Exoplanet TOI-4603 b, ~13x Jupiter mass, ~1.04 Jupiter diameter

[Astronuc]

The group of astronomers led by Akanksha Khandelwal of the Physical Research Laboratory (PRL) in India, report that a transit signal has been identified in the light curve of a sub-giant F-type star known as TOI-4603, or HD 245134. The planetary nature of this signal was confirmed by follow-up radial velocity measurements taken with the PARAS (PRL Advanced Radial-velocity Abu-sky Search) and TRES (Tillinghast Reflector Echelle Spectrograph) spectrographs.

https://phys.org/news/2023-03-massive-giant-exoplanet-tess.html

TOI-4603 b has a radius of approximately 1.04 Jupiter radii and its mass is estimated to be about 12.89 Jupiter masses, which yields a density at a level of 14.1 g/cm³. The planet orbits its host every 7.24 days, at a distance of some 0.09 AU from it. The equilibrium temperature of TOI-4603 b was calculated to be 1,677 K.

It is one of the most massive and densest exoplanets. For comparison, Mo has a density of 10.22 g/cm³ and Ta has a density of 16.6 g/cm³. I would suspect that some of the density is derived from the high compressive pressure of the interior.

https://arxiv.org/abs/2303.11841

 

[fresh_42]

Lead has a density of 11.3. Shouldn't there be fission processes at 16.6?

 

[snorkack]

Lead has a density of 11.3. Shouldn't there be fission processes at 16.6?

Why? Unlike fusion, there is little talk of pycnonuclear fission.

 

[BWV]

What would distinguish this from a brown dwarf? the size and density match the low end of the range

 

[Astronuc]

Lead has a density of 11.3. Shouldn't there be fission processes at 16.6?

No, not necessarily. We don't see fission in elements until about Thorium (Z=90, A = 232, density of 15.4 g/cm³). I would expect the composition to be some mixture of heavy elements, but then again, I haven't looked at models of large plants with a size like 13x mass of Jupiter.

https://www.lenntech.com/periodic-chart-elements/density.htm

Bk has a density of 14.78 g/cm³, but the most stable isotope, ²⁴⁷Bk, has a half-life of 1380 y, and it alpha decays to ²⁴³Am, which also alpha decays with a half life of 7364 y into ²³⁹Np. Such heavy isotopes may experience spontaneous fission, which would produce lighter elements.

Next to Mo is Tc, which has a density of 11.5 g/cm³, and Ru, Rh and Pd, with densities of 12.37, 12.41 and 12.02 g/cm³, respectively, assuming isotopic vectors similar to those of earth.

How much and what kind of heavy metals would be interesting to know, and how they formed.

On earth, heavy elements like the transactinides formed during the r-process; however such elements would be subject to fast fission, which would produce the middle mass elements centered around Pd (Z=46), or Ag (Z=47), . . . and so on. Moderate mass transition metals and lanthanides for during s-process, and also from fast fission. However, I would suspect that there is some combination or r-process to s-process to condensation (to planet) followed by fast fission. I think this is a developing area.

 

[snorkack]

No, not necessarily. We don't see fission is element until about Thorium (Z=90, A = 232, density of 15.4 g/cm³).

Also there are the elements Ta (Z=73, ρ=16,6), W (Z=74, ρ=19,3), Re (Z=75, ρ=21), Os (Z=76, ρ=22,6), Ir (Z=77, ρ=22,4), Pt (Z=78, ρ=21,4) and Au (Z=79, ρ=19,3), none of which is prone to fission. (Treasures would be dangerous to collect were it otherwise!)

 

[Astronuc]

On earth, heavy elements like the transactinides formed during the r-process;

I should clarify that the r-process and probably s-process would predate for the formation of the earth. In other words, something happened in the vicinity of our sun, Sol, that created the elements we find on earth.

There are three candidate sites for r-process nucleosynthesis where the required conditions are thought to exist: low-mass supernovae, Type II supernovae, and neutron star mergers.

