by Carl Sagan
Figure 18. Planetesimals
In this stage of formation of a planetary system, colliding asteroid-size bodies orbit around the central star.
Figure 19. BETA PlCTORIS
This 1997 false-color image shows a debris disk seen edge on in orbit around the star Beta Pictoris, which some twenty years earlier had provided the first evidence of planetary formation around a star outside our solar system. The telescope has blocked out the direct light from the star to reveal the fainter light reflected from the disk. The inner gap in the disk suggests that planets are forming there. Most young stars have such orbiting disks.
Figure 20. Comet Machholz
The extended atmosphere, or coma, of the comet blows away from the Sun to form faint tails of dust and ionized gas.
Figure 21. Olive Oil and Comets
English astronomer William Huggins compared the spectra of vaporized olive oil and ethylene (olefiant gas) with the spectra of two comets, which he observed in 1868. He correctly deduced that comets contain carbon-bearing substances.
Figure 22. Comet NEAT Spectrum
The light of Comet NEAT (shown on the jacket of this book) is spread out into its constituent rainbow of colors (bottom), revealing the presence of different molecules at particular wavelengths (middle).
Figure 23. End of the World
An illustration by R. Jerome Hill, published in Harper's Weekly, May 14, 1910, depicting the romantic fatalism inspired by the coming of the "cyanide laden" Halley's Comet.
Figure 24. Iapetus
The surface of this mysterious satellite of Saturn has two distinct zones, one icy and very bright, the other covered by a very dark red material of unknown composition. This bimodal distribution of brightness is unique in the solar system, as is the ridge around the satellite's equator.
Figure 25. Saturn Small Moons
The satellites shown here range in size from about 20 to 200 kilometers. They lack sufficient gravity to enforce a spherical shape.
Figure 26. Uranus Rings
This infrared image, taken at a wavelength of 2.2 microns, reveals several distinct rings encircling the planet. The isolated bright spot is the moon called Miranda.
Figure 27. Phobos
This curiously potatolike cratered inner moon of Mars has an average diameter of 22 kilometers and an orbit period of about eight hours.
Figure 28. Deimos
The outer moon of Mars has an average diameter of 13 kilometers and an orbit period of thirty hours.
Figure 29. Mars Surface by Firing 1
The view from the Viking 1 Lander on the surface of Mars, in 1977, shows a rocky landscape and a ruddy sky. The lander in the foreground has its meteorology arm extended.
Figure 30. TlTAN DISK
The largest moon of Saturn, with its intriguing features photographed by the Cassini orbiting space probe in 2005.
Figure 31. TlTAN COAST
Showing icy highlands with dry rivers and what appears to be the shoreline of a vanished sea, as seen by the Huygens descent probe from an altitude of about 10 kilometers in 2005.
Figure 32. Sagittarius Stars
The Spitzer Space Telescope turned its gaze toward the constellation Sagittarius. Its infrared camera was able to penetrate the obscuring curtains of gas and dust for a thrilling look at the crowded center of the Milky Way Galaxy.
Figure 33. SETI SPECTRUM
A graph of the natural radio background noise over a wide range of frequencies. At lower frequencies (left), charged particles in our galaxy emit increasing noise. At higher frequencies (right), the intrinsic quantum noise of any radio receiver increases. Between them is a relatively quiet "window," where interstellar hydrogen (H) and hy-droxyl (OH) emit radio energy at discrete frequencies. This plot does not include radio emission from molecules in the Earth's atmosphere.
Figure 34. Simulated SETI Signal
The search for extraterrestrial intelligence includes the monitoring of stars at many radio frequencies simultaneously over time. A successful detection might resemble this signal, which actually came from the Pioneer 10 spacecraft in the outer solar system. The drift in frequency over time shows that the source is not rotating with the Earth, but is of extraterrestrial origin.
Figure 35. The Cretaceous-Tertiary Record in the Rocks at Gubbio
The evidence for the event that caused the extinction of the dinosaurs sixty-five million years ago was discovered in this sequence of sedimentary strata from Gubbio, northern Italy. The pale limestone layers at the lower right were deposited in the Cretaceous period, when dinosaurs ruled the Earth. The darker limestone layers at the upper left are from the subsequent Tertiary period, when they had become extinct. In between, the diagonal layer of black clay contains the worldwide iridium-rich fallout of debris from the crater excavated by the collision of an asteroid or comet. This layer is found everywhere on Earth where rocks of this age are exposed. The edge of a coin at the top is for scale.
Figure 36. Cretaceous-Tertiary Impact
Don Davis, one of the greatest painters of science-based art, takes us to the panicky last second of the age of the dinosaurs. An asteroid or comet some 10 kilometers in diameter plunged through the shallow ocean near what is now Yucatan in Mexico, igniting global wildfires and producing a dense cloud of smoke and dust that darkened and froze the surface of the Earth.
Carl Sagan
***
[1] The Lorentz transformations specify how time slows down and length contracts in any frame of reference depending on its relative speed. Einstein's theory of special relativity derived the Lorentz transformation by assuming a constant speed of light for all observers.
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[2] There is something anthropocentric without a doubt in talking about liquid water, but let's grant them that. It's curious in these arguments to find organisms who are made largely of liquid water saying that liquid water is central to the universe. But put that aside.
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[3] In July 2006, NASA announced that the Cassini space probe in the Saturn system observed evidence for numerous great lakes of liquid hydrocarbons on Titan.
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[4] In 2006 the Planetary Society and Harvard University inaugurated the SETI Optical Telescope, the first-ever optical observatory dedicated to the search for intelligent extraterrestrial signals. For the history of the Planetary Society and SETI, see www.planetary.org, and for the thrill of actually participating in the search, go to www.setiathome.ssl.berkeley.edu/.
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[5] In 1998 two international teams of astronomers independently reported unexpected evidence that the expansion of the universe is accelerating. These findings suggest that the universe is not oscillating but will continue to expand forever.
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[6] Earth-based telescopes provided the answer in 1998. See previous note.
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[7] By 2006 the world nuclear arsenals had been reduced to about twenty thousand weapons-still roughly ten times what would be necessary to destory our our global civilization. The principal reductions since 1985 were due to the 1993 Start II Treaty between the United States and the Soviet Union.
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[8] In 1988 the Vatican allowed samples of the original shroud material to be dated by the radiocarbon method. Three laboratories (in Arizona, Oxford, and Zurich) independently determined that the fabric dates from the period A.D. 1260 to 1590.
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