Fjordman files the following report with the Tundra Tabloids. KGS
Human Accomplishment: Medicine and the Earth Sciences
The leading names in medicine are as follows: Louis Pasteur (1822-1895) of France; Hippocrates of Cos (ca. 460-375 BC);Robert Koch (1843-1910) of Germany (Prussia); Galen of Pergamum (ca. AD 129-200); Paracelsus (1493-1541) of Switzerland;Paul Ehrlich (1854-1915) of Germany; René Laennec (1781-1826) of France; Elmer McCollum (1879-1967) of the USA; Alexander Fleming (1881-1955) of Scotland; Ambroise Paré (1510-1590) of France; Emil von Behring (1854-1917) of Germany;Joseph Lister (1827-1912) of England; Kitasato Shibasaburo (1853-1931) of Japan; Thomas Sydenham (1624-1689) of England; the Flemish anatomist Andreas Vesalius (1514-1564); Gerhard Domagk (1895-1964) of Germany; Alexis Carrel (1873-1944) of France; Sigmund Freud (1856-1939) of Austria; John Hunter (1728-1793) of Scotland; and finally Ignaz Semmelweis (1818-1865) of Hungary.
Hunter and Semmelweis each have a score of 33, the same as Girolamo Fracastoro received. Hippocrates and Galen were founders of Western medicine as a profession although wrong in most of their medical pronouncements. Robert Koch, while less famous, was second only to Pasteur in establishing the germ theory of disease, the greatest revolution in medical history.
Just behind them follow the influential Greco-Roman pharmacologist Pedanius Dioscorides and the English immunologist Edward Jenner at 32 out of 100. Jenner’s work in the 1790s as the discoverer of vaccination for smallpox was so important that he deserves to be mentioned among the top twenty at least as much as Freud, although Freud here was ranked for purely medical contributions and the clinical description of mental illnesses, not for psychoanalysis.
Some other notable names in medicine are Thomas Addison, Leopold Auenbrugger, Thomas Beddoes, Claude Bernard, Herman Boerhaave, Daniel Bovet, Josef Breuer, Richard Bright, Frank Macfarlane Burnet, Joseph Caventou and Pierre Joseph Pelletier, Aulus Cornelius Celsus, Jean-Martin Charcot, Harvey Cushing, Pierre Fauchard, Werner Forssmann, William Halsted, Sahachiro Hata, Friedrich Henle, Oliver Wendell Holmes, Edwin Klebs, Friedrich Loeffler, Richard Lower, Patrick Manson, Giovanni Battista Morgagni, Philippe Pinel, Walter Reed, Muhammad ibn Zakariya al-Razi (Rhazes), Howard Taylor Ricketts, Ronald Ross, Pierre Roux, Santorio Santorio and Thomas Clifford Allbutt, John Snow, Max Theiler, Rudolf Virchow, Selman Waksman, Thomas Willis and William Withering.
Alexandre Yersin was a Swiss-born French physician and bacteriologist and one of the discoverers of the plague bacillus believed to have caused the Black Death in Eurasia in the 1300s, now called Yersinia pestis in his honor. He is given the lowest possible rating of 1 out of 100 in biology and is not mentioned at all in medicine, although the Japanese co-discoverer Kitasato Shibasaburo receives a very high ranking. This represents a rather strange omission.
The eminent British historian of medicine Roy Porter, author of the book The Greatest Benefit to Mankind: A Medical History of Humanity, explains that “The idea of probing into bodies, living and dead (and especially human bodies) with a view to improving medicine is more or less distinctive to the European medical tradition. For reasons technical, cultural, religious and personal, it was not done in China or India, Mesopotamia or pharaonic Egypt.”
After the Italian Renaissance period, the knowledge of human anatomy greatly improved in Europe, and only there, partly thanks to medical institutes at the rapidly expanding network of universities, where dissections of human corpses were sometimes performed to train students.
The Brussels-born physician Andreas Vesalius performed dissection demonstrations himself, thereby raising the status of surgery, which had previously been regarded as inferior medical practice. He employed artists to make illustrations for his On the Fabric of the Human Body from 1543. Science historian Toby E. Huff claims that Vesalius corrected many errors in Galen’s account of human anatomy and that the “illustrations are far superior to anything to be found in the Arabic/Islamic tradition (where pictorial representation of the human body was particularly suspect) or, for that matter, in the Chinese and (I presume) the Indian one.”
