First pic of a planet orbiting a Sun-like star..? Options

[Stu]

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

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

[tasp]

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.

[Alan Stern]

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?

[Juramike]

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.

[JRehling]

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.)

[JRehling]

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.

[brellis]

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

[Greg Hullender]

But does it clear its zone? Who could know?

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

[brellis]

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

[Alan Stern]

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

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

[Del Palmer]

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

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.

[Del Palmer]

I haven't read the paper in question, but presume it rules out such a case from the observables.

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."

[Greg Hullender]

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.

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

[ngunn]

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.

[Juramike]

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.

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