NASA sponsored astronomer Michael Brown of CIT just announced he have found a 10'th planet.
The claim was made for one object based on its brightness alone and that for one object at 3 times the distance of Pluto. In short its smack in the middle of the belt of other KBO's.
The guy claim he was forced to reveal his data since a hacker had threatened to release information about the object.
Im strongly unconvinced about that story.
Why then claim it to be a planet rightoff. More likely think this guy must be looking for the fame of Clyde Tombaugh.
Without any infrared measurements or to establish the albedo properly which would have given a guesstimate of the objects size he singlehandedly claim a KBO planet, this should get the Bad astronomy 1'st price prize for preposterous extrapolation from a single unconvincing piece of scientific data.

Myran:

I really don't have a lot of background information on this discovery, but I suspect you are correct about the decision to "go for the glory." But who wouldn't try for that if they had some strong data and the data somehow escaped to the Internet? Especially, consider the fact that there is no clear definition of the word "planet." It is certainly time for the scientific community to define that imprecise word.

I think there is some IR data from the Spitzer Space Telescope.

I think his thought that his data was hacked was a misunderstanding, if this explanation is accurate. http://groups.yahoo.com/group/mpml/message/15283

Perhaps the most significant outcome of this event will be the IAU finally coming to grips with the definition of a planet. This article claims we will have a definition this week!

http://www.nature.com/news/2005/050801/full/050801-2.html

I think I know how I would define a planet. It will be interesting to see how the IAU does. I now see that there is a lot of discussion on these topics elsewhere in this forum, but I'll have to explore them tomorow...

Even near 100%, this object would still be about the size of Pluto.

CosmicRocker: When I posted this, we didnt have much information either.
But thank you for the info and links.
It turned out that this discovery got a lot of attention in another thread whereas my post here got left in the cold until now. But it will be interesting to learn what
IAU thinks.

volcanopele: If its somewhat larger or smaller than Pluto doesnt matter.
If we could timetravel and tell Clyde Tombaugh and the astronomical community back then the true size of the object they had found -Pluto-, im certain they would he have to think not only once or twice before using the term 'planet' for one object of the diminutive size it turned out to have. Size alone, and now we know so much more and have put Pluto into a context, if the discovery of Pluto had taken until recent years, im personally certain we wouldnt have this discussion at all!

Viewing the other discussion of this same subject here, it obvious than many have gotten so used to the notion that Pluto is a planet that we might have to live with that idea.
But one mistake made 70 years ago, does in no way neccesitate that we make the same mistake again!
-"-

(Some background that might or might not be correct written off the top of my head from what I remember reading in many old astronomical textbooks:
Pluto was named a planet at its dicovery for several reasons, one of them that it was thought to be much larger and massive than what it eventually turned out to be.
Pluto was thought to be so massive that it affected the orbits of Uranus and Neptune, when astronomers couldnt match the values they had gotten for Plutos albedo, magnitude and the resulting size there were some wild suggestions that Pluto would about 5000 km and be incredibly dense. Another suggestion was that we did only see Pluto as a starlike object since we did only see the reflection of the sun in one ocean of liquid gas of a larger world.

Plutos status as a planet have been questioned before, then in connection with speculations that it might be one escaped moon of Neptune - turned out to be wrong, Neptune have brought Pluto into a resonance but they might not have had any common past at all, with the exception of Triton that could turn out to be Plutos twin.)

I'm not sure size should be the only, or even principal, criterion for determining "planetary" status; that is, if we are going to retain the term "planet" at all.

Remember that "planet" was originally used as a word for any celestial body that had visible, regular motion against the background of "fixed" stars: not just Mercury, Venus, Mars, Jupiter, and Saturn, but also the Sun and Moon. Comets, whose periods were so long that they could not be identified as the same objects when they returned, were viewed as transient (perhaps atmospheric) phenomena, not similar to planets; other objects were invisible from Earth without apparatus that did not yet exist.

Following the Copernican revolution, the Sun ceased to be "a planet", as (in terms of the entire system), it did not "move". As motion, as seen from earth was no longer a criterion, then the Earth itself could be "a planet".

