Hot answers tagged

23

I feel it's a cheap answer but heavy Jupiters can get much denser than Earth because planets with Jupiter's mass stop adding size as they add more mass. A planet with Jupiter's size and 10-12 times Jupiter's mass would be over twice Earth's density. As far as Earth-like planets, there's a cool property of terrestrial planets, more mass means more tightly ...


21

There is very little mixing in the core of the Sun, where the stratification is fixed by radiative (rather than convective) heat transfer. The heavier helium does "fill the core", but takes about 12 billion years to do so, during which time, the concentration of helium gradually increases. During its main sequence lifetime, most of the energy generation ...


19

After H burning has finished, the he mass of the He core gradually increases, as does its density and temperature. Low-mass stars have denser cores when they reach a temperature at which He is ignited. The density is high enough that the electrons in the core are degenerate. In such conditions the heat from the nuclear reactions goes almost exclusively into ...


17

Jupiter does not have a "surface" and nor is there anything but an arbitrary division between interplanetary space and where its atmosphere begins. The crushing pressure is its atmospheric pressure. The deeper into the atmosphere you go, the greater the column of gas that lies above you. It is the weight of this column of gas that is responsible for the ...


15

Hydrodynamic models of the Sun allow one method of estimating its internal properties. To do this, the Mass, radius, surface temperature, and total luminosity (radiative energy emitted)/s of the Sun must be known (determined observationally). Making several assumptions, e.g., that the Sun behaves as a fluid and that local thermodynamic equilibrium applies, ...


14

Comet Shoemaker–Levy 9 crashed into Jupiter a few years back. As well as these molecules, emission from heavy atoms such as iron, magnesium and silicon was detected, with abundances consistent with what would be found in a cometary nucleus. Those heavy elements are consistent with the comet being at least being partially composed of rock. So Jupiter is ...


13

It doesn't matter if the body is made of gas, rocks, liquid or plasma, the four states of matter all have mass. So, as we know, mass create a gravitational field, and the more mass the stronger the gravity - and Jupiter has 317x Earth mass.


13

http://spaceplace.nasa.gov/review/dr-marc-solar-system/gas-giants.html We think of a gas as something very . . . well, airy. After all, air is the gas we all know and love. We breathe it and fly planes right through it with no trouble. So it makes sense to think that a gas planet must be like a big, airy cloud floating out in space. Saturn in true color. ...


9

I concur with everyone else here (of course) that the gravity at the "surface" of Jupiter is entirely determined by the mass contained within that surface. The composition makes no difference. However I differ with some on the answer to the headline title question. We simply do not know whether Jupiter has a rocky core. A popular theory for the formation ...


9

No, nothing on Europa could possibly be photosynthesizing as we know it. Jupiter doesn't emit light, and what it reflects from the sun is not enough, plus there's no significant amount of carbon dioxide there. However, the first life on Earth was not plants, it was chemotrophs. These bacteria gained their energy from the heat of hydrothermal vents, and if ...


9

From the Wikipedia page on Chthonian planet: Transit-timing variation measurements indicate for example that Kepler-52b, Kepler-52c and Kepler-57b have maximum-masses between 30 and 100 times the mass of Earth (although the actual masses could be much lower); with radii about 2 Earth radii, they might have densities larger than that of an iron planet of the ...


8

The most-widely accepted hypothesis at the moment is that Mercury was struck by a large impactor that removed a significant fraction of its mantle (I believe this theory was originally proposed by Cameron & Benz in 1987, and the qualitative theory hasn't changed very much). For planets that are close to their parent stars (such as Mercury), the collision ...


8

I've learned that the Earth's core is hot due to decay of radioactive elements. This is unproven, non-standard geophysics. There are several arguments against this. One is that all of the long-lived radioactive isotopes are isotopes of uranium (two isotopes, 235U and 238U), thorium (232Th), and potassium (40K). The problem: Uranium, thorium, and potassium ...


8

TL;DR: 1000 K (according to differentiated model of Pluto) According to the density value of Pluto, astronomers proposed three types of structural models: Undifferentiated or "cold" model: rocks mixed with water-ice Differentiated or "hot" model: rocky core and water-ice mantle Rocky core only (temperature high enough to boil off water-...


