http://www.spaceref.com/news/viewpr.html?pid=26414

See also: http://blogs.discovermagazine.com/badastro...-a-sunlike-star

Interesting the planet is 330 AU from the star.

I also note the picture would seem to suggest detection would have been possible down to ~100 AU, and even less for a star system closer than the 500 light years away to us than that one is.


Wonderful news.

But does it clear its zone? Who could know?

And if there was a habitable world orbiting at 1 AU distance, and they sent their New Horizons spacecraft out to explore their distant big planet, (assuming the requisite gas giants were close in as well), it would take 100 years or more to get there.

So for those aliens, even exploring their own system runs into the AI and lifetime problems discussed for the Alpha Centauri proposed mission.

Wow. We are soooo lucky.

Interestingly, given the parameters, and if the semimajor axis is approximately the planet's current distance, then this planet has only completed 1000 orbits around its star. That's pretty fascinating, not only from the perspective of orbit-clearing, but even with regards to accretion. That's not very much time for stuff to have been blotted up by this giant planet.

To put it another way, Io has orbited Jupiter more times since the end of the Galileo mission than this planet has *ever* orbited its star. (Again, given the nominal parameters -- the error bars are nonzero.)

Also, those aliens have only have 5 million years to evolve, which is about 1/800th the time it took multicellular life to get into the fossil record here. And with that giant only having completed a thousand orbits, there has to be a lot of collision still going on in at 1 AU.

Are there (or were there) other stars in the neighborhood? Perhaps this planet is a relic expelled from another solar system and captured?

Alan, this is a question I've wanted to ask for a while, so maybe you'll indulge me. If I recall correctly, a big difference between stars and planets (other than size) is that stars form directly from a gas/dust cloud whereas planets form from the accretion disk around a star. Is it possible that this body is just a planet-sized star? I saw an article in Science a year or two back that posited a lower bound on the mass of stars, but (if I remember right) that was based only on luminosity.

Or am I wrong to think there's a meaningful difference between something that formed from a nebula vs. something that formed in an accretion disk?

--Greg

This would also be the first time a potential planet was captured first of all in an image. I'm still hoping Hubble gets fixed in time to image Epsi eri b on its next transit

Greg-- A planet-sized star cannot exist, in that such a body does not have the mass to generate high enough central temperatures to do fusion, and thus would not be a star. Of course, it could be a stellar remnant, like a white dwarf, which is planet-sized, but then it's thermal and spectral properties would give it away as such. I haven't read the paper in question, but presume it rules out such a case from the observables.

-Alan

There are 82 stars nearby, but they estimate that the chances of an interloper are 1-in-30,000. Nevertheless, we really need follow-up proper motion studies to verify that this planet is truly bound to the star.

Yes, the authors state: "...the spectrum of the companion confirms that it is very cool, showing important water vapor absorption on either sides of the H and K bands and strong CO band heads beyond 2.29 µm."

Instead of "star" maybe I should have said "brown dwarf," meaning a body that formed in the same way stars form, but which lacked the mass to ever fuse (except maybe deuterium). I see that no one appears to be suggesting that this is just a binary star system where one of the companions is a brown dwarf that's still young enough to glow. That surprises me, since I've wondered for a while whether you could get planet-sized brown dwarves and, if so, would they differ a lot from large planets that formed from accretion disks. But no one ever seems to talk about this, and I've wondered if there's some reason to think brown dwarves of ~10 jovian masses just can't form that way.

Given the present observation, though, I do think the separation is hard to swallow if you think the smaller body formed from an accretion disk, but I think its unexceptional for a stellar binary. (Albeit one of the "stars" is a runt that will never fuse hydrogen.)

Anyway, the fact that no one seems to offer that as an explanation makes me think something is wrong in one of my assumptions; I'm just wondering which one it is.

Thanks!

--Greg

Greg, your thinking parallels mine on this topic more or less exactly. I see no compelling reason why stars cannot have sub-stellar companions over the full range of distances and dynamical arrangements that we find among stellar binaries and multiple systems. Theories of star formation may suggest otherwise, and hence we get a sharp distinction made between objects that had their own accretion discs and objects that formed within the accretion disc of a larger primary. I'm pretty sure that nature will confound this neat categorisation as we find ways of observing smaller and smaller objects over stellar distances.

I think you are bang on. It makes sense that different size gas clouds orbiting each other should be able to condense in a full spectrum of sizes. Some big enough to form a companion star, some that only condense to make a runt. I could imagine a case where even a mini-solar system could end up orbiting around the brown dwarf - not just big moons but even planets "large objects halfway between the accepted definition of a moon and a planet".

Those might have differentiated out of the proto-runt nebula, so the terrestrials are in close, and maybe a mini-gas giant or mini-ice giants are further out in the big brown dwarf system. What is the minimum size would we have been able to detect at this distance?