The telescopic discoveries of Galileo, Huygens and Cassini showed that there were many objects moving around Jupiter and Saturn just as the Moon moved around the Earth; as their motions, viewed from Earth, were not independent of their primaries, they were given a secondary status and not classed as "planets", though by earlier criteria they might well have been. By analogy with these satellites, the Moon also
was demoted, and "a planet" was now defined as "an object moving around the Sun".

One problem with this general definition came with the realization that comets were also satellites of the Sun -- but they were eccentric enough in other ways to merit their own classification. A more serious problem arose with the discovery of the asteroids. Indeed, the questions regarding Pluto and 2003 UB313 were foreshadowed in Piazzi's discovery of Ceres in 1801. Initially Ceres was celebrated as a new planet, just like Herschel's discovery of Uranus in 1781. By the criteria then used -- an object revolving around the Sun with a not-too-elongated orbit -- Ceres was a planet. The trouble came as astronomers over the next few years began to find more and more "planets" in the Main Belt. By the 1850s, the list was becoming unmanageable and it was clear that the asteroids were much smaller than the other planets -- by now eight (with the addition of Neptune in 1846). The asteroids were therefore packed off into their own section of the almanacs. Only at this point does size become an issue in terms of planetary definition. At this point (and up to the present day) the criteria include at least the following:

1) A planet is a natural satellite of the Sun
2) A planet has a not-too-elongated orbit (i.e., it is not a comet)
3) A planet is at least bigger than Ceres (a criterion to some extent redundant with 2), as no comet is bigger than Ceres)

Using these criteria, Pluto was correctly labelled "a planet" in 1930; the only cause for concern being the fact that its orbit is both elongated (somewhat) and tilted (a lot), and I recall that before we ever started talking about KBOs there were proposals to reclassify Pluto as "a comet" -- which was, indeed, the only alternative at the time, as it was obviously neither a Main Belt asteroid nor a moon. On the other hand, Pluto was believed to be, and is, far larger than any comet, which would make its presence in a list of comets far more anomalous than in a list of planets. After all, in the context of all the thousands of objects in the Solar System, Pluto is not that small; besides the other eight planets, only seven moons are larger (the four Galilean satellites, Titan, Triton, and our Moon).

Now of course we have a new list of additional objects (e.g. Sedna, Orcus, Quaoar, Varuna) that fit criteria 1) and 2). Whether they fit 3) is the present dilemma. They are (probably) larger than Ceres; but criterion 3) only says "at least bigger", but does not tell us how much larger than Ceres "a planet" has to be. As these objects are currently not being labelled "planets", one supposes that the real answer is "at least as large as Pluto". And indeed, if we want to avoid the planetary crunch occasioned by the accumulation of asteroids in the first half of the 19th century, that will have to be the answer.

Now we have 2003 UB313. And if our criteria for "a planet" are now: 1) A natural satellite of the Sun whose orbit is not 2) too elongated and is 3) at least as big as Pluto, then 2003 UB313 is a planet. And that is a conclusion that is not, in itself, unacceptable; there is no special reason to limit the number of planets to nine or fewer, and we would be in an even worse terminological muddle if, in 1781, tradition-minded astronomers had sought ways to avoid calling Uranus "a planet".

The problem, of course, will arise if a lot of objects bigger than Pluto are discovered out in the Kuiper Belt or beyond. Once we get beyond half-a-dozen (and so up to fifteen planets) the situation, if it gets to that (and there's no saying it will) will probably be felt to be intolerable. At that point, I would expect Pluto and his transneptunian siblings to be demoted to some new status, somewhere between "planet" and "asteroid". However, that situation has not yet been reached, and may never be reached; and there is plenty of time to think about possible consequences. At present, however, it seems to me that the safest thing to do is to accept 2003 UB313 as a planet, with the proviso that the term can be revoked if it becomes inconvenient.

However, if Pluto is pre-emptively demoted, simply in order to exclude 2003 UB313, I have to wonder what will be done if a distant transneptunian object is discovered that is larger than Mercury? Will Mercury also lose its status as "a planet"? Or will we add a fourth criterion to the three above, "A planet must not orbit beyond the orbit of Neptune"?

David: That was an insightful description of some of the historical perspectives the IAU must be considering, and I learned a lot reading it. Thanks. I would have to guess that they must also be considering recent discoveries and our better understanding of the origin and evolution of the solar system.

