Rogue super-Earths/mini-Neptunes...

agent009 · 2014-06-28 01:08:55

Josh: Basically, when a hot cloud of interstellar medium cools down enough to form molecules, any atoms of F you might have there will first form F₂ molecules, but those will readily react with anything they come in contact with except for Ne (though F wouldn't normally form any stable compounds with O, He and heavier noble gases). If lots of S happens to be nearby at that point, lots of different sulfur fluorides would be formed. Most of those would readily react with other stuff to form different compounds, but SF₆ is extremely stable and inert, so any amount of it initially produced would likely stay that way. As the cloud further condenses and cools down (below about 200 K), SF₆ would become solid - so, it would basically be rock under cool enough conditions and a rocky planet could get quite a bit of it. But then, as such ball of rock is heated by either a star or some internal processes, SF₆ would sublimate and form atmosphere - which would be unlikely to escape since those molecules are so heavy.

Nope, not publishing yet, but I'll be there eventually, I hope

Void: Noble gases have no greenhouse effect to speak of. Radiative forcing mainly comes from interaction of atoms in a molecule, and you can't have any of that if your molecule is a single atom. Diatomic molecules are slightly better in that respect, but not by much. Generally, the more atoms you have in a molecule and the more atomic weight difference there is between them - the stronger greenhouse effect this will produce. Hence, even CO₂ only has a relatively mild greenhouse effect (as carbon and oxygen are pretty close in atomic weight) compared to hydrocarbons and H₂O. This is also the reason why SF₆ is an extremely potent greenhouse gas - you've got 7 atoms in the molecule and sulfur is so much heavier then fluorine. In the environment you describe, you might get some marginal greenhouse effect from N₂ and H₂, but you shouldn't count on Ne and Ar to produce any. However your overall reasoning seems sound - nitrogen would behave much like water on Earth between 64 and 126 K, provided the pressure stays in 12.5 - 3395.8 kPa range.

Last edited by agent009 (2014-06-28 01:10:09)

Void · 2014-06-28 10:25:33

Neon and Argon could provide a cloud deck however to trap heat.

I don't expect any such ready made planets, unless it is a particularly young planet, or has an unusual amount of radioactive content.

Otherwise, I am thinking that multiple cloud decks could only occur, if a heavy thick high pressure H2 atmosphere existed above. In that case terraformation would require the removal of it and the addition of additional energy on the surface from fusion I presume. But that is OK. At least for some rogue planets, there might be a way.

I would suppose that a deep atmosphere at first would require robotics operated from orbit, and/or Humans using special equipment such as a Helium/Oxygen atmosphere, and perhaps powered deep sea type suits.

I presume that they would have arrived by orion type fusion propulsion, so they would have Hydrogen bombs to erode the H2 atmosphere away with.

In the improbable case that they found a ready for use planet they would not need those things, but more likely they would.

Using a very close replica of Earth in that situation, I might want to see a Hydrogen Helium atmosphere intruding to the Plateau of Tibet, which would be very very cold.
Further down would be "Puddles" of other atmospheric gasses starting with a small diluted layer of Neon @~25 K, and then below that Nitrogen, Argon, and perhaps in some low places Methane and just maybe CO2.

But that would require that 7 bars of Hydrogen/Helium could hold a temperature of almost ~25 K heat, which might be unlikely. If it was naturally more, then some would have to be removed, and in the "Puddles" Fusion energy would have to be added to keep the Neon, Nitrogen, and Argon inflated.

A world like that @7 Bars (I have been reading your posts) on the Plateau of Tibet, would allow humans to have habitats at ambient pressure on the Plateau, and would allow more favorable thermal characteristics at lower elevation, but less favorable pressure characteristics in exchange. It might be that some type of pressure blocking hull filled with Helium and Oxygen might be able to operate at lower elevations. Or perhaps air planes with pressure hull cabs. Most likely much of any work activities done at the lower elevations would be done with telepresence.

Of course, if the fusion power is ramped up, then more Hydrogen and Helium could be dispersed, and the pressures planet wide lowered.

Perhaps there would be an evolution in that direction over time.

