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By Root 1509 0

the principal glories of the Uranus encounter were the pictures. With Voyager’s two television cameras, we discovered ten new moons, determined the length of the day in the clouds of Uranus (about 17 hours), and studied about a dozen rings. The most spectacular pictures were those returned from the five larger, previously known moons of Uranus, especially the smallest of them, Kuiper’s Miranda. Its surface is a tumult of fault valleys, parallel ridges, sheer cliffs, low mountains, impact craters, and frozen floods of once-molten surface material. This turmoiled landscape is unexpected for a small, cold, icy world so distant from the Sun. Perhaps the surface was melted and reworked in some long-gone epoch when a gravitational resonance between Uranus, Miranda, and Ariel pumped energy from the nearby planet into Miranda’s interior. Or perhaps we are seeing the results of the primordial collision that is thought to have knocked Uranus over. Or, just conceivably, maybe Miranda was once utterly destroyed, dismembered, blasted into smithereens by a wild careening world, with many collision fragments still left in Miranda’s orbit. The shards and remnants, slowly colliding, gravitationally attracting one another, may have reaggregated into just such a jumbled, patchy, unfinished world as Miranda is today.

For me, there’s something eerie about the pictures of dusky Miranda, because I can remember so well when it was only a faint point of light almost lost in the glare of Uranus, discovered through great difficulty by dint of the astronomer’s skills and patience. In only half a lifetime it has gone from an undiscovered world to a destination whose ancient and idiosyncratic secrets have been at least partially revealed.

*There was one moment in the last 4,000 years when all seven of these celestial bodies were clustered tightly together. Just before dawn on March 4, 1953 B.C., the crescent Moon was at the horizon. Venus, Mercury, Mars, Saturn, and Jupiter were strung out like jewels on a necklace near the great square in the constellation Pegasus—near the spot from which in our time the Perseid meteor shower emanates. Even casual watchers of the sky must have been transfixed by the event. What was it—a communion of the gods? According to the astronomer David Pankenier of Lehigh University and later Kevin Pang of JPL, this event was the starting point for the planetary cycles of the ancient Chinese astronomers.

There is no other time in the last 4,000 years (or in the next) when the dance of the planets around the Sun brings them so close together from the vantage point of Earth. But on May 5, 2000, all seven will be visible in the same part of the sky—although some at dawn and some at dusk and about ten times more spread out than on that late winter morning in 1953 B.C. Still, it’s probably a good night for a party.

*After whom the European-American mission to the Saturn system is named.

*He so named it because of the words spoken by Miranda, the heroine of The Tempest: “O brave new world, That has such people in’t.” (To which Prospero replies, “Tis new to thee.” Just so. Like all the other worlds in the Solar System, Miranda is about 4.5 billion years old.)

CHAPTER 9

AN AMERICAN SHIP AT THE FRONTIERS OF THE SOLAR SYSTEM

… by the shore

Of Triton’s Lake …

I will clear my breast of secrets.

—EURIPIDES, ION (CA. 413 B.C.)

Neptune was the final port of call in Voyager 2’s grand tour of the Solar System. Usually, it is thought of as the penultimate planet, with Pluto the outermost. But because of Pluto’s stretched-out, elliptical orbit, Neptune has lately been the outermost planet, and will remain so until 1999. Typical temperatures in its upper clouds are about -240°C, because it is so far from the warming rays of the Sun. It would be colder still, except for the heat welling up from its interior. Neptune glides along the hem of interstellar night. It is so far away that, in its sky, the Sun appears as little more than an extremely bright star.

How far? So far away that it has yet to complete a single trip