To your list of parameters, I would also suggest adding orbital inclination and some other measure of orbital stability. If an object's future is uncertain, I don't think it should be classified as a planet.

What I find most amazing is that we have the opportunity to be at least peripherally involved in the discussion of the definition of a word that is thousands of years old. It has been reported that the IAU has been working on this definition for the past year and that they expect to finalize a definition this week.

That should be quite interesting.

Um hold a second here David , I didnt question the status of Pluto in my reply, only had a lookback on some of the reasons that world ended up with the label.
And again, since people (including many astronomers) have gotten used to view Pluto as a planet quoting myself 'I think we have to live with the idea'.
So I didnt talk about demotion of Pluto, Mercury or any other world that have been declared a planet.

But as said, we have found many more pieces of the puzzle that makes up the solar system. And one far from unimportant one is this Kupier belt.
UB313 is just one more addition to a list that have become rather long already.

And yes, I do look ahead, since im personally convinced theres not only a dozen larger objects still to be found, but far more perhaps several hundreds.

You used the terms "planet" and "asteroid" and there have been a suggestion some years back thats based on both; 'planetoid' where the name would hint that its the building block that planets are made from.

So yes, I have no problem using the term planetoid for UB313 keeping both sides of the fence happy.

I figure this is going to turn out like Saturn. How many moons do they say it has? It keeps increasing. And what exactly is a moon? Chunks only a few miles wide are being found and called moons. "Big boulder" or "debris" seem more appropriate terms.

In the coming decades, as we send more probes out into the Kupier Belt, and as better telescopes are built, we'll no doubt find a great many objects orbiting out far, as Myran also believes.



Hm, new idea for declaring something a planet - an orbiting body must be a specific percentage of either the mass or diameter (or a combination of both) of the body that it orbits.
Example - Mars has two moons, and they're both fairly small. But it seems ok because they are the only ones there, and because it's a small planet. Now put those moons around Saturn. There are lots of things there that are that size, and they are puny compared to the big gas ball they orbit. Are they still moons?

Very good example, and there you happened upon the core of my thinking.
One of those boulders that are inside the ring system should be considered to be part of the same rings.
But those outside the rings might be considered a moon, unless if very minor in size.
So lets apply this line of thinking to the Kupier belt: Pluto are at the inner edge of same belt and could be viewed as being outside it, so Pluto can keep its planetary status. Yet UB313 are firmly placed among many other Kupier belt objects with orbits both inside and further out from the sun and so it belong to the group and can in no way be seen as a member of the planetary family.

Forty-seven at last count. But there's a way to go before it matches Jupiter's sixty-three.



I've often thought that a distinction should be made between "moons" (objects similar in size and shape to our Moon) and other natural planetary satellites, which - on the model of the coinage "planetoids" - might be called "selenoids". If the former category were restricted to objects at least as big as Mimas, no one planet would have more than seven "moons".



Well - let's try that scheme. Ranking objects in order of relative size in relation to their primary, we have:

.49 Charon
.27 Moon
.1 Jupiter
.087 Saturn
.055 Triton
.043 Titan
.037 Uranus
.036 Ganymede
.035 Neptune
.034 Callisto
.031 Titania
.030 Oberon
.025 Io
.023 Umbriel
.023 Ariel
.022 Europa
.013 Rhea
.012 Iapetus
.0093 Dione
.0092 Miranda
.0092 Earth
.0088 Tethys
.0087 Venus
.0084 Proteus
.0069 Nereid
.0065 Phobos
.0049 Mars
.0041 Enceladus
.0039 Larissa
.0037 Deimos
.0035 Mercury
.0033 Mimas
.0032 Galatea
.0032 Puck
.0030 Despina
.0029 Sycorax
.0026 Portia
.0022 Hyperion
.0018 Juliet
.0017 Pluto
.0012 Amalthea
.0010 Phoebe
.0007 Ceres

I think the list is complete for relative sizes larger than Pluto/Sun, but I have only listed a few that are smaller for use as signposts. I guess Jeff7's definition works as well as others, but it provides no obvious answer to the question: "Where do you draw the line?"

