What’s the smallest known four-body system?

What’s the smallest known three-body system?

Or get controversial and confusing and call it Russell’s Teapot? On second thought, save that one for something gaseous that might contain a tempest.

Rama should be the name of Earth’s “Trojan” asteroid.

This gives IMO a much better reason than the widely propagated CT in Alecto of the “Moon around a real planet not a dwarf planet” folks. Clyde Tombaugh was, is, and will be the discoverer of Pluto. So there is no real need of a tribute to CT.

Yes but Jupiter is located in a belt or zone of its fellow gas giants

Actually it isn’t.

There’s a huge distinction between the configuration of Jupiter, Saturn, Uranus and Neptune and the configuration of all the objects in the asteroid belt.

But hey I guess whatever it takes to make your beloved Pluto a planet again… even if it means rendering the asteroid belt and Kuiper belt a morass of confusion.

Whatever I see this is going nowhere.

But even that doesn’t work particularly well because there is substantial evidence from open clusters that stars can form below the deuterium fusion limit, so you can get stars of 6 Jupiter masses which never undergo fusion.

I’d call those planets that happen to be born in a star-like manner and are free-floatuing in space.

Is that unreasonable in your view – and if so why?

This then leads to a very confused state of affairs.

Uh, like its not already?

The IAUdefinitionis more confusing and worse. It’s not a sclear-cut or inclusive as my alternative or many other better ones. We’re having this discussion now because things aren’t now clear.

Following the observational evidence leads to the conclusion that there are two different populations of objects in the mass range: the low-mass tail of the stellar distribution, which are a natural extension of the brown dwarfs, and the high-mass tail of the planetary distribution, which group naturally with the planets. In different environments the distributions change, e.g. for objects in orbit around solar mass stars there appears to be a lack of objects at around ~35 Jupiter masses or so, which may indicate that in that particular environment, the brown dwarf and planetary populations are (for the most part) separated there.

Okay, so? Is this set in stone anyhow or just the result of our observations so far which may lead to a bias in what we can and can’t detect?

For 2M1207b the mass ratio essentially rules out a planet-like formation – what we have is a low-mass binary star where one of the two stars is below the fusion limit. These naturally group with the brown dwarfs.

Hmm.. not so sure this is true or that we know enough to say given our understanding of planetary formation remains incomplete. The univverse keeps surprising us in this area.

We do know one object -2M1207b is mor eplanet-like inmass and probably other qualities than star-like whereas for its larger partner tehreverse is the case.

Distinction based on fusion just leads to unhelpful confusion. Applying both the terms “planet” and “brown dwarf” to the same object obscures the distinction between the two groups of objects which is naturally suggested by the observations.

I disagree [shrug.]

Fusion seems a natural and reasonable point of distinction to me here.

In short, going with the observations we see that there is a process of top-down collapse which builds stars, and a process of formation from discs which builds planets. Sometimes the star formation mechanism produces objects which are too small to undergo fusion, sometimes the planet formation process forms objects which are massive enough to do so (just as it doesn’t particularly care about whether the resultant object has a magnetosphere, plate tectonics, a solid surface, satellites, etc).

Um, again my resposne is more, okay so?

Nature builds astronomical objects out of nebulae in a wholerange of sizes. I’m notsur eIunderstand what youare getting at here.

Some are large and capable of being sel-fluminous by nuclera fusion -we callthese stars.

Soem are not capable of shining on their own fusion – we call them planets.

Some are intermediate capable of some brief limitedfusion but notmuch. We call those brown dwarfs.

The planet formation process results in a small number of massive objects and leaves behind also various reservoirs of objects which never quite made it

It also builds up some worlds so they are not-so-much “failed stars” as “really successful jupiters” instead!

(e.g. the main asteroid belt, the Jupiter Trojans, the Edgeworth-Kuiper belt and the scattered disc). Objects such as 1 Ceres, 4 Vesta, 136199 Eris and 134340 Pluto are merely the largest objects in the various small-body reservoirs, and are qualitatively distinct from the planets which substantially outmass everything else in their vicinity by several orders of magnitude: for example Jupiter is clearly distinct from the population of small objects that cross its orbit, there is no reasonable argument that it is a member of a belt population.

Yes but Jupiter is located in a belt or zone of its fellow gas giants and it is radically different from Earth and Mercury as well! Earthis aplanet -and has more in common with Pluto than it does with Jupiter!

