Beta
×

Welcome to the Slashdot Beta site -- learn more here. Use the link in the footer or click here to return to the Classic version of Slashdot.

Thank you!

Before you choose to head back to the Classic look of the site, we'd appreciate it if you share your thoughts on the Beta; your feedback is what drives our ongoing development.

Beta is different and we value you taking the time to try it out. Please take a look at the changes we've made in Beta and  learn more about it. Thanks for reading, and for making the site better!

First Exoplanet Discovered Orbiting Two Stars

timothy posted more than 2 years ago | from the good-to-visit-not-to-live dept.

Space 88

astroengine writes "For the first time, astronomers have discovered an exoplanet orbiting binary stars. Kepler-16b, a Saturn-sized world approximately 200 light-years away, orbits Kepler-16, two stars locked in a mutual dance. Although other exoplanets are known to exist in binary systems, they have only been known to be orbiting one star of the binary pair; Kepler-16b orbits both. No doubt Kepler-16b will excite memories of Tatooine, Luke Skywalker's homeworld, but the double sunset is where the similarities end. Kepler-16b would be anything but a desert world; it is the approximate size of Saturn, it is extremely cold, and its average density is that of water."

cancel ×

88 comments

Sorry! There are no comments related to the filter you selected.

The only question I have is... (-1)

Anonymous Coward | more than 2 years ago | (#37412636)

...does Luke Skywalker live there?

Re:The only question I have is... (1)

maxwell demon (590494) | more than 2 years ago | (#37412750)

No, but they built planets there. [wikimedia.org]

Re:The only question I have is... (2)

JoshuaZ (1134087) | more than 2 years ago | (#37412862)

No. This planet is not like Tatooine. It is likely to be very cold because both of the two stars are in fact quite dim. Much closer to Hoth than Tatooine. See Phil Plait's description here where he discusses how you can estimate the planet's probable temperature- http://blogs.discovermagazine.com/badastronomy/2011/09/15/astronomers-discover-a-wretched-hive-of-scum-and-villainy/ [discovermagazine.com] .

Wouldn't that be (2)

AvitarX (172628) | more than 2 years ago | (#37412640)

The first planet orbiting two stars?

The exoplanet part being redundant.

Re:Wouldn't that be (0)

Anonymous Coward | more than 2 years ago | (#37412662)

well, if sol is one of the stars it is orbiting, it would be confusing, so no, its not redundant.

sol? (1)

DanCooper (2191988) | more than 2 years ago | (#37413068)

Is sol our sun?

Re:sol? (1)

VGPowerlord (621254) | more than 2 years ago | (#37413762)

Is sol our sun?

Yes, hence the name "Solar System" which is specifically Sol and its 8 planets and other bodies (er... sorry Pluto).

Re:sol? (1)

i kan reed (749298) | more than 2 years ago | (#37413788)

Is sol our sun?

Yes. Sol is the name for our sun. Luna is the term for our moon.

Sun and moon are generic terms, Sol, and Luna are proper nouns for the specific sun and specific moon. Any other really easy questions?

Re:sol? (1)

gmaslov (1983830) | more than 2 years ago | (#37414420)

While I agree that using "Sol" and "Luna" is really cool, and common in science fiction, I was under the impression that most serious astronomers are rather boring and simply refer to those bodies as "the Sun" and "the Moon".

Re:sol? (0)

Anonymous Coward | more than 2 years ago | (#37415354)

Especially since Sol and Luna mean "sun and "moon" respectively (in Latin).

Re:sol? (0)

Anonymous Coward | more than 2 years ago | (#37417976)

In English our sun and moon are called "Sun" and "Moon" and should capitalized when referring to them as such. As generic terms they are not capitalized.

Re:sol? (1)

Tim C (15259) | more than 2 years ago | (#37418674)

Indeed; when I did my physics degree we referred to them simply as the Sun and the Moon.