The major problem that I see with this approach is that it makes it harder to draw parallels between bodies in the Solar System that may be similar overall, but happen to be in orbit around a different primary; e.g., if a particular moon happens to be a captured asteroid or comet, it would fall in a very different place in this list than its closest relatives would, because its primary is so much smaller than the Sun.

Then you also get into the asteroids with moons, like Ida/Dactyl. And what about the asteroids that are essentially two bodies in contact with each other?

Definition of 'Planet' Expected in September

http://www.space.com/scienceastronomy/0606...definition.html

Historians and educators have joined astronomers in an effort to break a
deadlock on contentious discussions over a definition for the word planet.

Wonderful! Think of all the fun they can have next trying to officially define "moon", "asteroid" and "comet". The debates in Laputa won't be in it by comparison.

Not speaking on going "up" is size. Jupiter, a gaz giant, orbiting round the Sun, is a planet... But larger gaz giants can still do this. When a gaz giant is much larger than Jupiter, it can remain luminous like a star for many hundred millions of years. When it is large enough to burn its deuterium, it becomes a brown dwarf, and still larger a red dwarf. Star or planet? where to set the limit? If it has nuclear reactions, it is a star, but if it turns around a star, it is a planet. Most stellar companions would rank after Charon, and even after Jupiter, into David's classification above.

Throw this stone into the debate, and look what happens (while keeping at safe distance)...

Note scientists' attempts to introduce two new terms to strange new
worlds: Pegasids and Planemos.


Inside Exoplanets: Motley Crew of Worlds Share Common Thread

http://www.space.com/scienceastronomy/0606...m_pegasids.html

Scientists have discovered a correlation between the amount of heavy elements in
giant Jupiter-like extrasolar planets known as "Pegasids" and their parent
stars.


* Strange New Worlds Could Make Miniature Solar Systems

http://www.space.com/scienceastronomy/060605_planemos.html

Planet-like objects floating alone through space harbor disks of material that
could make other planets or moons, something like miniature versions of our
solar system, astronomers said today.

Just as small stars are much more common than massive ones I'd expect these brown dwarf systems to greatly outnumber all the visible stars. This is just the kind of system that could have brought us Sedna.

I've said this before, but: Assigning names to groups of objects this early in the game just seems awfully premature to me. Obviously we have to come up with classifications at some point, but when *so much* more data is likely to be available within the next 10 years...

"Pegasids" are probably a safe bet, since even now it's fairly evident that these things are pretty common. But, for example, arguing about what group Sedna belongs to is a waste of time... we need to find *at least* another dozen Sednas before there will be any point to classifying objects of that type.

I agree with you about assigning names prematurely. However I don't agree that it's a waste of time trying to think of a plausible dynamical history for Sedna (even while we have still only found one of them!) As I argued on another thread capture from a passing loosely-bound multiple system is one such plausible history. My suggestion was criticised there on the basis that loosely bound (low mass) binary or multiple systems were not likely to be common, if they existed at all. Well, now we have them.

Still, at least in this case we do have an actual physical phenomenon which can serve as a divider: nuclear fusion, of different types.

Alan Stern would claim that we have a similar physical principle that can provide a lower-level threshold for distinguishing planets from nonplanets -- namely, a gravitational field strong enough to make the object spherical -- but I will repeat that it seems to me that in that case, there are far too many seriously doubtful cases here which make the borderline hopelessly fuzzy. Consider the serious irregularities in the shapes of some quite large moons -- are Iapetus and Proteus "spherical" or not? -- and the fact that there are also important differences in the triaxial dimensions of even the three biggest asteroids, which Alan wants to officially list as "planets". And among the KBOs, we already have the horrendous case of 2003 EL61, as long as Pluto on one axis but only half as wide on another. Who knows how many other similar little surprises await us in the Kuiper Belt?

We could try defining a planet as something above a certain average diameter (or mass) whose difference between its longest and shortest diameters is below some (small fraction), making it "near-spherical". But in that case, we're really not that far from the same kind of arbitrariness that would be involved in simply defining a planet as some object whose largest (or smallest) diameter is above a certain size. And I honestly don't think that astronomers can continue to wrangle endlessly over this question without confusing schoolkids and nonscientist adults even more than they're already confused. Besides, they're starting to make themselves look like fools. Just admit that, given what we now know about the Solar System, the question is hopelessly ambiguous, and set some arbitrary planet/nonplanet dividing line that openly recognizes that fact.

