Interesting - Earth Has a Second Moon?

[eclark1894]

Well, to add my 2 kb or maybe 2 mb worth (and because my long time interest in things astronomical since high school when I lectured at a now dismantled planetarium in Charlotte, NC)...

There was a planetarium in Charlotte? Never knew that. Of course the only one I ever went to was the one in Chapel Hill when I was in the fifth grade.

 

[Zaarin]

I rather agree Pluto should not have been downgraded. The part that got Pluto downgraded is that a planet has cleared the neighborhood around its orbit while a dwarf planet hasn't.

But even that clause turned out to be rather arbitrary because several other planets have also not cleared their neighborhood. Earth hasn't (something like 20,000 asteroids are in our orbit). Jupiter hasn't (100,000 Trojan asteroids no less). Mars hasn't. Neptune hasn't (Pluto is in Neptune's "neighborhood").

Perhaps if Earth were in the middle of something like the Kuiper Belt (or had an orbit the size of Pluto's), we'd have a bit more trash in our neighborhood too. Not that we haven't been filling our neighborhood with trash ... what with all the junk we keep leaving in space. Trash the land, trash the sea, trash space ... is there anywhere humans don't fill with trash?

So ... at the point where humans have filled the space in Earth's orbit with enough trash that Earth barely outmasses its trash ... will Earth be downgraded?

The discovery of Eris ... which NASA announced as the 10th planet of our solar system ... is the cause of Pluto being downgraded. The reluctance of some IAU members to add Eris (which has more mass than Pluto) as our 10th planet resulted in the new definition to exclude Eris and all those trillions of other planets that are being and will be discovered in our solar system.

Nothing new in redefining what is a planet. It's been done any number of times throughout history. After all, planets used to be only those heavenly bodies that could be seen by the ancient's naked eyes. In another 50 years or so when Earth is in danger of being downgraded because of all the trash in our orbit, the IAU (or its descendant organizations) will have to redefine planets yet again.

It would have been ever so much simpler (and cleaner) if the IAU had simply defined a planet as a nearly round celestial body in orbit around the Sun which can naturally support Human life.

There. Done. Our solar system has one planet. All the rest is just junk in space. Now it doesn't matter how much trash we spew into our orbit. Earth will always be a planet ... until we push ourselves into extinction. Then it won't matter whether Earth or anything else in our solar system is or isn't a planet.

The definition of a planet is always going to be arbitrary, because a naturalistic definition will be too broad to be useful: by the most naturalistic definition we'll have hundreds of planets, some of which don't even orbit the Sun (after all, why shouldn't Ganymede and Titan--both larger than Mercury--be planets?). Personally, I would have gone the other way with the definition, though: call the eight bodies that are currently labeled planets "major planets" (they're the ones we memorize in grade school), and let any body that has attained hydrostatic equilibrium be called a planet--whether that be an asteroid like Ceres, a moon like Titan, or a dwarf planet like Pluto. Especially since by the IAU's current definition, we can't actually confirm that any planets exist outside the Solar System--our equipment just isn't sensitive enough to prove that every exoplanet has cleared its neighborhood.

Anyway, as for the new "moon," technically it's just a co-orbital asteroid and is certainly no more moonlike than 3753 Cruithne, Earth's largest and overall most significant companion aside from the Moon.

So true! I don't think there's any planet that has a completely clean neighborhood - except for Mercury!

Well, while "Planet Vulcan" has definitely been disproved, the jury is still out on "Vulcan asteroids." On the one hand, our Solar System seems to be atypical with how empty the near-solar neighborhood is--many systems we have observed are tightly crowded with planets inside the orbit of Mercury--but our sample may be biased since these systems are also easier for us to detect by our current methods. Still, there is also a theory that our inner system used to be more crowded--before the Sun ate the inner planets.

 

[Zaarin]

Re: Pluto. I have always thought Pluto had some strange characteristics (mainly its orbit inclination and its approach to Neptune's orbit) which gives it a special status as a planetary body. So, it's down grade was a bit much to accept. But to play semantics, the inner planets are called terrestrial planets (terrestrial being an adjective) and the outer planets (until we get to Pluto) are the Jovian planets (Jovian = adjective). Therefore, Pluto is still a planet with the adjective of dwarf. So take that IAU...

BTW... If because of the relationship of Charon and Pluto orbiting a central point, then the two together creates a binary planet (in the same way we have a some binary stars orbiting a central point). Therefore Pluto/Charon become a unique structure and again gain a stronger planetary status. And we can just give Pluto top billing.

