Faint Echoes, Distant Stars

by Ben Bova

  That is the sum and substance of Darwin’s idea of evolution through natural selection. Organisms change; that is, they evolve. Natural selection allows the organisms that are best suited for their environment to leave more offspring.

  Through painstaking research over many decades, Darwin provided nearly incontrovertible evidence that evolution through natural selection explains the way nature works. His ideas were widely criticized in his day; unthinking people claimed that Darwin was trying to replace the idea that God created the world and everything in it. They were particularly upset with the notion that human beings were not specially created by God, but evolved from a line of ape ancestors.

  To this day, critics try to tear down Darwin’s work. Creationists work hard to remove Darwin from school curricula. This makes about as much sense as trying to repeal the law of gravity or changing the value of ¼ to an even three rather than its uncomfortable, but actual, value of 3.14159 . . . (this was actually proposed in the Pennsylvania state legislature when I was a schoolboy).

  Glossary

  Abiological: Not associated with biology, therefore not associated with living organisms. An abiological explanation for an observation is one that does not involve biology or living organisms.

  Abiotic: Something characterized by the absence of life.

  Absolute magnitude: A measure of how bright a star would appear if it were at a distance from the Sun of ten light-years. Absolute magnitude is a way of assessing how luminous a star is intrinsically.

  Accretion: The process of growth by adding material from outside the accreting body.

  Accretion disk: A flat disk of gas and dust spun out by the early Sun from which the planets and other solid bodies of the solar system grew. Accretion disks have been seen around other stars.

  Acidophiles: Organisms that can survive in environments that are highly acidic.

  Aerobraking: The technique of using atmospheric drag to slow down a spacecraft for landing or to establish it in an orbit around the target planet.

  Alkalophiles: Organisms that can survive in environments of high alkalinity.

  Angular momentum: The inherent property of matter that makes a rotating body continue to rotate. Sometimes referred to as “spin energy.”

  Aphelion: The point in a planet’s orbit that is farthest from the Sun.

  Apparent magnitude: How bright a star actually appears in the sky, regardless of its distance.

  Archaea: A distinct family of microorganisms that resemble bacteria but are probably of an older lineage. Many of the extremophiles (q.v.) are archaea. Also called archaic bacteria.

  Asteroid: A minor planet, more properly called a planetoid. Millions of asteroids orbit between Mars and Jupiter in a region called the Asteroid Belt. The largest of these is Ceres, with a diameter just under 1,000 kilometers. The smallest are no larger than dust grains.

  Asteroid Belt: The region between the orbits of Mars and Jupiter where most of the solar system’s asteroids are found.

  Astrobiology: The study of life’s origin, extent, and future in the universe.

  Astrometric: The technique of measuring perturbations in a star’s proper motion to determine if the star is accompanied by an unseen companion, either a dim dwarf star, a brown dwarf, or a planet.

  Astronomical Unit (AU): The average distance between the Earth and Sun, 149,597,870 kilometers. The AU is used as a convenient “yardstick” for distances within the solar system.

  Biomarkers: Observable features that are caused by biological activity and therefore evidence for the existence of life.

  Biosphere: The zone that supports life. Earth’s biosphere extends from the upper atmosphere to the bottoms of the oceans and several kilometers underground.

  Black smoker: See Hydrothermal vent.

  Brown dwarf: A “failed star”; a gaseous body less than seventy-five to eighty times the mass of Jupiter and therefore not massive enough to ignite fusion reactions in its core and become a true star.

  Chemosynthetic: Organisms that build organic matter (such as carbohydrates) out of inorganic chemicals using heat energy. Contrast to photosynthetic. Chemosynthetic bacteria are the basis of the food chain at the black smoker sea-bottom vents.

  Comet: Bodies composed primarily of water ice, laced with dark, sooty, carbon-rich compounds that are the precursors of living organisms.

  Cryptoendoliths: Literally, “hidden within the rocks.” Cryptoendoliths are tiny colonies of lichen that exist in the cracks a few millimeters below their surfaces of rocks in Antarctica.

  Eccentric orbit: An orbit that is not circular. No planet’s orbit is perfectly circular, therefore all the planets discovered to date have orbits of some eccentricity.

  Eukaryotic: Cells that have a nucleus. Eukaryotes include the single-celled protists, slime molds, fungi, plants, and animals.

  Exobiology: The search for extraterrestrial life.

  Extrasolar: Beyond the solar system. Extrasolar planets are planets that orbit stars other than the Sun.

  Extremophiles: Organisms that live in conditions of extreme temperature, pressure, pH, etc. “Extreme,” in this definition, is based on the conditions that we humans consider comfortable and therefore “normal.”

  Flux tube: An electrically charged doughnut-shaped torus of plasma circling the planet Jupiter that consists of sulfur-rich gases ejected from the Jovian moon Io by its constant volcanic activity.

  Gaia hypothesis: The concept that Earth (and presumably other planets where life exists) is a single interrelated entity that actively maintains optimal conditions for life’s continued existence.