As far as I'm concerned, the very discovery which has made the planet/nonplanet distinction impossible to decide any more -- the Kuiper Belt, an entire new major division of the Solar System which was totally undiscovered until the 1990s -- is remarkable and facinating in itself, and trying to maintain some artificial "planet/nonplanet" distinction simply obscures that marvelous new discovery from the general public.

I am waiting for the discovery of a star orbiting a planet.

We will have to call them Ptolemetoids.

I propose 'Moomoon' for a moonlet orbiting a moon.

Would there be Moomoons in the Cowper Belt?

I've always liked the fact that the Sun-Jupiter barycentre is above the surface of the sun

Only if they're in the Milky Way!

I think this debate is not by itself a astronomy/science debate: what is important is to study the objects, giving them a name is a lesser issue. However there was such an issue into biology, when scientists were to name the different animal/vegetal species and classify them (a much more complex problem than in astronomy). In the beginning it seemed an impossible task, as there was so many different species, apparent families and deep structures hidden under apparend diversity. It took centuries to disentangle this (an important stake, as the classification of species was the key to understand the history of life) and there are still some small moves taking place today.


I shall anyway try some classification, keeping with a "naturalistic mind".

-is a star something which has permanent nuclear reactions.

-a brown dwarf is a more ambiguous object, which has transitory nuclear reactions, or which at least shines like a star for a great span of time, one billion years or more. (In practice it is difficult to guess if an object has nuclear reactions or not. A clue is that deuterium is burned between 20 an 22 Jupiter mass. But smaller bodies without reaction can shine a long time like a small star).

-is a planet an unique object which orbits around one of the previous, more or less in a Titus-Bode step. A planet (with moons or not) formed from an unique original cloud or ringlet. On the countrary if this cloud or ringlet was unable to give a single object, but many objects which don't orbit around each other, then we have asteroids into an asteroid belt. With this meaning, Pluto is a planet, even if it don't have a correct positioninto the Titus Bode structure, while asteroids (Vesta) and KBOs are not, even if Vesta and its belt are in a correct Titus-Bode position.

-would also be a planet something free into space, but too small to fall into the star/brown dwarf categories. May somebody propose another name for this special category, something simpe and easily retainable for the general public.

-Is a moon an object which orbits around another which is not a star or brown dwarf.

-Is an asteroid an object which is wandering alone, or which is a part of a belt.


-For a star orbiting around a planet, I wait for observations of these. Please ljk1-4 quote your sources



We must also cope with a variety of structures for multiple systems. In multiple systems, we keep with the above classification of individual objects. So we have star-star systems, star-brown dwarf systems, with planets orbiting about any of their members. An important thing to understand is that the mass ration of a primary object in a system, over its secondary objects, are not much depending of the size of the primary. We could have for instance the solar system scaled up 30 times: the sun would be a blue giant, Jupiter would be a red dwarf, and Saturn a brown dwarf. If the solar system was scalled down, it could become a planet (or other name for this category) and Jupiter a moon.

It is also important to understand that multiple stars can also come into relatively equal sizes. For instance two stars of relatively equal mass are called double stars. With this in mind, the Earth-Moon system could be called a double planet, or Pluto-Charon also. But the recent discovery of other satellites makes the Pluto system a true planet-moons system, a true miniature of a double star system. So the concept of "double star" or "double planet" is not really relevant, unless the two objects are of relatively equal mass or have close relations like mass exchange. If they are real twins, in a sense. But there is no clear limit, so this classification is not very useful. Only prevails the habit of calling double stars, star systems which can be more unbalanced than the Sun- and Jupiter.

This classification don't remove any unambiguity, but it removes some mess. To make it complete, remains to name planet-like objects wandering alone in space (not bound to a star). Two categories:

-with moons
-without moons.

