The Planets (21 page)

131
. More science fiction has been written about Mars than about any other planet, so that our view of that world is shaped as much by artistic imagination as by science. Meteorites and aliens converge here. The small whitish globe in the red dust is Lowell’s Mars, covered with canals, and the bluish one the wet Mars we now believe existed eons ago.

154
. The natal chart superimposed on this image of Jupiter belongs to the
Galileo
spacecraft, whose ghostly outline appears at lower right. The four Galilean satellites flank the planet along a straight diagonal line, while the comet approaching
Jupiter’s lightning-studded cloud tops seems poised to be engulfed or torn to pieces at any moment.

176
. The song of Saturn, à la Gustav Holst, figures as the wallpaper motif here. Kepler’s shorter Saturn song fills the staff inside the doorway, its notes modeled after the moon Titan. Below that snippet of heavenly harmony,
Huygens
descends into Titan’s cloud tops. On the tiled floor,
Huygens
icons alternate with
Cassini
’s round white antenna.

200
. The telescope that Herschel used to spot Uranus stands in the foreground of a wintry landscape with views of ice giants looming. In the fractured picture frame is a comet—the mistaken identity of Uranus at first sight. The larger frame holds
Voyager 2
’s view of the planet, before the current change of season made Uranus look more like blue Neptune.

222
. Pluto and Charon occupy the upper right corner, with Sedna and all manner of yet-to-be-discovered worlds on the floor below. The oddly shaped window, which looks out on Ellis Island, repeats the outline of the Lowell Observatory building that housed Clyde Tombaugh’s telescope. That’s his cat, also named Pluto, underneath.

235
. Each of these planets is painted, using traditional techniques, from life—as seen through the best available telescopes and spacecraft imagery—and then superimposed on the photo of the green leaves. The resulting surreal scene of planets growing on plants expresses the hope that readers will come to feel more familiar with the other worlds of our Solar System.

Model Worlds (Overview)

Model Solar Systems big enough to walk or drive through can be visited in Aroostook County, Maine; Boston, Massachusetts; Boulder, Colorado; Flagstaff, Arizona; Ithaca, New York; Peoria, Illinois; Washington, D.C.; Stockholm, Sweden; York, England; and in the Alps near St.-Luc, Switzerland.

The Soviet spacecraft
Venera 4
made the first probe of the Venusian atmosphere in 1967;
Venera 7
landed on Venus in 1970, and
Venera 8
in 1972. In November 1971, America’s
Mariner 9
became the first Mars orbiter—the first spacecraft to orbit a planet beyond the Earth-Moon system. The Soviet
Mars 3
lander arrived the following month, but survived only twenty seconds on the Martian surface.

Michel Mayor and Didier Queloz of the Geneva Observatory made the first discovery of an exoplanet, and announced their findings about 51 Pegasi in October 1995. Two Americans—Geoffrey W. Marcy, University of California at Berkeley, and R. Paul Butler, now at the Carnegie Institution in Washington, D.C.—quickly confirmed the Swiss claims and went on to identify other extrasolar planets.

Genesis (The Sun)

The extraordinary phenomenon of hydrogen fusion requires the tremendous heat and pressure found inside stars. Under normal circumstances on Earth, two hydrogen nuclei would never unite with one another, because both carry positive charge, and the electromagnetic force that causes two positively charged particles to repel each other is stronger than gravity. Inside the Sun, in contrast, high temperature pushes particles together so hard and fast that they collide despite electromagnetic repulsion. And once the particles are that close together, they succumb to a third force—called the “strong force” because it is the strongest known in nature—which binds them together. The great power of the strong force, however, operates only over the tiniest distances, such as the size of an atomic nucleus.

In a single second inside its core, the Sun converts 700 million tons of hydrogen to 695 million tons of helium. The five-million-ton difference between input and outcome is transformed into the energy of light. This is a great deal of energy, according to the formula that describes energy (E) as the equivalent (=) of a given mass (m), or 5 million tons in this case, multiplied by the speed of light (c) squared (
²
). Since the speed of light is a very high number to begin with (186,000 miles per second), squaring it—multiplying it by itself—yields a truly astronomical figure (34,596,000,000), which indicates the phenomenal power lurking inside even the tiniest amounts of matter.

