Faint Echoes, Distant Stars_The Science and Politics of Finding Life Beyond Earth

by Ben Bova

  5The Moon’s major features were named centuries ago, when the dark areas were thought to be regions of water. Thus we have the Ocean of Storms, the Sea of Tranquility, etc. There is no liquid water on the Moon.

  6The others were Hermann Bondi and Fred Hoyle. Most cosmologists believe that the available evidence favors the rival Big Bang theory rather than the Steady State.

  7Harvard University, University of California at Los Angeles, University of Colorado at Boulder, Arizona State University, Pennsylvania State University, Michigan State University, University of Rhode Island, University of Washington, Carnegie Institution, Scripps Research Institute, Woods Hole Marine Biological Laboratory, NASA Ames Research Center, NASA Johnson Space Center, Jet Propulsion Laboratory (two teams).

  8The Moon rocks, of course, were brought to Earth for analysis by the Apollo astronauts.

  9Albert Einstein’s special theory of relativity showed that matter can be converted into energy; that is the meaning of his famous equation, E = mc2.

  10The makers of airships originally used hydrogen to “float” their dirigibles, but hydrogen’s flammability made it too dangerous. Now they use helium, which is an inert gas and perfectly safe.

  11NEAR is an acronym for Near-Earth Asteroid Rendezvous; Shoemaker is in honor of planetary astronomer Eugene Shoemaker (1928–1997), who was killed in a car accident in Australia.

  12The science fiction writer Kurt Vonnegut used this information to concoct the fanciful “ice-nine” in his novel Cat’s Cradle. Vonnegut’s brother, Bernard, was involved in studies of ice-particle formation as part of his work on cloud seeding.

  13DNA is deoxyribonucleic acid; RNA is ribonucleic acid. See the Appendix for details on their structure and functions.

  14Symbiosis means, literally, “living together.” In biology, a symbiotic relationship is where two organisms live in physical contact with each other and actively help each other, such as the nitrogen-fixing bacteria that provide nitrogen for certain green plants in return for some of the carbohydrates the plant produces.

  15Cameras needed long exposure times in those days, which meant that the object to be photographed might fade in and out of focus, blurring the picture. The human eye could see more detail. It was not until well into the twentieth century that fast photographic film began to prove its value in astronomy.

  16Lichen are themselves a symbiotic combination of two life-forms, algae and fungi.

  17Any object at a temperature above absolute zero radiates electromagnetic energy. Planets radiate mostly in the infrared and microwave wavelengths.

  18Earlier landers were crushed by the enormous atmospheric pressure before they reached the ground. Even the successful landers transmitted data only for a few minutes before their electronic systems were fried by the intense heat.

  19Based on Latin, the proper possessive of Venus is Venerian. Yet to some, the term has an unwanted erotic overtone, so they use Venusian, which purists claim is ugly and grammatically incorrect.

  20Jupiter’s fortieth moon was discovered on Halloween night 2002, by astronomer Scott S. Sheppard of the University of Hawaii, using the 2.2-meter telescope atop Mauna Kea. S/2002 J1 is estimated to be 3 to 4 kilometers in diameter. It was the twenty-third Jovian moon discovered by Sheppard.

  21Pop artist Andy Warhol predicted in the 1960s that, “In the future everyone will be famous—for fifteen minutes.”

  22Since Sirius has been known as the Dog Star from time immemorial because it is in the constellation of Canis Major, the Big Dog, its dwarf companion was quickly dubbed the Pup.

  23For comparison, the full Moon covers slightly more than 31 arc minutes (60 arc minutes make one degree). Barnard’s Star, therefore, travels a distance of roughly one two-hundredths of the Moon’s apparent diameter in the course of a year. Not much by everyday standards, but among astronomers it’s a speed demon.

  24Many stars are cataloged in order of their brightness and the constellation in which they are found: 61 Cygni, for example, is in the constellation Cygnus, the Swan.