Ref: https://en.wikipedia.org/wiki/R-process#Nuclear_physics
Two-neutron capture reactions and the r process
https://journals.aps.org/prc/abstract/10.1103/PhysRevC.74.015802

So an interesting question is "What happened in the vicinity of the sun way back when?" that produced the elements we see today.

 

[fresh_42]

Also there are the elements Ta (Z=73, ρ=16,6), W (Z=74, ρ=19,3), Re (Z=75, ρ=21), Os (Z=76, ρ=22,6), Ir (Z=77, ρ=22,4), Pt (Z=78, ρ=21,4) and Au (Z=79, ρ=19,3), none of which is prone to fission. (Treasures would be dangerous to collect were it otherwise!)

And on the other hand, there are things like the Oklo mine even on earth.

I appreciated @Astronuc 's answer: "not necessarily" since in the end, we cannot know, yet. Why shouldn't there be Uranium present if other high-density elements are?

 

[Astronuc]

Why shouldn't there be Uranium present if other high-density elements are?

There probably is uranium and thorium. We'd have to know the predominant stellar nucleosynthesis process(es) that occurred in the vicinity of the neighborhood star.

Consider that TOI-4603 is a sub-giant F-type star. How old is it? What was it's partner(s) like? Assuming it was part of a binary or trinary system.

For that matter, what was the Sun's partner? It's no longer around. Was there a giant neighbor that went supernova, or a pair of colliding neutron stars?

 

[snorkack]

Why shouldn't there be Uranium present if other high-density elements are?

Because of the r- and s-process difference.
If you look at the lifetimes of nuclei then between Bi-210m (half-life 3 million years) and Ra-226 (half-life 1600 years), no nucleus with nucleon count from 211 to 225 included has half-life over 15 days. Which means that s-process stops around Bi due to rapid alpha decay of Po back to Pb. It takes r-process to cross the gap to long lived isotopes like Th-232 (half-life 14 Gyr)

Also note that "density" is not solely due to nuclear mass. The densest element is Os - because the electronic shell structure of Os allows to accommodate a large number of atoms in a given volume. From Ir to Bi, the individual atoms get heavier, but the electrons get bulkier so the density increases. The shell structure again allows the density to increase from Ra to Np - but not so much, the atom count in a volume of Np is still so much smaller than in a volume of Os that despite Np atom being heavier than Os, Np is less dense.

 

[Vanadium 50]

I'm not sure if this thread is being serious or not. "Maybe it's a giant ball of tungsten!" Really?

On the off chance that this is a serious discussion, there are some things that deserve closer scruitiny:

(1) The density is well withing the range of red dwarfs.. It's a little low for brown dwarfs.
(2) The temperature is well withiin the range of brown dwarfs. It's a little low for red dwarfs.
(3) The inferred density depends on the distance (in a non-simple way). The distance is claimed to be known to half a percent. This is astoundingly accurate - we know the distance to Sirius about that well, and this is a lot farther out, Other stars at similar distances are known to 30% or so..

My take-away is that the numbers are likely less precise than claimed, and there may well be room for this object as the reddest brown dwarf or the brownest red dwarf.

It is not, however, a giant ball of tungsten.

 

[JLowe]

We'll assume it's Cybertron until proven otherwise.

 

[snorkack]

So the serious question: does it undergo deuterium fusion, or has it? How much has its core D abundance decreased from its initial value?

 

[AlexB23]

https://phys.org/news/2023-03-massive-giant-exoplanet-tess.html
It is one of the most massive and densest exoplanets. For comparison, Mo has a density of 10.22 g/cm³ and Ta has a density of 16.6 g/cm³. I would suspect that some of the density is derived from the high compressive pressure of the interior.

https://arxiv.org/abs/2303.11841

I am kinda curious what the core temperature of this exoplanet is. I'm betting it is in the hundreds of thousands of kelvin.

