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Planck Observatory: Cold Enough for You?

Sunday, July 05, 2009 at 03:08 PM EDT

The BBC News reports that the European Space Agency’s Planck observatory, which was launched along with the Herschel telescope in mid-May, has reached its rather chilly normal operating temperature, −273.05 degrees Celsius (−457.7° F), just 0.1° C above absolute zero (0° Kelvin). The observatory operates in the microwave part of the electromagnetic spectrum, and is designed to operate at a very low temperature to maximize the sensitivity of its detectors (called bolometers). It will attempt to make the most precise measurements yet of the oldest “light” in the universe, the Cosmic Microwave Background, left over from a short time (in cosmic terms) after the Big Bang, when the nascent universe had cooled enough (to about 3000° K) that electrons and protons could combine to form hydrogen atoms.

The existence of this background radiation, and the Doppler shift (”red shift”) of light from distant objects, provide perhaps the best evidence for the Big Bang theory of how the universe began. The existence of the radiation was postulated by George Gamow, Ralph Alpher, and Robert Herman, in 1948. Although measurements of low-level background radiation had been made previously, their suggestion was the first that it might be a relic of conditions when the universe was young.

The background radiation was finally found, more or less definitively, by two reasearchers, Arno Penzias and Robert Wilson, at the Bell Telephone Laboratory’s Crawford Hill station in New Jersey. They had constructed a large astronomical radio antenna, to be used for astronomy and satellite communications experiments; but when they connected it, they found a persistent low-level signal, corresponding to a temperature of about 3.5°K. They checked various ideas of what might cause this, including the possibility of bird droppings on the antenna, until they called Prof. Robert Dicke at Princeton, whose team was working on detecting the background radiation.

Serendipity aside, detecting and measuring this radiation requires extremely sensitive instruments: it has been compared to trying to measure the heat emitted by a rabbit sitting on the surface of the Moon from the Earth. The observatory’s detectors are arranged so that they always point away from the Sun, and the spacecraft is in an orbit around the Sun in tandem with the Earth, at the second Lagrange point [L2]. It also carries an active cooling system to maintain its frigid environment.

Previous probes, particularly WMAP, the Williamson Microwave Anisotropy Probe, have shown that the CMB radiation is not uniform:

CMB Background from WMAP

The microwave background corresponds to a “black body” spectrum, as predicted by the Big Bang Model, and is found mainly in the range of wavelengths from 3.2 to 13 millimeters (corresponding to frequencies of about 23 to 94 GHz). The Planck instrument should enable astronomers to make even better measurements of the background. The results are potentially fascinating:

Planck investigator Professor George Efstathiou from Cambridge University, UK, thinks the telescope could throw up fundamentally new discoveries.

“We will be probing regimes that have never been studied before where the physics is very, very uncertain,” he said.

“It’s possible we could find a signature from before the Big Bang; or it’s possible we could find the signature of another Universe and then we’d have experimental evidence that we are part of a multi-verse.”

The observatory is scheduled to start making “live” observations around the end of August.