The Planets

Title: The Planets

Author: Dava Sobel

Publisher: Harper Perennial 2006 (First published 2005)

ISBN: 978-1-84115-621-7

Pages: 258

Dava Sobel is a famous popular science writer having many titles like Galileo’s Daughter and Longitude to her credit. This is her first book to be reviewed here and from the style of it, I can safely assume that more will follow in due course. Her easy flowing, fluid style has made her a prominent figure in the genre and it is no wonder that an asteroid is named 30935 Davasobel after her. Astronomy is the most stressed aspect of science in many of her works.

The present volume is in essence, a survey of the solar system starting the journey from the hot centre of it all, the sun and ending with the cold extremity, in the Oort Cloud. The author takes each celestial object in turn and explains about them in the context on which that object has enriched popular culture. For Mars, it is science fiction, for Venus it is beauty and for Jupiter, it is astrology! The narration mostly follows this thematic approach proving a great attraction to general audience not well versed in science. On every chapter, the way in which the structures are related to human aspects are carefully laid out.

Mercury is the first of all planets, being closest to the sun. It is associated to the messenger of gods in Greek mythology with Hermes being an alternate name. The perturbations in the orbit of mercury which upset astronomical calculations were long puzzling the scientists as they couldn’t figure out why Newton’s laws are violated in this case. Urbain J J Leverrier, who also found Uranus detected deviations in the perihelion of mercury on every rotation. He proposed that another body, named Vulcan was affecting the orbit due to its gravity, but the painful search by astronomers worldwide failed to locate the elusive body. It was in 1915 that Einstein proposed an answer to the vexing problem in his General Theory of Relativity. He argued that the nature of space-time is different when gravity is very strong like the neighbourhood of the sun and mercury’s orbits were precisely obtained using Einstein’s relativity theory. Spacecraft Mariner 10 flew by the planet in 1974-75 and sent back pictures of its surface full of impact craters, the largest being Caloris Basin. Another mission, christened Messenger is expected to orbit and send pictures later this year.

Venus is the brightest object in the night sky after the moon and reflects 80% of the light it receives due to its cloud cover. The moon would have paled into insignificance if Venus was nearer, as the Moon reflects only 8% of the light it gets from sun. Even though Venus is only second in distance to the sun, it is the hottest planet of the entire system, due to the greenhouse effect of its cloud cover. The atmosphere consists of carbon dioxide, sulphuric acid, hydrochloric acid and hydroflouric acid and the pressure is 90 times atmospheric pressure on earth. Russian crafts Venera and Vega landed there between 1970 and 1984 and pictures were transmitted to earth before the crafts were damaged because of the extreme surface conditions. The craft Magellan circumnavigated the planet for four years from 1990. Radar exploration of the surface features are possible from earth and the largest mountain thus located is named Maxwell Montus in memory of the great Scottish scientist who proposed the theoretical framework of electromagnetic waves of which radar is also a part. All the other surface features are given feminine names to rhyme with the female aspect of the planet of beauty. Many of the characters in womens’ history have found a place there, and even female first names from various countries are chosen.

Describing earth would seem preposterous in a book of astronomy dealing with planets, but the author included it with a prominent theme of exploration of her geography. Attempts on the mapping efforts of its surface, atmosphere and inner parts are given. Earth has a solid core of iron and nickel which rotates at a rate faster than the outer parts by one second a day. Seismologists can hear the sound of the core making upon its contact with the mantle due to this difference in rotating speeds.

The Moon is the only natural satellite of earth and is somewhat larger for a satellite. This causes larger gravitational attraction between the two bodies, making the tidal forces slowing down the rotation of earth by a minute fraction. Meanwhile, the moon drifts away by an inch or two every year. This slowing down and slipping away would end in a stalemate at which earth’s rotation and moon’s recession is stabilized and both would be in a geo-stationary orbit such that moon will be always visible from one hemisphere of earth whereas it would disappear forever from the other.

Mars is smaller than earth, but the early conditions prevailed on the planet allows the possibility of life forms. While all life has been wiped off from the martian soil long ago, the concept of terraforming, the artificial manipulation of the atmosphere is being discussed among the scientific community. Mars is tilted 25 deg about its axis, as compared to earth’s 23.5 deg. This tilt causes seasons as it revolves around the sun, making the polar ice caps consisting of CO₂ and water to recede and advance as the seasons change in a martian year of 687 earth days. Crafts Viking 1 and 2 landed there in 1976 and analysed soil samples.

