Boiling hot rock the mass of Uranus discovered!

[Aphex_Twin]

Got it. I extracted the cube wrong. But essentially the method was correct. Thank you

 

[Bozo Erectus]

Ok so as far as I can make out the consensus seems to be that it has about 2.4 gees. The original article said that the planet didnt have enough gravity to build up a big gaseous atmosphere like the gas giants. How much gravity is required? IIRC what Turner said earlier, Jupiter only has about 2.5

 

[betazed]

Actually it will hold above the surface (you just change r to your distance from center), but below the surface gravity will start to cancel itself out as the stuff above you pulls opposite the stuff below you)

you are right. What was I thinking? :suicide:

 

[Perfection]

I have my own data of Jupiter from one of my astronomy programs. I hope It will be of assistance:

Why would we need that?

Got it. I extracted the cube wrong. But essentially the method was correct. Thank you

No problem!

 

[PlutonianEmpire]

THIS POST IS NOW IRREVELANT

 

[Perfection]

Ok so as far as I can make out the consensus seems to be that it has about 2.4 gees. The original article said that the planet didnt have enough gravity to build up a big gaseous atmosphere like the gas giants. How much gravity is required? IIRC what Turner said earlier, Jupiter only has about 2.5

That's on the outside if it was just its rocky core it is likely to be higher. It's probable that the planet has more than 2.5 times earth's gravity, and still not able to sustain an atmopshere, remember it is in close proximity to its sun, so it's going to be much hotter making gas escape much easier, with such higher temperatures comparisons to jupiter wouldn't work.

Edit: @Plutonian, It's just that I'm confused on why you thought it to be helpful.

 

[Aphex_Twin]

That's on the outside if it was just its rocky core it is likely to be higher. It's probable that the planet has more than 2.5 times earth's gravity, and still not able to sustain an atmopshere, remember it is in close proximity to its sun, so it's going to be much hotter making gas escape much easier, with such higher temperatures comparisons to jupiter wouldn't work.

Also, being so close to the sun whatever atmosphere would be severely punded by solar radiation and if there's no magnetic field, whatever would be left would be simply blown out in space.

 

[Bozo Erectus]

Ok I think I understand. The 'true' gravity of Jupiter is down in its core, not in its outer atmosphere. So the gravity down there would be much more than 2.5. Makes sense, I couldnt see how just 2.5 would be enough for a gas giant to form.

 

[Bozo Erectus]

Also, being so close to the sun whatever atmosphere would be severely punded by solar radiation and if there's no magnetic field, whatever would be left would be simply blown out in space.

It must have a magnetic field because it probably has an iron core.

 

[Perfection]

Ok I think I understand. The 'true' gravity of Jupiter is down in its core, not in its outer atmosphere. So the gravity down there would be much more than 2.5. Makes sense, I couldnt see how just 2.5 would be enough for a gas giant to form.

Exactly, my point [thumbsup]

It must have a magnetic field because it probably has an iron core.

That is true, but solar wind/radiation could still overcome it like in the below example.

http://www.space.com/scienceastronomy/shrinking_planet_030312.html

 

[Sword_Of_Geddon]

Interesting...what would happen if 99% of Jupiter's atmosphere was blown away? How big would Jupiter be then?

 

[Straybow]

Jupiter has layers of "core." The outer layer is thought to be a liquid hydrogen "sea." Below that is hydrogen in solid (metallic) form, which can only exist under extreme pressures. The exact surface will be indistinct, gradually phasing from gas to liquid to solid, discernable only as the increasing orderliness of the molecules. Several Earth-masses would represent a substantial depth due to low density.

This surrounds a rocky core of believed to be 13 Earth-masses. (I'd call it a "terrestrial kernel" just to avoid confusion, but that may not be the term used by planetologists.) This in turn has a liquid iron core approximately one third of those 13 Earth-masses.