The use of systematic dissections for scientific purposes led to great advances. Nevertheless, until the late nineteenth century, Europeans did not necessarily have a better understanding of what actually caused diseases than Asian nations did, nor always more effective treatments.
At the beginning of the 1800s, surgery was still extremely painful and dangerous, conducted quickly and as a last resort, only when absolutely necessary. Some cultures like the Chinese one barely practiced it at all, with certain limited exceptions such as the castration of eunuchs. India had somewhat more promising beginnings in this field in ancient times, but progress eventually stagnated. This situation changed dramatically over the next 150 years, largely thanks to advances made in Europe and the wider Western world. Several of these were initially unrelated, but eventually merged to cause an unprecedented revolution in surgery.
Drugs such as opium, certain herbal remedies, alcoholic drinks or even tobacco among Native Americans had been used for millennia to reduce pain. Even though these drugs could be useful in a limited way they didn’t prevent most patients undergoing surgery from being fully conscious and feeling extreme pain, sometimes literally dying from the suffering associated with a major operation. This changed dramatically during the nineteenth century with the development of general anesthesia in the form of ether and chloroform. This was closely related to European advances in chemistry, for example the discovery of laughing gas.
These trends made surgery a lot less painful, but not necessarily less hazardous. What eventually made it so was the realization that microorganisms were directly related to infections and the subsequent adoption of efficient methods used to reduce this danger.
Thanks to advances in mathematics and medical statistics, it was clear to Enlightenment Europeans that there was a correlation between dirt and disease, but the specific nature of this was not yet understood; many scholars believed that diseases were transmitted through smells. The notion that microorganisms too small to be seen by the unaided human eye cause many common diseases met with surprisingly stubborn resistance, as the tragic fate of Semmelweis reminds us, until better microscopes and the careful work of such authorities as Louis Pasteur finally managed to convince most of the medical community in the late nineteenth century.
In Human Accomplishment, William T. G. Morton and Horace Wells are listed for anesthesia, as is James Young Simpson, but not Crawford Long, nor Hua Tuo or Hanaoka Seishu in East Asia. The latter two might be briefly mentioned although their line of research did not win out, in contrast to the general anesthesia developed in the West in the 1800s. And why isn’t the fine Russian physiologist Ivan Pavlov mentioned at all? Ernst Chain and Howard Florey are listed for the introduction of penicillin in addition to Alexander Fleming; Frederick Banting and Charles Herbert Best for the discovery of insulin in Canada shortly after 1920, which revolutionized the lives of people suffering from diabetes, but not John James Macleod.
The Austrian-born Jewish physician Karl Landsteiner developed the ABO blood group system, the most important (but not the only) blood type system currently in use, in the early 1900s. Other pioneers include Alexander Wiener from the USA and the Czech serologist Jan Janský. The Czech experimental physiologist Jan (Johannes) Purkinje, a friend of the German poet Johann Wolfgang von Goethe who also did valuable research into the human brain in the 1800s, introduced protoplasm and plasma (blood plasma, the clear, fluid portion of the blood in which the blood cells are suspended) as scientific terms. Important in classifying blood is also the Rhesus factor. It, too, was discovered by Landsteiner and colleagues before 1940.
Failed experiments with blood transfusions, the transfer of blood into a person’s blood stream, had been carried out for hundreds of years at the cost ofmany lives. Both the blood type and the Rhesus type must be matched in a transfusion, otherwise the patient may experience potentially lethal complications. The American surgeon William Halsted performed one of the first known human blood transfusions in the USA in 1881 by giving some of his blood to his sister save her life. Following the above mentioned breakthroughs, blood transfusion became a common medical practice worldwide. Millions of liters of blood are now donated from people around the world and used to replace blood lost through accidents or major surgery.
Coupled with other Western advances from the mid-1800s to the mid-1900s in physiology, antiseptics, general anesthesia and antibiotics, this made possible a veritable revolution in surgery; what had previously been rare, painful and dangerous operations suddenly became safer, more widespread and comparatively painless, eventually involving transplants of vital organs such as kidneys. The first successful human-to-human heart transplant was achieved in 1967 in Cape Town by Christiaan Barnard, the son of a minister in the Dutch Reformed Church in South Africa. Since then, heart transplants – totally unthinkable merely a few generations ago – have become a routine operation in major hospitals around the world.