I think the physics of solar system formation (which I am ignorant of) might tell you if this type of system should be common or not.

If this finding is confirmed, it's fantastic and stretches our concepts of solar systems. If not, it provides a placeholder for something that we might eventually find, or need to come up with an explanation for their apparent absence.

-Mike

Grin. Yep, that's where a lot of the fun in science comes from, isn't it? The unexpected result that gives someone a chance to create a better explanation.

Naively, I'd expect a brown dwarf to be mostly hydrogen and helium, with no icy or rocky core to speak of, but a planet -- even a giant planet -- formed in an accretion disk would be more like Jupiter or Saturn. My reasoning is that the heat of the star ought to push some of the hydrogen and helium out of the disk, making planets rather different from brown dwarves, even if they had the same mass.

Obviously we'd have to observe a few for real to know much for sure, but since we have the privilege of talking to some real experts in here, I'm hoping to learn whether there's some a priori reason either not to expect brown dwarves at all, or else not to expect them to differ much from gas giants.

--Greg

2M1207 was the first exo-planet "imaged" but it orbits a brown dwarf...

This time a planet that orbits at 330 AU from its star, this distance compared to our Sun, means this planet would be in the Kuiper Belt

It's a giant Sedna.

Spectrally, brown dwarfs appear to have similar composition to Jupiter (and even similar weather activity!) Bear in mind that the early solar nebula disk was 99% H and He compared to the heavy elements -- if the Sun had driven-off the H and He, you would not be able to build a Jupiter, which also shares the same H/He ratio as the Sun.

If this is a binary system, it would be remarkable, as star-formation simulations are unable to produce systems with such extreme mass ratios.

If a 'planet' formed from a nebula of its own, but orbits a star and is too small to do fusion, isn't it a planet? (Assuming it's cleared its zone, of course )

I thought "brown dwarf" was a category based on size, not origin. Has this been changed? Is there an official definition? (Not that official definitions mean anything anymore...)

Some discussion here:

http://www.astrobio.net/news/article546.html

I'm trying to find an up-to-date report on the mass distribution of discovered extrasolar giant planets / brown dwarfs. It would be fascinating to see any nonmonotonicities.

JR, That's a great pair of articles! Here are some relevant snippets. First, on the question of what to call them:

On the question of could such things form at all:

And on the question of composition:

So I think that actually covers all my questions.

JR: Thanks again!

--Greg

How long until we're stuck with "dwarf brown dwarf"..?

I take it you didn't like "runt." :-)

Other options could be "sub brown dwarf," which the article used, or maybe "brown sub-dwarf" which I like better, or even "black dwarf." More exotic might be "rogue planet," which various SF authors have used, or "planistar" which I just made up on the spot. :-)

--Greg

Everybody knows it's hobbits that are smaller than dwarfs.

I know - let's call it "Pluto"!

If this recent paper is any indication, there isn't any significant gap in the mass distribution of orbiting bodies separating large planets from small brown dwarfs.

http://www.global-edge.titech.ac.jp/abst/abst_Sato.pdf

See: Figure 3

It looks like there is an inverse exponential relationship with mass, to within the density of the data to determine. At least it makes sense that the sharp dividing line between fusion and non-fusion wouldn't have anything to do with whether or not the body forms in the first place.

Another thought on the classification: It's pretty hard to operationalize a definition based on the origin of the body rather than the nature of the body. It would create more cases where we'd be guessing about the origin. I'd say if we want to classify them, we ought to base that on directly observable characteristics, and leave the dynamics regarding the origin as a research matter.

Spot on JR. I was thinking that astronomers must have a collective masochistic streak to propose creating named categories based on unobservable criteria and unknowable histories. Why not just call them all substellar objects - that is observable - or, as in this case (probably), substellar companions? It could save a lot of trouble down the road.

Strictly speaking, distance between bodies is also an objective, easily-observable property. However, as the number of observed objects increases, I suspect the most useful categorization(s) will become apparent. It's fun to speculate, but I wouldn't sweat it right now.

--Greg

I would remind people of rule 1.9
http://www.unmannedspaceflight.com/index.php?act=boardrules

Digging around a little, it appears that brown dwarfs ought to radiate with a peak anywhere from 1.5 microns to 4 microns. I couldn't find an existing space telescope that was particularly sensitive in this region, but I note that the Webb Telescope has a near-IR camera and a near IR spectrograph that seem ideal for these regions. I had thought that the Webb was mainly intended to study very distant objects, but it turns out that studying planetary formation is also part of its mission.

http://www.jwst.nasa.gov/birth.html

As a result, I'd expect us to get a lot more information about brown dwarfs once the Webb is in operation.

Oh it also appears that there's an easy test to distinguish a brown dwarf from a star: stars consume all their lithium in about 100 Myears but brown dwarves don't.