  25Pulsars are identified by the abbreviation PSR and the coordinates of their location in the sky. Thus a pulsar’s “I.D.” tells you where it is located.

  26Some astronomers dubbed them Vulcans, after a hypothetical planet of our own solar system that was presumed to orbit the Sun closer than Mercury. Fans of the television series Star Trek (which includes many astronomers) were pleased.

  27The idea of self-replicating machines, machines that make copies of themselves, was first proposed by the Hungarian-born mathematician John von Neumann in the late 1940s.

  28Paleontologists use the letter C to denote the earlier Carboniferous Era, so to denote the Cretaceous they use the letter K, from the German Kreide, meaning “chalk” and derived from the extensive chalk deposits that mark Cretaceous sites.

  1Even the value for the first factor, R*, which represents the number of stars in the Milky Way, is debatable. Estimates have ranged from 100 to 400 billion.

  ASTRONOMY IN A WELL

  Eratosthenes lived in Alexandria, Egypt. He heard that at noon on midsummer’s day the Sun shone straight down a well in the town of Syene (today called Aswan, site of the great dam across the Nile). He measured the angle of the Sun’s shadow at noon on midsummer’s day in Alexandria, which was about 7° from the vertical.

  The distance between Alexandria and Syene was known at that time as about 5,000 stadia. Using simple geometry, Eratosthenes reasoned that if 5,000 stadia represented 7° of the spherical Earth (or about 1/50 of the 360° sphere), then the entire planet must be 50 times 5,000, or 250,000 stadia in circumference.

  The stadium was a Greek unit of length that varied somewhat from place to place; there was no Bureau of Standards to make units, well, standard. Eratosthenes probably used a stadium that was roughly 167 meters. If so, his result for the Earth’s circumference was within 1 percent of the correct value of 40,000 kilometers.

  WHO SAID IT FIRST?

  The word astrobiology was apparently coined by the Russian astronomer Gavriil Adrianovich Tikhov (1875–1960) in 1953. Director of the Institute of Astrobotany at Alma Ata, Kazakhstan, Tikhov spent much of his career studying Mars, and he was one of those who believed at that time that “primitive” life-forms such as lichens might exist on the red planet. Also in 1953, Hubertus Strughold, of the U.S. Air Force’s School of Aviation Medicine, used the term in his book about Mars, The Green and Red Planet: A Physiological Study of the Possibilities of Life on Mars. In 1956, the Brazilian scientist Flavio A. Pereira published a book he titled Introduction to Astrobiology.7Harvard University, University of California at Los Angeles, University of Colorado at Boulder, Arizona State University, Pennsylvania State University, Michigan State University, University of Rhode Island, University of Washington, Carnegie Institution, Scripps Research Institute, Woods Hole Marine Biological Laboratory, NASA Ames Research Center, NASA Johnson Space Center, Jet Propulsion Laboratory (two teams).

  INTERSTELLAR DISTANCES

  While distances within the solar system can be conveniently measured in astronomical units, where one AU is the average distance between the Earth and the Sun (roughly 150 million kilometers), the AU is much too small to serve as a yardstick for distances between the stars.

  For example, consider the distance to Alpha Centauri, the closest star to our solar system. Imagine a map in which the distance between the Earth and the Sun—150 million kilometers—is shrunk to one inch. (Forgive me, this simile doesn’t work with metric units.) On our map, one inch equals one AU. On such a map, how far from the Sun must we place the nearest star, Alpha Centauri? A distance of 4.3 miles. There are approximately the same number of inches in a mile (63,360) as there are AUs in a light-year (63,000), and Alpha Centauri is 4.3 light-years from the Sun.

  Light, traveling at some 300,000 kilometers per second, needs 4.3 years to cross the distance between the Sun and Alpha Centauri. And Alpha Centauri is the closest star to our solar system.8The Moon rocks, of cours
e, were brought to Earth for analysis by the Apollo astronauts.