Re:Wouldn't that be (1)

AvitarX (172628) | more than 2 years ago | (#37416020)

I would imagine so, because it'd be all wtf, another star discovered close by.

Re:Wouldn't that be (1)

toddestan (632714) | more than 2 years ago | (#37416294)

Some people actually believe that. For a real WTF, try googling for 'Comet Elenin Dwarf Star'.

Re:Wouldn't that be (1)

Maritz (1829006) | more than 2 years ago | (#37429632)

Yeah I think 'Nibiru/Planet X/Nemesis' is also thought of by such fruit-loops as being a brown dwarf (the Sun's dead aborted twin if you like). Because the likes of the ancient Sumerians (or whoever) knew a hell of a lot more about astronomy than we do.

Deserts can be cold (2)

0racle (667029) | more than 2 years ago | (#37412654)

A desert doesn't have to be hot and covered in sand.

Re:Deserts can be cold (2)

MightyMartian (840721) | more than 2 years ago | (#37412664)

But it does have to be on land...

Re:Deserts can be cold (1)

blair1q (305137) | more than 2 years ago | (#37412698)

Who said this planet wasn't land? Maybe it's half rock and half air.

Re:Deserts can be cold (4, Informative)

MightyMartian (840721) | more than 2 years ago | (#37412840)

It's Saturn sized with density of water. It's a friggin' gas giant. It has no surface, unless you count the super-dense core that's probably hydrogen in a metallic state.

Re:Deserts can be cold (1)

AstroMatt (1594081) | more than 2 years ago | (#37414300)

I watched the press conference, and they suggested it likely had about half of it's mass as a solid rocky core, the other half as gas.

Re:Deserts can be cold (1)

IHateEverybody (75727) | more than 2 years ago | (#37417282)

It's Saturn sized with density of water. It's a friggin' gas giant. It has no surface, unless you count the super-dense core that's probably hydrogen in a metallic state.

Of course if it's Saturn sized, it might have large moons with a rocky surface, water, and possibly life. And while the sunsets on such a moon are likely spectacular, the eclipses would be even more amazing.

Re:Deserts can be cold (1)

Agripa (139780) | more than 2 years ago | (#37421652)

Of course if it's Saturn sized, it might have large moons with a rocky surface, water, and possibly life. And while the sunsets on such a moon are likely spectacular, the eclipses would be even more amazing.

The eclipses would only be amazing until the nocturnal predators come out and start hunting down the crew and passengers one at a time.

Re:Deserts can be cold (1)

Maritz (1829006) | more than 2 years ago | (#37429656)

There are certainly all kinds of possibilities, especially when you consider the stars wouldn't have to be the only heat source on such theoretical moons. Tidal flexing could generate plenty of heat, and then you might have a heat retentive atmosphere. Something like an atmosphere of the density of Titan's, but composed of a better greenhouse gas like carbon dioxide could certainly retain ample heat to be at water's triple point. Or of course it could shoot way over that and be a boiling oven like Venus. Obviously I'll never know, but I'd suspect that there are more life-bearing moons than planets, if only because there are likely to be so many more of the former out there.

Re:Deserts can be cold (1)

PopeScott (1343031) | more than 2 years ago | (#37414540)

Wouldn't rock be land?

Re:Deserts can be cold (1)

0racle (667029) | more than 2 years ago | (#37413192)

That's one definition, another is -

a lifeless and unpleasant place, esp. one consisting of or covered with a specified substance.

A gas giant would be a place covered with specified substance, the gas. Being really pedantic now, but, take that.

Re:Deserts can be cold (1)

MightyMartian (840721) | more than 2 years ago | (#37414822)

The problem with a gas giant being that the whole thing is just transitional phases all the way down. There's no real point that one can declare the divide between lithosphere and atmosphere. It's turtles all the way down...

Well, that's probably not true. The sub-giants like Neptune probably do have a surface of some sort, but I still don't buy that anything Saturn sized does.