Last edited by Void (2014-06-28 12:38:31)

JoshNH4H · 2014-06-28 17:57:54

agent009- My expectation would be that rather than finding their counterparts, F2 would instead react with the ubiquitous Hydrogen to form HF, which is both energetically more favorable, and more logical if you have F atoms floating around. Once this has happened, you will probably see any HF that collects on solid objects reacting with oxides to form fluorides and water, as it is wont to do. However, it's not inconceivable that if the system cools quickly enough, there will be a zone where you find HF freezing before it interacts with rocky objects, and also possibly intermixing with water and other ices. If a planet were to conveniently coalesce in just the right place, and the system had an excess of fluorine relative to what one would expect, it's possible that you could end up with a planet that has enough fluorine to make this kind of atmosphere happen.

Void-

I think the multiple cloud deck idea is very feasible. Anything ices at the right temperature, after all. I could see each hydrocarbon forming its own cloud deck, as they liquify or solidify at various levels.

Tom Kalbfus · 2014-06-30 06:41:37

Here is an example of a world that might be terraformed:
http://newmars.com/forums/viewtopic.php … 90#p121390
I reproduce this first post for discussion purposes:
http://phl.upr.edu/press-releases/gliese832
Press Releases >

A Nearby Super-Earth with the Right Temperature but Extreme Seasons
posted Jun 25, 2014, 4:53 AM by Abel Mendez Torres [ updated 5 hours ago ]

Artistic representation of the potentially habitable Super-Earth Gliese 832 c against a stellar nebula background. Credit: PHL @ UPR Arecibo, NASA Hubble, Stellarium.

UPDATE: Check figure 5 for an alternative version.

Gliese 832 c is the nearest best habitable world candidate so far

An international team of astronomers, led by Robert A. Wittenmyer from UNSW Australia, report the discovery of a new potentially habitable Super-Earth around the nearby red-dwarf star Gliese 832, sixteen light years away. This star is already known to harbour a cold Jupiter-like planet, Gliese 832 b, discovered on 2009. The new planet, Gliese 832 c, was added to the Habitable Exoplanets Catalog along with a total of 23 objects of interest. The number of planets in the catalog has almost doubled this year alone.

Gliese 832 c has an orbital period of 36 days and a mass at least five times that of Earth's (≥ 5.4 Earth masses). It receives about the same average energy as Earth does from the Sun. The planet might have Earth-like temperatures, albeit with large seasonal shifts, given a similar terrestrial atmosphere. A denser atmosphere, something expected for Super-Earths, could easily make this planet too hot for life and a "Super-Venus" instead.

The Earth Similarity Index (ESI) of Gliese 832 c (ESI = 0.81) is comparable to Gliese 667C c (ESI = 0.84) and Kepler-62 e (ESI = 0.83). This makes Gliese 832 c one of the top three most Earth-like planets according to the ESI (i.e. with respect to Earth's stellar flux and mass) and the closest one to Earth of all three, a prime object for follow-up observations. However, other unknowns such as the bulk composition and atmosphere of the planet could make this world quite different to Earth and non-habitable.

So far, the two planets of Gliese 832 are a scaled-down version of our own Solar System, with an inner potentially Earth-like planet and an outer Jupiter-like giant planet. The giant planet may well have played a similar dynamical role in the Gliese 832 system to that played by Jupiter in our Solar System. It will be interesting to know if any additional objects in the Gliese 832 system (e.g. planets and dust) follow this familiar Solar System configuration, but this architecture remains rare among the known exoplanet systems.

Contacts
Original Research: Robert A. Wittenmyer (rob@phys.unsw.edu.au), Mikko Tuomi (miptuom@utu.fi)
Habitable Exoplanets Catalog: Abel Méndez (abel.mendez@upr.edu)

Additional Resources
•Paper: GJ 832c: A super-earth in the habitable zone
•Habitable Exoplanets Catalog

Images

Figure 1. Artistic representation of the potentially habitable exoplanet Gliese 832 c as compared with Earth. Gliese 832 c is represented here as a temperate world covered in clouds. The relative size of the planet in the figure assumes a rocky composition but could be larger for a ice/gas composition. Credit: PHL @ UPR Arecibo.

Figure 2. Orbital analysis of Gliese 832 c, a potentially habitable world around the nearby red-dwarf star Gliese 832. Gliese 832 c orbits near the inner edge of the conservative habitable zone. Its average equilibrium temperature (253 K) is similar to Earth (255 K) but with large shifts (up to 25K) due to its high eccentricity (assuming a similar 0.3 albedo). Credit: PHL @ UPR Arecibo.

