Holy crap, they must be breeding!
For those of you scoring at home, it means Saturn has 22 moons. Uranus (here come the jokes…) has only 21.
Oh, and yesterday, it was announced that a asteroid about 373 miles in diameter was found orbiting the Sun between the orbits of Neptune and Pluto.
It’s gettin’ crowded up there…
Hmph. We can find planets and moons in other galaxies, but somehow a moon in our own escaped our attention.
Lissa, I’m sure you were just being clever, but it should be pointed out that:
–We have not discovered moons in other galaxies.
–We have not discovered planets in other galaxies, either.
–We have discovered planets in other star systems in our own galaxy, but only inferentially, through their gravitational effects on the stars they orbit.
–According to jab’s link, the four moons are 6 to 30 miles across. Saturn is nearly 1.5 billion km from the Sun. At that distance, an object 6 miles across subtends an arc on the human eye of . . . well, I don’t remember the math, but suffice to say you’d probably need a space-based telescope of huge aperture to even infer the existence of such an object, let alone confirm it visually.
–By way of contrast, Jupiter is 700 million km closer to us than Saturn is. The four Galilean moons, that are just visible as tiny points of light through a small backyard telescope, average about a third the size of the Earth.
I still think astronomers need to have firmer guidelines on what constitues a planet vs. a moon, and a moon vs. a rock. 10km across is a moon?
jab1 Cool! Thanks for the link. I thought some more potential moons of Uranus have been recently found too. Not sure, offhand.
Lissa - Like pldennison said, no planets or moons have been identified in other galaxies. No moons have been discovered outside our own solar system for that matter. These moons are tiny (comparatively) and have odd orbits…so (1) they’re hard to see and (2) the orbit around the planet is not readily apparent.
Arnold Probably (ditto for planets/stars). But I think the bottom line is…if it orbits a planet, then it’s a moon. (aside from artificial satellites of course). Hey, a 10 km object wiped out the dinosaurs, so it’s nothing to sneeze at.
general comment
It would be cool if astronomers found a “10th planet”…i.e., another Pluto-sized planet in the Kuiper Belt (a definite possibility). Also, astronomers still haven’t verified the existence of the Oort Cloud.
There’s lots more stuff to discover in our own solar system.
If you use a mirror properly, you can discover the rings around Uranus.
I think that may be slightly larger than Deimos, which is considered a moon (Mars)
I may be wrong, but I think they got visual evidence on one extrasolar planet earlier this year. The rest are mathematically predicted.
lurkernomore: You’re referring to a planet orbiting the star HD209458 in the constellation Pegasus. Last November, it passed directly between its star and Earth and cast its shadow on us. This phenomenon was visible only through a very powerful telescope, of course. A green glare from a planet orbiting the star Tau Bostis was observed last December. Anyone interested in extra-solar planets can read the guide published in Discover Magazine last March.
Arnold, if it orbits a star, it’s a planet. If it orbits a planet, it’s a moon. Titan, one of the moons of Saturn, is bigger than either Mercury or Pluto. Pluto, for that matter, isn’t even as large as our own Moon. But since it has its own orbit around the Sun, it’s a planet. Pictures of all the planets and their physical characteristics can be found here.
Deimos is about 12.6 km
http://www.seds.org/billa/tnp/deimos.html
Sort of. Many non-planets can orbit stars (like comets, asteroids, dust, other stars, etc.). In general, a planet orbits a star, is greater than x km in diamater (where x = something like 1000…large enough to be spherical anyway), and is not so massive that fusion occurs within in (then it would be a star).
Definition gray-areas are not uncommon in astronomy.
Don’t get me started on asteroids or the pen that some space shuttle astronaut dropped on an EVA and is now orbiting the earth (OK, I made up that part about the pen.)
We need strict rules! Or at least I do.