Yo Astronomer: I'm asking-- Hot Jupiters

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aretis

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<p><font face="Arial" size="2">&nbsp; Every article you see about so called "Hot Jupiters," always assumes that they have to be gas giants. It seems to me that the only things we really know (in most cases)&nbsp;about these worlds are their masses and their close proximity to their parent star, correct?</font></p><p><span><font face="Arial" size="2">&nbsp;&nbsp;&nbsp; By&nbsp;our limited observations techniques so far, is there anything from excluding the possibility that a lot of these large planets are actually, albeit HUGE, rocky &nbsp;terrestrial ones?</font></span></p><p><span><font face="Arial" size="2">Thanks,&nbsp;&nbsp; Aretis</font></span></p> <div class="Discussion_UserSignature"> <p><font size="4" color="#0000ff"><strong>Aretis</strong></font></p> </div>
 
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aretis

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<p><font face="Arial" size="2">&nbsp; Every article you see about so called "Hot Jupiters," always assumes that they have to be gas giants. It seems to me that the only things we really know (in most cases)&nbsp;about these worlds are their masses and their close proximity to their parent star, correct?</font></p><p><span><font face="Arial" size="2">&nbsp;&nbsp;&nbsp; By&nbsp;our limited observations techniques so far, is there anything from excluding the possibility that a lot of these large planets are actually, albeit HUGE, rocky &nbsp;terrestrial ones?</font></span></p><p><span><font face="Arial" size="2">Thanks,&nbsp;&nbsp; Aretis</font></span></p> <div class="Discussion_UserSignature"> <p><font size="4" color="#0000ff"><strong>Aretis</strong></font></p> </div>
 
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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>&nbsp; Every article you see about so called "Hot Jupiters," always assumes that they have to be gas giants. It seems to me that the only things we really know (in most cases)&nbsp;about these worlds are their masses and their close proximity to their parent star, correct?&nbsp;&nbsp;&nbsp; By&nbsp;our limited observations techniques so far, is there anything from excluding the possibility that a lot of these large planets are actually, albeit HUGE, rocky &nbsp;terrestrial ones?Thanks,&nbsp;&nbsp; Aretis <br /> Posted by aretis</DIV></p><p>I'm only making an assumption here, but I would imagine there would be a limit simply based on the amount of resources available within a stellar system.&nbsp; Quite simply, stellar systems wouldn't be metal (anything heavier than helium) rich enough to form such rocky behemoths.&nbsp; Even if you took all the rocky planets, moons, asteroids and comets within our own system and combined them to make one planet, I doubt it would be much larger 4-5 earth masses.</p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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neilsox

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I'm only making an assumption here, but I would imagine there would be a limit simply based on the amount of resources available within a stellar system.&nbsp; Quite simply, stellar systems wouldn't be metal (anything heavier than helium) rich enough to form such rocky behemoths.&nbsp; Even if you took all the rocky planets, moons, asteroids and comets within our own system and combined them to make one planet, I doubt it would be much larger 4-5 earth masses. <br />Posted by derekmcd</DIV><br />I&nbsp;think 4 or 5&nbsp; earth mass&nbsp;is about correct, but, each of our gas giant planets may have several earth mass of metal, and our sun could have&nbsp;thousands of earth mass of metal. With a bit less metal in the sun and gas giant planets, there would likely be enough metal for&nbsp;one 50 earth mass terrestral planet. That is not to say that there are any&nbsp;50 earth mass rocky&nbsp;planets, but it is likely possible.</p><p>The cloud that made our solar system, likely got most of it's metal more than 5 billion years ago. Newer clouds could have twice as much metal thus producing double mass terrestrial planets, on the average.</p><p>Hybred planets may be possible, with 50 earth mass rocky cores,&nbsp;and atmospheres 1000 miles thick. The surface air pressure would be so great it is unlikely a probe could ever detect the surface, even if the internal temperature was much lower than our 4 gas giant planets.&nbsp;&nbsp;&nbsp;Neil</p>
 