Figure 3. The Habitable Exoplanets Catalog now has 23 objects of interest including Gliese 832 c, the closest to Earth of the top three most Earth-like worlds in the catalog. Credit: PHL @ UPR Arecibo.

Figure 4. Stellar map with the position of all the stars with potentially habitable exoplanets including now Gliese 832 (lower left). Credit: PHL @ UPR Arecibo, Jim Cornmell.

Figure 5. Artistic representation of the potentially habitable Super-Earth Gliese 832 c with an actual photo of its parent star (center) taken on June 25, 2014 from Aguadilla, Puerto Rico by Efrain Morales Rivera of the Astronomical Society of the Caribbean. Original annotated image available here. Credit: Efraín Morales Rivera, Astronomical Society of the Caribbean, PHL @ UPR Arecibo.

Notice they aren't sure about the density of this planet, it could be a rocky super Earth, or a mini-Neptune, or even possibly a water world of the same mass. If it is a Water World, much like my drowned Moon example in another post, http://www.newmars.com/forums/viewtopic.php?id=7088
then perhaps it could be made suitable for humans. A rocky super-Earth would have too high gravity, mini-Neptune gas giant maybe. It is possible that a gas giant could have lower gravity than Earth.

This article contains information on what we know about this system:
http://en.wikipedia.org/wiki/Gliese_832
seems the b planet has 64% of Jupiter's mass, so it is like a mini version of our Solar System, it is 16 light years away, so it might be visited by humans in the next few centuries. I'm willing to bet that their is probably an asteroid belt inside the orbit of the b planet for similar reason there is one inside of Jupiter's orbit, these asteroids would likely be icy comet like bodies, except closer together than our Kuiper belt or oort cloud, so within this system likely is the resources needed to terraforming, the gas giant receives the equivalent radiation as an object orbiting our Sun at 80 au.

So if Gliese 832 c is a water world, would you want to live under a red sun? I'm not sure a water world would be tidally locked with a red dwarf, since water is a fluid that stretches with tidal forces without much friction, the ocean would bulge out toward the star without anyone on the surface noticing. The other thing is would Earth plants grow under this light? I think Gliese, while a red dwarf also has enough light in the other parts of its spectrum from green leaves to absorb. Gliese C orbit is shaped much like Mars, it is elliptical, it has a 36 day orbit, we could call it a month as it is similar to the orbit period of our Moon. A human settlement of Gliese 832 C would probably count ten orbits of Gliese C as their "year".

Last edited by Tom Kalbfus (2014-06-30 07:05:26)

Void · 2014-06-30 10:17:16

It also could be like Venus, or like Venus with a Hydrogen additive floating at the top of the Atmosphere, or if it does not have a sufficient magentic field, it's atmosphere could have been stripped away, since Red Dwafs tend to do that to their planet in the habitible zone (It is thought).

I see that the orbit is eliptical. To me that means it could be resonating with another planet. If if is the gas giant already mentioned, then their may be no other planets. If another planet is inside the habitible zone, then that third planet would be unfavored for terraforming.

However if their is a planet of reasonable size outside of the habitible zone, but between the gas giant and the super earth found, then perhaps if it is of reasonable size, it might have potential.

Resonation (Tidal heating) could make it more attractive. If it has retained a thicker atmosphere than 1 bar, (but not too thick), it might be suitable for liquid water, or at least possible to warm up.

But I guess there is some chance the super Earth identified might be "Habitible" so I will add this link which speaks of super Earths and continents.

http://www.space.com/26330-super-earth- … nents.html

I wonder what the gravity would be like on that world if it does have solid ground?

Last edited by Void (2014-06-30 10:24:58)

Tom Kalbfus · 2014-06-30 11:35:54

Void wrote:

It also could be like Venus, or like Venus with a Hydrogen additive floating at the top of the Atmosphere, or if it does not have a sufficient magentic field, it's atmosphere could have been stripped away, since Red Dwafs tend to do that to their planet in the habitible zone (It is thought).
I see that the orbit is eliptical. To me that means it could be resonating with another planet. If if is the gas giant already mentioned, then their may be no other planets. If another planet is inside the habitible zone, then that third planet would be unfavored for terraforming.
However if their is a planet of reasonable size outside of the habitible zone, but between the gas giant and the super earth found, then perhaps if it is of reasonable size, it might have potential.
Resonation (Tidal heating) could make it more attractive. If it has retained a thicker atmosphere than 1 bar, (but not too thick), it might be suitable for liquid water, or at least possible to warm up.
But I guess there is some chance the super Earth identified might be "Habitible" so I will add this link which speaks of super Earths and continents.
http://www.space.com/26330-super-earth- … nents.html
I wonder what the gravity would be like on that world if it does have solid ground?