Jupiter is the largest planet and was closely linked to astrology till the time of Galileo. Astronomy and its false brother astrology was separated conclusively, by Galileo’s discovery of the moons of Jupiter which he named Medicean planets to ingratiate himself to his patrons, the Medici family. Astrologers couldn’t assign these new-found objects of anything worthwhile. Astronomy thus proved that it is possible for a planet to have satellites rotating them while at the same time going around the sun as a single system. It conclusively put down earth-centric views on this ground. Jupiter is a gas planet and there is no hard ground to walk on. The Great Red Spot first observed in 1879 is a giant storm raging across the Jovian atmosphere changing colour as time goes on. Scientists believe that the planet has a liquid metallic hydrogen core due to extreme high pressure, is the cause of its magnetic field which is 20,000 times stronger than earth’s. The Jovian magnetosphere even reaches saturn’s orbit, so all of Jupiter’s own satellites are well inside it. A prominent moon, Io, has 150 active volcanoes on the surface due to tidal effects, pouring a constant stream of ions and electrons into the magnetic stream inducing a huge current of several millions of amperes between Io and Jupiter. The space probe Galileo reached Jupiter in 1995 relaying details of its atmosphere.

Saturn was a curious entity for astronomers ever since it was detected to possess concentric rings. The rings containing tiny particles of rock, ice and such space debris may be the remnants of a satellite or planetoid which couldn’t resist the planet’s pull. The spacecraft Cassini flew by the planet in 2004. Close observation of saturn resulted in observing more concentric rings than the three found by telescopic measurements. In fact, it was established that all outer planets starting from Jupiter do possess them.

Uranus and Neptune are similar in many respects. The former was first observed by William Herschel in 1781. Being a long period planet (83.7 years), it was not practical for astronomers to follow it on its course around the sun and obtaining measurements. They tried to extrapolate from previous unintentional observations by other people, but the system failed to obtain correct results. As Mercury’s perturbations were also plaguing the community at that time, it was thought that another planet was deviating Uranus’ path ever so slightly. Very complex theoretical exercises ensued and Urbain J J Leverrier and John Couch Adams did calculations extending over thousands of sheets to pinpoint the location of the planet. The report was published in 1845 and in the very next year, Neptune was observed at the suggested spot by Johann Gottfried Galle. Voyager 2 flew by Uranus in 1986 and by Neptune in 1989. The astronomers were not fully convinced that the deviation of Uranus was due to Neptune alone, as the estimated size of the planet was smaller than the actual. The natural wayout was to look for another planet in the periphery and Pluto was first observed by Clyde Tombaugh in 1930. But later observations from advanced telescopes and probes gave a higher figure for Neptune’s size, obliterating the need for another planet. Compounding on such a revelation was the discovery in 1992 of another Pluto-like object on the fringes of solar system. In 1993, five more planetoids was detected in that area and the fate of Pluto hung in balance. The International Astronomical Union demoted Pluto to a minor planet in the first decade of 21^st century. (This fact is not given in the book).

The book provides interesting reading of Columbus on his explorations to the New World. We can deduce the religious zeal affecting the people of those times from Columbus’ self-professed mission statement, “In the name of Our Lord Jesus Christ, sent by the most Christian, exalted, excellent, and powerful princes’ the King and Queen of Spain, to the regions of India, to see the Princes there and the peoples and the lands, and to learn of their disposition, and of everything, and the measures which could be taken for their conversion to our Holy Faith” (p.79).

Even though appealing to readers who are staunch believers, some references in the book equating revelations in scripture with scientific concepts might be grating on the nerves of sceptics. The author has included those portions without any logical basis other than placating a section of her audience. Take for instance that solar eclipse can be total only on earth, because the moon is apparently the same size as the sun because of its shorter distance. The author asks “Is this startling manifestation of the sun’s hidden splendour part of a divine design?”. Superfluous and avoidable argument, really. In another part she says that solar wind is reminiscent of the wind from god mentioned in the Bible. In the chapter on Jupiter, the author examines Galileo’s horoscope and argues that some of the predictions had come true, while several of them failed equally. She then proposes to vindicate even the failed ones, the prediction that he would do foreign travel being one of them. Galileo never set foot outside Italy, but the author asserts that his invention, the telescope has virtually made him go far off places. Such unscientific mumbo jumbo would rather better be omitted from such books. The chapter on Venus is laced with poetry, some of them really amazing, but one gets the impression that it was overdone. Also, the thematic collection of ideas which the author takes pride in, is not as appealing as she might have thought. Saturn’s theme was music, but it was dull and rather short, leaving much to be desired.

The book is recommended.

Rating: 3 Star