I don't quite follow this. Isn't Pluto a prominent member of the Kuiper Belt? And Ceres is much more prominent a member of the asteroid belt (depending on who you believe, she has anything from 25% to 40% of the total mass of the main belt -- much seems to depend on 1) what mass you attribute to Ceres, 2) what mass you attribute to the asteroids as a whole, 3) where the boundaries of the main belt are -- and I don't know what the latest thinking on the matter is) than Pluto is of the Kuiper Belt, I think. I wouldn't venture to say what percentage of the total mass of the Kuiper Belt is Pluto, but I'm guessing it's not 25%.

It's getting so deep in chocolate (and chewy nougat!) in here that I need something to scoop with... anybody got a Big Dipper?



-the other Doug

Maybe. The best time to look would be during a grazing occultation.

Even I would fear to have made these atrocious puns.

Perhaps this subject is best put put out to grass...

Bob Shaw

".... I'd expect these brown dwarf systems to greatly outnumber all the visible stars....."

The IMF (Initial Mass Function) or size distribution of new stars shows a rather sharp rolloff in the frequency of very low mass M stars and that appears to continue and get stronger into brown dwarfs. It's very hard to measure the IMF of mature stars in the solar vicinity as the faintest are so faint that catalogs become very incomplete at distances of very few light years.

However, It's much easier to study mass/abundance distributions of stars in young clusters, where low mass M stars and brown dwarfs and even rogue-planets still have very substantial thermal output from formation. In addition, they're studying faint object abundances all the way from star-forming regions like Orion, to young clusters like the Pleiades to older clusters like the Hyades.

There is also a *LOT* of theoretical work on variations in the IMF between different types of star forming regions, low-mass-leisurly-accreting nebula to super-star-forming-complexes with high supernova rates and lots of super-heavy stars.

I'm barely familiar with the literature, but it's out there. The main point is that low mass M and brown dwarf stars are much less abundant than simple extrapolation of brighter star abundances used to suggest.

I hope so, as the curves I already seen were increasing sharply with lower masses. If so, there would be such an abundance of brown dwarves that it could explain the dark matter. But searches of MACHOS (objects like brown, red or white dwarves) found essentially objects with half of the sun masses, probably red or white dwarves, and in much less quantity than expected to explain the dark matter. So objects like lone brown dwarves or lone planets (free in space) must be not so common than stars. But the theory predicted too that the IMF could go at such low masses than Earth. Also lonely planets could result from interaction between forming stars, or later of star encounters (especially in close clusters).

So we can still envision systems with small planets as primaries.

Even if the number of low mass systems is much less than indicated by simple extrapolation that doesn't mean that the number actually decreases with decreasing mass. As we have several orders of magnitude of mass range to consider that still leaves the possibility of relatively abundant low-mass systems, even without considering the secondary formation processes such as ejection or collision that Richard mentions.

No there doesnt seem to be any decrease in number and I dont think it was edstrick's idea to suggest anything such either.
But there appear to be somewhat like a cutoff where the curve of even increasing numbers for lower mass objects flatten out. I say 'appear' since brown dwarfs are very hard to find. Even so, with out current knowledge it appears that brown dwarfs might not be as plentiful as some theoreticans first proposed.

O.K. let's make the very conservative assumption that the distribution is completely flat - in other words for each decreasing order of magnitude there are the same number of systems. All the nearby visible stars fall within just 2 orders of magnitude, 0.1 to 10 Msun approx. From there downward we have 5 orders of magnitude to get to terrestrial planet sizes, so on the above assumption low mass systems of terrestrial mass or greater would still outnumber visible stars by 5:2. My guess is that this is a gross underestimate and I predict that over the next couple of decades we will start finding numerous low mass systems closer than Alpha Centauri - if we look for them.

My *VAGUE* recollections of abstracts I've skimmed and PDF papers I've downloaded and glanced contains a phrase something like the "brown dwarf desert", where we're seeing very few BD's as planet-like companions of stars. I just don't know if the total abundance of BD's is less than the equivalent mass range of red dwarfs or what.

Xarchive.org has had many and various papers float by on relevent topics float by. Have at'm! (I currently just don't have enough time and "effort")

Thnks for that phrase edstrick:
http://www.aas.org/publications/baas/v36n4/dps2004/163.htm
I wish I could see that histogram, but I suspect the word desert is really a bit of an overstatement -it's only a relative thing.

