Is This Moon Three?

tetrad writes "The BBC reports that a new object has been discovered orbiting Earth. It's possible that it's just a piece of space junk, but more likely it is a rock that has been recently (in the last year) captured by our planet's gravitational field. If the object is confirmed to be natural, this would be Earth's third moon. (Did you know there were two already?)" Here's our earlier mention of Earth's alleged second moon. Update: 09/12 04:52 GMT by T : Reader cscx adds a link to an article running on space.com which says this newfound object may be some trash from the Apollo missions.

Comments

size matters?

[Anonymous Coward]

Doesnt an orbiting object need to be of some specific minimum size? or does Saturn have billions of moons that just end up looking like rings?

What's in a moon?

[(H)olyGeekboy]

Just out of curiosity, what is the scientific criterion for a moon?

The "trojan asteroid" described in the previous story is only 3 miles wide and take 770 years to orbit the earth. That is not what elementary schoolteachers say is a moon, a la Jupiter's many moons... giants like Europa and IO.

I also heard a while back that Charon might not be a real moon either, because of size or rotation or something? Huh?

I'm not versed in astronomy enough to know, so does anyone have an answer for laypeople, so I can talk with people at work about this? :)

Re:What's in a moon?

[Bonker]

IANAA, but a professor once told me that a body that orbits another non-stellar body is a moon while a body that orbits a star is a planet or an astroid (astro- from star) depending on its size and regularity of its orbit.

Thus, the Pluto-Charon system is probably much more accurately labeled as either a pair of asteroids due to size considerations, or a dual-planetary system because their orbits are highly regular, albeit at a significant pitch compared to the other 8 planetary systems.

I've also heard that the Earth/Luna system should be considered a dual-planetary system because Luna has a much higher percentage of it's parent planet's mass than other moons... This jives with the 'Planetary Collision' theory of moon formataion, in which the moon is actualy a significant chunk of Earth, torn off early during our planet's formation.

The 'second moon', Cruithne, fits in with a large category of non-moon, non-planetary, non-asteroid bodies in the solar system. If you ever study the 'Trojans', you know that there are huge bodies of apparent moonlets that sit on a sixty-degree angle from Jupiter's, directly along Jupiter's orbit from the sun. (They are apparently held in such a strange place by the gravity of Jupiter vs. the gravity of Sol.) Rather than calling Cruithne a moon, we're probably better off adding a new 'common' cetegory to our solar classification to include it and the Trojans. AFAIC, there's no reason not to call these all Trojans and be done with it.

Re:What's in a moon?

[kzinti]

Just out of curiosity, what is the scientific criterion for a moon?

Isaac Asimov, in one of his popular-science articles, once presented a well-reasoned argument that the Earth and Moon should not be considered a planet and satellite, but a double planet. He formed his argument by comparing the masses of all the other moons in the Solar system to the masses of their primaries, and showed that the Moon:Earth mass ratio was far greater than that of any other planet/satellite pair. He suggested that we could account for this "outlier" by considering the Earth and Moon to be a double planet.

Whether this argument would stand up to real scientific scrutiny, I don't know. It sounded pretty good to me, but I was just 10 at the time. Maybe it was just gee-whiz stuff made up to impress 10-year-olds, but that doesn't really seem like Isaac's style.

Does anybody else remember this essay?

--Jim

Ask Buzz what he thinks about it.

[dargaud]

Read this and this and have a good laugh. Go Buzz, go !!!

Re:If this is true..

[Magila]

First off the parent post was refering to telescopes in earth orbit (read: hubble). Secondly while there would be little/no advantage for optical telescopes, a radio telescope on the far side of the moon would have a huge advantage over earth based dishes because the moon would block virtualy all radio waves coming from earth. Thus giving it a much clearer view over the entire spectrum instead of being limited to a few unused frequencies like it's earth-bound conterparts.

Re:The Martian Space Defence...

[AndroidCat]

According to the inner teachings of Scientology* this is the 4th Invader Fleet. (The 5th Invader Fleet had to make do with Venus, but don't call them Venusians!)

* Sort of inner. Scientology is like a Mystic Onion. You peel it off layer by expensive layer until you reach the center of the onion. (Where you have nothing -- except tears.)

Stop laughing, this is science damn it!

Scientists suspect object is space junk

[AndroidCat]

Scientists suspect object orbiting Earth is space 'junk'

Scientists think a newly-found object orbiting the Earth could be a remnant from the Apollo era.

Experts at Nasa's Jet Propulsion Laboratory believe its brightness and distance shows it's a rocket booster.

'J002E3' was discovered on September 3 and listed by scientists as a minor planet or asteroid.

But Nasa's Donald Yeomans believes that designation is erroneous.

He told Space.com: "It's most likely a spacecraft. It's not likely to be a natural object, not in that kind of orbit."

He said minor planets or asteroids tend to be on strange orbits gravitationally-influenced by the Sun. This does not appear to be the case with this object.

Nasa are currently running computer calculations and expect to be able to identify the object conclusively soon.

Story filed: 10:39 Thursday 12th September 2002

Another Criteria

[Royster]

If the path of an object is concave with respect to the sun, the object is a planet.

In the case of the Earth/Moon system, it is called a double planet because the path of the moon from the point of view of the sun in strictly concave -- that is it dosn't loop back on itself as do other moons.