The German Jewish scientist Paul Ehrlich together with his Japanese student Sahachiro Hata in 1909 discovered Salvarsan, an arsenical compound that proved to be an effective treatment for syphilis. Until then, mercury had been the primary choice for this disease, recommended by Paracelsus in the sixteenth century. Ehrlich effectively founded modern chemotherapy, thus realizing Paracelsus’ earlier vision of scientifically applying chemistry to medicine.
The German bacteriologist Gerhard Domagk in 1932 found the first effective drug against infections caused by bacteria, which was called prontosil. He tested it on his daughter to save her life and received the Nobel Prize in Medicine in 1939 for this magnificent breakthrough.
The first observation of penicillin was probably made by the physicist John Tyndall in 1875. He noticed that the fungus Penicillium notatum killed bacteria, but soon passed on to other matters. The credit for discovering penicillin is usually granted to the Scottish biologist Alexander Fleming in 1928. It was a lucky find. Fleming published articles on the subject but then abandoned it. The German Jewish biochemist Ernst Boris Chain, a fugitive from the Nazis, went to the Australian-born pharmacologist Howard Florey with a suggestion that they investigated the anti-bacterial properties of Fleming’s discovery. In 1940 a report was issued describing how penicillin was capable of killing germs in the living body. Great efforts were soon made to enable significant quantities of the drug to be made for use during World War II. The Nobel Prize in Medicine for 1945 was awarded jointly to Fleming, Chain and Florey.
Another revolution in medicine in the early twentieth century was the realization that small traces of certain substances are vital to human health. A few illnesses are not caused by bacteria or germs, but by deficiencies of trace elements. Certain crucial substances cannot be manufactured by the body from other nutrients and need to be supplied through the diet.
The English biochemist Frederick Hopkins in the early 1900s discovered that food contains ingredients essential to life that are not proteins or carbohydrates. This led to the discovery of vitamins, a concept first formulated by the Polish Jewish biochemist Casimir Funk in 1912. Hopkins shared the Nobel Prize in Physiology or Medicine in 1929 with the Dutch professor of physiology Christiaan Eijkman for this achievement. Eijkman had discovered that the illness known as Beriberi is caused by a deficiency of vitamin B1, Takaki Kanehiro, a British-trained medical doctor working for the Japanese Navy, had found already in the 1880s that Beriberi was caused by malnutrition. His name is not mentioned in Charles Murray’s book.
Some notable figures in addition to the American biochemist Elmer McCollum, who participated in the discoveries of several vitamins such as A and D, are related to research on vitamins: Marguerite Davis, Christiaan Eijkman, Casimir Funk, Joseph Goldberger, Albert Szent-Györgyi, Charles Glen King, Edward Mellanby and James Lind, although Lind’s pioneering clinical trials with citrus fruits in the British Royal Navy regarding the cause of scurvy (a lack of vitamin C) around 1750 took place before this concept had been formulated.
The Hungarian physiologist Albert Szent-Györgyi was awarded the Nobel Prize in Physiology or Medicine in 1937 for the discovery of vitamin C, although as often happens, others had aided in this breakthrough. The Swiss organic chemist Paul Karrerwon the Nobel Prize for Chemistry that same year together with Walter Haworth of Britain for research into vitamins.
The invention of the stethoscope by the French physician René Théophile Hyacinthe Laennec revolutionized the diagnosis of lung disorders and gave unprecedented access to the internal organs of the human body. The most efficient way to do this, however, is by aiding our eyes rather than our ears, since vision is normally mankind’s most important sense for gathering information about our surroundings. When news spread in 1896 of Wilhelm Conrad Röntgen’s discovery of X-rays, this phenomenon was quickly adopted by physicians. Röntgen is ranked in physics, and his achievement earned him the very first Nobel Prize in Physics in 1901, but his discovery was to have tremendous implications in the medical field as well.
X-rays continue to be employed by physicians and dentists worldwide but were supplemented during the course of the twentieth century by ultrasound and other techniques for imaging in medicine and the life sciences. For instance, Godfrey Hounsfield, an English electrical engineer, shared the 1979 Nobel Prize in Medicine with physicist Allan MacLeod Cormack, born in Johannesburg, South Africa to Scottish parents, for developing the theoretical foundations for the diagnostic technique now known as X-ray computed tomography (CT).