It has 5.4 Earth masses. Take the cube root, and we have a diameter of 1.75 Earths, so if its a solid terrestrial, we're talking about a surface gravity of about 1.75 times that of Earth. I'm kind of hoping that it might turn out to be a gas dwarf or a water giant 30,000 km in diameter, it would then have a gravity of 0.95 that of Earth, so I'm kind of hoping for a water world or sub-gas giant about 30,000 km in diameter humans can either float on the surface of its global ocean or high in the atmosphere where the temperature is more amenable to human life. I think if its a super Venus, at least the upper atmosphere is likely to be wetter, as a larger world is less likely to throw of hydrogen from disassociated water molecules, which then recombine to form water again. It would probably be a wet Venus with water clouds in the upper atmosphere, there is little that can be done with a high gravity though, a terrestrial of this mass would probably have a surface gravity of around 2 g due to gravitational compression.

Last edited by Tom Kalbfus (2014-06-30 11:37:35)

Void · 2014-06-30 12:48:00

Low odds also but more favorable might be to find that Gliese 832 b (Gas Giant) had a moon system that was a Hybrid of Jupiter and Saturn.

A moon Like Titan with a nitrogen based atmosphere, and tidal heating from a partner moon. Perhaps shielding for the moons from Red Dwarf flares with the magentic field of the gas giant. But that's poor odds.

As for 832 c, I think 1.7 gees is quite a lot. Life could be there, but transplanting humans there would mean that to adapt they could have to have quite a lot of humanoid. Maybe short legs, and ape like mobility, or also amphibious behaviors, letting waters boyancy compensate for the large gravity.

Humanoid.

Last edited by Void (2014-06-30 12:50:50)

Tom Kalbfus · 2014-07-01 06:26:17

Void wrote:

Low odds also but more favorable might be to find that Gliese 832 b (Gas Giant) had a moon system that was a Hybrid of Jupiter and Saturn.
A moon Like Titan with a nitrogen based atmosphere, and tidal heating from a partner moon. Perhaps shielding for the moons from Red Dwarf flares with the magentic field of the gas giant. But that's poor odds.
As for 832 c, I think 1.7 gees is quite a lot. Life could be there, but transplanting humans there would mean that to adapt they could have to have quite a lot of humanoid. Maybe short legs, and ape like mobility, or also amphibious behaviors, letting waters boyancy compensate for the large gravity.
Humanoid.

Or we could be like the Martians in War of the Worlds we walk around in exoskeletons, most likely we would require breathing apparatus if there is a thriving ecosystem already there, so we would be the "Invading Martians" to them.

karov · 2014-07-01 06:48:24

We mustn't forget that ALL adaptations will be quickly reversible.

Void · 2014-07-01 08:03:11

Ok, I see your points. Low tech would be to have a swimming pool, and be able to do a lot of your work with voice commands to computers. Also a wheel chair to get around the house a lot of the time. Then as suggested machines to reduce the load on your body when you did serious walking.

Also if you were already a cyborg, perhaps you would just change out your legs to suit the task. But you would need some pretty good surface to orbit lifting method to get off the planet.

Tom Kalbfus · 2014-07-01 10:00:30

Wheelchairs would be thoroughly obsolete by the time we got to the stars, it is a 19th century invention after all.

JoshNH4H · 2014-07-01 11:16:53

Why should wheelchairs be obsolete if they still work? Given the time and the reason to, I'm sure I could come up with literally thousands of technologies that are at least three hundred years old and still in common use today.

Terraformer · 2014-07-01 15:06:49

Eh, they'll go the way of knives. Thousands of years old, why would we be using them today?

Though, I don't see much point using a wheelchair when an exoskeleton is available...

Tom Kalbfus · 2014-07-01 15:53:02

JoshNH4H wrote:

Why should wheelchairs be obsolete if they still work? Given the time and the reason to, I'm sure I could come up with literally thousands of technologies that are at least three hundred years old and still in common use today.

