Adam commented:

"Triton's radius is NOT 1900 Km, but a mere 1350 Km..."

The value of 1900 km was quoted from page F3 of "The Astronomical Almanac" for the year 1986 which was jointly published by the US Navy and Royal Greenwich Observatory. The "Astronomical Almanac" is usually the canonical source concerning astronomical data. However Voyager 2 did not reach Neptune until June 1989. The data in the 1986 almanac was obsolete. Ironicly, Adam's value of 1350 km is also slightly incorrect (forgive me for nitpicking). After searching the web, I found the following numbers for Triton's radius:

http://www.lpi.usra.edu/research/outerp/trit.html
Triton (diameter 2700 kilometers)

http://www.museum.vic.gov.au/planetarium/solarsystem/neptune.html
Triton (diameter: 2620 km)

http://users.skynet.be/sky03361/html2/reis2neptunus.html
The south hemisphere of the moon Triton (diameter 1350 km).

http://scienceweek.com/search/iveejeh.htm
the moon Triton (diameter 2705 kilometers)

http://www-astronomy.mps.ohio-state.edu/~pogge/Ast161/Unit6/icyworlds.html
Diameter of 2710 km (0.21 REarth)

http://ssd.jpl.nasa.gov/sat_props.html
Triton mean radius 1353.4 ± 0.9 km

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For these different values, I would trust the last one (mean radius 1353.4 ± 0.9 km) because it is from JPL and includes a standard deviation. Funny that there was so much scatter in the different reported diameters for Triton.

Gary