Shulou(Shulou.com)11/24 Report--

Last time we introduced planets as fluffy as marshmallows and the least dense exoplanets known so far. Its density of less than 0.1g per cubic centimeter makes it a well-deserved "gaseous planet".

We have already seen low-density planets. How high can high-density planets be?

Because our theme in this series is exoplanets, the remnants of stars such as white dwarfs and neutron stars are ignored. After all, these celestial bodies are not planets. As stars, their original mass is much larger than that of the planets, and the density after collapse is ridiculously high, which is an order of magnitude less than that of the planets.

Neutron star map source Pixabay usually says that the density of planets is how many grams per cubic centimeter, but the density of white dwarfs is how many kilograms or even tons per cubic centimeter, and the density of neutron stars reaches hundreds of millions of tons per cubic centimeter. Among the exoplanets discovered so far, Kepler-131c is the densest, with a density of only 78g/cm ³, which is nothing compared to the dense star debris.

Kepler-131c (imaginary) Kepler-131c is an exoplanet with a mass of 8.25 times the Earth discovered by the Kepler telescope about 750 light-years away. 8 times the mass of the earth, indicating that it belongs to the super earth. But as a super earth, although it has a large mass, it is only 60% of the size of the earth, so it should have a very high density.

Although the mass and radius of Kepler-131c cannot be compared with those of dense stars such as white dwarfs and neutron stars, the density of 78g / cm ³has been greatly exaggerated for a planet.

As mentioned before, the Earth, as the densest planet in the solar system, has an average density of about 5.5g/cm ³. Even in the core, the density is estimated to be more than ten grams per cubic centimeter.

Pexels should know that the density of gold is only 19.32g / cm ³, so even if the planet is a big golden pimple, its density is only 1max 4 of Kepler-131c.

Will the planet be made up of denser elements?

But even if you look through the periodic table, except for man-made elements, osmium (Os) is the densest element that can be found naturally, and its density is only 22.59g/cm ³.

Generally speaking, the denser the elements are, the rarer they are. So osmium is one of the rarest elements in the earth's crust, with a content of only 5/100000000000. Even in the universe, osmium accounts for an estimated 60/100000000000, so osmium can be said to be one of the rarest elements in the universe. But even if a planet is made entirely of osmium, its density is only 78g / cm ³, which shows what kind of existence Kepler-131c is.

Is it possible for artificial elements to reach this density?

First of all, the artificial production of superheavy elements usually requires the help of a particle collider to force two nuclei together with extremely high energy. For example, the densest element metal 𬭶 (Hs), which is obtained by crashing iron nuclei into lead targets at high speed, can reach the density of 41g/cm ³, almost twice that of osmium.

But this element is usually radioactive, very unstable and has a very short half-life, usually only a few milliseconds. Even a relatively stable isotope has a half-life of more than ten seconds. In fact, many similar artificial elements can only produce a few atoms at present, and they decay immediately, so it is almost impossible to get a stable piece of 𬭶 material.

If you look at it this way, is it possible that Kepler-131c is a planet made entirely of this radioactive element? Can only say: yes, but really not many.

If the problem of radioactivity is not considered first, if its density is really so high, what kind of experience will it be on such a planet?

First of all, for a planet with a similar radius but such a high density, the gravity above it should be much greater than that of Earth. If we ignore the effects such as rotation and simply add the gravity acceleration formula, we can see that the gravity acceleration of such a planet is about 11.7 times that of the Earth.

G = GM/ r ^ 2

8.25 / 0.84 ^ 2 ≈ 11.7g

What is the concept of gravitational acceleration of nearly 12 grams?

In a high g environment, the blood of the human body will be pressed to one side, for a longer time, not only will the body tissue lack oxygen, but also have the risk of capillary rupture. The average person may be in a coma for a little longer in an environment of 3 g, and even a trained fighter pilot is at risk of losing consciousness if he lasts more than 8 g for more than ten seconds.

But when you get to this planet, you will have to withstand a gravitational acceleration of 12 g for a long time. This is equivalent to a person with an original weight of 80 kilograms suddenly having to bear nearly a ton of weight.

In addition to gravity, which is difficult for humans to bear, the temperature on Kepler-131c is also very bad. Its parent star (Kepler-131) is a G-type main sequence star, almost the same size and mass as our sun. Kepler-131c is only about 0.17 astronomical units (AU) from the star, about half the distance from Mercury to the sun. So on this planet, as long as it is in direct sunlight, it must be hundreds of degrees Celsius. But if it lacks an atmosphere like Mercury, its back should be very "cool" and minus one or two hundred degrees Celsius should not be a problem.

In fact, there is another planet, Kepler-131b, tested inside the orbit of Kepler-131c.

However, the density of this planet is not so outrageous, only about 6g per cubic centimeter, which looks not much different from that of Earth. However, as a super earth with 16 times the mass of the earth, its density is not low. Normally, planets with more than 10 times the mass of Earth are usually gaseous planets like Neptune, rather than high-density rocky planets.

Kepler-131b (imaginary picture) but do these planets really have such a high density? Especially for things like Kepler-131c, if the density is really that high, what would it be if it wasn't made up of radioactive elements? Is it possible that part of its core has become as electronic degenerate as a white dwarf? But with its quality, there is no reason at all.

In fact, the estimation of the characteristics of exoplanets usually has a large error, especially when the observed data such as Kepler-131c are not very sufficient. Although it is estimated to have 8.25 Earth masses, this data also has an error of ±5.9 Earth masses. In terms of density, although it is 78g/cm ³, the error is also ±55g.

But think about it, even if we really calculate 55g, its density is still as high as 23g / cm ³, which is still the same level as metal osmium. Considering the non-uniformity of density, the density of the core is bound to be higher, so it is still difficult to explain what the planet is made of.

But then again, after all, the universe is so large that even bizarre things can be considered reasonable as long as they do not violate the laws of nature.

This article comes from the official account of Wechat: Linvo says ID:linvo001, author: Linvo

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