Precisely. That's why here in Mexico... (1)

gwolf (26339) | more than 2 years ago | (#37415664)

Just outside Mexico City we have "Desierto de los Leones" (the lions' desert). It is a beautiful forest with a 400 year old convent in it.

Why?

Because it used to belong to the "de León" family, and it was far enough from the city that it became a perfect spiritual retirement place - A desert.

Wrong sci-fi planet? (3, Interesting)

muecksteiner (102093) | more than 2 years ago | (#37412686)

Tatooine? Would that thing not be much more like Solaris [wikipedia.org] (the planet from the novel, not the OS), especially since it's density is that of water?

Re:Wrong sci-fi planet? (0)

Anonymous Coward | more than 2 years ago | (#37413940)

KLENDATHU!

Re:Wrong sci-fi planet? (0)

Anonymous Coward | more than 2 years ago | (#37414012)

Well considering this one is a gas giant it's really not like either.

Re:Wrong sci-fi planet? (1)

muecksteiner (102093) | more than 2 years ago | (#37414348)

Well, yes, of course - the planet itself is apparently not the same thing (although little is said about the size of Solaris in the book, if I remember correctly).

However, Tatooine orbits a close binary, while the planet in the novel Solaris orbits a much more widely spaced system that (sort of, at least) resembles the system this planet belongs to.

"locked in a mutual dance"??? (0)

Anonymous Coward | more than 2 years ago | (#37412688)

What kind of science reporting is that? "locked in a mututal dance"? what?
"excite memories of Tatooine, Luke Skywalker's homeworld" huh?

this is science reporting?

Re:"locked in a mutual dance"??? (2)

GameboyRMH (1153867) | more than 2 years ago | (#37412846)

I think they're using the same AI that writes up spam comments to do their articles.

Re:"locked in a mutual dance"??? (1)

swanzilla (1458281) | more than 2 years ago | (#37412902)

FWIW, the summary is sort of spot on...FTA

As the stars slipped toward the horizon, they would change places in the sky, like partners in a square dance.

and

You would not need to be Luke Skywalker visiting his home planet of Tatooine in the movie "Star Wars" to watch the twin sunset.

...poor science reporting, but apt science reporting summarizing.

Obligatory (0)

cashman73 (855518) | more than 2 years ago | (#37412744)

This is not the planet you're looking for. Move along.

Density? (2)

Hatta (162192) | more than 2 years ago | (#37412768)

How do they calculate the density of these things? I get that they can detect the mass from the wobble of the star. How do they calculate the volume?

Re:Density? (1)

maxwell demon (590494) | more than 2 years ago | (#37412838)

If it passes in front of the star (resp. one of them), then it can be determined how much light it blocks, and thus how large it is. I don't know if this applies here, though.

Re:Density? (1)

Chris Burke (6130) | more than 2 years ago | (#37413548)

This was detected by Kepler, so yep it applies.

Re:Density? (3, Informative)

cnettel (836611) | more than 2 years ago | (#37413400)

Kepler is observing the dimming of the light of the star (basically a part of the star disc is shadowed by the planet), when the planet transits directly in the line of sight between Kepler/Earth and the star. Hence, you can get a cross-section area, and by assuming the planet to be reasonably spherical (a fair assumption), you get the volume.

Re:Density? (1)

Anonymous Coward | more than 2 years ago | (#37414754)

We get the radius from the size of the star, the depth of the transit, and the semi-major axis. As you noted, we can get the mass by measuring the radial velocity (RV, Doppler-effect, or red shift) but for small planets, or large planets that are too far away from the star, this method doesn't work. For smaller planets in multi-planetary systems, we can measure the mass with transit timing variations (TTVs).

We always get the radius with our transit photometry, but we can't always get the mass.

Hmmm .... (1)

gstoddart (321705) | more than 2 years ago | (#37412910)

So, can anybody who understand this explain a little more.

Is the orbit of the planet around both stars, making it like the orbit is eccentric around some center of mass common to the two stars?