 

[Vanadium 50]

I am kinda curious what the core temperature of this exoplanet is.

How do you propose to measure it?

 

[Astronuc]

I am kinda curious what the core temperature of this exoplanet is. I'm betting it is in the hundreds of thousands of kelvin.

Could very well be. It is somewhere between Jupiter's core temperature, estimate to be 36000-43000°F (20000-24000 K) and the an upper bound temperature assigned to brown dwarfs, or about about 3 million K.

Ref: https://www.weather.gov/fsd/jupiter
https://spaceplace.nasa.gov/jupiter/en/

Then again, from yet another NASA source, "It could be up to 90,032 degrees Fahrenheit (50,000 degrees Celsius) down there, made mostly of iron and silicate minerals (similar to quartz)." Or about 2-2.5 times the previous estimates.
https://solarsystem.nasa.gov/planets/jupiter/in-depth/#otp_structure

Brown dwarfs are sometimes referred to as ‘failed stars’ since they are more massive than planets but have insufficient mass to sustain nuclear fusion in their cores. According to current theories, the mass required to sustain nuclear fusion is about 1/12th of a solar mass (or about 90 times the mass of Jupiter). This therefore sets the upper mass limit for brown dwarfs. The lower limit for classification as a brown dwarf is somewhat more arbitrary, but generally a mass greater than 1/80th of a solar mass is required for an object to be classified as a brown dwarf and not a planet.

The core temperatures of brown dwarfs must be below about 3 million degrees, as at this temperature fusion becomes sustainable. Surface temperatures are 1,000 degrees Kelvin or less. In 2011, the NASA Wide-field Infrared Survey Explorer (WISE) discovered six extremely cool brown dwarfs known as Y dwarfs, which have temperatures as low as 300 Kelvin, which is the temperature of the human body! At such cool temperatures the atmospheres of brown dwarfs contain many molecules, including methane and even water.

https://astronomy.swin.edu.au/cosmos/B/brown+dwarf

https://www.stsci.edu/~inr/ldwarf3.html

It is interesting about the characterization of large planets, sub-brown dwarfs and brown dwarfs. The object in question has an estimated mass of 12.89 M_J. The 'equilibrium' temperature is 1677+/- 24K, but the temperature in the core is certainly hotter.

I'm sure someone has estimated a core temperature based on various models, since we find estimates of Jupiter's core temperature and those of brown dwarfs, but it not readily apparent, at least not to me.

Looking at Figure 3 in the Arxiv paper, the authors have a diagram/plot of showing, "Planetary density as a function of planetary mass for transiting giant planets and brown dwarfs (0.25-85 _J). The shaded area represents the overlapping mass region of massive giant planets and brown dwarfs based on the deuterium burning limit, . . .". The estimated mass of puts it just below 13 M_J arbitrary limit.

Could we just say/estimate a temperature based on taking Jupiter's estimate, e.g., 20000-24000 K, and multiply by 13, which would give 260000 - 312000 K, as an estimate? It could be higher/lower.

I was looking for other examples, which are inferred by the plot in Figure 3, e.g., WISE 0855−0714, which is estimated to have a mass of about 3-10 M_J, which is quite a range, compared to 12.89 +0.58/-0.57M _J. Maybe it's hard to estimate the mass of a cold large planet or sub-brown dwarf.

So the serious question: does it undergo deuterium fusion, or has it? How much has its core D abundance decreased from its initial value?

Like V50 asked in a previous post, "how would one propose to measure that"?

What even is the composition of the core? Is it deuterium, deuterium and helium, D+He+Li (C, N, O, Mg, Al, Si, P, . . . ?) and in what proportions? Is it a planet, sub-brown dwarf, or the lightest brown dwarf. Is the composition much the same as the parent star, TOI-4603 (HD 245134)?

See also,

(3) The inferred density depends on the distance (in a non-simple way). The distance is claimed to be known to half a percent. This is astoundingly accurate - we know the distance to Sirius about that well, and this is a lot farther out, Other stars at similar distances are known to 30% or so..