Would we measure gravity at the liquid hydrogen "surface," the solid hydrogen "surface," or the more easily defined terrestrial surface? Dunno. But yes, in general gravity is proportional to density·radius, so that given Earthlike average density the surface gravity would only be cube-root(13) = 2.35 gees. An arbitrarily defined hydrogen surface will have higher gravity since the radius increases faster than the density decreases until a critical radius is reached. Thereafter the gravity decreases.

I don't think that a gas giant forms around a large terrestrial kernel. Comets have significant quantities of non-volitiles but are clearly far to small to condense around a solid core. Therefore it is unnecessary to assume, in the formation of a giant, that a rocky core develops first and then volitiles and gasses accumulate by gravity.

I don't think a gas giant can "boil away" either. If a hot gas giant lost 10,000 tons/sec (as cited for HD209458b) it would still only lose about one-twentieth of an Earth-mass over a billion years. That's less than ½% of the smallest gas giant in our system. HD209458b will still be there when the primary enters red giant phase and engulfs the planet in 5-10 billion years.

 

[Perfection]

Jupiter has layers of "core." The outer layer is thought to be a liquid hydrogen "sea." Below that is hydrogen in solid (metallic) form, which can only exist under extreme pressures. The exact surface will be indistinct, gradually phasing from gas to liquid to solid, discernable only as the increasing orderliness of the molecules. Several Earth-masses would represent a substantial depth due to low density.

This surrounds a rocky core of believed to be 13 Earth-masses. (I'd call it a "terrestrial kernel" just to avoid confusion, but that may not be the term used by planetologists.) This in turn has a liquid iron core approximately one third of those 13 Earth-masses.

Would we measure gravity at the liquid hydrogen "surface," the solid hydrogen "surface," or the more easily defined terrestrial surface? Dunno. But yes, in general gravity is proportional to density·radius, so that given Earthlike average density the surface gravity would only be cube-root(13) = 2.35 gees. An arbitrarily defined hydrogen surface will have higher gravity since the radius increases faster than the density decreases until a critical radius is reached. Thereafter the gravity decreases.

I would say that the core would be best described as the point where it's mostly heavy elements (not H and He)

I don't think that a gas giant forms around a large terrestrial kernel. Comets have significant quantities of non-volitiles but are clearly far to small to condense around a solid core. Therefore it is unnecessary to assume, in the formation of a giant, that a rocky core develops first and then volitiles and gasses accumulate by gravity.

By terrestrial kernal you are correct, it would be more of a rock/ice Kernal like those of the large outer solar system moons and planetoids (save Io, which has lost its icy mantle). The key is the rock/ice/metal comes first

I don't think a gas giant can "boil away" either. If a hot gas giant lost 10,000 tons/sec (as cited for HD209458b) it would still only lose about one-twentieth of an Earth-mass over a billion years. That's less than ½% of the smallest gas giant in our system. HD209458b will still be there when the primary enters red giant phase and engulfs the planet in 5-10 billion years.

I can see three reasonable explanations, all may be applicable:
1. Space.com may be accidentally reporting an incorrect number
2. When you lose atmophere the rate of loss increases due to decrease in gravity
3. As main sequence stars age they burn brighter and brighter, the star may increase the planet's temperature enough to boil off its atmophere long before going into its death throes.

 

[Singularity]

136 planets and counting. So far only Jovian Giants and Fried Rocks that's competing to lap their stars in the shortest time. This sounds like the perfect reason to kickstart an international project to launch the space interferometer satelites that will link up to spot those slower moving smaller planets in the ~1 AU belt orbiting G4 stars. Then we need to zoom in and spot wether they have a magnetosphere like earth do, to support brittle creatures like ourself. I speculate that a spinning iron core is much less abundant than a lump of rock orbiting 1 AU from sun-like stars.

It's not very interesting to keep counting 'mutant' planets in freak systems. Let us find out exactly how unique we are by buying ourselves the proper astronomical glasses to do just that job. I wonder if any astronomer really think they can calculate the 365'ish day wobble of an object the size of the earth with todays telescopes? I'm a member of the 'scrap hubble and get a bigger one' camp.

