flights in the not so distant future. SOFIA even put in an appearance in Bay Area skies a couple of weeks ago with a quick visit to NASA/Ames Research Center in Mountain View--then it was off again to its base of operations in the Mojave Desert.

Having worked on SOFIA's predecessor, the Gerard P. Kuiper Airborne Observatory (KAO), in the last seven years of its operation, I thought I'd focus a bit on the science of airborne infrared astronomy, touching a bit on science done on the KAO over its 21-year career at NASA/Ames.

Why put a telescope on an airplane? Earth's atmosphere, while transparent to the visible light the human eye can detect, is less so to many other wavelengths of light, including most infrared light. In fact, the water vapor in our atmosphere is pretty much opaque to a wide range of infrared wavelengths.

KAO flew at and altitude of 41,000 feet to get above as much as 99% of Earth's atmospheric water vapor, giving astronomers a view of the infrared emissions from objects in space almost as if the telescope was out in space.

What's so interesting about looking at infrared light? Aren't visible light images taken from ground-based observatories enough?

Apparently not. Visible light is only a tiny fraction of the overall spectrum of electromagnetic radiation (the general term for "light" of all types--including gamma rays, X-rays, ultraviolet light, infrared light, microwaves and radio waves). There is a wealth of information contained in the entire electromagnetic spectrum that is only hinted at in the visible portion.

Visible light in our universe comes mostly from the photospheres of stars, either directly or by being reflected by objects such as dust, planets, comets, and the like; all of the light you see in the sky is starlight, either first hand or second hand.

Infrared light, however, is a lower energy form of electromagnetic radiation, and is emitted by any object or substance that is even slightly warm. So, interstellar clouds of molecules, rings of dust surrounding stars, atmospheres of planets--just about anything, in fact--emits its own infrared light, and observing the infrared emissions from these objects reveals a great deal about them: their chemical composition, their temperatures and densities, their velocities and structure--and a lot more.

One KAO astronomer observed the atmosphere of Venus to measure the relative abundance of hydrogen and deuterium (heavy hydrogen), looking for evidence of past oceans. Another observed Mars, looking for telltales of limestone (a mineral left behind by marine organisms) as evidence of past life on Mars. Others created detailed maps of clouds of complex molecules, probing the composition of the cooler material in our galaxy, as well as other galaxies.

The list goes on, as there's plenty more cold matter in the universe than hot matter. Cooler matter can be more interesting, too, since complex molecules, like organic compounds and even life, don't form in the sterile heat of stars.

So where KAO blazed an infrared contrail in the night skies, SOFIA may now follow and carry on the torch of astronomy, on the wing....
Benjamin Burress is a staff astronomer at The Chabot Space & Science Center in Oakland, CA.

latitude: 37.8768, longitude: -122.251