51

It's a matter of how "day" is defined. Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following: The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III) The radio emissions of the gas giants have well-defined ...


28

In an isothermal atmosphere, the exponential scale height of the atmosphere is $$ h \sim \frac{k_\mathrm B T}{\mu g},$$ where $g$ is the gravitational field, $\mu$ is the mean mass of a particle and $T$ is the temperature (in kelvin). i.e. The pressure/density of the atmosphere falls exponentially, with an e-folding height given by the above expression. I ...


22

There are two common definitions in use for the surface of gas planets: The 1-bar surface: As pressure increases, the deeper in we go into the gas planet, we will hit a pressure of 1 bar at some altitude. Gas at this altitudes will usually sit deep enough in the gravitational well and be of a near-uniform density and temperature, as to not be influenced by ...


19

No such planet has been announced as having been discovered. The paper only shows evidence for the 7 (really 6 because the 7th can't be officially confirmed with only 1 observation) terrestrial planets and does not make the case for any other planets. The paper doesn't indicate that more planets could exist, but does remark that there are large error bars on ...


14

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 ...


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.


12

There is no "orbital path" detected, that's why it is a "free-floating planet". There is no radial velocity mesured, but the informations given by its kinematic location show that it belongs to the beta Pictoris group, that is a stellar group. For more dirty details, have a look at the submitted paper on PSO J318.5-22: http://arxiv.org/abs/1310.0457 ...


12

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 ...


12

The answer is the Coriolis effect, on Earth this produces cells within which storms move, converging towards the cell boundaries as you can see below. Jupiter however spins much faster that the Earth which produces a stronger Coriolis effect and thus more cells. This is the reason why there are so many different coloured bands on Jupiter (see image below). ...


11

Jupiter won't evolve into a star, it is not big enough. A body would have to have about 80 times the mass of Jupiter for there to be significant fusion occurring in the core. The end of life of the Sun won't change the mass of Jupiter. Jupiter will continue to orbit the Sun as it evolves into a red giant. Although the solar wind will be much much more ...


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

Newton's shell theorem proves that inside a gas giant, any layers that are further than you from the centre have a zero gravitational effect on you. So if you are inside a gas giant (and by some magic not dead) the only gravity comes from the layers that are closer to the centre. So the gravitational pull is always down. If fact, the pressure increases as ...


9

Super-Earths and Mini-Neptunes are the "in-between" types of exoplanets you're looking for. A sweeping generalization would put most in the range of $\sim1$-$10M_{\oplus}$ (Earth masses), with some outliers a bit above that. They may have significant quantities of hydrogen and helium in their atmospheres, as well as water, in liquid or vapor form. The latter ...


9

First, it's a great question. Mostly the answer is straight forward, so I can answer it, but it's still a great question. and I'll add a similar, but slightly more detailed picture to the one you posted. Source You're right that there is a clear difference between Earth's surface where liquid water can exist, evaporate, make clouds, rain and repeat. ...


9

In the early stages of the formation of the solar system, planetesimals start condensing and everything rotates with angular momentum inherited from the collapsing cloud of gas and dust, so the planetesimals all have their orbit and spin axes closely aligned with that of the proto-Sun. And while a planetesimal continues to grow by attracting nearby material ...


8

There are a few major problems with calling something a small gas planet and of course depends on your definition of a planet. By currently accepted classification (that excludes Pluto), a planet has to be: massive enough to be rounded (i.e. held together) by its own mass, has to orbit a star, and has cleared its orbital neighborhood. All of these ...


8

Radius inflation seems to mainly occur in planets with irradiation in the range 105–106 W/m2, see Sestovic et al. (2018). In contrast, at 1 AU from the Sun, the irradiation is 1361 W/m2, which is well below the threshold at which the inflated gas giant radii are observed. It seems unlikely to me that there would be a significant increase in the radius of ...


7

Here is a plot I generated in 5 minutes at the site exoplanets.org To construct this I took planets discovered by the transit method and which had a $M \sin i$ measured using radial velocities. I divided the $M \sin i$ by the sine of the measured inclination angle (this is required to avoid using masses that have been estimated using an assumed mass-radius ...


7

There is no direct evidence of change of orbits of the gaseous planets of the Solar System. But one could wonder about the stability of the Solar System, and if such events could happen again. Theory: The Solar System is a chaotic system, as most of gravitational systems involving $N$ bodies. The KAM theorems (for Kolmogorov, Arnold and Moser, the three ...


7

Stars turn into Red Giants not because they're running out of fuel, but because they're accumulating material they can't use for fusion (yet) in the core. The star isn't so much dying of starvation as it is wallowing in its own muck. Red giants form when the fusion is no longer taking place in the centre of the star, but instead in a shell around the centre....


7

In most planet formation theories, the boundary is around 10 Earth masses - the build up of the core mass before that is relatively slow, but once it crosses that threshold, the planet gains mass quickly via attracting gas from the surrounding nebula via the core’s gravitational pull, a process called “runaway accretion.” As this summary shows, you can ...


6

This may help you KOI-314c is small even when compared to Uranus or Neptune. Also, look for "Mini-Neptune" on Wikipedia. So, it seems those "dwarf-giant" planets are possible. Although I do not have the required knowledge, I wonder if it is possible to exist a planet smaller than the earth that still could be considered a gas planet. For example, just ...


6

Short answer: 1) Yes and no; 2) Yes, there is a supercritical fluid, of hydrogen. Long answer: It's fairly hot deep down in Jupiter; estimates range from 10,000 K to 24,000 K. You would think that anything in the core would be liquefied, and you could be right. Many models predict that Jupiter's core is rocky, but others predict that it is liquid. Still ...


6

To answer this, we have to consider the definition of an atmosphere. A popular way of looking at it is to think of an atmosphere as a layer of gases surrounding a body. by that definition, we can say that gas giants are really just planets that are massive enough to accrete substantially large atmospheres (because deep down, they have a rocky core - although ...


6

"At high altitudes, Neptune's atmosphere is 80% hydrogen and 19% helium" (Wikipedia). No significant abundancy of free oxygen to react with. A source of oxygen could easily made burn on Neptune, like a source of hydrogen on Earth. Or take a sample of Neptun's atmosphere. It would easily burn in Earth's atmosphere. Hydrogen oxygen combustion is sufficiently ...


6

Pretty much by definition, no. In order for "object A" to orbit "object B", "object B" needs to be substantially more massive than "object A". In order for your red dwarf to orbit something, that "something" needs to be more massive than a red dwarf. With the current composition of the universe, that "something" will be mostly hydrogen, and once you reach ...


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. ...


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