Infrared Astronomical Satellite (IRAS)

The Infrared Astronomical Satellite (IRAS) was a joint space mission conducted by the United States, the Netherlands, and the United Kingdom over ten months in 1983. It used infrared technology on four bandwidths to scan the universe for indications of infrared emissions. The mission more than doubled the amount of known infrared sources in the universe and made a number of other discoveries about the universe, comets, numerous stars, and the Milky Way galaxy. It also set the stage for future infrared satellite missions.

Background

The IRAS mission began on January 25, 1983, when the satellite was launched from Vandenberg Air Force Base in California. The satellite was a joint effort of the US National Aeronautics and Space Administration (NASA), the Netherlands Agency for Aerospace Programs, and the Science and Engineering Research Council of the United Kingdom. It was the first time any country had launched a mission to observe the universe on the infrared level.

Infrared is a type of light that cannot be seen by the eye but can often be felt as warmth on the skin. It was discovered in 1800 by William Herschel (1738–1822), a German-born British astronomer who was also responsible for the discovery of the planet Uranus. Herschel noticed that when he split light through a prism to create a color spectrum, or rainbow, the red light was warmer than the light next to it. When he went above red on the color spectrum, the warmth increased. This led Herschel to the conclusion that invisible light waves existed above the red level of the spectrum, and these became known as infrared light. Infrared technology has many practical uses, including medical applications and keeping cooked food warm. In space, infrared waves can indicate the presence of an otherwise invisible heat source.

The IRAS mission was the first to have a telescope calibrated to detect infrared light. It searched about 96 percent of the universe for infrared waves in four bands; twelve, twenty-five, sixty, and one hundred microns. The searches increased the number of known astronomical bodies capable of producing infrared by more than 70 percent, revealing about half a million new space bodies capable of generating heat, such as stars and comets.

Infrared telescopes require special cooling to remain functional. IRAS was cooled by liquid helium, a cryogen, or cooling agent. The cryogen was exhausted after ten months in space, and the mission came to an end on November 21, 1983. While the satellite continued to orbit Earth for some time, it was no longer capable of making infrared observations.

Discoveries and legacy

During the ten months that the IRAS telescope was functional, it was responsible for a number of very important observations. These observations affected nearly every aspect of astronomy. Three of the most important observations were the discovery of six previously unknown comets, the collection of infrared data on more than two thousand asteroids, and the discovery of information about the core of the Milky Way galaxy for the first time. IRAS was also the first satellite to detect a new comet and find debris from a comet.

The satellite also helped scientists to see that the galaxy is full of dust. Some of this dust is cast off by comets, while other dust surrounds the solar system in what are known as zodiacal bands of infrared dust. Scientists studying the data from IRAS also noticed these zodiacal bands around stars in other parts of the universe. The infrared observations revealed that Earth's galaxy is set up in what is known as a barred spiral format. This means that the center of the galaxy is a thicker bar-like area, from which a number of spiraling arms extend.

The IRAS mission also helped scientists understand much more about neighboring galaxies and stars. The telescope revealed the presence of what was at the time the brightest object in the universe. Researchers believe this object, known as IRAS F10214+4724, may eventually form a new galaxy. The IRAS telescope also detected and documented thousands of hot balls of gas clouds and dust that could possibly be new stars in the making and found several protostars, or newly formed stars. These protostars were hidden in clouds of hot gas and dust and were only identified because of their infrared emissions.

Researchers used the infrared technology to peer into Bok globules, very cold, dense clouds of gas floating in space, and reveal that some of them also contain protostars. This helped confirm the theory of Bart Bok (1906–1983), the astronomer for whom the globules are named, who suspected the small clouds might surround a protostar. The Dutch-American astronomer died the same year as the IRAS mission.

Before it ran out of cryogen, IRAS cataloged more than twelve thousand variable stars, or stars that change in brightness. This was the largest number of such stars identified to that point. The mission also revealed a ring of dust grains around the star Vega and several other stars and detected the presence of about seventy-five thousand starburst galaxies, or galaxies with large numbers of newly forming stars within.

Although it was a relatively short mission of less than a year, the IRAS project provided information that was useful to scientists in every field of astronomy. It also paved the way for additional in-space infrared observation missions. These included the European Space Agency (ESA) Infrared Space Observatory (ISO) mission, which lasted from 1995 to 1998 and built on the observations of the IRAS mission; the NASA Spitzer Telescope mission (2003—); ESA's Herschel Observatory (2009—); and the Akari infrared satellite launched by the Japan Aerospace Exploration Agency (JAXA) in February 2006. The IRAS project also was a precursor of the James Webb Space Telescope, which launched on December 25, 2021, and detects near-infrared and mid-infrared wavelengths.

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