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Voyager Finds Apparently Active Nitrogen Ice Volcanoes On Triton

August 28, 1989

PASADENA, Calif. (AP) _ Voyager 2′s close-up photos of Neptune’s moon Triton reveal what look like active ice volcanoes that erupt explosively, spewing nitrogen ice particles and gas nearly 20 miles high, scientists said Sunday.

″I believe they are active,″ or erupted at least within the past 100 years, said U.S. Geological Survey geologist Larry Soderblom, a member of the Voyager photographic imaging team at NASA’s Jet Propulsion Laboratory. ″There’s 10 or 20 or 30 - lots.″

″This is a crazy idea ... but it’s the best we have at the current time″ to explain the pockmarked terrain, he added.

While more evidence is needed to prove the volcanoes are active, ″the whole process makes physical sense,″ said Bradford Smith, leader of the Voyager 2 imaging team. ″That is a perfectly sensible explanation.″

If Soderblom and Smith are right, Triton is only the third object in the solar system known to have active volcanism. Earth and Jupiter’s moon Io are the others.

Soderblom compared the new type of ice volcanoes with sulfur-spewing volcanoes on Io. But he said the volcanoes on Triton are produced when liquid nitrogen rises in underground pools rises to the surface, where reduced pressure means ″it’s got to explode and will shower ice particles and gas.″

Based on dark-colored, plume-shaped deposits that stretch up to 50 miles downwind from the volcanoes, Soderblom estimated the eruptions eject debris at scores of mile per hour, perhaps faster, sending it 12 to 19 miles skyward.

″The stuff comes shooting up like gas out of a gun barrel,″ said Smith, a University of Arizona planetary scientist. The deposits apparently contain radiation-darkened ices that fell to the surface after being carried skyward by the blast, he added.

Voyager 2 made its closest approach to Neptune on Thursday night when it skimmed about 3,000 miles over the planet’s north pole cloud tops. Early Friday morning, the spacecraft zoomed about 24,000 miles past Triton, taking the photos that have revealed at least three kinds of icy volcanism on the moon.

Voyager earlier discovered icy flows that oozed up from the floors of long valleys, a process likened to toothpaste coming out of a tube slit with a razor blade.

On Friday, scientists announced that Voyager had discovered a different type of ice volcanoes, which appeared inactive and possibly extinct. They are huge flat craters, called calderas, similar to the one in which Yellowstone National Park rests.

Some calderas, such as the crater atop Hawaii’s Kilauea volcano, fill with lava lakes. Triton’s calderas, measuring up to hundreds of miles wide, fill with flows of viscous ice, possibly water ice, that gushes up from below, Smith said.

New evidence released Sunday shows Triton’s ice-lava lakes ″can come up and overflow. You see that happen in Hawaii all the time″ when molten rock lava overflows crater walls, Smith said.

So eruptions from Triton’s calderas once produced ″a sea of ice-like lava in repeated eruptions,″ resulting in ″massive, oceanic-scale flooding,″ Soderblom said during a Sunday news conference. He said at least four such calderas have been spotted on Triton.

Soderblom said he believes the newly discovered nitrogen ice volcanoes either are currently active or erupted within the past century because they are located on Triton’s huge south polar ice cap.

A year on Neptune and Triton lasts about 165 Earth years. So if the ice cap had gone through a summer, evidence of volcanic deposits would have been erased as the ice cap receded, he added.

So far, Voyager has discovered six moons orbiting Neptune, in addition to Triton and Nereid, which were discovered from Earth. It also has found five rings of debris orbiting the planet, including two that are broad bands of dust.

The latest ring photo released by NASA Sunday shows one of those bands is even broader than thought, forming a beautiful, circular sheet of dust that extends throughout the plane of Neptune’s rings and extends inward toward the planet.

NASA’s latest results from Voyager’s close encounters with Neptune and Triton found that:

-Winds up to more than 700 mph have been measured in Neptune’s atmosphere.

-A day on Neptune lasts 16 hours and three minutes, give or take four minutes.

-Neptune’s south pole and equator, while incredibly cold, are much hotter than the planet’s middle latitudes.

-The planet’s magnetic poles are tilted an extreme 50 degrees away from from the poles around which the planet rotates, a much greater tilt than the minimum of 30 degrees scientists initially estimated. That means Neptune’s magnetic north pole is closer to its equator than to its rotational north pole.

It also means Neptune is much more similar to Uranus, which has a magnetic field tilt of 58 degrees. Earth’s magnetic poles are tilted 12 degrees from its true, or rotational poles.

By 9 a.m. PDT Monday, Voyager will be 2.76 billion miles from Earth and 3.19 million miles behind Neptune, speeding away from the planet at 37,621 mph.

The probe on Sunday was looking for lightning and auroras on Triton. It also sent back its best picture of heart-shaped moon 1989N1, which has usurped Nereid as Neptune’s second-largest moon.

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