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New Moon of Uranus Discovered
paulnuyu writes "A group of international astronomers have found a new moon orbitting Uranus. This brings Uranus's total moon count to 21. The newly discovered moon is speculated to be a remaining fragment from a collision that occured when the solar sytem was still forming."
The moon ... is between six and 12 miles across.
Wow. In 100 years we'll have space stations that big. it's hardly Moon (x00miles+) size is it? Y'know theres a golf ball floating arround the Earth's moon - a moon of a moon?
Ok, lots to say here.
I think perhaps the best way to look at the terrestrial (aka, inner) planets - moon-wise - is that they don't form with moons, so any moons we find are probably anomalous in some senses. Earth's Moon is a bit of a freak, having formed in a very stochastic even. Mars's two moons are most likely captured asteroids. Venus and Mercury are in some ways more like what I'd expect to see in a large fraction of a larger terrestrial planet population.
The outer solar system has it good, moon-wise. First off, the giant planets are thought form with accretion disks about them in the later stages. (I believe Canup and Ward have a paper coming out on this topic in Astrophysical Journal in not too long.) This makes a good place to form moons, it is thought.
It gets even better, though. The jovian planets also probably had larger gas envelopes early on, making it easier to capture a moon (like Triton). You need some way to ditch energy in order for capture to occur, and drag is a nice method.
And better still: it's easier for giant planets to affect objects in their area. Their Hill spheres (domains of gravitational dominance compared with the Sun's gravity) is larger thanks largely in part due to their greater distances from the Sun. This leaves a larger volume around them in which they can start to mess with small bodies and potentially capture them, under the right conditions.
All in all, if you want to either form (in situ) or capture a moon, the outer solar system is your best bet. It's still possible to pull some tricks in the inner solar system, but they're less likely.
(Data from here, specifically these pages.)
Bugrit! Millenium hand and shrimp!