The Jewish physicist and Nobel laureate Isidor Isaac Rabi in the 1930s developed a technique for measuring the magnetic characteristics of atomic nuclei. His method was soon independently improved upon by Edward Purcell from the USA and Felix Bloch from Switzerland, whose work on nuclear magnetic resonance (NMR) garnered them the 1952 Nobel Prize in Physics and laid the foundations for magnetic resonance imaging (MRI). The English physicist Peter Mansfield shared the Nobel Prize in Medicine in 2003 with the American chemist Paul Lauterbur for contributions to making magnetic resonance imaging practical in the 1970s. Its use for medical imaging thereafter quickly spread around the world.
Virtually all cultures have had their versions of physicians or healers since all cultures have to deal with injuries and diseases. One possible objection to Murray’s work is that is does not credit non-European cultures in Australia, Africa, the Americas or the various regions of Asia for their intimate, ancient knowledge of many herbs and plants, some of which have later been scientifically demonstrated to possesses genuinely useful medical properties. For this reason, representatives of modern pharmaceutical companies occasionally follow native peoples to take notes of their comments about local plants and investigate their properties further.
Nevertheless, the empirical knowledge of plants, while undoubtedly very useful, does not alone establish true medical science, and traditional shamanist healers with their amulets and incantations to ward off evil spirits are very different from the practices of modern physicians.
Moreover, we should remember that European peoples in prehistoric times probably had an equally good understanding of useful plants and herbs in their local environment. For instance, Ötzi the Iceman, the well-preserved natural mummy who lived around 3,300 BC in the Alps, along with his tools carried a modest first-aid kit. His implements included the fruiting body of the birch polypore fungus, which is known to have antibacterial properties.
The Earth sciences category primarily includes geology, geophysics, meteorology and oceanography. The leading names here are, starting from the top down: Charles Lyell (1797-1875) of Scotland; James Hutton (1726-1797) of Scotland; William Smith (1769-1839) of England; Georgius Agricola (1494-1555) of Germany; Abraham Gottlob Werner (1749-1817) of Germany; Roderick Murchison (1792-1871) of Scotland; Matthew Fontaine Maury (1806-1873) of the USA; Louis Agassiz (1807-1873) of Switzerland; Jean-Étienne Guettard (1715-1786) of France; Carl Gustaf Mosander (1797-1858) of Sweden; Horace-Bénédict de Saussure (1740-1799) of Switzerland; Nicolas Desmarest (1725-1815) of France; Alfred Wegener (1880-1930) of Germany; Alexandre Brongniart (1770-1847) of France; Adam Sedgwick (1785-1873) of England; Thomas Chamberlin (1843-1928) of the USA; Vilhelm Bjerknes (1862-1951) of Norway; Eilhard Mitscherlich (1794-1863) of Germany; Per Teodor Cleve (1840-1905) of Sweden; and William Maurice Ewing (1906-1974) of the USA.
Modern geology can be said to have been born in the 1800s with Charles Lyell’s extension and popularization in his Principles of Geology of James Hutton’s uniformitarianism from the late 1700s. It emphasized that the most important forces shaping landforms, for instance erosion, are still ongoing today and happen at a very slow and gradual pace, not primarily through a few major upheavals or catastrophes. In order to account for the creation and destruction of entire mountain ranges, this view indirectly implied that the Earth had to be many millions of years old. Lyell’s book was a major influence on the young Charles Darwin.
The term “geology” was popularized in the late eighteenth century by the Swiss (Genevan) naturalists Horace-Bénédict de Saussure and Jean-André Deluc. The aristocrat Saussure is often considered the founder of modern mountaineering and conquered Mont Blanc (4,810 m) in 1787. At the summit he tested the boiling point of water as well as the pulse of his guides.
Georges Cuvier and Alexandre Brongniart produced a geological map of the Paris region in 1812, thereby establishing a scientific approach to stratigraphy and demonstrating that strata could be recognized by the fossils found within them. The self-educated English surveyor, canal engineer and geologistWilliam Smith published his Geologic Map of England and Wales with Part of Scotland in 1815, which was the world’s first nationwide geological map.
