Voyager Unveils Mysterious Moon : Cold World of Ice-Spewing Volcanoes and Quakes Revealed in Photographs
Exhausted but ecstatic scientists devoured their latest treasures from space Friday as the Voyager spacecraft provided a spectacular climax to a 12-year journey that will not be matched for decades, and possibly centuries.
Researchers pored over photos that unmasked Neptune’s mysterious moon, Triton--a cold world of ice-spewing volcanoes, moonquakes and a tortured past--the first of an expected three days’ worth of historic data and images of the moon and its mother planet.
Voyager is now on its way to the stars, where it will wander in the darkness of space, perhaps forever. As of this morning, Voyager is already more than a million miles past Neptune.
“All we can say now is, wow, what a way to leave the solar system,” said Laurence Soderblom, one of many scientists who will spend years analyzing the mountains of data that are Voyager’s legacy.
Made Oceans Roar
Triton, named after the part-man, part-fish god of Greek mythology who made the oceans roar by blowing in his horn, did a little roaring itself Friday.
“The images revealed a world that is unlike any we have seen,” Caltech physicist Edward Stone, the Voyager’s chief scientist, told hundreds of scientists and reporters who have converged on NASA’s Jet Propulsion Laboratory for the encounter.
Triton bears the scars of a billion years of torment, and while it seems a quieter body today, the rips in its skin and scores of peculiar geological formations suggest much about its past.
Scientists who are literally stumbling around in fatigue but unwilling to abandon their work are just beginning to interpret the images of Triton, so anything they say at this time is somewhat of an educated guess.
Any conclusions help, however, because before Voyager was launched “we only knew two things about Triton, where it was and what its name was,” NASA astronomer Dale P. Cruikshank said.
From Earth, Cruikshank added, Triton is “a thousand times fainter than the faintest star you can see with your naked eye.”
Voyager, however, has changed all of that.
The evidence collected by the one-ton robot suggests that scientists who had theorized that Triton formed someplace else and was captured by Neptune’s gravity were probably right. That has been a popular theory for years, partly because it would explain why Triton is the only major moon in the solar system that orbits in the opposite direction of its planet’s rotation.
Scientists had theorized that if Triton had strayed close enough to be captured by Neptune, it would at first have entered a highly eccentric, oblong orbit. And over the billion years or so after that Triton would have crashed into any other Neptunian satellites in the wide range encompassed by its orbit.
Thus scientists had expected to find no moons in the region that Triton would have swept clear, and Voyager found none.
Few Craters
During the billion years before Triton’s course evolved into a circular orbit, the satellite would have been subjected to enormous tidal forces as it swept close to--and then sped far away from--Neptune. The forces would have squeezed and twisted the small moon like a tennis ball gripped in a powerful hand.
Frictional heat from that process would have kept the surface of Triton extremely soft, possibly even molten, during the early years of the solar system when planets and moons were severely bombarded by rocks and ice from space.
Thus if the “captured moon” theorists were correct, Triton should not have been severely cratered like the Earth’s moon. And Friday’s images verified that there are relatively few craters on the surface of Triton.
Voyager’s evidence suggests that Triton has continued to evolve, and it may still have active ice volcanoes, scientists said.
Soderblom noted that Triton’s volcanoes are quite different from Earth’s. Lava that erupts on Earth is more than 1,000 degrees in temperature, compared to Triton’s “ice lava,” which is several hundred degrees below zero.
The surface of Triton features huge areas, hundreds of miles long, that look like dry lake beds. And that may be just what they are, said Soderblom, a geologist with the U.S. Geological Survey in Flagstaff, Ariz.
Flexible Surface
The giant basins reveal that the surface of Triton is extremely flexible. For some reason not yet fully understood, from time to time the surface apparently slumps, forming a basin that fills with slurry, he added. The surface is primarily ice, although its exact composition is not known.
“You can think of them as frozen lakes,” Soderblom said.
Scientists are still debating what causes the basins to form, but there is evidence that they are fairly young geological features. The basins, as well as the rest of Triton photographed by Voyager, have very few impact craters.
Much of the surface of Triton, which is a little smaller than Earth’s moon, looks something like a cantaloupe with a slightly rippled surface. Scientists are still unsure of the dynamics that created giant scars across the face of the moon, but the leading theory is that they probably were caused by moonquakes.
Soderblom speculated that the long, narrow features, which look like rivers but seem to be raised above the surface, were caused when Triton’s skin was ripped open in a process similar to the faulting that occurs on Earth.
That could have permitted the spongy material below to ooze to the surface, “just like slicing a razor blade through a tube of toothpaste,” Soderblom said. The softer material below the surface would flow up, creating the long, elevated structures.
Triton has an atmosphere, complete with occasional snowstorms and, quite possibly, its own brand of smog. Voyager detected a faint haze in Triton’s atmosphere, possibly caused by nitrogen.
While scientists continue to debate the finer points, it was clear Friday that their understanding of the solar system has taken a quantum leap because of Voyager. Stone likened the aging craft to “a finely trained athlete that performed right at the peak of its capability.”
Voyager was more than a scientific success, he added.
“This is also a major engineering success” because Voyager performed flawlessly years after its projected life span and three times farther away than it was designed to operate.
All of its instruments worked remarkably well, although there was a time late Thursday night when some scientists were a bit apprehensive. Voyager was bombarded by dust particles as it crossed the equatorial plane outside Neptune’s thin rings.
“I found it kind of scary,” said physicist Donald A. Gurnett of the University of Iowa.
Not to worry. Voyager came through undamaged.
The venerable spacecraft was more than 2.7 billion miles away Friday when scientists and engineers popped the Champagne corks in celebration of a unique adventure.
One of those joining in the festivities was Vice President Dan Quayle, who told JPL employees: “We are witness today to truly an amazing feat of American space technology.”
VOYAGER MISSION: A CHRONOLOGY
THE JOURNEY SO FAR 1972: Voyager project receives approval as part of 1972-73 federal budget. Aug. 20, 1977: Voyager launched. July 9, 1979: The spacecraft passes by Jupiter and finds thin rings of dust encircling it and active volcanoes on the moon Io. Aug. 25, 1981: Voyager photographs Saturn’s rings, which are found to be dynamic because of the gravity effects of small “shepherd” moons in and around them. Jan. 24, 1986: Voyager detects a strange magnetic field with a corkscrew-shaped tail extending from Uranus into space. Moon Miranda also has geological activity. Aug. 24, 1989: The close encounter with Neptune. WHAT’S NEXT? The Voyager 2’s encounter with Neptune will formally end Oct. 2. Voyager 2 will then join Voyager 1 in variety of studies outside the solar system. The Voyagers will then begin the search for the heliopause--the boundary between solar wind and interstellar space. No spacecraft has ever reached the heliopause. Sometime in the next 20 to 30 years, scientists expect the Voyagers to cross the heliopause. Around the year 2020, communications with the two Voyagers are expected to end. The two spacecraft will eventually remotely pass by many stars and continue their travels forever, destined to continually wander the Milky Way. The craft contain recordings of Earth sounds and messages to any intelligent life that might find the craft.