If it's that, then I think I get this. If it's anything beyond that, then I'm afraid my meager understanding of Kepplers laws falls apart.

Most importantly, I love this part:

Computer models show that in early 2018, the planetary transits across the larger star will disappear from Kepler' view until around 2042. The passages across the smaller star's face, already slipping from view, will vanish in May 2014, and won't be back for 35 years.

the stuff we've just discovered will go away for the next 30+ years. That's really quite cool, since the window in which we could have identified this and worked it out is likely fairly short ever since we identified the very first exoplanets back in the 90s or so.

Re:Hmmm .... (1)

BergZ (1680594) | more than 2 years ago | (#37413136)

I wonder if, in 30 years, we'll be talking about the discovery of exomoons.

Re:Hmmm .... (1)

JulianDraak (1918564) | more than 2 years ago | (#37413310)

That's not a moon. It's a space station!

Re:Hmmm .... (1)

gstoddart (321705) | more than 2 years ago | (#37413390)

I wonder if, in 30 years, we'll be talking about the discovery of exomoons.

It wouldn't surprise me.

I seem to recall in the early-mid 90's, some of my astronomy geek friends ... at the time detecting an exo-planet was an exciting prospect, gravitational lensing was something to hope for, and possibly that black holes hadn't been confirmed by observation but were widely accepted.

Now exoplanets get discovered almost daily, we've confirmed through observation a bunch of black holes, and the universe continues to be even cooler and more complex than we'd even realized.

It really is interesting to watch.

Re:Hmmm .... (1)

LordNacho (1909280) | more than 2 years ago | (#37414524)

I'm hoping they find signs of life somewhere. Alternatively, and less cool, that they find some reason why life is exceedingly rare.

Re:Hmmm .... (1)

fisted (2295862) | more than 2 years ago | (#37415614)

And who said life was exceedingly rare? Bear in mind that distances in our universe are exceedingly large.

Re:Hmmm .... (1)

LordNacho (1909280) | more than 2 years ago | (#37417818)

I didn't. But I suppose it might be, and if that's the case, it would be good to know. Of course it would be more interesting to find a universe teeming with life. But whatever the truth is, it would be nice to know.

Re:Hmmm .... (1)

Mt._Honkey (514673) | more than 2 years ago | (#37413168)

Kepler's laws only apply for the 1 planet + 1 star case. They're really just some consequences of the more general Newton's laws, applied to that simple scenario. If the two stars are much closer together than their distance from the planet, then Kepler's laws will probably be a fine approximation for the short term, just using the center of mass of the stars and their average mass. Eventually (or soon, if the stars aren't so close to each other), deviations from the simple elliptical orbit from Kepler's laws will show up. You could get the planet changing its orbital radius, eccentricity, and precession of the major axis.

I'm betting it's the precession that will cause the predicted loss of signal for Kepler. Maybe the planet's orbital plane is not the same as the stars, and we're just lucky that the point where they all line up is pointed at Earth, but as the orbit precesses that direction will shift elsewhere.

Re:Hmmm .... (0)

Anonymous Coward | more than 2 years ago | (#37413870)

center of mass of the stars and the sum of both their mass

Re:Hmmm .... (1)

amRadioHed (463061) | more than 2 years ago | (#37413416)

Like with with multiple star systems, it pretty much has to be structured with the planet orbiting the binary stars much further then the stars orbit each other. Otherwise the system would not be stable.

As for catching this star system in the short window of discoverability, on the one hand we could be a little lucky. But on the other hand there are probably many other systems out there that will be just entering a window of discoverability as this system exits it. So while the odds of us catching this particular star system were low, it was probably pretty close to inevitable that we would discover one like it once we started looking.

Re:Hmmm .... (1)

Maritz (1829006) | more than 2 years ago | (#37429710)

About a minute into this [space.com] video, after all the fair-use Star Wars guff, there's an animation which will make it pretty clear to you. Put very simply, the smaller star goes around the bigger one (or rather they both revolve around their barycentre) and the planet describes a larger ellipse around both.

