Ice-Spewing Volcanoes May Be Scarring Triton
Admitting it is a “crazy idea,†scientists analyzing photographs from the Voyager spacecraft said Sunday that they believe they have discovered active ice volcanoes on Neptune’s moon, Triton.
The bizarre volcanoes appear to have blasted frozen nitrogen crystals into the air, possibly as much as 15 miles above the frigid, tortured surface of Triton. The darkened crystals were then apparently carried downwind before falling back to the surface and forming a black scar.
“I believe these things are occurring now,†planetary geologist Larry Soderblom said.
Soderblom and fellow planetary geologists working on the Voyager data at NASA’s Jet Propulsion Laboratory came up with the ice volcano theory in an effort to explain strange black marks on the surface of Triton.
Although Soderblom acknowledged that the theory could be wrong, Voyager’s chief scientist, Caltech physicist Edward Stone, said Triton is now known to have the conditions that could make such a process possible.
If he and his colleagues are right, Triton would join a tiny group of objects in the solar system that have active volcanoes. Jupiter’s equally strange moon, Io, has volcanoes similar to some found on Earth, and Venus is also believed to have volcanoes.
The “volcanoes†on Triton appear to be “gentler†than those found on Earth, Soderblom said. They compare very loosely to geysers, he said, but apparently are unique in the solar system.
Ever since the first close-up images came back from Voyager, scientists have been struggling to explain the darkened features scattered around Triton’s southern hemisphere.
At first, some thought the areas had been created by the wind that swept ice crystals away, revealing a darkened layer below. That theory was supported by the fact that the features lie in patterns consistent with the direction of Triton’s predominant winds.
But other instruments aboard Voyager have determined that Triton’s atmosphere is not very dense. Triton’s thin air could not have winds that would be strong enough to create such patterns, which are up to 30 miles wide and 45 miles long, Soderblom said.
Although the wind could not be strong enough to have carved out those features, even a slight breeze in a thin atmosphere could carry airborne particles far enough to create them, he theorized.
Theories Offered
The dynamics of such a volcanic system are highly speculative at this time, but scientists on the Voyager project offered various theories.
Bradford Smith of the University of Arizona, leader of the imaging team, said nitrogen below the surface of Triton could be under enough pressure to be in a liquid form. If somehow that liquid began to migrate toward the surface through a fissure, it would suddenly expand into a gas as it approached the surface, where the pressure would be less.
“It explodes,†Smith said.
The nitrogen would then blast through the surface, “carrying all the black crud with it,†he added.
Above the surface, the eruption would create an “umbrella†of dark particles that would rain down on Triton, creating the dark features.
The black material is presumably a layer of hydrocarbons created on Triton by the constant bombardment of the small moon by high-speed subatomic particles, then buried beneath a layer of ice crystals.
Soderblom startled some scientists from other disciplines when he announced the theory Sunday morning.
“This is a crazy idea,†he acknowledged. “But it’s the best we have at the present time.â€
Smith commented later, however, that he sees nothing “crazy†about the theory.
“It’s a perfectly sensible explanation,†he said.
May Be Active
There is some debate over just how recently the ice volcanoes might have erupted, but Soderblom said dozens have been found in a very young region on Triton’s surface, suggesting that they were active in the very recent past. And he sees no reason why they would not be active now.
The scientists said the volcanoes could have contributed to the “smog†in Triton’s atmosphere.
Andrew Ingersoll, an atmospheric scientist at Caltech, said “the haze layer could be a remnant of active volcanoes.â€
But he quickly added that Soderblom’s theory “came as a complete surprise to me†and noted that there are many other theories that could explain Triton’s smog. For instance, nitrogen, a component in Southern California’s smog, is the chief ingredient in Triton’s atmosphere.
In addition to the exploding ice volcanoes, Triton’s surface also includes huge calderas, similar to the volcanic craters on the island of Hawaii, Soderblom said.
Just as lava floods the craters in Hawaii and then solidifies in a constantly repeated process, water apparently flooded Triton’s calderas, melted, receded and flooded them again and again.
Sometimes, he said, the calderas overflowed, causing massive flooding. The fluid later froze, forming the smooth geological structures that blanket much of Triton’s surface.
“Large-scale flooding is the first rational explanation†for the smooth formations, he said.
Northern Lights
Meanwhile, other Voyager scientists reported Sunday that the spacecraft may have been looking in the wrong place when it tried to detect Neptune’s “northern lights.â€
Physicist Norman F. Ness of the University of Delaware said the Voyager’s magnetometer determined that Neptune’s magnetic field is tilted a “remarkable†50 degrees from the planet’s axis of rotation.
No one is sure why that should be the case, he said. But it means that if Neptune has auroral activity, its “northern lights†would be over the equator, not over the north pole where Voyager was looking.
The 12-year-old spacecraft may have missed the northern lights, but it had no trouble finding a band of dust when it flew over Neptune’s rings.
The Voyager has two antennas designed to detect waves traveling through the interplanetary medium. At Neptune, the plasma wave experiment was used for something it was not designed to do--detect dust.
Plasma physicist Donald J. Gurnett of the University of Iowa said that when a particle of dust flying at high speed collides with the spacecraft the particle “explodes.â€
‘Completely Vaporized’
“It is completely vaporized at 100,000 degrees,†he said. “That releases a pulse of charged particles†that hit the antennas.
The instrument counts the number of “hits,†and Gurnett said the rate was rather startling.
“We first started detecting dust impacts two hours before the ring crossing,†he said. The one-ton spacecraft was bombarded at a rate of up to 300 impacts per second.
The bits of dust were only about the size of smoke particles, too small to do much damage to the craft, so the Voyager made it through in perfect condition.
Today, Voyager scientists will continue analyzing data they are still receiving from the spacecraft. They will wrap up their work here Tuesday, but the Voyager has given them much to do over the coming years.
SPACE BUSINESS
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