Herschel uses a 3.5 meter primary mirror – the largest ever built for use in space, designed to observe in the 55 to 672 micrometer wavelength range. This area of the spectrum is extremely difficult to observe from Earth and objects radiating at 5 to 50 degrees Kelvin are only visible in this range. Furthermore, colder gases (up to a few hundred degrees Kelvin) have their strongest spectral emission lines within this range. Among other things, Herschel should help scientists explore how galaxies formed in the early universe, and provide valuable information on the relationship between stars and the interstellar medium, the chemistry of the galaxy, and the molecular chemistry of various bodies in the solar system.
Herschel includes three different instruments for detecting light in its target wavelength range. The Photodetector Array Camera Spectrometer (PACS) is an imaging photometer (also called an area photometer) and medium resolution grating spectrometer. PACS is optimized to observe forming planetary systems as well as stars and galaxies emitting light with wavelengths in the 60 to 210 micron range.
The Spectral and Photometric Imaging Receiver (SPIRE) also includes an imaging photometer as well as a low to medium resolution imaging Fourier Transform Spectrometer. SPIRE uses arrays of bolometers in web-like meshes to directly detect photons in the approximate range of 208 to 583 microns – ideal for observing distant galaxies and the earliest stages of star formation. The array design significantly reduces the mass of the bolometers compared to previous designs and reduces interference from cosmic rays.
The Heterodyne Instrument for the Far Infrared (HIFI) is a high resolution heterodyne spectrometer. Because a heterodyne spectrometer mixes the frequency of observed photons with frequencies generated by the instrument, HIFI signals actually reside in the microwave rather than the far infrared range of the original source. This makes analyzing the signals significantly easier and results in much higher resolutions than those possible in the original frequency ranges.
All three instruments require extreme cold (near absolute zero) to operate properly; their shared optical bench (where the instruments are mounted to the telescope) will be cooled by over 2000 liters of liquid helium.
Herschel will be launched on an Ariane rocket from ESA’s primary launch site French Guyana in May 2009. It will arrive at the L2 orbit about four months later with an expected operational lifetime of approximately three years since the arrival.
TFOT has previously reported on other telescopes including the recent launch of the Kepler Telescope, designed to search for habitable planets in our solar system. We have also covered initial reports from the Fermi Gamma-ray Space Telescope (formerly the Gamma-ray Large Area Space Telescope or GLAST) and the High-Resolution Soft X-Ray Spectrometer (SXS), which was designed for inclusion on Japan’s NeXT telescope. You are also welcome to read our coverage of the construction of the French Antares underwater Neutrino Telescope, and the construction of one meter lenses for the Blanco 4 meter telescope that’s part of the Dark Energy Survey observing dark matter.
Read more about the Herschel Space Observatory at its mission page on NASA’s website (part of the Jet Propulsion Laboratory website), its main ESA page, or its page at the California Institute of Technology (Cal Tech).