What I couldn't find was enough information to calculate how small a brown dwarf (or sub brown dwarf) it might find in local nebulae. That'd be nice to know, though.

--Greg

Are there diagnostic lithium bands in the near-IR spectrum?

-Mike

Fortunately there is a good definition of a substellar object - no fusion at all.

Rule 1.9 - no problem with those of us talking here at the moment. Doug - if the discussion's attracting stuff you've had to delete please let us know.

Extrasolar discussion is a guest here - it hasn't anything to do with robotic exploration - so I guess we're here only as long as no aministrative hassle ensues. That's fair enough.

Yes, but isn't fusion a statistical process? Even at lower temperatures and pressures some fusion can occur, how do you determine the cutoff point then?

It's pretty clear whether the evidence for fusion is observable or not on the global scale. I don't deny that objects might have to be reclassified occasionally. But it's an easier boundary to patrol than most of those proposed.

If I had to invent a system from scratch I'd base it entirely upon powers of ten in the mass: 10 to the 27 objects and 10 to the 23 objects and so on.

If we believe Wikipedia, there's already a naming system in place.

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

And brown dwarves get classed as type L and T stars. (Apparently some type L stars really do fuse hydrogen, but not all.)

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

There doesn't seem to be consensus on sub-brown dwarves though.

http://en.wikipedia.org/wiki/Sub-brown_dwarf

And that's consistent with what we saw in better places than Wikipedia.

Where this connects with UMSF, in my opinion, is if there are some current or proposed missions that might detect these -- either in other systems or (potentially) even in our own. The notion that our sun might have a massive, distant, unseen companion has been around long enough I'd expect there to be some reasonable bounds on how big/close such a thing could be, but I haven't found it yet. I know Pan-STARRS will look for it, as may the WISE mission.

http://wise.ssl.berkeley.edu/news.html

Things like Sedna's "impossible" orbit and the Kuiper cliff all seem to point to SOMETHING interesting out there.

--Greg

I think it was my fault, trying to make a joke about what to name it.

That's an interesting question though -- I've seen posts on UMSF about telescopic observations of Jupiter, Titan, Mercury, etc., and telescopic observation is often if not always an adjunct and precursor of exploratory spaceflight -- and the imaging results from telescopes often make an interesting comparison with spacecraft-based observations. While I'm sure "how do you classify this object in space" is of only peripheral interest, it would be a shame to create rules so narrow that telescopic observations could not be discussed at all. It seems to me that telescopic exploration is a kind of space exploration, even if it doesn't involve launching something into space. Does a telescope have to be in space before its imagery is topical?

I'll posit that the in-depth investigations and in situ observations of things in our own solar system can be extended to other bodies beyond our solar system.

Take all the descriptions of things we've explored: terrestrial planets, gas giants, rocky moons, icy moons, ice giants, and put those out there as possible extrasolar world types. The Jupiter missions have all shown us how fascinatingly different the moons orbiting a gas giant can be. From that, we can now begin to imagine how moons orbiting that planet, way out there, might each also have their own persona, and just how different they might be to what we've seen. The geology of Mars will have relevance to extrasolar worlds, the spray of Enceladus will extend to other types of objects, and the exploration of Titan hints that there are other ways to develop and incredibly complex world that doesnt' use the exact same material-phases as Earth. (And I suspect Pluto is really going to wow us with it's complexity)

I'll bet we find an extrasolar analog of every planet we've explored in the solar system, and there will be hybrids of planets/processes/materials we know, and new combinations of things that we haven't seen yet.

We're developing a "solar system view", so hopefully we can get an "intersystem view".

It's all part of the big picture....

That's Astronomy. Not Unmannedspaceflight.

Imagery that ties into unmannedspaceflight from ground based or orbital assets is fair game. Just general observations I don't think should be.

Images of extra-solar planets, nebulae, novae etc etc - can't really be considered on topic for UMSF. Just because UMSF is a good venue for the discussion of , err, UMSF, that doesn't mean it should be a good venue for the discussion of anything space science related.

If you do find that information please let me know. I seem to remember something posted here way back during an earlier brown dwarf/accretion disc discussion, but I'm never going to be able to find it. Anyhow it could be unreliable or out of date by now.

[...]

IIRC the mass gap is only for relatively close companions of larger stars. I think that for distant companions and free floaters there is no observed gap.

[...]

We do have a very fine line, here -- it seems absurd to say that an imaging campaign by Hubble is proper, while an identical imaging campaign by Keck would be out of bounds.

He also explores the Cosmos who just sits and stares into the sky...

-the other Doug

Well, Keck is manned

Hubble or Keck looking at some nebulae or frankly, exoplanets - both off topic.

Hubble or Keck looking at a target also being observed by spacecraft - on topic.

That Hubble is a spacecraft is essentially irrelevant. It's just a telescope.

[...]

Hubble is manned too. The operators are just sitting a little further back from the 'scope.