Let me think. For one the planet might not be perfectly flat with solid ground that wheels are capable of rolling over. Legs are superior to wheels in traversing uneven terrain and doing stuff like climbing cliffs and such, and I think by the time we have starships we should have robots with fully articulated legs and arms that operate through force feedback. So why would anyone want to be confined to a chair if he could walk? One of the things I have to be critical in Asimov's foundation novels is that Hari Seldon, over 11,000 years in the future is confined to a wheelchair. Use your imagination, would you choose a wheel chair if you could walk around in an exoskeleton? I wouldn't.

Last edited by Tom Kalbfus (2014-07-01 15:53:50)

Void · 2014-07-01 20:14:27

Well, I can't just leave Josh surrounded by arrow flinging barbarians. He has been quite polite which must be painful

Are you saying the wheel has no value? I have had many jobs. Among them I was a miner. Drippy dirty. Play with electronics and electrical devices there and understand natures will. I have also worked for a more diverse entity. Even so, murphy's law applies.

I recently carried a heavy load down a staircase, tripped and did a good wack to my head. "Explative Deleted" happens. If I was in a 1.7 gee gravity field, likely very dead.

Respect nature. Yes, wheel chairs down stairs, not so good. Devices that help crippled people, good!

Unless you choose to alter the human body plan, it's structure and create an alien, you must obey the laws of gravity. Trust an exoskelton? Oh sure. We just buy this new crap, and it's tra-la-la Ha Ha!

Blood pressure. I'm lying down in my bed and getting up, or I am emerging from a swimming pool (Because my spinal disks are killing me). I stand up, and what the **** I faint in a 1.7 gee situation. Maybe I am not dead, or I don't have to go to a hospital for observation, but if so I am extremely lucky.

Why not a transformer wheel chair if you are so worried? Or maybe a regular wheel chair as a intermediary between lying down or being in the swimming pool. After my body has adjusted, then I can put on the exoskelliton. Otherwise just genetically engineer the people/creatures that are going to live on the "Super Earth".

Tom Kalbfus · 2014-07-01 21:06:41

You could have an exoskeleton who's pilot's compartment is filled with water, that way increased pressure on the lower body would compensate for the effects of higher gravity, The exoskeleton would then have to carry around the weight of the water around the pilot as well as the pilot himself, but we have plenty of material that is stronger that is stronger than muscle and harder than bone, a 1.7 g gravity field isn't an insurmountable challenge. No intelligent signals have been detected from this planet, so if their is a thriving ecosystem similar in complexity to Earth's under a red sun, then explorers will want something more useful that a wheelchair to walk through this environment and study all the alien life. The planet may resemble Earth before humans, that means their will be no roads or sidewalks, their may be forests their may be something like grass, their will undoubtable be swamps, sandy deserts and oceans to explore, and a wheelchair just isn't the best thing for exploring those places.

karov · 2014-07-02 05:52:43

this

31TG0kshxxL._SY300_.jpg

made of something like this

http://www.sciencemag.org/content/343/6173/868

(with powersource)

will be enough to conquer and thrive into much more then 1.7 gees environment.

it won't be a exosceleton precisely, but rather octopus-like external kinetically self-supporting musculature.

this covers the options of living there whole lives without 1. genetic modifications and/or 2. cyborgization or 3. "technological metempsychosis" ( body to body "soul" uploads).

All: 1, 2, 3 are reversible and temporary, not more "supramundane" or speciating then using other exosomatic tools - like garments, glasses, etc.

Tom Kalbfus · 2014-07-02 05:56:12

You forgot to put a 'S' on the chest, could use a cape too!
This suggests a name we could call this planet, one that is easier to remember, after all it has a red sun. Also its on the inner edge of the habitable zone, this probably makes it more likely that we could breathe its atmosphere, because the Earth too is at the inner edge of its habitable zone, greenhouse gases like carbon-dioxide would be minimized so there is just enough for plant life, not something like 30% carbon-dioxide which would support plant life but which would be fatal for humans.

Last edited by Tom Kalbfus (2014-07-02 06:04:33)

karov · 2014-07-03 08:38:23

http://www.gdnordley.com/_files/QSG.rtf

Quantization of surface gravities with factor of 2.55.

It seems that what holds here ( with dozens to hundreds , soon - to thousands and counting SolSys examples ), must be in force universally.

