Page:Concepts for detection of extraterrestrial life.djvu/33

 CHAPTER VI

The use of ultraviolet spectrophotometry for detecting peptide bonds is being studied to determine whether it can be applied to the search for life on other planets. This program is under the direction of Dr. Sol Nelson at Melpar. Since all proteins contain peptide bonds, and since all living things on Earth contain proteins, the detection of extraterrestrial peptide bonds might be consistent with the presence of living things.

Before going any further, it would be worthwhile to explain what ultraviolet spectrophotometry is, and what proteins and peptides are.

Suppose a child is in a swing that is moving at a rate of two swings each second. We can say that the frequency is 2 cycles per second. If you stand behind him and push the swing at the same frequency (2 times per second), the swing absorbs the energy and its amplitude increases. Your pushing frequency is said to be in resonance with the swinging frequency. If you try to push at a frequency of 3 cycles per second, it is obvious that the swing will not absorb the energy as efficiently.

As another example, let us consider the case of sound. Picture a room with two pianos, one with a full set of strings and one with only one string—middle C. Now, if the keys of the complete piano are struck one at a time, you will note that the single string on the incomplete piano emits a sound only when middle C (or a note of which it is an overtone) is struck on the complete piano. Here, too, the single string absorbs energy and begins to vibrate when it is in resonance with the energy. Thus, striking a D does not cause the C string to vibrate because their vibration frequency is different.

Although the examples deal with mechanical energy, the same phenomenon occurs with electromagnetic energy which includes X-rays, ultraviolet, visible light, infrared, radar and radio waves. Each of these terms applies to a range of electromagnetic energy. The highest frequencies are in the X-rays, and the lowest frequencies are in the radio. Now, if we recall that matter consists of 23