Here is the actual paper online:

http://arxiv.org/abs/astro-ph/0412356

EXCELLENT, thanks.

So: The 'brown dwarf desert' refers to objects in the range one tenth to one hundredth Msun, but applies only to the population of fairly close stellar companions with periods under 5 years. More generally the IMF (initial mass function) derived from cluster studies shows only a modest decrease in the continuing rise in numbers of objects at lower masses, and this decrease in the rate of increase could be due to observational selection anyhow. dN/d(log M) comes nowhere near to changing sign, as would be required to make the population of smaller objects lower than the population of visible stars. These observations do not constrain the number density of independent low-mass systems in the solar neighbourhood at all. In fact there could be thousands of them within 10 parsecs.

Googling "Initial Mass functions" I found several articles of interest (among many others)

curve:
http://webast.ast.obs-mip.fr/hyperz/hyperz...ual1/node7.html
theory:
http://www.astro.caltech.edu/~george/ay20/Ay20-Lec17x.pdf.

From these it appears that the IMF is a power law. So that the number of zero mass stars would be infinite... in reality ther would be a cutoff somewhere, but it is rather a matter of conjecture where this cutoff is. What happens in the 0.1-0.5 solar mass range is already uncertain (some flattening seems to appear), below it is purely speculative. See the curves on the second link, p16, according to various hypothesis.


So theoricians still don't know today where is the baryonic mass, in red dwarves or into brown dwarves sytems, which then would be very numerous, down to some Jupiter size, or even smaller (interstellar KBOs??

So we cannot rule out the discovery of some brown dwarves systems even closer than Proxima Centauri. But in the same time we cfannot yet state that this must happen.

http://www.aas.org/publications/baas/v34n4/aas201/679.htm

Gragh of log(N) vs log(M) in this paper
http://www.astro.psu.edu/~kluhman/BDreview.pdf

I've seen an estimate of brown dwarf population, based on 2MASS observations, as being roughly 2x the population of regular stars.

OK.... There's an inflection in the log-log curve, not a actual decrease in numbers per fractional delta-mass. That's what I couldn't remember.

The Japanese, wkith their current infrared whole-sky-survey mission in orbit, may be able to dectect near solar-system BD's. They've got much higher resolution than IRAS did except at the very longest wavelengths (70 micrometer is on the long-wavelength side of even primordial BD emission blackbody curves, anyway)

I've hoped and hoped that we do find some BDs or rogue planets nearer than Alpha/Proxima Centauri. The biggest problem in the search is the stellar background we have to search against. Until we can search against the milky way background for high proper motion BD like objects with sensativity and resolution to capture everything more massive than Jupiter out to maybe 15 or so light years, we won't have an essentially complete local census.

Thanks alan for your links, especially the second which is very interesting.

It is impressive to see how science advanced since my last post. From your second link, we can conclude:

-the Innitial Mass Function peaks into the red dwarves region, and then decreases into the brown dwarves region. The reason for this is still not clear, but observational evidences seem safe enough.

-The total number of brown dwarves may be great, but not much larger than of stars. The total mass of brown is not greater of that of normal stars.

-Brown dwarves have proven accretion disks qimilar to stars
-They may have planets too (not proven, but likely)


I should add:
-Brown dwarves are not numerous enough to be the dark matter

-brown dwarves are not so numerous that we may find many closer than Proxima Centauri. Discovering one is however far from impossible.

-Free planets lighter than Jupiter seem unlikely (unless they were ejected from a larger solar system. This may be rare in our region, but very common in dense star clusters)

At last some studies (see the thread on Pioneer effect) give narrow limits to the presence of massive objects near the solar system.

Sorry to disagree Richard but these conclusions are far from secure.
The last paragraph of the SUMMARY AND DISCUSSION section of Grether and Linewaver, May 27 2006 posted by ljk4-1 yesterday clearly refers to "The fact that there is a close orbiting brown dwarf desert but no free floating brown dwarf desert . . ." So at the very least the jury is still out on this. Furthermore, we have ABSOLUTELY NO IDEA what happens to the numbers below 0.01 Msun. I cannot believe that the mass function conveniently terminates just at the point where the objects cease to be visible. So I'm sticking with my hypothesis of many small objects closer than Alpha Centauri for now. However I am not suggesting that they outweigh the stars in terms of total mass.