THEN, super-earths will tend to cluster into 1gee (+/-25%) surface gravity, and the higher gees - 2.6 ( Jupiter like) or 6.3 (brown dwarves like) would apply only for rocky heavier class super-earths and gas-giant mass range mega-earths ...

1 gee, 0.4 gees, 0.15 gees surface gravity worlds by the force of the (eventually most probable) Universal Mass function would be literally millions of times more numerous then the 2.55 times or 2x2.55 times surface gravity worlds.

All above 1 gee "attractor" class would comprise of planemos and fusors which suit better to serve as underbodies for supramundane habitats then to be directly inhabited on natural surface.

karov · 2014-07-03 12:34:11

Tom Kalbfus wrote:

You forgot to put a 'S' on the chest, could use a cape too!
This suggests a name we could call this planet, one that is easier to remember, after all it has a red sun. Also its on the inner edge of the habitable zone, this probably makes it more likely that we could breathe its atmosphere, because the Earth too is at the inner edge of its habitable zone, greenhouse gases like carbon-dioxide would be minimized so there is just enough for plant life, not something like 30% carbon-dioxide which would support plant life but which would be fatal for humans.

Ha-ha. Krypton. Superman.

SpaceNut · 2020-11-02 21:37:42

Not planet x but still not from the area... Mars-sized rogue planet found drifting through the Milky Way

Mars_B4_Moon · 2023-03-07 06:37:21

Different to rogue planet or free-floating planet FFP

Marauding Moons Spell Disaster for Some Planets. In solar systems beyond our own, some moons might eventually collide with their host planets, new simulations suggest.

https://eos.org/articles/marauding-moon … me-planets

Escapes Gravity but comes back later to collide?

Calliban · 2023-03-07 07:37:17

SpaceNut wrote:

Not planet x but still not from the area... Mars-sized rogue planet found drifting through the Milky Way

This is interesting. A rogue planet could be the ultimate slow boat to the stars. On a different thread, Void and I discussed the idea of interstellar world ships. The idea is to find a rogue world that is passing through the edge of our solar system and heading towards the vicinity of a star system you want to colonise. You send a relatively small group of humans to the rogue world, who establish a base there. Over the course of millenia, their numbers grow. They build cities and they gradually terraform the body. By the time they reach the destination, hundreds of thousands of years later, what had started as just a few thousand people, would be a society of billions, ready to colonise the entire new solar system. Journey times exceed the existance of the homosapiens to date. But the ship they are travelling on is a whole world. So they can afford to wait for however long it takes. Cities and civilisations could rise and fall on this world, as it slowly completes its journey.

Last edited by Calliban (2023-03-07 07:43:18)

Void · 2023-03-07 10:16:47

I believe that Mars sized is considered to be the smallest size for a Steppenwolf Planet.

https://www.wired.com/2011/02/steppenwolf-planet/

At its extreme, such a planet might have so much atmosphere of Hydrogen and Helium, that the pressure would be like the bottom of an ocean. In that case open water seas could be possible.

But what we should really want would be enough Hydrogen and Helium to allow Argon and Nitrogen to be vapor. And then also ice-covered seas.

Not sure if that can be. Alternately if the Argon and Nitrogen were still frozen, then a thick ice layer might cover liquid seas of water.

I am guessing that on such a world, 1/3 to 5 bar might be convenient. If there is too much Hydrogen and Helium, they would be easy to eject from the planet with some heat.

On such a world, you could have various types of shelters. But you almost certainly need fusion power. The planets gravity may continually suck in more Deuterium and Helium3, so virtually infinite energy.

Done

Last edited by Void (2023-03-07 10:24:58)

Calliban · 2023-03-07 18:34:59

Fusion would definitely be needed. I wonder if it would be possible to build an orbiting fusion reactor around the planet that would function as an artificial star? A Mars sized planet with Earth insolution levels would need some 5E16 watts of power. Scale economies suggest that the cost of an industrial plant declines with the 0.82 exponent of scale.
https://evcvaluation.com/the-cost-to-ca … e-factors/

If a 3GWth (1GWe) fusion reactor costs $1 billion dollars, then a reactor 15 million times as powerful should cost 766,000x as much, or $766 trillion. For a planet with a population of 10 billion, that adds up to one time bill of $76,600 per capita. If a reactor can be made to last a century, then its cost would be $766 per capita per year. That is likely to be a small fraction of GDP per capita for a space faring civilisation. It is feasible I think, provided that the scaling law holds for such a huge reactor.

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