The 14.1 +1.7/−1.6 is an interesting estimate, which I guess is some nominal value. The surface would be less and core would be greater. Is the core solid or superfluid, or . . . . ?

I was looking at the earth's density, nominally about 5.515 g/cm³, which is given in the following paper, which gives a nice overview of the history of such estimates.
https://adsabs.harvard.edu/full/2006JBAA..116...21H

The crustal/surface density is lower, and the core density if much greater; inner core density ~ 9.9-12.2 g/cm³ and outer core density ~ 12.6-13 g/cm³, and that is determined by various factors including composition.
https://www.ucl.ac.uk/seismin/explore/Earth.html

What about Jupiter's core? About 10 to 20 g/cm³
See the Summary and Table 3 in https://www.aanda.org/articles/aa/pdf/2018/05/aa32183-17.pdf

?????Edit/update with some miscellaneous material
https://en.wikipedia.org/wiki/Brown_dwarf (reasonable source for references)

Space Tiger (2005) - https://www.physicsforums.com/threa...exceed-14-times-earths-size.86555/post-729546

https://chandra.harvard.edu/xray_sources/browndwarf_fg.html

Brown dwarfs: Failed stars, super jupiters
https://physicstoday.scitation.org/doi/pdf/10.1063/1.2947658

From 2014 - 50 Years of Brown Dwarfs - we need an update for 2024 - "60 years of brown dwarfs"
https://link.springer.com/book/10.1007/978-3-319-01162-2

 

[Ken G]

On @Vanadium 50 's point, now that we are thinking more in terms of a brown dwarf, the possibility that we are dealing with a Jupiter-like composition comes to the fore. One must then ask, what would happen if we added 12 more Jupiter masses of hydrogen to Jupiter?

The result might surprise you-- Jupiter has lost so much heat in its lifetime that it is really not all that much different from a white dwarf. That means, it is basically a ball of degenerate hydrogen gas. The way you can tell this is that the mass-radius relation (https://www.astro.princeton.edu/~burrows/classes/403/white.dwarfs.pdf) of a nonrelativistic hydrogen+helium white dwarf is $R = 0.028 R_{Sun} (M_{Sun} / M)^{1/3}$. Since $M_{Sun} / M \sim 1000$ for Jupiter, $R \sim 0.3 R_{Sun} \sim 30 R_{Earth}$, which is in the right ballpark. But we must note it is large by a about a factor of 3 from the reality. So that tells us that Jupiter is starting to feel some interparticle attractions other than gravity. But if we assume that a more massive Jupiter could be more like a white dwarf, so not have those extra attractive forces, then we can use the above R for $M_{Sun} / M \sim 80$, and we get $R \sim 0.065 R_{Sun} \sim 6 R_{Earth}$ so is about the right size. In other words, removing the attractive forces that make Jupiter about 3 times smaller than a degenerate gas of electrons would pretty well compensate for this new planet being an order of magnitude more massive, and you end up with a planet about the same size as Jupiter, using simple hydrogen+helium content.

This might raise for some the additional question of, how big would the Earth be if its electrons were a degenerate gas and there were no interparticle attractions other than gravity? Using the above formula, the answer would be, about twice the size of the Sun! So obviously the interparticle attractions within rock and metal are vastly larger than the attraction of gravity (and we know what they are, electrostatic attraction within rock molecules and the metal lattice). But we see this same effect only weakly in Jupiter, so it is likely that when we go an order of magnitude higher in mass than Jupiter, we should transition into a more white-dwarf-like regime, explaining why the radius of this planet is not much larger than Jupiter.

 

[AlexB23]

How do you propose to measure it?

One might be able to estimate the core temperatures, just like we have done with Jupiter, which is around 20,000°C or more.

