# Dark energy in a planet?

Is it possible that a tiny amount of dark energy(much smaller than even the iron core of earth) could lower the gravity on a planet without breaking the planet apart? I mean, dark energy is basically anti-gravity. If our universe did not have much dark energy, the gravity of dark matter would overcome the anti-gravity of dark energy and our universe would go through a Big Crunch and possibly after some time, another Big Bang.

If so than could this allow earth-like planets with larger radii and more mass than earth, possibly even mega-earths(rocky planets above 10 earth masses) to have a reasonable amount of gravity for human colonization while still having a density comparable to that of earth?

I mean, with super-earths and to a higher extent, mega-earths, the only way you could have a similar density to that of earth with a larger mass and radius is for gravity to be higher. If gravity gets too high, the heart would work itself to exhaustion and our bones would more likely break, even with perfect balance. Broken bones can lead to arterial bleeds and untreated arterial bleeds are most often fatal because of the high pressure in the arteries. And if gravity was similar to earth gravity, it would most likely be a gas planet a lot like Saturn.

So basically without dark energy, for a massive planet, there are 2 possibilities.

Either you have a similar density but with much higher gravity like that of Jupiter: Or you have a similar gravity but with much lower density like Saturn:

Could dark energy solve this problem if it was in the core of the planet? Could it make it so that it has a density comparable to earth(so it is rocky) without the Jovian gravity and instead with a similar gravity to that of earth despite its higher mass and radius?

• No-one has any idea what Dark Energy and Dark Matter is or how it works. Dark Matter/Energy are — thus far — placeholder names for something which can account that the universe is not behaving according to classical Newtonian physics. But what it is, how it behaves and what the practical usages of it is, is entirely unknown. So your question is either unanswerable ("We cannot say") or you can simply use your Author's Prerogative and simply say "When we found out what it is, it turned out it can be used as such". – MichaelK Apr 11 '17 at 13:42
• @MichaelK but dark matter is an explanation to more gravity than expected, not less. Thus, this question can probably be answered with well explained "probably not". – Mołot Apr 11 '17 at 15:10
• @Mołot Except the question asks about Dark Energy, not Dark Matter. – ApproachingDarknessFish Apr 11 '17 at 17:25
• – HDE 226868 Mar 16 at 18:39

The dark energy is not very well understood, and is currently actively researched, with many competing hypothesises.

But all of them states that dark energy does not clump and form structures. It fills up space quite evenly.

So it's is impossible to have a bunch of dark energy in a planet.

• I think saying "it is impossible to have a bunch of dark energy on a planet" is stating the case much to strongly, when we have absolutely no idea what dark energy is. – Werrf Apr 11 '17 at 19:16
• @Werrf ''The final component, dark energy, is an intrinsic property of space, and so has a constant energy density regardless of the volume under consideration (ρ ∝ a0).'' (From Wikipedia) I warned about the hypotetical status and limited understanding of the dark energy in the first sentence, but it is safe to say that what is nowadays defined as dark energy can not be concentrated or collected. – b.Lorenz Apr 11 '17 at 19:22

Now, am not a space expert, but why not try (even if it is a little far fetched) having the dark energy in the planet, whilst it is not there? Let me explain: Have another dimension, zone, or similar holding the dark energy PHYSICALLY, but the attributes in that zone/dimension leak out, so the dark energy's anti-gravity powers go into the planet's (physical) space. And the thing that keeps the energy there is that the planet's gravity well also goes into the dark energy zone.

Hope this helps (and makes sense)!

-The First VUer

The simple answer is a no. We've gotten some pretty good constraints from the Planck satellite; their final results indicated a dark energy density of $$\rho\approx6\times10^{-30}\text{ g cm}^{-3}$$. Within a planet of about twice the radius of Earth, you'd find a total of 51 milligrams of dark energy - clearly not enough to influence the surface gravity.

That said, this is an average - a mean density throughout the observable universe. We can certainly ask whether there are dark energy variations on small scales. While the cosmological constant model requires dark energy to be constant in space and time, other models like quintessence allow it to vary. There's been work done on placing upper limits on these variations and therefore constraining the viable dark energy models. Battye et al. 2015 concluded that these variations should take place on scale no smaller than $$\sim 30h^{-1}\text{ Mpc}$$, where $$h$$ is the Hubble constant in units of $$\text{km s}^{-1}\text{ Mpc}^{-1}$$. According to the Planck results, $$h\approx0.68$$, so we'd see variations on scales of $$\sim44\text{ Mpc}$$. That's about the size of the Local Supercluster!

Therefore, there appear to be no variations of dark energy density on planetary scales. We can assume that $$\rho$$ is essentially constant in our pocket of the universe, and if your planet is in our galaxy - or in our home supercluster - it must contain only insignificant amounts of dark energy. Besides, even on those cosmological scales, I would be extraordinarily surprised if the dark energy density was within several orders of magnitude of the density of baryonic matter within a galaxy or a planet.