  PLASMA: THE FOURTH STATE OF MATTER

  Physicists call plasma the fourth state of matter: solids, liquids, gases, plasmas.

  A plasma is a gas that has been ionized, that is, some or all of its atoms have been stripped of their orbital electrons. Thus a plasma consists of free electrons and ions, which are atoms that have lost electrons. A plasma behaves much like a gas, but there is one very significant difference between the two.

  Although a plasma is electrically neutral, since the positive charges of the ions are balanced by the negative charges of the free electrons, those free electrons can carry electrical currents. This means that a plasma can be moved, shaped, or influenced by electromagnetic forces such as electric currents or magnetic fields.

  Plasmas are rare on Earth. A lightning strike briefly ionizes the air around it, forming a whiff of ozone from normal oxygen. The ionized gas in a fluorescent lamp is a weakly ionized plasma. However, the Sun, the stars, and most of the universe are composed of highly ionized plasmas. It is only in small, cold, out-of-the-way places such as our planet Earth that the other three forms of matter prevail.10The makers of airships originally used hydrogen to “float” their dirigibles, but hydrogen’s flammability made it too dangerous. Now they use helium, which is an inert gas and perfectly safe.

  METEOROIDS, METEORS, AND METEORITES

  It’s been said that the Eskimos have a hundred names for snow. Scientists have three different names for the solid chunks of matter that fall into our atmosphere from outer space.

  Whether the object is a dust mote or a mountain-sized chunk of rock, while it is in space it is called a meteoroid. When a meteoroid hits the Earth’s atmosphere and begins to glow from the heat of aerodynamic friction, it is called a meteor, from an ancient Greek root meaning roughly “something in the air.” Nonscientists call them “shooting stars.” Most meteors burn up in the high atmosphere, but some of the larger ones make it through their blazing flight and hit the ground. When a meteoroid reaches the ground it is called a meteorite.

  A meteoroid is the solid body, regardless of its size; a meteor is the blaze it makes as it burns in our atmosphere (usually higher than 95 kilometers altitude); and a meteorite is what is left of the object if it survives to the ground.

  Meteoroids almost certainly are actually asteroids that have fallen into the trap of Earth’s gravity field. So there are actually four names for the same object. Considering that asteroids are more properly called planetoids, make it five names.11NEAR is an acronym for Near-Earth Asteroid Rendezvous; Shoemaker is in honor of planetary astronomer Eugene Shoemaker (1928–1997), who was killed in a car accident in Australia.

  IS VENUS HOTTER THAN HELL?

  At some 500°C, the surface of Venus is certainly the hottest planetary surface in the solar system. Could it be hotter than hell?

  Stephen Strauss, in his book The Sizesaurus, reports on certain calculations attributed to a mysterious Mr. Wensel of the U.S. National Bureau of Standards, which were reputedly made more than a half century ago. With tongue undoubtedly in cheek, Wensel tried to determine how hot hell might be.

  Wensel suggested that the biblical statement in Revelation 21:8 provides a key to hell’s temperature: “But the fearful, and unbelieving . . . shall have their part in the lake which burneth with fire and brimstone.” Brimstone is an ancient term for the element sulfur. To permit the existence of a lake of molten sulfur, the temperature in hell would have to be below 444.6°C. If it were hotter, the brimstone would become a cloud of gaseous sulfur rather than a lake of liquid sulfur.

  Of course, this is true only if the pressure in hell is the same as the pressure on the Earth’s surface at sea level. Since hell is always depicted as being rather deep underground, the pressure must be somewhat higher. Under intense pressures, brimstone can stay liquid to 1,040°C, which means that hell could be twice as hot as the surface of Venus.20Jupiter’s fortieth moon was discovered on Halloween night 2002, by astronomer Scott S. Sheppard of the University of Hawaii, using the 2.2-meter telescope atop Mauna Kea. S/2002 J1 is estimated to be 3 to 4 kilometers in diameter. It was the twenty-third Jovian moon discovered by Sheppard.