 

[AlexB23]

Could very well be. It is somewhere between Jupiter's core temperature, estimate to be 36000-43000°F (20000-24000 K) and the an upper bound temperature assigned to brown dwarfs, or about about 3 million K.

Ref: https://www.weather.gov/fsd/jupiter
https://spaceplace.nasa.gov/jupiter/en/

Then again, from yet another NASA source, "It could be up to 90,032 degrees Fahrenheit (50,000 degrees Celsius) down there, made mostly of iron and silicate minerals (similar to quartz)." Or about 2-2.5 times the previous estimates.
https://solarsystem.nasa.gov/planets/jupiter/in-depth/#otp_structurehttps://astronomy.swin.edu.au/cosmos/B/brown+dwarf

https://www.stsci.edu/~inr/ldwarf3.html

It is interesting about the characterization of large planets, sub-brown dwarfs and brown dwarfs. The object in question has an estimated mass of 12.89 M_J. The 'equilibrium' temperature is 1677+/- 24K, but the temperature in the core is certainly hotter.

I'm sure someone has estimated a core temperature based on various models, since we find estimates of Jupiter's core temperature and those of brown dwarfs, but it not readily apparent, at least not to me.

Looking at Figure 3 in the Arxiv paper, the authors have a diagram/plot of showing, "Planetary density as a function of planetary mass for transiting giant planets and brown dwarfs (0.25-85 _J). The shaded area represents the overlapping mass region of massive giant planets and brown dwarfs based on the deuterium burning limit, . . .". The estimated mass of puts it just below 13 M_J arbitrary limit.

Could we just say/estimate a temperature based on taking Jupiter's estimate, e.g., 20000-24000 K, and multiply by 13, which would give 260000 - 312000 K, as an estimate? It could be higher/lower.

I was looking for other examples, which are inferred by the plot in Figure 3, e.g., WISE 0855−0714, which is estimated to have a mass of about 3-10 M_J, which is quite a range, compared to 12.89 +0.58/-0.57M _J. Maybe it's hard to estimate the mass of a cold large planet or sub-brown dwarf.Like V50 asked in a previous post, "how would one propose to measure that"?

What even is the composition of the core? Is it deuterium, deuterium and helium, D+He+Li (C, N, O, Mg, Al, Si, P, . . . ?) and in what proportions? Is it a planet, sub-brown dwarf, or the lightest brown dwarf. Is the composition much the same as the parent star, TOI-4603 (HD 245134)?

See also,

The 14.1 +1.7/−1.6 is an interesting estimate, which I guess is some nominal value. The surface would be less and core would be greater. Is the core solid or superfluid, or . . . . ?

I was looking at the earth's density, nominally about 5.515 g/cm³, which is given in the following paper, which gives a nice overview of the history of such estimates.
https://adsabs.harvard.edu/full/2006JBAA..116...21H

The crustal/surface density is lower, and the core density if much greater; inner core density ~ 9.9-12.2 g/cm³ and outer core density ~ 12.6-13 g/cm³, and that is determined by various factors including composition.
https://www.ucl.ac.uk/seismin/explore/Earth.html

What about Jupiter's core? About 10 to 20 g/cm³
See the Summary and Table 3 in https://www.aanda.org/articles/aa/pdf/2018/05/aa32183-17.pdf

?????Edit/update with some miscellaneous material
https://en.wikipedia.org/wiki/Brown_dwarf (reasonable source for references)

Space Tiger (2005) - https://www.physicsforums.com/threa...exceed-14-times-earths-size.86555/post-729546

https://chandra.harvard.edu/xray_sources/browndwarf_fg.html

Brown dwarfs: Failed stars, super jupiters
https://physicstoday.scitation.org/doi/pdf/10.1063/1.2947658

From 2014 - 50 Years of Brown Dwarfs - we need an update for 2024 - "60 years of brown dwarfs"
https://link.springer.com/book/10.1007/978-3-319-01162-2

Wow, your estimate of ~300,000 K seems the most realistic, assuming core temperature is linearly related to mass.