Exoplanets: the new Bitcoin (0)

Anonymous Coward | more than 2 years ago | (#37412912)

Yo, dawg, I heard you liked exoplanets so I put a small exoplanet orbiting your exoplanet.

Sincerely, Gawd

moD up (-1)

Anonymous Coward | more than 2 years ago | (#37412918)

Year cont8Act. partner. And if not anymore. It's very sick and its

Placet (1)

caviare (830421) | more than 2 years ago | (#37412924)

Fantastic, now all we need is a Placet (from Fredric Brown's Placet is a crazy place).

next Kepler data dump may have Earth-year planets (2)

peter303 (12292) | more than 2 years ago | (#37413176)

This planet had an orbit of 229 days. Kepler ideally desires three transits with two equal intervals to call it planet candidate. Kepler's observing duration is approaching the length where it could start detecting Earth-year planets now. The alternative experiments havent had enough sensitivity or duration to detect many Earth-year planets. Earth-year planets are likely to be in the habitable zone of G-type stars like the Sun.

I thought the next big Kepler data dump would be September 23 2011, after many of the preliminary papers had been published.

Mod Parent Up (1)

MyLongNickName (822545) | more than 2 years ago | (#37413798)

This is when things will get really exciting. Even though I have become jaded about space travel over the last three decades, I am still excited about the prospect of being able to observe the galaxy. Once we've cataloged a few hundred planets very similar to our own, we will finally get some good statastical support around how common life is in the universe. The first step is obviously finding them. The next is analyzing them.

If we can keep our society from falling apart and at least somewhat focused on science, we will see some pretty amazing discoveries this century.

Re:Mod Parent Up (1)

instagib (879544) | more than 2 years ago | (#37414378)

Also, after finding them, maybe SETI analysis could be focused on these areas for some time.

Re:next Kepler data dump may have Earth-year plane (1)

confused one (671304) | more than 2 years ago | (#37414836)

In this case they could cheat -- the two stars are orbitting each other fairly rapidly compared to the planets orbital period. They could see them alternately passing behind the planet. You would be able to see the phase shift in the light dip and from that you can deduce the orbital speed of the planet. Other clues from ground based observation would confirm the planet and allow its mass to be determined.

Re:next Kepler data dump may have Earth-year plane (1)

peter303 (12292) | more than 2 years ago | (#37415700)

Thats kind of why the Kepler Consortium suggests hundreds of "candidate" planets to be verfied by further study. Its estimated there may be alternative hypotheses explaining the light curves of 5% - 20% of the candidates.

Color me unimpressed (1)

mark-t (151149) | more than 2 years ago | (#37413592)

I *might* be able to get excited about these sorts of discoveries if once.... just once... they found a rocky planet in the habitable zone of a star having between roughly .75g and 2g... and I'd especially get excited if they could determine that it has a breathable atmosphere and presence of water.

We already know that we can detect gas giants around other stars. We've been doing it for years now and considering that binary stars are not that uncommon in our galaxy, it should come as no surprise that there might be planets around some of them.

Why is this news?

Re:Color me unimpressed (1)

MyLongNickName (822545) | more than 2 years ago | (#37413850)

The larger gas giants are much easier to detect. And frankly with a UID as low as yours, I am surprised at your jaded view of exoplanet discovery. These are amazing times we live in and as Keppler's observation time goes up, it will detect planets further from its host star. By this time next year, we should start to get confirmations of planets with the same orbital period as our Earth. We may not find hundreds of them with the g's you are looking for in 2012, but statistically we will almost certainly find some.

Re:Color me unimpressed (1)

oPless (63249) | more than 2 years ago | (#37414424)

That's not a low UID, whippersnappers - get off my lawn! :^)

Re:Color me unimpressed (1)

Tim C (15259) | more than 2 years ago | (#37418702)

No, you get off my lawn! (But yeah, a 6-digit UID is low? Pah!)