 

[Perfection]

I'm a member of the "Let's at least wait till we get the bigger one up before scrapping Hubble"

But those "freak planets" do make us wonder how the hell they got there.

 

[Straybow]

I can see three reasonable explanations, all may be applicable:
1. Space.com may be accidentally reporting an incorrect number
2. When you lose atmophere the rate of loss increases due to decrease in gravity
3. As main sequence stars age they burn brighter and brighter, the star may increase the planet's temperature enough to boil off its atmophere long before going into its death throes.

Except gravity doesn't decrease significantly, the mass loss is simply too small and total mass is simply too great for a true Jovian (which I think would include Saturn). A sub-Jovian of Jovian composition is still too massive, as my figures showed, even a ten-fold increase in loss would represent only a 3-4% loss to a small sub-Jovian.

Yes, luminosity increases but only by a factor of ~4 from ignition to hydrogen exhaustion. The star in question is reasonably mature, so it's luminosity is in the midrange and won't more than double in the future. Still needs that and nearly 2 orders of magnitude greater loss rate.

 

[Perfection]

Except gravity doesn't decrease significantly, the mass loss is simply too small and total mass is simply too great for a true Jovian (which I think would include Saturn). A sub-Jovian of Jovian composition is still too massive, as my figures showed, even a ten-fold increase in loss would represent only a 3-4% loss to a small sub-Jovian.

I was thinking along similar lines, but I'm not sure about the relation between mass and loss, it may be much more tempermental then in your model. Also it may be noted that you may not have to lose that large a percent in mass, the density hydrogen-helium atmophere is much less then the rocky core, however I couldn't tell you the exact proportion of the two mass. Still this does knock off a fair amount of mass.

Yes, luminosity increases but only by a factor of ~4 from ignition to hydrogen exhaustion. The star in question is reasonably mature, so it's luminosity is in the midrange and won't more than double in the future. Still needs that and nearly 2 orders of magnitude greater loss rate.

However a 2x increase in luminosity may not indicate a 2x increase in mass loss, it's about the amount of particles with velocities greater then the escape velocity. However, since I know little about thermodynamics I couldn't give you a satisfactory anwer. Also, on similar lines the solar wind may increase leading to loss.

Of course this is assuming space.com's figure is correct, and this doesn't rule out the possibility of this occcuring on different worlds.

 

[Straybow]

Well, the ratio for Jupiter is 318:13, or roughly 25:1. The core simply isn't a large enough percentage of the total mass, it can be treated as insignificant. Note that the calc shows the gravity at the surface of the rocky core is roughly 2.35 gee, which is only slightly less than gravity at the edge of the atmosphere. It just isn't going to change much as mass is "boiled" off, so the rate isn't going to accelerate dramatically.

 

[Perfection]

Well, the ratio for Jupiter is 318:13, or roughly 25:1. The core simply isn't a large enough percentage of the total mass, it can be treated as insignificant.

Okay, so that's likely not the case.

Note that the calc shows the gravity at the surface of the rocky core is roughly 2.35 gee, which is only slightly less than gravity at the edge of the atmosphere. It just isn't going to change much as mass is "boiled" off, so the rate isn't going to accelerate dramatically.

That is correct that the gravity won't change much but the small change in gravity may result in a much larger rate of loss. However I'm not sure of this.

Now let's get a bit more data

A different article here on the topic and it claims it HD 209458b has 2/3 Jupiter's mass and says it's at least 10,000 tonnes/sec and could possibly be much more. So It appears that the idea that this may be occuring is correct, and the presence of a "puffed-up" atmophere shown by Hubble measurements provides additional evidence.

 

[Straybow]

Yes, but even at 10 times that 10,000 ton/s rate it still isn't a significant drain to the total mass. If you have to up 2 orders of magnitude then either the measurement is meaningless or the supposition that the atmosphere will be lost is absurd.

A hypothetical planet around a similar star loosing hydrogen at 100 times the rate would have to be 1/10 the distance—that could even be inside the Roche limit. You'd really need a brighter star and a moderately closer orbit to cook off all the volitiles of a Jovian.