# Binary planets?
**URL:** https://boards.straightdope.com/t/binary-planets/725519
**Category:** Factual Questions
**Created:** [July 18, 2015, 2:34pm UTC](https://boards.straightdope.com/t/binary-planets/725519 "2015-07-18T14:34:43Z")
**Posts on this page:** 12
**Page:** 2
### Author:  [@sbunny8](https://boards.straightdope.com/u/sbunny8)
#### Post date: [July 19, 2015, 7:54am UTC](https://boards.straightdope.com/t/binary-planets/725519/21 "2015-07-19T07:54:38Z")
The center of mass in the Earth-Luna system is inside the surface of Earth, but Luna is receding. Eventually there will come a day when the center of mass is outside Earth’s surface. However, I don’t think Earth will ever become tidally locked with Luna. Rather, it will become tidally locked with Sol.
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### Author:  [@eburacum45](https://boards.straightdope.com/u/eburacum45)
#### Post date: [July 19, 2015, 8:47am UTC](https://boards.straightdope.com/t/binary-planets/725519/22 "2015-07-19T08:47:49Z")
Our moon was probably formed in a collision between the Proto-Earth and another planet, which might have been about as big as mars. In the process some of the material from the Mars-sized object was transferred to Earth, making that a bit bigger; what was left went into orbit.
Given a slightly different approach speed and angle the remnant might have been bigger; the Moon might have been closer in size to Mars, making our system a true double planet. If the incoming object had been a bit bigger there may have been a similar result.
Pluto and Charon were probably separate objects that somehow came to orbit one another; this might have been by a process of lithobraking, like the Earth-Moon system, or there may have been other objects involved. But two near-binary planets in one system suggests to me that binary planets are not uncommon.
(Here’s some images of [fictional binary planets](http://www.orionsarm.com/eg-article/503cd400819a6), including some [made](http://www.orionsarm.com/eg-article/53a6c927ecaf8) [by me](http://www.orionsarm.com/eg-article/5385f65c43e09))
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### Author:  [@John\_Mace](https://boards.straightdope.com/u/John_Mace)
#### Post date: [July 19, 2015, 2:58pm UTC](https://boards.straightdope.com/t/binary-planets/725519/23 "2015-07-19T14:58:46Z")
> [@LSLGuy](#):
>
> What’s odd to me about the basketball team name is that the word Celt or Celtic in any context other than basketball is pronounced correctly by damn near everybody as Kelt or Keltic.
>
> So how/why did they screw up the basketball team name? It’s a mystery. As another devout anti-basketballer, it’s not a mystery I much give a hoot about, but it \*is \*a mystery.
The thing is, language is all about communicating. If you said: “My sone really likes the Keltics”, most people wouldn’t understand what you were talking about. In order to communicate effectively, you usually need to say SELL-tics.
My “favorite” Greek derived word mispronunciation is “kudos”, which most people pronounce “KOO-doze”, as if it were the plural of “kudo”. In this case, though, saying it correctly (KOO-dos) does not generally cause confusion.
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### Author:  [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)
#### Post date: [July 19, 2015, 3:19pm UTC](https://boards.straightdope.com/t/binary-planets/725519/24 "2015-07-19T15:19:31Z")
> [@John\_Mace](#):
>
> The thing is, language is all about communicating. If you said: “My sone really likes the Keltics”, most people wouldn’t understand what you were talking about. In order to communicate effectively, you usually need to say SELL-tics.
>
> My “favorite” Greek derived word mispronunciation is “kudos”, which most people pronounce “KOO-doze”, as if it were the plural of “kudo”. In this case, though, saying it correctly (KOO-dos) does not generally cause confusion.
Language can be use to distinguish us and them. In a conference of planetary scientists, perhaps anyone using “sharon” can be identified as an outsider, perhaps someone with extensive experience in other subfields, a newbie grad student, or a journalist.
Someone who, say, is at a party where some enthusiastic laymen are talking about ALL THE COOL PLUTO STUFF, and insists on telling them that “kayron” is the correct pronunciation every single time, is a bit of a pedantic asshole.
Someone who brings it up on certain message boards is the kind of pedant who is entirely welcome here, even if only because it lets us start a new round of prescriptivists vs descriptivists…
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### Author:  [@Knorf](https://boards.straightdope.com/u/Knorf)
#### Post date: [July 19, 2015, 3:28pm UTC](https://boards.straightdope.com/t/binary-planets/725519/25 "2015-07-19T15:28:27Z")
> [@John\_Mace](#):
>
> The thing is, language is all about communicating. If you said: “My sone really likes the Keltics”, most people wouldn’t understand what you were talking about.
Also, hardly anyone knows what a sone is.
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### Author:  [@Yumblie](https://boards.straightdope.com/u/Yumblie)
#### Post date: [July 19, 2015, 4:57pm UTC](https://boards.straightdope.com/t/binary-planets/725519/26 "2015-07-19T16:57:23Z")
> [@AK84](#):
>
> Why were they theorized to be nearly impossible, and what explanation has been given since the observations?