Let’s just admit that there is a very wide range in types and masses of planet just as there is with stars shall we?

“If you had a chance to name this new moon what would you name it – and why did you pick that name? Oh yea, the IAU claims to have a monopoly on naming objects and features in our solar system – and beyond. But there is nothing legally binding to the names they decide to use. Everyone just goes along with them because … well … because. And who gave them this role anyways? Answer: they appoint themselves. So why can’t the rest of us have a say in naming the things in our universe? The IAU is so 20th century. Its time to change this process.”

This then leads to a very confused state of affairs.

Following the observational evidence leads to the conclusion that there are two different populations of objects in the mass range: the low-mass tail of the stellar distribution, which are a natural extension of the brown dwarfs, and the high-mass tail of the planetary distribution, which group naturally with the planets.

In different environments the distributions change, e.g. for objects in orbit around solar mass stars there appears to be a lack of objects at around ~35 Jupiter masses or so, which may indicate that in that particular environment, the brown dwarf and planetary populations are (for the most part) separated there.

For 2M1207b the mass ratio essentially rules out a planet-like formation – what we have is a low-mass binary star where one of the two stars is below the fusion limit. These naturally group with the brown dwarfs.

Distinction based on fusion just leads to unhelpful confusion. Applying both the terms “planet” and “brown dwarf” to the same object obscures the distinction between the two groups of objects which is naturally suggested by the observations.

In short, going with the observations we see that there is a process of top-down collapse which builds stars, and a process of formation from discs which builds planets. Sometimes the star formation mechanism produces objects which are too small to undergo fusion, sometimes the planet formation process forms objects which are massive enough to do so (just as it doesn’t particularly care about whether the resultant object has a magnetosphere, plate tectonics, a solid surface, satellites, etc).

The planet formation process results in a small number of massive objects and leaves behind also various reservoirs of objects which never quite made it (e.g. the main asteroid belt, the Jupiter Trojans, the Edgeworth-Kuiper belt and the scattered disc). Objects such as 1 Ceres, 4 Vesta, 136199 Eris and 134340 Pluto are merely the largest objects in the various small-body reservoirs, and are qualitatively distinct from the planets which substantially outmass everything else in their vicinity by several orders of magnitude: for example Jupiter is clearly distinct from the population of small objects that cross its orbit, there is no reasonable argument that it is a member of a belt population.

Going along these lines, Ups And c is clearly a planet and not a brown dwarf, 2M1207b is clearly a brown dwarf and not a planet, and 134340 Pluto is not a planet but a large member of a belt population.

(Note this is not the IAU definiton either, “not a member of a belt population” is not precisely the same as “cleared its orbit”, and it generalises to exosystems too…)

http://stars.astro.illinois.edu/sow/upsand.html

http://www.universetoday.com/9879/first-direct-image-of-an-exoplanet/

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http://www.space.com/2179-newly-discovered-failed-star-added-stellar-neighborhood.html

For Upsilon Adromedae, 12M1207A and SCR 1845-6357 frutehr details and sources. Hope this is interesting /helpful for y’all.

http://en.wikipedia.org/wiki/Brown_dwarfs

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http://en.wikipedia.org/wiki/Teide_1

&

http://en.wikipedia.org/wiki/AB_Pictoris

Plus a few other sources to follow separately as too many links in one post equals very big trouble here.

MTU : “Ultra-super-massive gas giants that overlap with brown dwarfs in their nature get an “upgrade” to brown dwarf class, ice dwarf planets like rock (terretsrial /earthlike) dwarfs are rightly considered as planets in their own right – as they are – and the Jovian and Neptunean mass gas giants remain planets as they also are. Where’s the problem with that?”

The problem is it leads to an unnatural description of the system.

‘Unnatural’ is an odd and sometimes confusing word. I don’t think it is an “unnatural” description.

Given the configuration, the intuitive description is that Upsilon Andromedae c is the second planet and Upsilon Andromedae d the third. But if you say Ups And c is a brown dwarf not a planet, things become a lot messier (pun on your pseudonym fully intended): is Ups And d the second planet? Or the first circumbinary one? Or what? Neither provides an intuitive description of the system.