  Geocentric theory: The astronomical theory that Earth is the center of the solar system and, by extension, the center of the universe.

  Halophiles: Organisms that live in extreme concentrations of salt, as much as thirty-seven times saltier than sea water.

  Heliocentric theory: The theory that the Sun is the center of the solar system.

  Hot Jupiters: Extrasolar planets as massive as the gas giant Jupiter (or more so) that are in very close orbits around their parent stars and therefore much hotter than the gas giants of our solar system.

  Hydrothermal vent: A sea-bottom vent that ejects superheated water rich in sulfur and other chemical compounds. Over time, these vents build extensive chimneys of stone and are the sites of colonies of extremophiles and other life-forms. Also called black smoker.

  Interferometry: The technique of splitting a light signal from a luminous object (such as a star) into two parts in order to form an interference pattern of dark and light bands that can yield very precise measurements of the luminous object’s distance, size, etc.

  Ion: An atom that has lost (or gained) one or more electrons orbiting its nucleus and therefore is no longer electrically neutral, since the number of its electrons are not balanced by the number of protons in its nucleus; hence, an atom that has a net electrical charge, either positive (due to electron loss) or negative (due to electron gain).

  Ionized: Consisting of ions.

  Kuiper Belt: The inner fringes of the Oort Cloud; the source of most short-period comets (those that return to the inner solar system in less than 200 years).

  Magnetosphere: The volume of space surrounding a planet in which the planet’s magnetic field is a dominant force. Earth’s magnetosphere is a lopsided shell that extends some 64,000 kilometers in the Sunward direction and beyond the orbit of the Moon in the direction away from the Sun.

  Meteor: The light caused when a body falling into the Earth’s atmosphere begins to glow from the heat caused by friction with the air. Also called a “falling star.”

  Meteorite: The remains of a meteoroid that has fallen to the ground.

  Meteoroid: The solid body of an object that falls to Earth. Most meteoroids are no bigger than dust grains.

  Methanogens: Archaea that give off methane as a result of their metabolic processes.

  Near-Earth Asteroid (NEA): Asteroids in orbits that are close to the orbi
t of Earth. The orbits of some NEAs cross the Earth’s orbit.

  Neutron star: A star that has collapsed to a size of a few tons of kilometers across and is so dense that the protons and electrons of its atoms have merged to form neutrons.

  Oort Cloud: A vast cloud of uncounted millions of icy bodies lying beyond the orbit of Neptune and stretching more than 100,000 AUs from the Sun. (See also Kuiper Belt.)

  Paleontology: The study of organisms that lived ages ago and are now extinct.

  Perihelion: The point in a planet’s orbit that is closest to the Sun.

  pH: A system for classifying substances by their acidity or alkalinity. The term pH stands for “potential of hydrogen”: that is, how strongly the substance will attract and hold hydrogen atoms. The scale runs from pH = 0, which is as acidic as possible, to pH = 14, which is maximum alkalinity. Pure distilled water is pH = 7, exactly in the middle of the scale.

  Photosynthesis: The process of building carbohydrate foodstuffs out of water, carbon dioxide, and sunlight.

  Photosynthetic: Organisms that build organic compounds (such as carbohydrate sugars) out of inorganic materials using the energy of sunlight. Photosynthetic bacteria and plants are the basis of the food chain on Earth’s surface.

  Planetesimal: A body of rock or ice, less than the size of a planet, that forms in a star’s primordial accretion disk.

  Planetoid: See asteroid.

  Plasma: An ionized gas.

  Polycyclic aromatic hydrocarbons (PAHs): Highly stable carbon-hydrogen molecules that have been detected in comets, meteorites, interstellar gas clouds, and galaxies beyond the Milky Way. PAHs may be an important prebiotic molecule.

  Prebiotic: Literally, before biology; usually referring to chemical processes that occur before life begins.

  Prokaryotic: Cells that do not have a nucleus. Bacteria and archaea are prokaryotes.

  Proper motion: A star’s motion across the observer’s field of view.

  Protists: Single-celled eukaryotic organisms such as amoebas or paramecia.

  Protostar: A cloud of gas and dust that is collapsing and will ultimately form a star and (perhaps) planets.

  Psychrophiles: Organisms that live in extremely low-temperature environments.

  Pulsar: A neutron star that emits pulses of visible light and radio energy.

  Radial velocity: A star’s motion either toward or away from the observer.

  SETI: Search for Extraterrestrial Intelligence.

  SLiMEs: Subsurface Lithotropic Microbial Ecosystems; bacteria that live deep underground and metabolize rock.

  Supernova: The explosion of a massive star, capable of emitting as much energy in twenty-four hours as the Sun puts out in millions of years.

  Symbiosis: An interdependent relationship between two organisms of different species; usually the two organisms are in physical contact with each other.

  Symbiotes: Organisms that have symbiotic relationships.

  Thermally habitable zone: An area where the temperature environment is suitable for life to exist.

  Thermophiles: Organisms that exist in environments of extremely high temperature.

