TIME: Almanac 1990/1990 Time Magazine Compact Almanac, The (1991)(Time).iso/time/080789/08078900.002

Text File | 1990-09-17 | 4KB | 65 lines

SPACE, Page 44

Next and Final Stop: Neptune
Voyager sees some intriguing sights as it nears the eighth

planet

By Michael D. Lemonick


    After a marathon journey of twelve years and more than 4
billion miles, the remarkable Voyager 2 space probe is finally
approaching its last port of call. Having made historic flybys of
Jupiter in 1979, Saturn in 1981 and Uranus in 1986, it is poised
for an Aug. 24 rendezvous with Neptune, the most distant of the
giant planets. (It will not encounter Pluto, whose bizarre orbit
now places it closer to the sun than Neptune is.) Voyager's aging
cameras and electronic sensors are somewhat impaired, and the probe
is so distant that its signals take four hours to travel to earth.
Still, scientists expect mounds of fresh data and some 8,000
photographic images, entirely new information about a little known
object that is almost four times the size of earth but appears in
earthly telescopes only as a fuzzy blue-green ball.

    Though Voyager is still about 22 million miles from Neptune,
it has already made several discoveries. It has found a new moon
to add to the known duo, Triton and Nereid. Labeled 1989-N1, the
object is between 125 and 400 miles across and has a surprisingly
ordinary orbit. Like most moons, 1989-N1 orbits nearly over its
planet's equator and in the same direction as the planet's
rotation, implying that it formed with or soon after Neptune.

    By contrast, Triton, which is about the size of earth's moon,
orbits in the opposite direction. That has led astronomers to guess
that Triton might be a large asteroid that was captured by
Neptune's gravity. Such an intrusion should have disrupted the
paths of any existing moons. This would explain tiny Nereid's
highly elongated and tilted orbit. But 1989-N1 is just "sitting
there," says Voyager project scientist Torrence Johnson, of the Jet
Propulsion Laboratory. Johnson expects that the probe will discover
more moons, shedding light on Triton's origins. "All of the outer
planets have lots of junk around them," he notes. Jupiter, Saturn
and Uranus have at least 15 moons apiece. "It would be amazing if
we got to Neptune and didn't find a bunch of these things."

    Like Jupiter and Saturn, but unlike its near-twin next-door
neighbor, Uranus, Neptune appears to have distinct weather
patterns. The probe's cameras have glimpsed a streak of white that
may be an atmospheric jet stream, longitudinal bands that could
mark prevailing winds, and a dark blotch, perhaps similar to
Jupiter's ancient high-pressure system known as the Great Red Spot.
Neptune, Jupiter and Saturn all generate more heat than they
receive from the sun, while Uranus does not; the excess heat may
be the source of the turbulence.

    Another focal point of scientific interest is Neptune's rings.
Indirect evidence suggests that they exist, but as arcs rather than
true rings. Voyager's photographs may help explain how they formed.
The space probe will also examine reddish Triton, whose methane
atmosphere is believed to overlie a surface puddled with liquid
nitrogen.

    While astronomers are eager to solve existing riddles about
Neptune, the most exciting prospect is that Voyager 2 will find
something unanticipated. That happened at Jupiter, where its sister
probe, Voyager 1, found volcanoes on the moon Io. It happened at
Saturn, where both spacecraft found many more rings than anyone had
predicted. And it happened at Uranus, where Voyager 2 found that
the planet's magnetic field was tilted an unprecedented 60 degrees
from the axis of rotation. Given that track record, the unexpected
is a virtual certainty.