Expert: Paul Wagner - 4/17/2004

Question
I was reading a book that said that astronomers believe that Triton may have been captured by Neptune. Why is this?

Thanks

Answer
Dear James:

Here's a nice description of the issue:

Triton orbits Neptune in what is known as a retrograde orbit. This means that it orbits Neptune a direction opposite the planet's rotation. It is the only large moon in the solar system to do this. Astronomers are not quite sure of the reason for this retrograde orbit. Some believe that it condensed this way from the original material of the early solar system. Others think that Triton may have been formed elsewhere and then captured by Neptune's gravity. In fact, many astronomers have noticed that the surface features of triton, as well as its size, is very similar to what they believe the planet Pluto to look like. Some even wonder if there is some connection between Triton's features and the fact that Pluto actually crosses Neptune's orbit from time to time. Just what that connection might be is anyone's guess at this point.

Does that help?

Paul Wagner