Strictly speaking, only Jupiter and Saturn are gas giants (i.e., Jovian); Uranus and Neptune are ice giants. Also, Pluto and Charon are not the only binary bodies in the Solar System--just the largest (by a considerable margin, as any other binary bodies we are aware of are asteroids). Given our discovery that asteroids can have rings, I was sorely disappointed that Pluto does not, but I still hope that we will observe KBOs that do.

 

[Gadget Girl]

First off, thanks everyone who's been sharing other astronomy related links. Haven't gotten through them all yet, but I really enjoy.

I wonder when we're going to downgrade most of the states in the US? Since 50 states seem rather extreme for students to have to memorize. For that matter ... we should probably downgrade most presidents so that students only have a handful that they need to memorize. Amazing that a SCIENTIST would actually state we can't keep adding planets to our list because it would be too difficult for students to have to memorize them. He even commented he wouldn't want to have to memorize even 20 planets.

Wonder if he can name all 50 states and the capitals, as well as all the presidents?

You know, I never had to learn all the presidents, although I did have to learn the state capitals. I'm not sure I could recite them or anything anymore, although funny thing, I can still recite the first lines of Caesars Gallic Wars in latin, well until I get to the part where either Celts call themselves Gauls, or the Gauls call themselves Celts, never could remember which way that worked.

Actually I can still recall a lot of stuff from Latin class, probably because I like it way more than US history/geography.

The definition of a planet is always going to be arbitrary, because a naturalistic definition will be too broad to be useful: by the most naturalistic definition we'll have hundreds of planets, some of which don't even orbit the Sun (after all, why shouldn't Ganymede and Titan--both larger than Mercury--be planets?). Personally, I would have gone the other way with the definition, though: call the eight bodies that are currently labeled planets "major planets" (they're the ones we memorize in grade school), and let any body that has attained hydrostatic equilibrium be called a planet--whether that be an asteroid like Ceres, a moon like Titan, or a dwarf planet like Pluto. Especially since by the IAU's current definition, we can't actually confirm that any planets exist outside the Solar System--our equipment just isn't sensitive enough to prove that every exoplanet has cleared its neighborhood.

Bringing it back to astronomy, if they had just called Pluto a dwarf planet, instead of a Kuiper Belt Object, maybe people wouldn't be quite as upset. I mean, who wants to learn 50 states, hic haec hoc, and an awkward term like Kuiper Belt Object.

Also interesting point Zaarin, about us not knowing whether extra solar planets have cleared their neighborhoods or not. I hadn't thought of that, even though I knew we are mostly aware of gas giants out there because it's easier to spot big things than little ones.

 

[Zaarin]

Bringing it back to astronomy, if they had just called Pluto a dwarf planet, instead of a Kuiper Belt Object, maybe people wouldn't be quite as upset. I mean, who wants to learn 50 states, hic haec hoc, and an awkward term like Kuiper Belt Object.

Also interesting point Zaarin, about us not knowing whether extra solar planets have cleared their neighborhoods or not. I hadn't thought of that, even though I knew we are mostly aware of gas giants out there because it's easier to spot big things than little ones.

Well, Pluto is a dwarf planet--and also a Kuiper Belt Object--and also a plutoid, which is a sub-class of KBOs that resemble Pluto in their orbital resonance with Neptune. So far we have four officially classified dwarf planets: Pluto, Eris, Makemake, and Ceres. (Fun fact: with the recent discovery of a moon of Makemake, all of them except Ceres have satellites.) What they're waiting for on some of the more obvious "dwarf planet candidates" is beyond me.

Yes, for quite a while hot Jupiters (large gas giants close to their suns) were all we knew about. Since then we've discovered a good number of super-earths and sub-Neptunes (planets with masses in between Earth and Neptune), and I think we've found a small number similar in size to Earth. I'm still eagerly awaiting the day we can confirm the existence of the first exomoon.

 

[robert952]

There was a planetarium in Charlotte? Never knew that. Of course the only one I ever went to was the one in Chapel Hill when I was in the fifth grade.

Yes - Charlotte A Kelly Planetarium, connected to the Charlotte Nature Museum which was across the creek from Freedom Park. 1969-70 I did four shows per weekend 1 Saturday and 3 on Sunday. They packed the planetarium somewhere - was supposed to be used in conjunction with Discovery Place. Not sure where the equipment is now. Planetarium portion of the building was turned into a butterfly exhibit last time I was there (MANY years ago).

 

[DigitalDreamsDS]

THIS!
This is why I love you guys, our 'little' community. We can talk about stuff like this, and actually have INTELLIGENT conversations.

 

[Miss B]

Yes, we're kind of unique in that sense.

