Neptune's New Icy Companions

An anonymous reader writes "The Harvard-Smithsonian Center for Astrophysics has announced new moons found around Neptune. The findings represent the first discovery of moons from ground-based telescopes in more than a half-century (1949), and required an international team to track and confirm. Notable about the ice-planet Neptune is also its largest moon-Triton-which is the coldest measured object in our solar system, and as a consequence even its volcanoes spew not lava, but ice."

Moon Size

[Obfiscator]

Thirty to fourty kilometers? How small does an orbiting object have to be to not be considered a moon anymore?

That's no moon...

[baldass_newbie]

it's a space station!

(sorry. had to be done.)

Re:Moon Size

[VikingBerserker]

According to Solar System Extrema [arizona.edu], there are thirteen moons with radii below 20km, including both orbiting Mars.

Re:Moon Size

[astroboscope]

It'd be nice if they read this and answered. But it seems like in practice any natural object in a reasonably stable orbit around a planet or even an asteroid is called a moon. I think at about 1.6 km Dactyl [nasa.gov] holds the record - Ida, the asteroid it orbits, is only about 30 km across. There is a size limit for moons, but it's based on whether we can determine a definite orbit.

Re:Moon Size

[cbogart]

It hardly seems fair that Dactyl can be a moon but Ceres and friends can't be planets. Maybe Mars' moons should be demoted. I vote that things heavy enough to pull themselves into a ball be called moons and planets; everything else is an asteroid regardless of what it's currently orbiting. Uppity rubble they are, those asteroids.

Re:Moon Size

[ke4roh]

You're right. Sputnik [nasa.gov] was billed as Earth's first artificial moon - and nobody complained that it was only as big as a basketball.

That's easy

[marcus]

It has to be so small as to be undetectable. ;-)

Hmm, not so easy afterall...Let me rephrase that.

Saturn obviously has millions of particles of various sizes in orbit. So...to be a moon, the body must be not only detectable, but individually discernable and uniquely identifiable. I don't think that there are any more requirements.

Re:Moon Size

[xv4n]

I've heard people saying it must be sphere-shaped.

Photos of Ice Volcano

[LudditeMind]

Here [nasa.gov]

Eh...I think your mistaken!

[Neck_of_the_Woods]

*snip*

moon-Triton-which is the coldest measured object in our solar system

*snip*

It is clear to me that NASA has not pointed thier little devices at my last CEO's heart....

Ice Volcanoes?

[jpsst34]

Man, if only I could witnoss those puppies erupting! It would be a marvelous, exciting phonomenon to watch... over the course of 3000 years.

One time I was watching Speed 3, you know, the one where that guy from Flashback with Keefer Sutherland strapped a bomb to a glacier. He was all, "There's a bomb on the ice river. If it drops below one ince per year the bomb's gonna blow!" It was wicked-awesome.

Blurb misleadingly incomplete

[astroboscope]

The findings represent the first discovery of moons from ground-based telescopes in more than a half-century

around Neptune. The same people (more or less) involved in this discovery have also been finding previously unknown moons around Jupiter and Saturn, using Earth based telescopes.

The cool (hee hee) thing here is that Neptune's largest moon, Triton, appears to be a recently captured Kuiper Belt object. The orbits of Neptune's other satellites should have some "memory" of the capture. But this is a bit like putting a Swiss watch back together after it's been hit with a hammer.