More about Herschel and HIFI

HIFI will measure in two wavelength areas within the submillimetre area: from 240 to 625 micrometres (or 480-1250 GHz) and from 157 to 210 micrometres (1410-910 GHz). These wavelengths can scarcely be measured from the Earth. The atmosphere has such a disruptive effect that reception is not possible at all for many wavelengths.

Due to the high resolving power (resolution) of the instrument, it is suitable for investigating interstellar gas, for example in star-forming areas and in the gas expelled by dying stars. In the far-infrared and the submillimetre areas where HIFI will work, a wide range of molecules absorb radiation, including water. HIFI is suitable for capturing this radiation and can unravel it into a spectrum in which the characteristic fingerprints of all the different molecules can be seen. This instrument can be used to determine exactly what the gases are composed of and the temperature and pressure they are at. Furthermore, HIFI is highly suitable for measuring the speed of gas.

Water
One of the most important molecules that will be measured is water. Water can only be detected from inside space. Even on the driest desert mountain, the atmosphere is too humid for this procedure. HIFI will be able to provide information about the presence of water in gas clouds and, more generally, the processes that occur within these. Closer to home, the instrument will perform measurements on the atmospheres of planets and comets in our own solar system.

Mixers
HIFI works with superconducting receivers that are cooled using super-cold liquid hydrogen. For the spectrum ranging from 240 to 625 micrometres, HIFI has sensitive heterodyne SIS (superconducting-isolator-superconducting) receivers, and for the 157 to 210 micrometre area there are the Hot Electron Bolometers. Both types of receiver convert the (high-frequency) signal that is received into a lower frequency without losing any information. Just as for FM radio, this process makes the reception clearer and the signal can be amplified better. The functioning of the mixers is based on advanced physics, which is the result of more than 15 years of research and development. Four mixers have been constructed by SRON and the others come from scientific institutes in France, Germany, Sweden and the US.

As Principle Investigator, SRON is responsible for the design and construction of HIFI. No less than 25 institutes and 12 different countries are taking part in this project.