Geologists knew that there was evidence of past upheavals, but many believed these had been caused by the alleged Biblical Flood of Noah. There were a few individuals who held that glaciation had been more extensive in the past than it is today. In Norway and the Alps there are still surviving glaciers, and the landscape was shaped by previous ones; the Norwegian fjords are valleys carved by glacial activity and now filled with seawater. These ideas of past “ice ages” were taken up by the Swiss glaciologist Louis Agassiz, who in 1840 published a major work entitled Etudes sur les glaciers (“Study on Glaciers”). Glaciology, the study of ice formations, has gained increased importance to planetary scientists and astrobiologists studying icy moons such as Europa and Enceladus elsewhere in our Solar System.
The French mathematician Joseph Adhemar suggested that ice ages were caused by astronomical forces. His theory was modified by the Scottish scientist James Croll and above all by the gifted Serbian geophysicist Milutin Milankovitch, who taught physics and astronomy at the University of Belgrade. His complex work on what has become known as Milankovitch cycles – astronomical contributions to ice ages on our planet – took years to complete and was carried out only with brain power. It was published in a 1920 work that met with widespread acclaim, yet Milankovitch’s name is totally absent from Murray’s book.
By the early twentieth century it was known that surprisingly similar fossils and landforms could be found on opposite sides of major oceans. Based on these findings the German scientist Alfred Wegener proposed a theory of continental drift in 1915 in his masterpiece Die Entstehung der Kontinente und Ozeane (“The Origin of Continents and Oceans”). He suggested that there was once a single giant continent which he named Pangaea (“All-Earth”).
When samples were finally obtained from the ocean beds it turned out that they were far younger than expected and that the youngest samples were found next to the volcanically active mid-ocean ridges. The existence of a “mountain range” in the middle of the Atlantic Ocean had been suspected since the laying of the first transatlantic telegraph cable in 1858, but the global system of mid-ocean ridges was mapped after 1950. Both the United States and the Soviet Union, the latter with less financial resources at their disposal than the former, needed to know more about the ocean environment to navigate with their nuclear submarines. The deep seas constituted an important frontline in their Cold War superpower rivalry.
Harry Hammond Hess in 1960 at Princeton University in the USA advanced the theory that the crust moves laterally from volcanically active oceanic ridges. The Earth’s crust and upper mantle form the lithosphere, broken up into giant plates that slowly move on top of the hotter mantle, which due to the temperature/pressure regime acts like warm wax. “Sea-floor spreading” helped to establish continental drift as scientifically respectable. The Canadian geophysicist John Tuzo Wilson created a synthesis which became known as plate tectonics. Fred Vine, Drummond Matthews and Xavier Le Pichon contributed to this transformation.
Ewing is followed on the Earth sciences ranking by Leopold von Buch, Clarence Dutton, Eduard Suess and the Swedish chemists Axel Cronstedt and Georg Brandt, both of whom might as well be listed under chemistry, along with Carl G. Mosander and Per Teodor Cleve, Eilhard Mitscherlich from Germany and Peter Waage from Norway. Among other names we find Jacob Bjerknes, James Dana, Gabriel Daubrée, Pentti Eskola and Johan Gadolin from Finland, Johan G. Gahn, Beno Gutenberg, James Hall, Harry H. Hess, Arthur Holmes, Gideon Mantell, Pierre Louis Maupertuis, John Milne, Andrija Mohorovicic, Charles Richter, Edward Sabine, Strabo of Amaseia, Léon Teisserenc de Bort and Felix Andries Vening Meinesz.
The Australian anthropologist Raymond Dart, who found a fossil of the extinct hominid Australopithecus africanus in South Africa in 1924, is listed under biology, as is Édouard Lartet of France, whereas the great British paleoanthropologist Louis Leakey is listed under Earth sciences, which seems a bit arbitrary. The Dutch paleoanthropologist Eugène Dubois, who found the first fossil of Homo erectus (the “Java Man”) in 1891, is left out entirely.
Paleontology, the systematic study of the remains of living organisms and their traces on rocks, emerged as a distinct area of investigation in Western Europe at the turn of the nineteenth century. Human beings had most likely encountered fossils earlier but had often connected them to dragons or other mythical creatures, not to extinct ancient animals. In the 1820s, William Buckland and Gideon Mantell separately discovered strange bones in English quarries and, crucially, came up with reasonably accurate, non-magical explanations for these creatures. The quarrelsome English paleontologist Richard Owen coined the term “dinosaur” in 1842. This means “terrible lizard” and is not scientifically accurate, but it stuck anyway.
