Two planets found sharing one orbit

**Descensus** · 02-26-2011 06:51 AM

Two planets found sharing one orbit - space - 24 February 2011 - New Scientist

Originally Posted by New Scientist

Buried in the flood of data from the Kepler telescope is a planetary system unlike any seen before. Two of its apparent planets share the same orbit around their star. If the discovery is confirmed, it would bolster a theory that Earth once shared its orbit with a Mars-sized body that later crashed into it, resulting in the moon's formation.

The two planets are part of a four-planet system dubbed KOI-730. They circle their sun-like parent star every 9.8 days at exactly the same orbital distance, one permanently about 60 degrees ahead of the other. In the night sky of one planet, the other world must appear as a constant, blazing light, never fading or brightening.

Gravitational "sweet spots" make this possible. When one body (such as a planet) orbits a much more massive body (a star), there are two Lagrange points along the planet's orbit where a third body can orbit stably. These lie 60 degrees ahead of and 60 degrees behind the smaller object. For example, groups of asteroids called Trojans lie at these points along Jupiter's orbit.

In theory, matter in a disc of material around a newborn star could coalesce into so-called "co-orbiting" planets, but no one had spotted evidence of this before. "Systems like this are not common, as this is the only one we have seen," says Jack Lissauer of NASA's Ames Research Center in Mountain View, California. Lissauer and colleagues describe the KOI-730 system in a paper submitted to the Astrophysical Journal (arxiv.org/abs/1102.0543).

Richard Gott and Edward Belbruno at Princeton University say we may even have evidence of the phenomenon in our own cosmic backyard. The moon is thought to have formed about 50 million years after the birth of the solar system, from the debris of a collision between a Mars-sized body and Earth. Simulations suggest the impactor, dubbed Theia, must have come in at a low speed. According to Gott and Belbruno, this could only have happened if Theia had originated in a leading or trailing Lagrange point along Earth's orbit. The new finds "show the kind of thing we imagined can happen", Gott says.

Will KOI-730's co-orbiting planets collide to form a moon someday? "That would be spectacular," says Gott. That may be so, but simulations by Bob Vanderbei at Princeton suggest the planets will continue to orbit in lockstep with each other for the next 2.22 million years at least.

Really cool stuff, especially about the section I underlined.

**mikeac** · 02-26-2011 07:06 AM

Wow. And just a few years ago, scientists thought that locating other solar systems that included planets was impossible. At this rate, no more than twenty years from now, warp speed will be achieved.

**cmind** · 02-26-2011 09:20 PM

^unlikely

Warp drive is a sort of red herring for futurists. The most impressive things that will happen in the future will not involve travelling faster than light. After all, the universe is extremely homogeneous. Chances are if you can find a particular resource in one star system, it probably exists in most star systems. There really isn't much point in travelling out beyond the very nearest stars.

**Xei** · 02-26-2011 09:40 PM

I wonder how this happens. There must be some kind of mechanism analogous to tidal-locking at play here. The probability of there being two planets in the same orbit, and then the probability of their not colliding very soon, is very small indeed, without such a mechanism.

**cmind** · 02-26-2011 09:53 PM

Yeah, the 60 degree lagranges (are they called L4 and L5?) are dynamically unstable I think. My (uninformed) guess is that there's some sort of large shepherding planet farther out that's controlling it.

**DrunkenArse** · 02-26-2011 10:18 PM

Originally Posted by mikeac

Wow. And just a few years ago, scientists thought that locating other solar systems that included planets was impossible.

Please back this up or quit slandering scientists. Thanks.

**Spartiate** · 02-27-2011 12:27 AM

Originally Posted by Xei

I wonder how this happens. There must be some kind of mechanism analogous to tidal-locking at play here. The probability of there being two planets in the same orbit, and then the probability of their not colliding very soon, is very small indeed, without such a mechanism.

Come on did you read the article

. We see stuff like this in our solar system now.

**Xei** · 02-27-2011 01:23 AM

That explains what the configuration is, it doesn't explain why an object would tend to fall into it. Lagrange points are unstable.

**Spartiate** · 02-27-2011 01:49 AM

Originally Posted by Xei

Lagrange points are unstable.

Not necessarily.

**mikeac** · 02-27-2011 03:08 AM

Originally Posted by PhilosopherStoned

Please back this up or quit slandering scientists. Thanks.

A search for substellar companions to solar-type stars

1988. I didn't know the exact year at first so I made an inaccurate post. I first heard about this from a documentary I borrowed from the library called "Universe". In the documentary, it stated that after so many false, failed, or unproven attempts to find planets, many deemed it impossible until the scientists mentioned in the link above located the first planet.

