From Stig Agermose

Source: Discovery (Channel) Online News,

Thursday, March 18, 1999

Neptune Moon May Harbor Water World

[Voyager 2 obtained this high-resolution color image of Neptune's
large satellite Triton during its close flyby in 1989. Tell-tale
features on this moon indicate a subsurface ocean and, perhaps the
stuff needed for life.

Picture: Jet Propulsion Laboratory/NASA]


The surface of Neptune's icy moon Triton appears to be fairly young,
indicating that it may hide a subsurface ocean, researchers say. If
such an ocean is there, it could provide yet another unlikely place
for life's chemistry within our solar system.

Findings based on an analysis of the moon's craters, were presented
this week at the Lunar and Planetary Science Conference in Houston.

The young, uncratered surface of Earth is kept that way by liquid
erosion from above and volcanic action from below. On icy moons like
Triton, researchers say, the most likely resurfacing agent is liquid
from below.

The new study fixes a young age on Triton's surface, indicating that
resurfacing is actively taking place there.

"No matter how you change the variables, the oldest possible age for
the surface of Triton seems to be about half a billion years, "
according to planetary scientist William B. McKinnon, who says that's
still fairly young, geologically speaking.

McKinnon labels Triton as one of the "the big five" -- large planetary
moons, such as Jupiter's moon Europa. These moons have shown evidence
of subsurface oceans kept liquid by gravitational heating from the
planets they orbit. On Earth, microbes thrive in similar conditions --
near hot volcanic vents on the deep ocean floor.

Over the past two years, data from the Galileo space probe has
suggested that a heated ocean lies beneath the ice of Europa,
prompting speculation that microbial life could exist in such
conditions. However, McKinnon cautions a subsurface ocean on Triton
might consists of ammonia or liquid methane instead of water --
conditions unsuitable for life.

Kevin Zahnle of NASA's Ames Research Center, disagrees with McKinnon's
conclusion about Triton's age, suggesting that it is even younger.

"The ages should be four times younger than what you've given," Zahnle
says. According to his calculations, Triton's surface is more likely
only 70 million years old, or approximately twice the age Zahnle has
estimated for Europa's surface in a separate study.

"But the images of Triton contain far fewer craters than similar
images of Europa, so resurfacing must be taking place at a more rapid
rate," Zahnle says. "One possible interpretation is that Triton's
subsurface ocean is even closer to the surface than Europa's."

By Michael Ray Taylor in Houston, Discovery Online News

March 1999
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