 

[Ken G]

Looking at Figure 3 in the Arxiv paper, the authors have a diagram/plot of showing, "Planetary density as a function of planetary mass for transiting giant planets and brown dwarfs (0.25-85 _J). The shaded area represents the overlapping mass region of massive giant planets and brown dwarfs based on the deuterium burning limit, . . .". The estimated mass of puts it just below 13 M_J arbitrary limit.

That's a very helpful figure. If you compare to the expressions I gave for fully degenerate hydrogen/helium mix, you see that the curves would cross at about 10 Jupiter masses. Brown dwarfs at 100 Jupiter masses are about 1.4 times larger radius than they would have if their electrons were fully degenerate (which makes sense since deuterium fusion is preventing them from becoming fully degenerate), whereas as I mentioned Jupiter is about 3 times smaller than it would be if it was only gravity pulling against fully degenerate electrons (rather than whatever additional nongravitational attractions are in there). So ironically, it looks like the super Jupiter of this thread is close to both the boundary between gas giants and brown dwarfs, and also to the point where non-gravitational attractions become negligible, which is the same boundary. This makes it a whole lot like a tiny white dwarf made of hydrogen.

 

[InkTide]

It is not, however, a giant ball of tungsten.

Obviously, it's clearly an enormous mercury sphere.

Joking aside, we can't use element densities very well to estimate structure or interpret element abundances by observed structure. For one thing, the density of the object is going to be at least partially dependent on the bulk modulus of its constituent materials at the range of temperatures experienced by the object before you even start considering nuclear reactions.

This makes it a whole lot like a tiny white dwarf made of hydrogen.

Is there a mass of white dwarf able to accumulate surface material without going type-Ia? Maybe not enough mass in the binary system for the dwarf to reach the Chandrasekhar limit? The proximity to the parent star might lead to accretion and form an occluding surface layer of gases, without triggering the type-Ia nova. We wouldn't be able to see an accretion disc well of because of the angle (transit detection means if the accretion disc is parallel to the orbital plane, it's also roughly parallel to our direction of observation). Is there anything in the light curve that would indicate an accretion-like structure, or is the resolution of the curve not good enough to tell?

 

[Ken G]

I don't think there's any reason to expect accretion onto the planet from the star, unless the star was puffing out into a red giant. It seems more likely the planet just formed with its high mass from the start, much as Jupiter itself did. As for Chandrasekhar level masses, the planet has only about 1/300 that kind of mass.

 

[InkTide]

Probably true, though I wonder if during the protostar stage it could have accreted that mass. With an F-type subgiant as the parent, there's probably not enough mass between them to hit the limit. Of course, it makes me also wonder if there's a potential new way to make type Ia supernovae that isn't capture of an extant white dwarf, or if the proximity of white dwarfs to substellar mass and luminosities is suggestive of a previously unexplored path of stellar/substellar evolution hiding in this overlapping region of definition ambiguity.

One lingering question I'd have is how much of the properties here might be explained simply by ablation of a (formerly) mundane substellar companion. According to the paper, TOI-4603 is relatively bright - would a low-mass eclipsing binary system have the potential of the more massive/energetic star ablating the volatile surface of a substellar companion? They did find a high metallicity for TOI-4603 and metal enrichment of TOI-4603b, which suggests to me that the exoplanet doesn't retain all the volatile mass from its formation. It does, however, pose the problem similar to Hot Jupiters of how the object formed at all during the system's protostellar stage. It's very close to the more massive star (<0.09 AU), and its current mass and density would both require it to have been well above 13 Jupiter masses at formation if it migrated inward, and likely severely disrupt the formation of the more massive star in the protostellar disk if it formed in-situ. The authors do suggest that the high eccentricity is evidence for tidal dissipation being ongoing in the system, like what's been suggested to occur with Hot Jupiters.

It may not be a massive metal sphere, but it is definitely a very interesting one.