It's kind of hard to locate the exact documentary since there are a lot with the same name.

PS. I would never try to damage any scientists' reputation. I am in fact interested in joining the scientific field myself.

**cmind** · 02-27-2011 03:43 AM

Originally Posted by Spartiate

Not necessarily.

So apparently you didn't read the article you posted. Which isn't a surprise coming from you, of course.

For L4 and L5 to be dynamically stable, their masses must be different by a factor of 24.

**Spartiate** · 02-27-2011 03:58 AM

Originally Posted by cmind

So apparently you didn't read the article you posted. Which isn't a surprise coming from you, of course.

For L4 and L5 to be dynamically stable, their masses must be different by a factor of 24.

It says that the difference in mass between M1 (say the Sun) and M2 (say the Earth) must be greater than a factor of 24.96. The Sun is more than 24.96 times as massive as the Earth. What don't you understand?

This is the case for the Sun-Earth system, the Sun-Jupiter system, and, by a smaller margin, the Earth-Moon system

Who's the one not reading the article?

**DrunkenArse** · 02-27-2011 11:46 AM

Originally Posted by mikeac

A search for substellar companions to solar-type stars

1988. I didn't know the exact year at first so I made an inaccurate post. I first heard about this from a documentary I borrowed from the library called "Universe". In the documentary, it stated that after so many false, failed, or unproven attempts to find planets, many deemed it impossible until the scientists mentioned in the link above located the first planet.

It's kind of hard to locate the exact documentary since there are a lot with the same name.

PS. I would never try to damage any scientists' reputation. I am in fact interested in joining the scientific field myself.

Right on. 1988 isn't just a few years ago

If a scientist actually did say that something like locating a planet around another star is impossible, then it was very sloppy of them. The planet exists. By causality, it exerts an influence on its light cone (that part of the universe that light emitted from it will reach). In this case, they are dimming and filtering the light from their sun. We detect that light. There's nothing even remotely impossible about doing it. It's incredibly impressive. A statement like "impossible without unforeseen technological improvement" or "impossible with our current level of technology" would make sense (edit: or even "I don't have a fucking clue how we would even go about starting to figure out how to do that"). But "impossible" is a very sloppy thing to say.

I sorta jumped because the idea that scientists say "impossible" or somehow deny possibility is very prevalent. It's unfortunate because scientists help the engineers make the "impossible" possible (though this isn't close to being their primary role). Scientists do say things like, "there's zero evidence to support that hypothesis: you're full of shit and should stop lying to people" but that's not saying that something is impossible.

I mean even with something like reincarnation it's perfectly possible that science could figure out a way to remove your "soul" (by which I mean the information contained in your body which makes you uniquely you) from your body at the time of death and put it in a new one.

Sorry for the digression Blueline. I'll just be on my way now.

**Rybread34** · 03-05-2011 05:32 AM

Originally Posted by mikeac

Wow. And just a few years ago, scientists thought that locating other solar systems that included planets was impossible. At this rate, no more than twenty years from now, warp speed will be achieved.

We just need to unearth that prothean technology on Mars...

**MindGames** · 03-05-2011 05:51 AM

Originally Posted by PhilosopherStoned

I mean even with something like reincarnation it's perfectly possible that science could figure out a way to remove your "soul" (by which I mean the information contained in your body which makes you uniquely you) from your body at the time of death and put it in a new one.

I agree with this. The soul is quite simply the subconscious, which is a collection of learned behaviors and emotions. Considering the subconscious is most likely stored entirely in the brain, if one were to make an exact copy of the brain, it would be possible to replicate one's subconscious mind.

**Jesus of Suburbia** · 03-07-2011 02:21 AM

What about it? Pluto and its moon orbit each other. There are millions of pairs of stars orbiting each other. I don't see why this is such a great discovery.

**Spartiate** · 03-07-2011 02:47 AM

Not orbiting each other, sharing an orbit.

**Jesus of Suburbia** · 03-07-2011 03:21 AM

Originally Posted by Spartiate

Not orbiting each other, sharing an orbit.

Ah, I see. I just read the title to be completely honest with you. *goes back and reads article*

[Edit:] Okay, now that I'm a bit more educated, I understand why people think this is interesting, but it doesn't hold my attention. It's a discovery, sure, but not one worth publicizing. I fit it into the category of "A pig's orgasm lasts 30 minutes". Sure, it's interesting, but not that interesting.