The index prepared by Murray is a bit weak on meteorology. The Norwegian father-and-son team Vilhelm and Jacob Bjerknes from the scenic, but rainy city of Bergen developed meteorology into a branch of atmospheric physics. Francis Beaufort with his scale for indicating wind force is here, as is William Ferrel and Carl-Gustaf Rossby, but the English scholar Luke Howard is not mentioned for his nomenclature system for clouds, nor is the Swedish meteorologist Tor Bergeron listed for explaining physically how rain forms, or the climatologist Wladimir Köppen, whose climate classification systems are still widely used.
The English mathematical physicist Lewis Fry Richardson is ignored. This represents a rather serious oversight. Following up advances made by Bjerknes, Richardson in 1922 developed the first numerical weather prediction system, not merely to explain how the weather is today but to scientifically predict how it will be like tomorrow. The Hungarian-born Jewish mathematician and computer pioneer John von Neumann in the USA in 1946, after the ENIAC electronic computer became operational, advocated the application of computers to weather prediction. The introduction of increasingly powerful computers was soon thereafter combined with weather satellites to develop weather forecasts of unprecedented accuracy.
One of the most curious aspects of Human Accomplishment is that it sometimes appears as if Charles Murray hasn’t read his own work. I have come across quite a few figures highlighted among central events in the various disciplines early in the book – Karl Jansky, Grote Reber, Christiaan Huygens, Bernard Lyot and Bernhard Schmidt in astronomy; Florence Nightingale and Willem Einthoven in medicine, Simon Stevin, Daniel Bernoulli and Joseph Fourier in physics, Regiomontanus, Alan Turing and Edmond Halley in mathematics or Fritz Haber in technology, to name a few prominent ones – who are then left out from the final indexes.
Among central events in the Earth sciences he states that Pythagoras in ancient Greece claimed that the Earth is spherical, that the geographer Pytheas of Massilia related the ocean tides to the Moon (although the nature of this correlation was not understood before Newton) and that Eratosthenes of Cyrene calculated a good estimate for the circumference of the Earth, yet none of them are listed in the roster of significant figures. The same goes for the Flemish cartographer Gerardus Mercator with his projection for maps, Jean Picard’s highly accurate calculations of the size of the Earth in the 1600s, Luigi Marsigli’s writings on oceanography in the 1720s and Benjamin Franklin’s scientific map of the Gulf Stream in the 1770s.
Gaspard de Coriolis discovered the Coriolis Effect, the deflection of a moving body caused by the Earth’s rotation. Charles Fabry discovered the ozone layer in 1913 and Oliver Heaviside, Arthur E. Kennelly and Edward V. Appleton the Earth’s ionosphere in the first decades of the twentieth century, yet all of these gentlemen are listed under the physics index. Jean Picard from France in the seventeenth century made a good estimate of the diameter of the Sun, too, but he is not credited for this in the astronomy section. This constitutes a mistake in my view.
The most serious omission in this section is Niels Stensen, or Nicolas Steno, from Copenhagen, Denmark, who lived for years in Italy. His law of superposition from 1669 concluded that layers of rock (strata) are arranged in a time sequence with the oldest on the bottom and the youngest on top, unless later processes have disturbed this arrangement. He might have made it to the top twenty list in the Earth sciences, yet while he is highlighted among central events, for some reason his name is later left out entirely from the final index.
The discipline of Earth sciences was invented in the 1960s and 70s when it replaced geology as the major discipline for studying our planet, just as geology had once replaced mineralogy. Geophysicists, oceanographers and meteorologists began working on related problems using similar techniques. At the same time, the first space probes were sent to directly investigate other bodies in our Solar System, which meant that geologists could extend the scope of their investigations to the domain formerly dominated by astronomers. If Murray had updated his book until, say, the year 2000, this section would have to be renamed “planetary sciences.”
The American geologist Eugene Shoemaker arguably founded astrogeology in the 1960s and did much to bring attention to the significance of impacts from comets and asteroids in the Earth’s history. Many people believe that the mass extinction which ended the age of the dinosaurs 65 million years ago was mainly caused by the impact of a large asteroid. The US physicist Luis Alvarez together with his son Walter Alvarez suggested this theory in 1980. It is now held to be correct by most scientists based on empirical evidence. A large impact crater from this time period has since been discovered outside of the Yucatán Peninsula in Mexico.
