Space Topics: Neptune
Neptune's Moon Triton
Triton's colorful, frosty surface was a surprise to Voyager 2.
Credit: NASA/JPL/A. Tayfun Oner |
Diameter: 2706 kilometers
Orbital distance: 354,800 kilometers from Neptune
Orbital period: 5.88 days
Orbital inclination: 156.8 degrees (retrograde, and inclined 33.2
degrees from Neptune’s equatorial plane)
Discovery: 1846 by William Lassell, only a few weeks after the discovery
of Neptune
Triton is overwhelmingly the largest of Neptune’s moons and the
only large moon in the solar system to travel in a retrograde (backwards)
direction around its primary. It’s an oddball for many other
reasons as well. It is denser, and thus rockier, than most outer planet
satellites. Its frigid surface is covered with a very bright coating
of methane frost, and it has a tenuous atmosphere of nitrogen and methane. Although
these characteristics do not match other icy planet satellites, they do
match the characteristics observed for Pluto and other Kuiper Belt Objects. Triton
may well be a captured Kuiper Belt Object, perhaps the only one seen by
a spacecraft.
Triton's South Polar Geysers
NASA/JPL
|
Seen up close by Voyager 2, Triton revealed itself to be a weird world. First,
it has a polar cap, covered with pink-stained nitrogen frost. Poking
through the cap were several apparent geysers, with long, dark plumes extending “downwind.” The
geysers could result from a “solid-state greenhouse,” in which
translucent frozen nitrogen produces a subsurface greenhouse effect, warming
material enough that it boils and erupts. But Triton’s lack of
craters indicates that it has been geologically active relatively recently
so the geysers could also result from an internal heat source. Some
researchers have even suggested that the geysers are Triton dust devils!
Cantaloupe Terrain on Triton
Credit: NASA/JPL |
The trailing hemisphere of Triton is covered with a terrain so far unique
in the solar system: a puckered surface that immediately became known as “cantaloupe
terrain.” The cantaloupe terrain is cut by a few, widely spaced,
paired ridges or troughs. There are very few impact craters. Some
areas are as smooth as lakes, and may represent volcanic flows of water, which
would behave on Triton as rock does on Earth. |
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