7

It may have a (silicate) core, but it's very small. There also is the possibility of an internal liquid water "ocean". Currently the most probable composition is that of rock and ice, with the density of rock steadily increasing as one digs deeper (This is in stark contrast with planets like Earth, where there are discontinuities in the density between ...


7

Actually, the core has two parts. The outer core is liquid, while the inner core is solid. As explained in the Wikipedia article about Earth's magnetic field: The Earth's magnetic field is mostly caused by electric currents in the liquid outer core, which is composed of highly conductive molten iron.


7

More massive stars indeed have higher pressures, but what's key is that they also have higher temperatures. After leaving the main sequence, they reach core temperatures of a few times $\sim10^8$ Kelvin while their densities remain at something like $\sim10^4$ g cm$^{-3}$ - which, you can check, is within the nondegenerate regime. Therefore, helium fusion ...


6

According to Newton's Law of Universal Gravitation, you simply need interacting masses in order to generate a gravitational force between them. Gases have mass and they therefore can contribute to gravity. So even if Jupiter is entirely gaseous, it is so incredibly massive besides (so much gas!), that it has a much stronger gravitational pull than Earth. ...


6

It's liquid. As detailed here, To figure out whether Mercury's core was liquid or solid, a team of scientists led by Jean-Luc Margot at Cornell University measured small twists in the planet's rotation. They used a new technique that involved bouncing a radio signal sent from a ground telescope in California off the planet and then catching it again in West ...


6

The composition can be determined by taking spectra. Additionally, the mass can be determined through dynamics. If you combine these two, under the assumption that the star is in a state of hydrostatic equilibrium (which means that the outward thermal pressure of the star due to fusion of hydrogen into helium is in balance with the inward tug of gravity), ...


6

I think that there isn't a strict answer to this question. However, I believe the answer is that there's a difference between the core of a hydrogen-burning star and the core of a protostar or star-forming, gas cloud. For a hydrogen-burning star, the core, as you say, is the region of the star where fusion is taking place. This is surrounded by the ...


6

Massive stars do not undergo helium flash because they have core temperatures high enough to prevent the helium core from becoming electron-degenerate. Check here for some more information. Therefore, the star can burn helium in a smooth transition, instead of undergoing helium flash. In more details, the massive star's core heats up past the helium burning ...


5

The short answer is no. Take Mercury for example in this comparison of Earth Mercury core. Mercury is thought to have a liquid outer core and solid inner core. The gas giants like Jupiter are thought to have a relatively tiny rocky core but the convective motion in the metallic hydrogen is what gives them the strong magnetic fields. See also: Is Mercury&#...


5

Mars core may or may not be solid, I'm of the opinion that it's not solid. See recent NASA press release here and a much earlier study here It has been known since 2003 that at least part of Mars’ interior is molten, based on how easily the Sun’s gravity distorts the planet’s shape, but no one knew whether it is completely liquid, or whether ...


5

You're mostly missing an important point to do with the geothermal gradient. The geothermal gradient used in that question, and applied to a $55\:\mathrm{km}$ depth is not consistent all the way through Mar's interior. They cite the Earth's geothermal gradient (see image below) and from that page you can see how the temperature profile changes with depth. ...


5

There are such evidence in the case of Mars. Observations from Mars Global Surveyor show evidences of crustal magnetization. In particular, this magnetization has extensive, east-west trending linear features in Terra Cimmeria and Terra Sirenum. These are probably reminiscent of magnetic features associated with a reversing dipole. There are no such ...


5

Here are the results of some arbitrary cutoffs for the "core" based on $2010$ solar models calculated by Guenther et al: Contributing $99\%$ of the total luminosity:$R = 25.5\%$, $M = 9.88\times10^{29}\,\mathrm{kg}$ ($49.7\%$). Nuclear reaction rate falls below $1\%$ of central rate:$R= 27.2\%$, $M = 1.07\times10^{30}\,\mathrm{kg}$ ($54.0\%$). Overall, $\...


5

usrLTK's answer provides a lot of good details and in particular explains why Mercury wouldn't have much of an atmosphere. Let me complicate the picture a little by pointed out that some recent research indicates that magnetic fields may not be the guaranteed, automatic atmosphere-protection devices that conventional wisdom suggests. In particular, Gunell ...


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