As Imke de Pater and Jack J. Lissauer state in their excellent book Planetary Sciences, “The Copernican-Keplerian-Galilean-Newtonian revolution in the sixteenth and seventeenth centuries completely changed humanity’s view of the dimensions and dynamics of the Solar System, including the relative sizes and masses of the bodies and the forces that make them orbit about one another. Gradual progress was made over the next few centuries, but the next revolution had to await the space age. In October of 1959, the Soviet spacecraft Luna 3 returned the first pictures of the farside of Earth’s Moon. The age of planetary exploration had begun. Over the next three decades, spacecraft visited all eight known terrestrial and giant planets in the Solar System, including our own. These spacecraft have returned data concerning the planets, their rings and moons. Spacecraft images of many objects showed details which could never have been guessed from previous Earth-based pictures. Spectra from ultraviolet to infrared wavelengths revealed previously undetected gases and geological features on planets and moons, while radio detectors and magnetometers transected the giant magnetic fields surrounding many of the planets. The planets and their satellites have become familiar to us as individual bodies. The immense diversity of planetary and satellite surfaces, atmospheres and magnetic fields has surprised even the most imaginative researchers.”
Unmanned spacecraft, mainly North American, European and Russian ones but increasingly Japanese, Indian and Chinese ones as well, have visited comets and asteroids in addition to planets and moons. We have taken photos of volcanoes on Jupiter’s extremely active moon Io spewing out plumes of sulfur and sulfur dioxide to a height of many hundreds of kilometers.
NASA’s Voyager 2 spacecraft in 1989 during its brief flyby visit spotted geysers of nitrogen gas on Neptune’s large moon Triton. Its twin, the Voyager 1robotic space probe, as of early 2012 will be 120 Astronomical Units from the Sun, a staggering 120 times as distant from the Sun as is our planet, which also equals more than 17.95 billion kilometers or 1.795×1013 meters. It now takes radio waves, travelling at the speed of light, more than sixteen hours to send information back from Voyager 1 to the Earth. It is the farthest human-made object from the Earth. The Voyagers were then still within a huge bubble called the heliosphere, made of solar plasma and solar magnetic fields, but were expected to leave it in the near future. This structure is sometimes considered the limit of our Solar System and the beginning of interstellar space, although the influence of the Sun’s gravity stretches far beyond this point.
The European Space Agency’s Huygens probe, named after the Dutch polymath Christiaan Huygens who explained Saturn’s rings and discovered its largest moon Titan, landed there in 2005, the first such undertaking in the Outer Solar System. Titan is the only moon known to possess a dense atmosphere and large amounts of liquid on its surface, in this case lakes of hydrocarbons (ethane and methane). NASA’s Cassini spacecraft, named of the Italian-French astronomer Giovanni Cassini and the first spacecraft to orbit Saturn, has also found geysers of water vapor and complex hydrocarbons venting from the surprisingly active moon Enceladus.
NASA’s Galileo spacecraft from the USA while orbiting the Jupiter system in the late 1990s found evidence indicating that the ice-crusted Galilean moon Europa could harbor an ocean of liquid salt water some kilometers beneath its frozen surface. Such an ocean, if it exists, might theoretically harbor primitive life-forms, a possibility that has made Europa one of the most intriguing objects of study for astrobiologists, next to the planet Mars and perhaps Enceladus.
From the 1990s on Western scientists have also discovered the first extrasolar planets or exoplanets, that is, planets orbiting stars other than our own Sun. These have substantially challenged some of our previous ideas about planet formation. Hundreds of them were found merely during the first generation of exoplanet research. Most of these were gas giants detected through indirect means by observing the tiny effects they have on the stars they orbit, but methods are rapidly improving and a few Earth-like planets have already been found.
Aleksander Wolszczan, a Polish-born USA-based radio astronomer, is credited as the co-discoverer of some of the first accepted exoplanets. In 1992, together with Canadian-born astronomer Dale Frail, he found evidence of planets orbiting around a pulsar (neutron star). 51 Pegasi b approximately 50 light-years away from us became the first planet found orbiting another Sun-like main sequence star. It was discovered in 1995 by Michel Mayor, a Swiss professor of astronomy at the University of Geneva in Switzerland, together with his associate Didier Queloz. Mayor and his team have discovered many more extrasolar planets since then.