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aphh

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<p>It is relatively simple to calculate the density of the exoplanet by measuring the radial velocity of the star itself. The more massive the exoplanet, the more the star itself would move.</p><p>The star-planet system orbits around their combined center of mass. Hence more mass for the exoplanet, more radial velocity and movement for the star.</p><p>Radial velocity of the star is the root of the sum of squares of both line of sight velocity and horizontal/vertical velocity.&nbsp;</p>
 
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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>It is relatively simple to calculate the density of the exoplanet by measuring the radial velocity of the star itself. The more massive the exoplanet, the more the star itself would move.The star-planet system orbits around their combined center of mass. Hence more mass for the exoplanet, more radial velocity and movement for the star.Radial velocity of the star is the root of the sum of squares of both line of sight velocity and horizontal/vertical velocity.&nbsp; <br /> Posted by aphh</DIV></p><p>I don't think they can figure the density from the radial velocity by itself.&nbsp; They would need need to know the actual size of the planet as well.&nbsp; The radial velocity only give the mass of the planet, not its radius.&nbsp; I think only in cases where the planet transits in front of the host star can they reasonably determine the size and thus the density.&nbsp;</p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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aretis

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<p><font size="3">This is Aretis getting back to all of you,</font></p><p><font size="3">First off, thanks for all of your feedback:</font></p><p><font size="3">&nbsp;&nbsp;&nbsp;&nbsp; Well it's always been said that 1st generation stars would have little or no metals (anything heavier than helium or maybe carbon.)&nbsp; I guess it's thought that our Solar System is probably at least 2nd generation for that reason.&nbsp;Therefore,3rd or&nbsp;4th generation star systems would more than likely have much more metals than our Solar System would,&nbsp;you'd think. It would seem to follow that these systems would have a heck of a lot more metals, but would it be enough for Mega-massive Earth's? I've never really seen any articles dealing with just how much rocky material might likely be available in these systems, have you guys?. If the theory about massive Jupiter's forming in the outer solar systems of these stars are correct, than Massive Earth's could form out near the boundary of inner solar system metals, migrate inward too, and sweep up all the avaiable metal on the way in. It just seems like an unusual assumption by the Astronomy Community to assume that they all HAVE to be hot gas giants. I mean, there's obviously a heck of a lot more hydrogen and helium in even a metal rich star forming nebula, so maybe that's&nbsp;the reason&nbsp;they are called "Hot Jupiter's" right there.&nbsp;But that implies that all of these big guys are only gas giants. Is that what everyone is really saying?&nbsp; We get used to the idea&nbsp;in Astronomy anything heavier than carbon is a "metal," right? &nbsp;Is this&nbsp;the same case of these so called&nbsp;"Hot Jupiters?" (In other words, are these Hot Jupiters also possibly rocky and the Asronomy Community simply uses the Jupiter analogy JUST because of their size? Just imagine the mass and volume of these exoplanet's metal cores!)That's kind of why I posted this as "Yo Astronomers;" I was hoping for some kind of "doctorial enlightenment" even if the answer was, "Gee, we don't really know!" That's why I appreciate your feedback, because it all comes down to how much metal one can expect to find in a forming solar system. Do any of us, even planetary astronomers, REALLY know?</font></p><p><font size="3">&nbsp;&nbsp;&nbsp;&nbsp; Another factor against me here is the question of, "Is there been enough time in our 13.7 ish billion year universe to have 4th, 5th, etc. generation star systems? Well, it would be easy for former O-types stars to supernova all kinds of metals out into the next generations star systems in a relatively short time, but they are&nbsp; small in number compared to Sun type, G stars and especially little K and M-type stars.</font></p><p><font size="3">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; I also don't think you can get the density of an exoplanet without having a rough idea of the radius by catching a planetary transit. Density is a factor of mass and radius-- or more specifically volume. That's kind of why I was curious about huge, "Terrestrial Hot Jupiters." (Ha! Oh my gosh,&nbsp;let's not start calling them THAT, for heaven's sakes!) </font></p><p><font size="3">&nbsp;&nbsp;&nbsp;&nbsp; </font></p> <div class="Discussion_UserSignature"> <p><font size="4" color="#0000ff"><strong>Aretis</strong></font></p> </div>
 