Helium, the second most common ingredient (after hydrogen) in the Sun and throughout the universe, accounts for 10 percent of the Sun’s makeup. All other elements detectable by analysis of the Sun’s light—carbon, nitrogen, oxygen, neon, magnesium, silicon, sulfur, and iron, taken together—total only 2 percent of the Sun’s mass.

During periods of high solar activity, conglomerations of
dark sunspots on the Sun dim its radiation by a few measurable tenths of a percent, but overall the Sun stays a constant source of steady light.

The Moon at apogee (its greatest distance from Earth) cannot completely cover the Sun, but instead produces an “annular” eclipse, in which the Sun appears as a glowing ring around the Moon and the corona may not be visible.

Although it is safe to look at the Sun during totality, viewing the stages of partial eclipse preceding and following totality requires eye protection.

Mythology (Mercury)

Procrustes gained notoriety by lopping off his tall guests’ legs and stretching short visitors on a rack to make them fit his bed, thus lending his name to violently or arbitrarily enforced conformity.

Mercury, traveling an elliptical orbit, reaches its peak velocity of thirty-five miles per second at perihelion, when it approaches within twenty-nine million miles of the Sun, and slows to twenty-four miles per second at the opposite orbital extreme, or aphelion, where the Mercury-Sun distance exceeds forty-three million miles.

The first of several mentions of “Rosy-fingered dawn,” as Homer called the reddish morning sky, occurs in Book I of
The Iliad,
line 477.

Transits of Mercury occur approximately thirteen times per century. Although the planet passes between the Earth and the Sun about four times a year, it most often travels above or below the Sun from our perspective, when no transit is seen.

Mercury’s period of spin is exactly two-thirds its orbital period, “coupling” the two time intervals in a ratio of 3:2, or three rotations for every two orbits. (The discovery of the actual rotation rate was made by bouncing radar from the Arecibo Observatory in Puerto Rico off the surface of
Mercury.) Most other tidally bound bodies in the Solar System display a 2:1 spin-orbit resonance. The most notable exception is the Moon, which completes one rotation per revolution about the Earth, giving it a 1:1 resonance.

Beauty (Venus)

William Blake wrote his ode to Venus in 1789, long before the discovery of the planet’s own westerly winds. His mention of “thy west wind” refers to evening breezes timed to her appearance.

Former President Jimmy Carter, while serving as governor of Georgia, reported Venus to the state police. During World War II, a squadron of B-29 pilots mistook the planet for a Japanese plane and tried to shoot it from the sky.

Donald W. Olson and Russell Doescher of Southwest Texas State University in San Marcos took their honors astronomy class to France in May, 2000, and successfully identified the building featured in “White House at Night” by using planetarium programs to recreate the sky over France in the summer of 1890, reading letters Van Gogh wrote during his last weeks, and consulting archived weather reports.

The duration of a solar day on Venus, measured from one noon to the next, is 117 Earth-days, so that periods of light and dark last nearly 59 Earth-days each. The sidereal day, or the time it takes the planet to rotate with respect to the background stars, is 243 Earth-days—longer than the Venus orbital year of 225 Earth-days. On Earth, as on Venus, the length of the solar day differs from the sidereal day; in Earth’s case the solar day is about four minutes longer than the sidereal.

A complete Venus cycle—from morning star apparition to disappearance behind the Sun, through evening star apparition and disappearance in front of the Sun—lasts 584 days. This time period formed the foundation of the Mayan calendar. Since Venus makes eight orbits of the Sun in five Earth
years, and passes between Earth and Sun five times in the process, there are five distinct 584-day Venus patterns in Earth’s sky. The Mayas had a name for each.

Since 1919, authority for planetary nomenclature has been vested in the International Astronomical Union. Although discoverers may suggest names for new satellites or other bodies, the choices must be approved by task and working groups, and ultimately voted into effect by the IAU General Assembly, which meets every three years.

Geography (Earth)

Even before Ptolemy, mapmakers applied concepts of latitude and longitude to the heavenly sphere and the globe of the Earth. After Ptolemy introduced a uniform coordinate system expressed in degrees, the ability to
determine
longitude awaited the late seventeenth century, and remained a problem at sea for another hundred years.

