Background and Technology
Infrared Astronomy From Earth Orbit
In the 1970s, astronomers around the world began to consider the possibility of placing an infrared telescope on a satellite in orbit around the Earth. This telescope would be above the Earth's atmosphere and could view the sky at the far-infrared wavelengths which were difficult to detect on Earth. It could view a large area of the sky and observe regions for a longer period of time.
In November 1989, NASA launched the COBE satellite to study both infrared and microwave characteristics of the cosmic background radiation (the remains of the extreme heat that was created by the Big Bang). Over a ten month period, COBE mapped the brightness of the entire sky at several infrared wavelengths and discovered that the cosmic background radiation is not entirely smooth, showing extremely small variations in temperature. These variations may have led to the formation of galaxies.
The Infrared Telescope in Space (IRTS), launched in March 1995, was Japan's first infrared satellite mission. During its 28 day mission, IRTS surveyed about 7% of the sky with four instruments: A Near and Mid Infrared Spectrometer which covered wavelengths of 1.4 to 4 microns and 4.5 to 11 microns respectively, a Far Infrared Line Mapper which studied Oxygen and Carbon spectral lines at 63 and 158 microns, and a Far infrared Photometer which studied the sky at four bands centered at 150, 250, 400, and 700 microns. This data should add to our knowledge of cosmology, interstellar matter, late type stars and interplanetary dust.
The European Space Agency launched the Infrared Space Observatory (ISO) in November 1995. ISO, which observed at wavelengths between 2.5 and 240 microns, not only covered a much wider wavelength range than IRAS but was also thousands of times more sensitive than IRAS and viewed infrared sources with much better resolution. ISO took data for about 2.5 years (3 times times longer than IRAS). It ceased operations in April 1998 when its supply of liquid helium ran out. ISO contained instruments which measured details of both the shorter and longer wavelength regions of the infrared spectrum, an infrared camera which had two infrared arrays, and a photometer. Unlike IRAS, which was an infrared survey mission, ISO is operated like a ground based observatory, having astronomers submit observing proposals to study specific astronomical objects in detail. As hundreds of astronomers from several countries study the data from ISO, important new discoveries about our universe are expected to emerge. ISO has already detected dry ice in interstellar dust and hydrocarbons in some nebulae.
The Midcourse Space Experiment (MSX) was launched in April 1996 and lasted until its liquid helium coolant ran out in Feb 1997. During its 10 months of operation, MSX gathered a vast amount of data at 4.2 - 26 microns. MSX studied the infrared emission from the gas and dust which permeates the universe. MSX had 30 times the spatial resolution as IRAS and surveyed areas of the sky which were missed by IRAS.