  FINDING THE UNSEEN

  While Uranus can barely be seen with the naked eye, Neptune is too dim to be seen without a telescope. So how did anyone know it existed?

  Within a few years of Herschel’s discovery of Uranus, astronomers began to find that the new planet was not precisely following the orbit they had predicted mathematically. Something was perturbing Uranus, tugging gravitationally at it.

  Two young mathematicians, John Couch Adams (1819–1892) of England and Frenchman Urbain Le Verrier (1811–1877), independently calculated the position where the unseen object must be. The British Astronomer Royal George Airy paid scant attention to Adams’ information. On the continent, however, Johann Gottfried Galle (1812–1910), director of the Berlin Observatory, used Le Verrier’s calculation to locate the “new” planet on September 23, 1846 (much to the mortification of the British because Adams had actually finished his calculations before Le Verrier, so that Britain would have had the honor of discovering the planet if Airy had taken Adams more seriously).

  While some Europeans wanted to name the planet after Le Verrier and Galle (a suggestion the British regarded dimly), the tradition of using the names of Roman gods eventually prevailed and the planet was named Neptune.

  This was the first time that the presence of an unseen heavenly body had been predicted by using Newton’s law of universal gravitation and its accompanying mathematics, a triumph for the long-dead Newton and verification that the universe is, in Einstein’s later words, understandable.21Pop artist Andy Warhol predicted in the 1960s that, “In the future everyone will be famous—for fifteen minutes.”

  THE DOPPLER-FIZEAU EFFECT

  Spectroscopic measurements can determine a star’s motion along the line of sight: that is, whether the star is approaching or receding from the observer. This is thanks to the Doppler effect. The Austrian physicist Christian Doppler (1803–1853) explained why a sound increases in pitch as it approaches the listener and then decreases in pitch as it moves away. You have heard this whenever a fire engine or ambulance wails past. In 1848, Doppler suggested that light would behave the same way, and the French physicist Armand Fizeau (1819–1896) proved him to be right.

  A source of light approaching the observer will show a shift in its spectrum toward the blue end. A light source that is receding will be shifted toward the red end of the spectrum. This holds true for any source of light: a candle, a flashlight, a star, or a galaxy. Slight shifts in a star’s spectrum can tell astronomers whether the star is moving toward or away from us.

  This is commonly called the Doppler effect, although when it deals with light it is more proper to call it the Doppler-Fizeau effect.26Some astronomers dubbed them Vulcans, after a hypothetical planet of our own solar system that was presumed to orbit the Sun closer than Mercury. Fans of the television series Star Trek (which includes many astronomers) were pleased.

  RADIO FREQUENCIES

  Radio waves are a form of electromagnetic energy, like infrared, visible light, ultraviolet, X rays, and gamma rays. The frequency of any wave is a measure of the number of wave crests (or troughs) that pass a given point in one second. Frequency is measured in hertz, named after Heinrich Hertz (1857–1894), who, in 1888, discovered that radio waves exist and can be produced at will with the proper electrical equipment. Hertz is the father of the electronics industry.

  For example, microwaves, which are used in radar and microwave ovens (and SETI), have frequencies of 300 to 300,000 megahertz (millions of hertz). Radio waves for AM broadcasting range from 530 kilohertz to 1.6 megahertz. FM and television broadcasting ranges from 100 megahertz to a few gigahertz.Fig 18-1. This was the message sent by Dr. Frank Drake to his friends.

  Fig 18-2. The 551 characters of the code message are arranged in a rectangl
e that is 19 units across and 29 units long. All the “ones” are represented by a dark space while all the “zeroes” are left blank.

  Fig 18-3. Below is the correct decoding of the “message from the stars.” Dr. Drake’s message shows that there is a chance to understand a race from another star system, once we make radio contact.