Ptolemy’s
Geography
survived in manuscripts copied by scribes. The oldest such extant manuscript dates to the thirteenth century.

In 1828, in his
History of the Life and Voyages of Christopher Columbus,
American author Washington Irving popularized the romantic image of Columbus fighting for the roundness of the world. Medieval knowledge of the world’s shape is well documented, however, in texts such as the thirteenth-century
Sphere
of Sacrobosco, and the world globe Martin Behaim completed months before Columbus left Spain. The Ancients could have concluded a round world from the stars visible at different latitudes, or the curved shape of the Earth’s shadow on the Moon during a lunar eclipse.

Amerigo Vespucci’s analysis of competing Portuguese and Spanish claims helped him estimate Earth’s circumference at 27,000 Roman miles—just fifty modern miles shy of today’s accepted value.

Earth’s water supply constitutes only one-tenth of 1 percent of the planet’s mass, while outer Solar System moons such as Ganymede, Callisto, and Titan consist of 50 percent water, most of it frozen.

After the next transit of Venus, predicted for June 6, 2012, there won’t be another pair until December 11, 2117, and December 8, 2125. Transits occur in June or December because Earth crosses the plane of Venus’s orbit in those months.

Lunacy (The Moon)

A “blue Moon,” widely reported to be the second full Moon in a calendar month, is more correctly (according to the 1937
Maine Farmers’ Almanac,
which defined the term) the third full Moon in a season that contains four of them. The
Almanac
reckons seasons by the tropical year, which begins on the day of the winter solstice, or “Yule” (December 22). A true blue Moon, therefore, can occur only in the months of February, May, August, and November.

Under a full Moon, a black-and-white landscape may reveal the greenness of grass, because the human retina is particularly sensitive to yellow-green wavelengths (the light the Sun emits most strongly).

Giovanni Riccioli (1598–1671), a Jesuit priest, established the system of lunar nomenclature still in use today. He and other selenographers (Moon mappers) named the mountains for Earthly ranges such as the Alps, Apennines, Caucasus, and Carpathians. Craters on the Moon’s near side honor great natural philosophers, from Plato and Aristotle to Tycho, Copernicus, Kepler, and Galileo. Russian names apply to the far side, which was first imaged in October 1959 by the unmanned Soviet spacecraft
Luna 3.

The Moon’s rotation rate equals its revolution—27.3 days—but by the time the Moon travels around the Earth to reach the point it started from, vis-à-vis the stars, the Earth has
also moved. Thus the Moon is seen to require 29.5 days to complete an Earthly revolution and go through all its phases from one Full Moon to the next.

Sci-Fi (Mars)

Meteoriticist Roberta Score of the U.S. Antarctic Program, in Denver, found the Mars rock known as ALH84001 on December 27, 1984. Scientists have successfully hunted meteorites in Antarctica since 1969. Analysis of ALH84001 began in mid-summer 1988, and tests confirming its Martian origin were completed by autumn 1993.

The hills near the Mawson and Mackay Glaciers, where the Mars rock was found, were mapped in 1957–58 and named for Prof. R. S. Allan of the University of Canterbury, New Zealand.

The so-called “Face on Mars,” a topographical feature widely perceived to resemble a human face, appeared in
Viking
orbiter photos from 1976. Several media promulgated the suggestion that the face was an alien artifact, until subsequent imaging by the
Mars Global Surveyor
destroyed the illusion.

Giovanni Schiaparelli found what he called
canali
on Mars in 1877, eight years after the completion of the Suez Canal. Schiaparelli, trained as a hydraulic engineer, thought the straight lines no more the product of artificial intelligence than the English Channel, but later changed his mind. When Schiaparelli’s sight failed, Percival Lowell took over observations—and interpretations—of the canals.

Johannes Kepler first imagined two moons for Mars in 1610, but the moons were not seen until August 1877, when Asaph Hall, working at the U.S. Naval Observatory in Washington, D.C., found them orbiting so close to the planet as to be nearly lost in its glare. He named them after two characters from Greek mythology, Phobos and Deimos, who were variously described by Homer as the sons of the war god Ares, or his attendants—or the horses that pulled his chariot.