Peering through the clouds of the universe
IRAS, an orbiting telescope that ''sees'' by infrared (heat) radiation, is ready to give astronomers an expansive new view of the universe. It should be able to survey the core of our Milky Way galaxy, now hidden by dust clouds, as well as to study the birth of new stars. It should detect objects thousands of millions of light years away. It should give new, detailed data on the nature of hundreds of asteroids within our solar system.
The US National Aeronautics and Space Administration (NASA) estimates, conservatively, that the all-sky survey planned for this joint British-Dutch-US satellite ''is expected to provide a map of 1 million infrared sources.''
IRAS (Infrared Astronomy Satellite) is scheduled to be launched Tuesday from Vandenberg Air Force Base in California, where the launch window opens at 6:17 p.m. Pacific Standard Time. NASA has provided the 810 kilogram (1,786 pound) infrared (IR) telescope itself as well as launch facilities. The Netherlands built the satellite - with a total mass of 1,076 kilogram (2,372 pound) - that carries the telescope. Britain will provide ground control.
For astronomers, having the IRAS in the sky will be like taking off a pair of foggy glasses. Virtually everything in the universe emits some form of IR radiation. Until now, however, astronomers have not been able to make much use of the information they know this radiation could provide. Earth's atmosphere absorbs incoming IR radiation heavily at many wavelengths. IRAS, orbiting well above the atmosphere, will have a clear view.
The puzzle of our own galactic center illustrates the kind of new insight astronomers expect to gain. Thick dust clouds obscure our view of that center. Astronomers estimate that only one part in 10 billion of the starlight emitted by the center ever reaches us. Dust absorbs the rest of the light and re-emits it as IR radiation.
Astronomers already know that this core region, which represents only a millionth of our galaxy's volume, emits a tenth of its total radiated energy. When they can ''see'' the core clearly by IR radiation, astronomers may be able to find out what the source of this abundant energy is.
Many clouds of dust and gas, such as the Orion Nebula, are places where new stars are being born. Again, the clearest view of what is going on is provided by IR radiation. Other objects, such as dying stars that have ejected clouds of dust and gas, should also be more easily studied at these wavelengths.
Until IRAS settles into orbit and is working, its designers can't be certain just how clear its IR view will be. It uses technology at the limit of what now is possible.
The telescope must be kept at 2 Kelvins (-271 degrees C.) so that it won't be blinded by its own heat radiation. This is an unprecedented low temperature that should provide a 90-fold gain in sensitivity over the best ground-based IR telescopes.
To achieve this, the IR sensors are cooled by liquid helium. The satellite also must be oriented so it never ''sees'' the Sun, Moon, or Earth, which are blindingly bright in the infrared.
Even at a temperature only 2 degrees above absolute zero, the helium will slowly vaporize and leak away. The rate of helium loss will set the upper limit of IRAS's useful life, now estimated at a maximum of about seven months.
If successful, IRAS should mark the beginning of a rapid expansion in IR astronomy. NASA is developing a Shuttle Infrared Telescope Facility. It also plans to launch a Cosmic Background Explorer satellite late in the decade which would study radiation left over from the birth of the universe at both IR and radio wavelengths. Meanwhile, the European Space Agency is considering an IR satellite of its own which would have three times the life expectancy of IRAS.