 

[eclark1894]

THIS!
This is why I love you guys, our 'little' community. We can talk about stuff like this, and actually have INTELLIGENT conversations.

Well, I AM a higher life form than the rest of you guys... but I'm not arrogant about it.

 

[quietrob]

Well, I AM a higher life form than the rest of you guys... but I'm not arrogant about it.

Boooo! Hissssss!!!

 

[eclark1894]

Boooo! Hissssss!!!

What? I'm being humble.

 

[Miss B]

Now now boys, play nicely.

 

[eclark1894]

Seriously, though, you know what would be cool to see? I'd like for NASA to send a stationary satellite in orbit on this side of the sun in Earth's orbit. The satellite would watch earth as it continued on it's way orbiting the sun. We'd see it get smaller and smaller and eventually disappear from view. The satellite would then rotate, and watch as earth approached from the opposite direction.

 

[Miss B]

You know, that would be fun to watch, though after a while it might get boring. Unless, of course, there's a major collision with an asteroid that throws Earth off course, and into a new orbit. Hmmmm, I haven't done an outer space render in a few years.

 

[Zaarin]

Seriously, though, you know what would be cool to see? I'd like for NASA to send a stationary satellite in orbit on this side of the sun in Earth's orbit. The satellite would watch earth as it continued on it's way orbiting the sun. We'd see it get smaller and smaller and eventually disappear from view. The satellite would then rotate, and watch as earth approached from the opposite direction.

A satellite would be photoevaporated long before it got close enough to the Sun to be in geostationary orbit. It could sit in one of our Lagrange points, but then it would only be stationary relative to us and the Sun--which means it would still be following us around. Jupiter and Saturn have some trojan asteroids (asteroids in their Lagrange points with the Sun), but as far as I know the rest of the planets just have pockets of dust there. Same with the Lagrange points between us and the Moon.

 

[quietrob]

Seriously, though, you know what would be cool to see? I'd like for NASA to send a stationary satellite in orbit on this side of the sun in Earth's orbit. The satellite would watch earth as it continued on it's way orbiting the sun. We'd see it get smaller and smaller and eventually disappear from view. The satellite would then rotate, and watch as earth approached from the opposite direction.

That might be fun as a single cable channel with that as it's singular purpose. I would allow only songs with celestial bodies as a soundtrack. Of course the Earth has it's picture taken from a distance. Voyager just as it was leaving the Solar System, looked over it's shoulder, and gave us a peek at ourselves.

It rather makes us seem insignificant doesn't it? How are the Ancient Aliens going to find us and save us from ourselves?

 

[eclark1894]

Actually, there was something like that just a few years ago. Unfortunately, I don't think the pictures were very good.

 

[Zaarin]

That might be fun as a single cable channel with that as it's singular purpose. I would allow only songs with celestial bodies as a soundtrack. Of course the Earth has it's picture taken from a distance. Voyager just as it was leaving the Solar System, looked over it's shoulder, and gave us a peek at ourselves. [snip] It rather makes us seem insignificant doesn't it? How are the Ancient Aliens going to find us and save us from ourselves?

And of course we've also been pictured by Curiosity on Mars and Cassini from Saturn (and again).

 

[3dcheapskate]

I liked the actual statement in the JPL/NASA news item (linked from the article in the OP) - "...It is too distant to be considered a true satellite of our planet, but it is the best and most stable example to date of a near-Earth companion, or "quasi-satellite."..." Once bitten, twice shy perhaps ? I noticed that the word 'moon' only appeared twice in that article, both times when comparing 2016 HO3's distance from the earth with that of the moon.

When I was a kid Pluto was definitely, unequivocally a planet. We knew full well that it was 'different', not formed in the same way as the rest with its elliptical orbit, inclined at a rakish angle to the orbits of all the other planets, that brought it closer to the sun than (quick check) Neptune. But who wants to be the same as the others? All the other planets were created from the proto-sun's accretion disc (didn't bother double-checking that one - it's what I remember from when I was a kid. I think it's correct, unless they've redefined things), which in my mind makes Pluto even more special! Hmmm... I guess Pluto was kind-of my role model... ;o)

And really, who gives a tinker's cuss what the 'official' definition of a 'planet' is - probably not the majority of the 9,600 members who weren't there for the vote, who were maybe too busy doing real science !

 

[3dcheapskate]

...I refer you to the ''Pale Blue Dot' (text)...

An old YTV interview with Richard Feynman is for me a nice companion piece to Carl Sagan's - there's a lovely bit in it (around 4 minutes in) where he talks about his father telling the words for 'duck'* in different languages. They should have played that at the 'how do we define a planet' fest...

*edit: actually a 'brown-throated thrush', not a duck