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derekmcd

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<p>I don't think anyone can give you a definitive correct answer to all this.&nbsp; We simply haven't been around enough to observe stellar systems form.&nbsp; Nor are we capable of the resolution in our telescopes to discern stellar systems in a specific way to judge the stage of their evolution other than basing it off the age of the star.&nbsp; Obviously, the only system we can really study is our own, so we base our observation of other systems in relation to what we see in our neighborhood.</p><p>Extrasolar planets are certainly not obligated to follow the same path as the planets in our own system, but it would seem logical that there would be some similarities.&nbsp; Physics are universal.&nbsp; The factors we are using to make these observations are fairly limited, but they are also quite educated.&nbsp; They are not just random guesses and speculation.</p><p>The metallicity of stars would seem to be quite important to how a stellar system forms.&nbsp; Considering our Sun is rather young given it's type, it should be on the higher end of the metallicity curve.&nbsp; Knowing this, it is not unreasonable to conclude the similar stellar system have similar metal distribution and their planets form in a similar fashion.&nbsp;</p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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aphh

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>I don't think they can figure the density from the radial velocity by itself.&nbsp; They would need need to know the actual size of the planet as well.&nbsp; The radial velocity only give the mass of the planet, not its radius.&nbsp; I think only in cases where the planet transits in front of the host star can they reasonably determine the size and thus the density.&nbsp; <br /> Posted by derekmcd</DIV></p><p>The movement that a giant hot jupiter exerts on it's parent star can be of the magnitude of 10 - 100 times compared to a rocky planet like Earth.&nbsp;</p><p>Using our solar system as a model, scientists have determined that such giant planets can only be jupiter-like planets. This does not exclude the possibility of a iron core inside the gas planet many times the size of earth.</p><p>One thing is, that it is possible to determine the composition of the parent star. Metal planets around a star would require a metal-rich parent star.&nbsp;</p><p>It is speculated that our Mercury might have once been a gas giant, that the solar wind blew the gasses away and exposed the metal core, which remained.&nbsp;</p>
 
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derekmcd

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<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>It is speculated that our Mercury might have once been a gas giant, that the solar wind blew the gasses away and exposed the metal core, which remained.&nbsp; <br /> Posted by aphh</DIV><br /></p><p>Highly unlikely.&nbsp; While there might be a non-zero probability, I certainly wouldn't bet money on it no matter how good the odds were.&nbsp; Two reasons:</p><p>1.&nbsp; There are extrasolar gas giants orbiting their host star at much, much closer distances than even Mercury is.&nbsp; Some of these stars are several billion years older than the Sun and these planets still retain their atmosphere.&nbsp; Certainly, some of the atmosphere bleeds away slowly, but it wouldn't be completely evaporated or boiled off for several billions of years.&nbsp; Given that Mercury is further away, it would still be retaining most of it's atmosphere.&nbsp; Our solar system simply hasn't been around long enough for Mercury to have lost that much.</p><p>2.&nbsp; It's still not known whether gas giants actually have solid rocky cores.&nbsp; If, however, the core accretion theory holds true for gas giants, it would have to be much larger than Mercury.&nbsp;</p> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>
 
