Neptune Moon May Harbor Water World

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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