  Van Allen Belts: Areas of charged particles (electrons and protons) held in shells around a planet by that planet’s magnetosphere.

  Bibliography

  INTERNET WEBSITES

  There are many Internet sites that deal with various aspects of astrobiology.

  NASA’s astrobiology site is: http://astrobiology.arc.nasa.gov

  The SETI Institute’s site: www.seti@home

  The Optical SETI site: www.coseti.org

  The Planetary Society site: http://planetary.org

  The National Space Institute: www.nss.org

  BOOKS AND JOURNAL PAPERS

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  Bernstein, Max P., Scott A. Sandford, and Louis J. Allamandola. “Life’s Far-Flung Raw Materials,” Scientific American, 281, 1 (July 1999).

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  Caro, G. M. Muñoz, U. J. Meierhenrich, W. A. Schutte, B. Barbier, A. Arcones Segovia, H. Rosenbauer, W. H.-P. Thiemann, A. Brack, and J. M. Greenberg. “Amino Acids from Ultraviolet Irradiation of Interstellar Ice Analogues,” Nature, 416, No. 6879 (28 March 2002).

  Carr, Michael H. Water on Mars (Oxford, U.K.: Oxford University Press, 1996).

  ——— and James Garvin. “Mars Exploration,” Nature, 412, No. 6813 (12 July 2001).

  Carrol, Susan B. “Chance and Necessity: The Evolution of Morphological Complexity and Diversity,” Nature, 409, No. 6822 (22 February 2001).

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  Cocconi, Giuseppe, and Philip Morrison. “Searching for Interstellar Communications,” Nature, 184, No. 2055 (2 September 1959).

  Cooper, George, et al. “Carbonaceous Meteorites as a Source of Sugar-Related Organic Compounds for the Early Earth,” Nature, 414, No. 6866 (20/27 December 2001).

  Cowen, James P., et al. “Fluids from Aging Ocean Crust that Support Microbial Life,” Science, 299 (3 January 2003).

  Croswell, Ken. Planet Quest (New York: Free Press, 1997).

  Darling, David. Life Everywhere: The Maverick Science of Astrobiology (New York: Basic Books, 2001).

  Davies, John. Beyond Pluto (Cambridge, UK: Cambridge University Press, 2001).

  Davies, Paul C. W. The Fifth Miracle: The Search for the Origin and Meaning of Life (New York: Simon & Schuster, 1999).

  Delsemme, Armand. Our Cosmic Origins: From the Big Bang to the Emergence of Life and Intelligence (Cambridge, U.K.: Cambridge University Press, 1998).

  Des Marais, D. J., and M. R. Walter. “Astrobiology: Exploring the Origins, Evolution, and Distribution of Life in the Universe,” Annual Review of Ecological Systems, 30, pp. 397–420 (1999).

  DeVincenzi, Donald L., et al. Mars Sample Quarantine Protocol Workshop, NASA/CP-1999-208772 (April 1999).

  Dick, Steven J. Life on Other Worlds: The
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  ———. The Biological Universe (Cambridge, U.K.: Cambridge University Press, 1996).

  Drury, Stephen. Stepping Stones (Oxford, U.K.: Oxford University Press, 1999).

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  Gillett, Stephen L. World-Building (Cincinnati: Writer’s Digest Books, 1996).

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  ———. The Deep, Hot Biosphere (New York: Springer-Verlag, 1999).

  Goldsmith, Donald. The Hunt for Life on Mars (New York: Dutton, 1997).

  ———. Worlds Unnumbered: The Search for Extrasolar Planets (Sausalito, Calif.: University Science Books, 1997).

  ———and Tobias Owen. The Search for Life in the Universe (Second Edition) (Reading, Mass.: Addison Wesley Publishing Co., 1992).

  Gonzalez, Guillermo, Donald Brownlee, and Peter D. Ward. “Refuges for Life in a Hostile Universe,” Scientific American 285, 4 (October 2001).

  Gould, Stephen Jay. Wonderful Life (New York: W.W. Norton and Co., 1989).

  ———. Bully for Brontosaurus (New York: W.W. Norton and Co., 1991).

  ———. Full House (New York: Harmony Books, 1996).

  ———. The Structure of Evolutionary Theory (Cambridge, Mass., and London, England: Harvard University Press, 2002).

  Grady, Monica. Astrobiology (Washington, D.C.: Smithsonian Institution Press, 2001).

  Grinspoon, David. Lonely Planets; The Natural Philosophy of Alien Life. (New York: HarperCollins, 2003)

  Grinspoon, David Harry. Venus Revealed (Reading, Mass.: Addison-Wesley, 1997).

  Halpern, Paul. The Quest for Alien Planets (New York and London: Plenum Press, 1997).

  Harrison, Albert A. After Contact: The Human Response to Extraterrestrial Life (New York and London: Plenum Press, 1997).

  Hart, M. H. “The Evolution of the Atmosphere of Earth,” Icarus, 33, pp. 22–39 (1978).