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aretis

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<p><font size="3">Again, guys-- this is why I posted the question in the first place.</font></p><p><font size="3">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;How do we really know that these objects aren't Mega Terrestrial planets? Is the catch phrase "Hot Jupiters" making us assume that they&nbsp;HAVE to be gas giants? It would certainly be logical to conclude that some of them certainly are. A recent planetary transit of one of these puppies seems to confirmed that. But as far as most of them are concerned, all we have is a mass range and an orbital radius calulated by the pull that these exoplanets have on their parent star, and that is it. We do not have a density as of yet. (Stick around though, because, excitingly, WE WILL!) </font></p><p><font size="3">&nbsp;&nbsp;&nbsp;&nbsp; The phrase, "Using our solar system as a model, scientists have determined that such giant planets can only be jupiter-like planets." is the crux of my question. What article, book, website did you see this? I doubt if they have-- or can at this point-- determine that. They would need a transit on ALL of them using existing tools.&nbsp;I've never seen or read ANY info on the density of these big ol' planets, except for the one's aready mentioned. That doesn't mean that you haven't, of course.&nbsp;Please enlighten all of us if it's true. I love to be enlightened, that also why I asked the question. If there is another way to calculate the density that is new that you've heard about, I'd really like to hear about that too!</font></p><p><font size="3">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;I also don't like to draw too many conclusions from our Solar System because it's only a model of one. It seems to be true that there are many types of solar systems out there. At this time, we&nbsp;certainly have the ability to find the ones with huge planets orbiting very close to the parent star and a few other types. The book on Solar System Types can't even get through the first few pages of the Introduction yet!</font></p><p><font size="3">&nbsp;&nbsp;&nbsp; Also, if some of these are indeed HUGE terrestrail planets, they would show the same gravitational tug as a hot Jupiter AND have a smaller radii. That is obvious&nbsp;because they are rocky and not made up of gas. That's my point. That's why a planet like Jupiter can have well over half of the mass in our Solar System (excluding the Sun, of course) and only have a "surface" gravity of 2.4-ish that of Earth. Or, in other words, a rocky world 10 to 100 times more massive than Earth WOULD tug on a star EXACTLY like a Hot Jupiter. After all, mass is mass. It's like the old joke of what weighs more: a pound of&nbsp;nails or a pound of feathers. A pound is a pound regardless of the "stuff" within it, right?</font></p><p><font size="3">&nbsp;&nbsp;&nbsp;&nbsp; &nbsp;Without getting too mathematical-- I know you would have to calculate the difference in density-- that kind of "Earth" would be much smaller than a real "Hot Jupiter," but have the same mass. I think us novices are on the right track when we were talking about just how much metals we could expect to find in these systems. If it turns out that my question is just another wrong assumption, it would probably be because of that. It seems to me that until we start to get a spectra back from these worlds, and I believe we are starting to, we can make no conclusion on if they are made up of mainly metals or gases.</font></p><p><font size="3">&nbsp;&nbsp;&nbsp;&nbsp; Remember, I'm not really even talking about Earth-type planets here, and that's the problem, I suppose, with using this type of phrasing. These would be terrestrial, and rocky, but nothing like our Earth. The surface gravity of these bad boys would be crushing! Their spectra might even mimic a gas giant by having a lot of hydrogen and helium (H, He)&nbsp;in the atmospheres. They would have the surface gravity to hold onto it.&nbsp;I don't know how large a potentially huge terrestrial planet would have to be to do this, but even the Earth itself is still leaking extremely small amounts of these gases into space eventhough 99.9.....9 % of our&nbsp;H and&nbsp;He is long gone.</font></p><p><font size="3">&nbsp;&nbsp;&nbsp;&nbsp; As far as whether real "Hot Jupiter's" have&nbsp;metal cores or not is easily calculated once we get&nbsp; densities for them. The gas giants we know best in our solar system cetainly do because we know their densities. I wonder if a purely H and He&nbsp;"Hot Jupiter" could survive in a close orbit of a star. I guess it would depend on how active the star is, just how close, the masses involved, etc. It would be intersesting to start finding mainly carbon gas giants out there. But let's face it, any thing heavier that H and He in these gas giants are going to sink to the center and be part of the core, (unless something&nbsp;REALLY weird is going on.) I'd have to conclude from that that most gas giants would have to have cores made up of what&nbsp; the Astronomy community calls&nbsp; "the metals." Also just remember that the temperatures inside these extremely large gas giants would bring any "rocky stuff" heated down into their individual elements. The pressures involved would indeed make them solid or "metalically liquid." Jupiter supposedly has metallic H and He as you go down towards the core. There is also another&nbsp;theory floating around that if Jupiter has a mainly carbon core that at such pressures would turn it into a diamond the size of Earth. </font></p><p><font size="3">&nbsp;&nbsp;&nbsp;&nbsp; Again, I appreciate all of your feedback!!!!!!!!!! It all makes you wonder, huh?</font></p><p>&nbsp;</p><p><font size="3">Thanks again you guys,&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; Aretis</font></p> <div class="Discussion_UserSignature"> <p><font size="4" color="#0000ff"><strong>Aretis</strong></font></p> </div>
 
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