Each picture consists of many numbers, each of which represents the brightness of a single picture element, or pixel, on the image. There are 640 000 pixels in each Voyager image, representing a square image of 800 × 800 points. This information content is more than twice that of an ordinary television picture, which has only 520 lines. For each pixel, eight binary numbers are required to specify the brightness; the total information in a single image is thus 8 × 640 000 = 5 120 000 bits. Even at a transmission of one frame per 48 seconds, the “bit rate” is more than 100 000 bits per second. For comparison, the bit rate from the first spacecraft to Mars (Mariner 4) was about 10 bits per second, requiring a week to transmit 21 pictures, with a total information content equivalent to a single Voyager picture. Altogether, Voyager took nearly 20 000 pictures at each Jupiter encounter, representing 10¹¹—a hundred billion—bits of information. [Illustration: Rudolph Hanel, infrared spectrometer Principal Investigator] Infrared Spectrometer The infrared investigation on Voyager is based on one of the most sophisticated instruments ever flown to another planet. In the past, most infrared instruments on planetary spacecraft measured at only a few wavelengths, but Voyager carries a true spectrometer, capable of measuring at nearly 2000 separate wavelengths, covering the spectrum from 4 to 50 micrometers. Twelve scientists, led by Principal Investigator Rudolph Hanel of the NASA Goddard Space Flight Center at Greenbelt, Maryland, proposed this infrared instrument. Hanel is an acknowledged world leader in infrared spectroscopy from space. With his co-workers at Goddard, he has pioneered in adapting the extremely complex art of interferometric spectroscopy to the rigors of space flight. His spectrometers have made many studies of the Earth’s atmosphere from meteorological satellites, and a Hanel interferometer flew successfully to Mars on Mariner 9. The primary goals of the infrared spectrometer investigation are directed toward analysis of the composition and structure of the atmosphere of Jupiter. Among the molecules to be searched for on Jupiter were hydrogen (H₂), helium (He), methane (CH₄), ammonia (NH₃), phosphine (PH₃), water (H₂O), carbon monoxide (CO), simple compounds of silicon and sulfur, and a variety of organic compounds consisting of atoms of carbon and hydrogen (e.g., C₂H₂, C₂H₄, C₂H₆). In addition to indicating the abundance of these constituents of the atmosphere, the infrared spectra also contain information on atmospheric structure, that is, on the variation of temperature and pressure with altitude. The presence of clouds or dust layers can also be inferred from the shapes of spectral lines.