Okay, I see what you are saying here. My suggestion would be to say that “brown dwarf” in this case is ALSO a type of planet just as we can say that Ceres is a type of asteroid as well as being an ice dwarf planet or our Sun is also a star. Things can be two things at once. That objects can overlap to a certain degree because nature is also messier ( ) than we’d like at times with distinctions not always being clear-cut.

Brown dwarfs are intermediate mass objects that span the gap between the smallest stars and largest planets. Thus there are are types of ‘Brown dwarfs’ over various ranges – they come in two spectral classes L and T they evolve in various ways and, yeah, there are many complexities and issues with them. There are high mass brown dwarfs that formed like stars and relatively low-mass brown dwarfs that formed like superjovian planets.

2M1207A (which famously boasts the first exoplanet directly imaged orbiting it), Teide 1 (the first brown dwarf ever confirmed in 1995 and a member of the Plieades star cluster) and the binary brown dwarfs orbiting Epsilon Indi are examples of high mass brown dwarfs that are more stellar than planetary in nature. Upsilon Andromedae c, AB Pictoris b (another candidate for first directly imaged exoplanet) and SCR 1845-6357 (a very nearby brown dwarf orbiting a red dwarf sun at 4.5 AU, the third closest brown dwarf known) are examples of brown dwarfs that are more planetary than stellar in nature.

Nature builds objects along a continuum starting with the most massive hypergiant stars down through the least massive brown dwarfs through to the largest superjovian planets and down through the rocky terrrestrial planets like Earth to the ice dwarf planets like Pluto at one end of the ice dwarf spectrum down to Ceres at the other.

It is hard to draw distinct lines. Sometimes dual classification make sense such as calling Ceres both a planet-variety ice dwarf – and the largest asteroid. Similarly UpsAnd c could be termed a brown dwarf – which it is based on fusing deuterium and mass – *and* an explanet* because of its orbit. We could then say Upsilon Andromedae has 4 exoplanets – and one of those planets is also a brown dwarf. Or that it has three planets and 1 brown dwarf and note that planet c is also brown dwarf that counts as a planet in some contexts too.

Yes, it is a little messy but that’s life. After all, in physics waves are particles as well!

——-

* Remember here too that the IAU definition is so bad it is restricted to our solar system alone. By IAU decree NO star other than the Sun has planets at all. Comonsense and common usage would prove that part of their dreadful definition wrong – as well as much else. I predict the IAU verdict against Pluto will be widely ignored and eventually corrected by public demand. Exoplanets are planets too – and so those in the ice dwarf class.

@Rift: Should we also grandfather in pi=3.1 because we don’t want the Egyptians to feel bad?

Ultra-super-massive gas giants that overlap with brown dwarfs in their nature get an “upgrade” to brown dwarf class, ice dwarf planets like rock (terretsrial /earthlike) dwarfs are rightly considered as planets in their own right – as they are – and the Jovian and Neptunean mass gas giants remain planets as they also are. Where’s the problem with that?

The problem is it leads to an unnatural description of the system. Given the configuration, the intuitive description is that Upsilon Andromedae c is the second planet and Upsilon Andromedae d the third. But if you say Ups And c is a brown dwarf not a planet, things become a lot messier (pun on your pseudonym fully intended): is Ups And d the second planet? Or the first circumbinary one? Or what? Neither provides an intuitive description of the system. Allow for the existence of deuterium-burning planets (and the deuterium burning phase will only comprise a relatively short part of the planet’s early history) and the description of the system falls into place and makes a lot more sense.

Furthermore this split ends up with both terms “planet” and “brown dwarf” referring to two fundamentally different groups of objects: “planet” ends up incorporating the low-mass tail of the stellar mass distribution and a cutoff on the planetary distribution, and “brown dwarf” ends up incorporating both star-like objects and the high-mass tail of the planetary mass distribution. This seems to me to be rather like paraphyletic groups in taxonomy, which are generally frowned-upon these days.

How can hubble take a picture of a galaxie many many more light years away and it is crystal clear, but it takes a picture of pluto which is reletivly very close and it looks so blury?

Pluto is tiny. The “photo” (for want of a better word) has had to be massively enlarged to we can see Pluto, so much so that we also see individual pixels.

Galaxies, OTOH, are huge, occupying a far larger piece of the sky. And features that we consider to be sharply-resolved on a picture of a galaxy are usually many tens of light-years across.

Of course, Hubble has imaged really, really distant galaxies, and these appear as faint little fuzzy blobs.