Notice in our solar system there’s a clear dividing line between the small rocky planets with a solid surface, and the massive gas giants. It’s thought that in order to form large Jupiter-sized planets, you need to be far enough away from the Sun to collect solid ice, which allows for more massive planet formation, which can build up really big atmospheres.
The fact that we found massive (and presumably icy) Jupiter-sized planets so close to their star was pretty shocking, given this line of reasoning. The leading theory is that they formed far away from their star but somehow migrated inward due to some gravitational interaction.
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### Author:  [@Chronos](https://boards.straightdope.com/u/Chronos)
#### Post date: [July 19, 2015, 7:00pm UTC](https://boards.straightdope.com/t/binary-planets/725519/27 "2015-07-19T19:00:21Z")
There’s also a problem with observation biases at work here. Back when our own solar system was the only one known, all of the models for planetary formation tended to produce solar systems that looked a lot like ours: A few rockballs close in, then a few gasballs further out, with a bunch of iceballs beyond them. But then we started discovering other solar systems, all of which have “hot Jupiters”, and now most of the models tend to result in systems like that, with ones like our own as rare outliers.
But the problem is, we don’t actually know that hot Jupiters are common or normal. We’ve discovered a lot of systems like that, but that’s just because most of the techniques we currently use can’t detect anything but hot Jupiters. For all we know, those could be just, say, 1% of all solar systems, and we’re just completely ignoring the other 99%.
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### Author:  [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)
#### Post date: [July 19, 2015, 8:29pm UTC](https://boards.straightdope.com/t/binary-planets/725519/28 "2015-07-19T20:29:13Z")
> [@John\_Mace](#):
>
> The thing is, language is all about communicating. If you said: “My sone really likes the Keltics”, most people wouldn’t understand what you were talking about. In order to communicate effectively, you usually need to say SELL-tics. …
Granted. You’ll notice I didn’t say that I insist on pedantically pronouncing the team name as “Keltics”. Because I don’t.
My question was entirely "Why did that proper name get pronounced that way when the same word used in the same way (“someone/something connected with the ancient Celts / modern Irish”) in other contexts is pronounced “Keltic”?
The team wasn’t formed or named before the mists of recorded history. Wiki says 1946. We ought to be able to advance a theory or find a record of when/why/how.
Mindful that this is turning into a hijack in a thread about binary planets.
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### Author:  [@OldGuy](https://boards.straightdope.com/u/OldGuy)
#### Post date: [July 20, 2015, 12:16am UTC](https://boards.straightdope.com/t/binary-planets/725519/29 "2015-07-20T00:16:54Z")
> [@LSLGuy](#):
>
> The team wasn’t formed or named before the mists of recorded history. Wiki says 1946. We ought to be able to advance a theory or find a record of when/why/how,
There were Celtic basketball teams long before the current Boston team. They date back at least to WWI. Google “Original Celtics” for more information.
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### Author:  [@eburacum45](https://boards.straightdope.com/u/eburacum45)
#### Post date: [July 24, 2015, 7:44pm UTC](https://boards.straightdope.com/t/binary-planets/725519/30 "2015-07-24T19:44:26Z")
The real original;
[Celtic F.C. - Wikipedia](https://en.wikipedia.org/wiki/Celtic_F.C).
1888 and still going strong, soft ‘c’ and all.
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### Author:  [@eburacum45](https://boards.straightdope.com/u/eburacum45)
#### Post date: [July 24, 2015, 7:58pm UTC](https://boards.straightdope.com/t/binary-planets/725519/31 "2015-07-24T19:58:40Z")
> [@lazybratsche](#):
>
> In a conference of planetary scientists, perhaps anyone using “sharon” can be identified as an outsider, perhaps someone with extensive experience in other subfields, a newbie grad student, or a journalist.
If it works as a shibboleth, it appears to work the other way around;
> [@](#):
>
> from **Wiki**
> However, Christy himself pronounced the ch as sh (IPA [ʃ]), after his wife Charlene. Because of this, as an acknowledgement of Christy and sometimes as an in-joke or shibboleth, the initial sh pronunciation is common among astronomers when speaking English,[16][15][17][18] and this is the prescribed pronunciation at NASA and of the New Horizons team.[19][20]
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### Author:  [@kanicbird](https://boards.straightdope.com/u/kanicbird)
#### Post date: [July 24, 2015, 9:29pm UTC](https://boards.straightdope.com/t/binary-planets/725519/32 "2015-07-24T21:29:13Z")
> [@Learjeff](#):
>
> …
>
> Are there any other known pairs in our solar system that could be called binary systems? Is there an accepted definition for binary system, among astronomers?
>
> Thanks!
Sun-Jupiter could be also with the barycenter outside the sun.
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