Re:Color me unimpressed (1)

i (8254) | more than 2 years ago | (#37431684)

Hm.

Re:Color me unimpressed (1)

mark-t (151149) | more than 2 years ago | (#37414582)

I'm jaded because it's always the same thing. I can't count how many times it's been headline news that we've discovered yet another jupiter or larger sized gas giant moving around another star. The first few are somewhat impressive, because they establish that exoplanets actually do exist, and that we have the technology to detect some of them. After that, however, it's just the same old story, as far as I'm concerned.

As for needing an orbital period that is exactly the as Earth, that isn't really required... because with a hot star, the planet can have a longer period and with a cooler star the planet could have a shorter period, all while still being within the habitable zone for a star.

I suppose it's possible that there might be a moon around one of these gas giants in a habitable zone that has the aforementioned criteria (rocky, 0.75g to 2g, and ideally with a breathable atmosphere and presence of water), but I suspect we're quite a long way from being able to deduce details about the moons of exoplanets.

Re:Color me unimpressed (1)

Jeng (926980) | more than 2 years ago | (#37413880)

I am not the most well versed in these topics, but I think it is surprising that they have detected a planet that orbits two stars.

With a regular star system planets orbit a single point, extremely easy to figure out and therefor rather obvious, with a binary system how do the planets maintain their orbits with the gravity fluctuating as the stars orbit each other?

Re:Color me unimpressed (0)

Anonymous Coward | more than 2 years ago | (#37414360)

There's two ways. Either the stars are orbiting each other much further than the planet orbits one of the stars (which we've seen before) or the planet orbits the combined center-of-mass of both stars much further than the stars orbit each other (as in this newly-discovered system).

If the planet is approximately the same distance as the stars to each other, its orbit is generally unstable, and it would impact a star or be flung free of the system in a cosmologically very short timescale. Finding one of these (either a special-case stable orbit, or a freshly formed/captured one that hasn't been around long enough for its orbit to deteriorate) would be the sort of marvel you're thinking of, finding one like we did was just a matter of time

As to mark-t's point about wanting some Minshara-class worlds, it's just silly to complain at this point. Kepler is mostly detecting close-in, and therefore hot, planets, because it hasn't been observing long enough -- the longer the orbit, the longer the observation period needed. Even this one, while cold because its suns are smaller, has an orbital period less than Earth's. Give it a while, we'll find them eventually.

Re:Color me unimpressed (1)

GumphMaster (772693) | more than 2 years ago | (#37415728)

If the distance between stars is very much smaller than the distance of the planet from the stars then you can grossly approximate the system as two bodies. The mass of the two stars is placed at their centre of mass and the virtual star and planet then orbit their centre of mass. In the real world there will be perturbations from the dual stars and the other bodies in orbit that we have yet to see.

The "obvious" nature of "regular" solar systems is far from simple. The barycentre [wikipedia.org] of a multi-planet solar system is a movable point especially in the presence of large planets.

We have discovered them (1)

Soralin (2437154) | more than 2 years ago | (#37414454)

And not just one of them. Kepler has previously found 5 Earth-sized planets, in the habitable zones around their stars. And quite a few that are either Earth sized, or in the habitable zone, but not both. Including things like super-Earth sized ones in the habitable zone. :) http://www.nasa.gov/mission_pages/kepler/news/kepler_data_release.html [nasa.gov]

The findings increase the number of planet candidates identified by Kepler to-date to 1,235. Of these, 68 are approximately Earth-size; 288 are super-Earth-size; 662 are Neptune-size; 165 are the size of Jupiter and 19 are larger than Jupiter. Of the 54 new planet candidates found in the habitable zone, five are near Earth-sized. The remaining 49 habitable zone candidates range from super-Earth size -- up to twice the size of Earth -- to larger than Jupiter. The findings are based on the results of observations conducted May 12 to Sept. 17, 2009 of more than 156,000 stars in Kepler’s field of view, which covers approximately 1/400 of the sky.