My case is : Don't rule them out or their continuing non-discovery could become a self-fulfilling prophecy over the next decade or two.

I (or rather the study I quote) never said that there are NONE, I (the study) just say that they are much less than we could predict with simply extrapolating the IMF. Progress was made into the determination of the IMF, and the cutoff and decreasing slope was found (thantks to studying recent clusters where Brown dwarves are much more luminous than in older ones). So the more numerous category is the red dwarves category, not the brown dwarves. And, about very low masses (3 Jup or less) we still don't know, we cannot exclude the IMF having a second peak for some reason. But it is not very likely.

To have several brown dwarves closer than Proxima Centauri would require that, statistically, the brown dwarves would be much more numerous than the red dwarves, which seems not the case. Of course we could be lucky and find one, and perhaps several. But the statistical average gives closest brown dwarf rather in the 10- 20 light years. Unless of course you disagree with the study.

I suppose what I'm saying is this:
1/ The different studies lead to very different conclusions about free floating brown dwarf numbers, although this is not the main focus of either study.
2/ Both agree that brown dwarfs are relatively more common among the free-floating population than they are as close orbiting companions to stars.
3/ Free-floating brown dwarfs are harder to find than brown dwarf companions, so the total observed sample is skewed in the direction of the (relatively scarce) brown dwarf companions.
4/ The smaller they are the harder they are to find so there is a very strong effect of observational selection at the low mass end which is difficult to quantify properly.
5/ There are at least some very loosely bound brown dwarf binaries (30-100 AU)
6/ All the observable brown dwarfs occupy only about one order of magnitude in mass.
7/ I am not saying brown dwarfs outnumber stars - only that low mass systems probably do, spanning at least 4 orders of magnitude below the presently detectable brown dwarfs.
8/ Low mass binary or multiple systems (30-100AU) would be dynamically the easiest places from which the sun could capture an object like Sedna.
9/ We need to be on the lookout, not only for more 'Sednas', but also for dark interstellar low-mass systems as soon as we have the means to search for these very difficult observational targets. If there are more objects in one category there are likely to be more in the other.
10/ We are still literally in the dark about all this but new developments are about to expand our observational powers enormously. That makes it an especially good time to keep an open mind while we look for what is there and what is not.

Middle-term, the really solid determination of the initial mass function for sub-stellar non-planets (BD's and rogue planets) will come from the James Webb Space Telescope. With high sensitivity and resolution in the near, middle and thermal infrared, it will be able to detect low-mass objects in reasonably nearby star forming regions down to very low masses, and get a decent observational (instead of theoretical) plot of luminosity-distribution vs. cluster age to test luminosity/spectral evolution models as a function of mass and age.

*eesh... long sentence warning!*

What we'll really need someday is an infrared version of the under-development Synoptic Survey telescope, to get an infrared sky survey down to something like 30'th magnitude. That would really nail down the "local" population of low mass objects.

The point is that, these objects are not only very weak, but also they dwelve in the infrared spectrum, see in radio.

Brown dwarves are in the 1000-2000°C, and as small as Jupiter (Jupiter is about the maximum diametre allowed for a cold body without nuclear reactions)
Large planets could be still colder: Jupiter, without sun warming, could be at something less than 50°K
Small planets, KBO-like, lone comets, fluffy balls, are in thermal equilibrium with the surrounding space. Thus they cannot be detected by their thermal radiation.


The IMF into an interplanetary cloud and around a parent body is likely not the same, as the presence of an accretion disk makes things much faster and at a much smaller scale. So we may expect that the IMF around a star is shifted toward smaller bodies with several orders of magnitude. But observational evidences are still far out of reach...

I thought Jupiter radiated more heat than it receives from the Sun?

I think that just means it re-radiates what it receives from the Sun plus a little bit more. Richard's estimate would be for the case where that little bit was all it had.

Yes thats correct, i've read that it is thought that the excess energy comes from gravitational contraction. Or in simple terms that Jupiter shrinks a very small bit each year.
(The powerhouse behind winds of Saturn on the other hand might, according to one theory, get the power from helium rain where the latent heat is released when the helium condenses.)