Re:Color me unimpressed (1)

Maritz (1829006) | more than 2 years ago | (#37429740)

Why is this news?

As far as I'm aware this is the first detection of a planet around a binary star. That alone makes it newsworthy even if not of interest to you. Not the most earth-shattering discovery ever but you have to at least note the first of a new batch.

Two suns in the sunset... (1)

Anonymous Coward | more than 2 years ago | (#37413654)

Looks like the human race is run.

miDnus 2, TroLl) (-1)

Anonymous Coward | more than 2 years ago | (#37413664)

What this actually means (0)

Anonymous Coward | more than 2 years ago | (#37413794)

This just means that they found a planet further from a binary system's barycenter [wikipedia.org] than the smaller star. The planet doesn't orbit both stars really, it orbits their common center of mass (assuming these stars are similar in mass).

The interesting (but not remarkable) thing here is finding a very tight binary system (with similar sized stars) that is still stable enough to have detectable exoplanets (through wobble), that aren't large enough to make the whole system unstable (it has to affect the parent stars, but not too much).

Re:What this actually means (1)

dotancohen (1015143) | more than 2 years ago | (#37415550)

That is incorrect. The idea that all the objects orbit the barycenter is valid for objects within a few orders of magnitude, which pull on each other. The planet's mass really is too little to have any nonnegligible effect on the stars (which do pull on each other). Thus the stars' barycenter is not wobbling to meet up with the planet.

Three-body problems are not intuitive, especially when you have objects of vastly different mass.

Re:What this actually means (0)

Anonymous Coward | more than 2 years ago | (#37416466)

The idea that all the objects orbit the barycenter is valid for objects within a few orders of magnitude, which pull on each other.

But to say this planet orbits one or both stars is less correct than saying they all orbit the barycenter of the system, which is effectively the barycenter of the two stars.

Nix, Hydra, and S/2011 P 1 can be said to orbit Pluto, but looking at the system you see this is kind of a silly thing to say, they more closely appear to orbit the Pluto/Charon barycenter (which they do).

Our solar system's barycenter can even appear outside the surface of the sun under certain conditions.

Re:What this actually means (1)

dotancohen (1015143) | more than 2 years ago | (#37417154)

I also wanted to bring up the Pluto - Charon system. You are correct regarding the orbits of Nix, Hydra, and apparently the newly-discovered Plutean moon. Their velocity vectors seem to be consistent in magnitude, and perpendicular to the barycenter.

However, the case of a planet orbiting two stars, assuming that the stars are within a few orders of magnitude of each other but that the planet's mass is quiet a few magnitudes less then the star's mass (Earth: 10^24, Sun/Sol: 10^30), will see it's velocity vector change magnitude often and it will rarely be perpendicular to the barycenter.

Re:What this actually means (1)

dotancohen (1015143) | more than 2 years ago | (#37417162)

I should also mention the possibility that the planet is not orbiting in the same plane as the stars! Though that is probably not a possibility here, considering how we detect dual-star systems and how Kepler detects planets.

Coming Closer to finding the Ultimate Truth (0)

Prince Vegeta SSJ4 (718736) | more than 2 years ago | (#37414738)

Whether Greedo actually shot first.

Re:Coming Closer to finding the Ultimate Truth (0)

stackOVFL (1791898) | more than 2 years ago | (#37415026)

Everyone knows that Han shot first.

saw this episode (1)

catmistake (814204) | more than 2 years ago | (#37415058)

It was my understanding that a planet made entirely of water [wikipedia.org] would not have enough mass to hold together, and would eventually disapate. Thus... wouldn't a planet made of something equal to the density of water also have trouble forming and maintaining coherence?

Re:saw this episode (3, Interesting)

sunspot42 (455706) | more than 2 years ago | (#37415416)

Not sure if that's true or not, but if the planet had a dense, large, rocky core, it could hold on to a thick, massive atmosphere that's far less dense than liquid water, at least for much of its overall volume.

Saturn is a good example in our own solar system - it has an overall density less than the density of water. If you had a big enough bathtub, you could float Saturn in it.

It would leave a ring, though...

Re:saw this episode (1)

Nyder (754090) | more than 2 years ago | (#37419744)

Not sure if that's true or not, but if the planet had a dense, large, rocky core, it could hold on to a thick, massive atmosphere that's far less dense than liquid water, at least for much of its overall volume.

Saturn is a good example in our own solar system - it has an overall density less than the density of water. If you had a big enough bathtub, you could float Saturn in it.

It would leave a ring, though...

The ring would still be better then what Uranus would leave...

Re:saw this episode (1)

Tastecicles (1153671) | more than 2 years ago | (#37417602)

um... nope. It's a little complicated, but it has to do with gravitational acceleration overcoming centripetal force to hold a body together. Same reason why the air on this planet, which is 1/1200 the density of liquid water, and 1/6000 the average density of the planet as a whole, doesn't just float off into space.

Re:saw this episode (1)

Maritz (1829006) | more than 2 years ago | (#37429748)

The average density might be that of water, i.e. when you add the gaseous layers to the solid rocky/metallic hydrogen core. The centre would still be very dense though.

Strange... (1)

Tastecicles (1153671) | more than 2 years ago | (#37417584)

...According to the BBC this morning Kepler-16 is only 20 LY away... of course, the BBC have it completely wrong; from the NASA initial press release:

"The distance from Kepler-16 to Earth has not been measured, but is probably about 200 light years, judging from the apparent brightness of star A and theoretical models of stellar structure that give a crude estimate of its intrinsic luminosity."

http://kepler.nasa.gov/Mission/discoveries/kepler16b/ [nasa.gov]

When does this become non-news? (0)

Anonymous Coward | more than 2 years ago | (#37417934)

Lately we have been seeing many submissions about new planets, new star systems, exoplanets etc., leading me to believe that there are new technologies being employed to look out for them. Considering that technology will only improve, when does this become common enough to be not news? When one planet is found every day? Its a perverse curiosity, but that is all I could think about when I saw this article...

AC

How do they calculate the density? (1)

ResidentSourcerer (1011469) | more than 2 years ago | (#37419950)

To calculate density they need both mass and volume. Mass is in principle calculated by the wobble of the source star, and assumes that you have an accurate measure of it's mass. However circling a binary, the wobble is that of the pair. The uncertainty of this is substantial.

To calculate the volume, you need the diameter. This would require having a reasonable curve of light drop as the disk of the planet transits one of the stars. Is Kepler sensitive enough to pick out the effect of the shadow of a single planet on the solar disk? E.g. if the planet is 100,000 km in diameter, and moves at 10 km/second then time from first contact to occlusion would be 10000 seconds. If the star itself is 1,000,000 km in diameter then the planet's disk represents 1% of the star's area, and that will be the decrease in illumination in transit. However to guage the time of first contact to occulsion, you are working with small chords overlapping. Which means that you need to record variations in output of something like 3 orders of magnitude smaller.

The orbital speed is also subject to error. A far out planet will not be observed for even a single orbit. So you have to deduce speed from the speed change of the orbited star. Is dopler that good.

A 10% error in diameter means a 30% error in volume. And I'm skeptical of even getting within 10%.

Check for New Comments
Slashdot Login

Need an Account?

Forgot your password?

Submission Text Formatting Tips

We support a small subset of HTML, namely these tags:

  • b
  • i
  • p
  • br
  • a
  • ol
  • ul
  • li
  • dl
  • dt
  • dd
  • em
  • strong
  • tt
  • blockquote
  • div
  • quote
  • ecode

"ecode" can be used for code snippets, for example:

<ecode>    while(1) { do_something(); } </ecode>