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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 ...


21

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 ...


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....


5

There is an observational bias and it is taken into account when you see inferences about planet frequency. The methods to find planets are inherently biased towards finding large, close-in planets. Both the transit and doppler-based methods suffer from this bias. The paper you reference takes into account this bias to arrive at the statistics you ...


5

According to Mashian & Loeb (2016) (also in ArXiv), one possibility is that planet formation may have occurred around carbon-enhanced metal poor (CEMP) stars in the early universe. The paper focuses on CEMP-no stars as the most metal-poor CEMP stars mostly fall into this category. CEMP-no stars are thought to form from material polluted by supernova ...


4

The Kepler-20 system has planets with masses in the following order, going outwards from the star: Kepler 20b: $\approx 10 M_\oplus$ Kepler 20e: $\approx M_\oplus$ Kepler 20c: $\approx 16 M_\oplus$ Kepler 20f: $\approx 1.5 M_\oplus$ Kepler 20g: $\approx 20 M_\oplus$ Kepler 20d: $< 20 M_\oplus$ If Wikipedia is to be believed, Kepler 20b may be a ...


4

> Do other stars have similar gaseous-to-rocky ratios among their planets? For any given stellar system, are there typically as many gaseous planets as there are rocky planets? With the current instruments and methods we have, we can only access certain population of exoplanets. Terrestrial-mass exoplanets are quite hard to find hence we have more ...


4

The currently-detected planets do not show a clear distinction between rocky and gaseous planets. While there seem to be somewhat two ensembles, the rocky planets of Earth-size and "super-earths" and the gaseous planets (Jupiter-size), there is a broad transition between them. The transition is roughly where we find Neptune and Uranus. Play around with ...


3

No one knows for sure, but the idea is plausible. There would not be enough radiation from a rogue planet to provide much help, but we know from the moons of Jupiter and Saturn that tidal heating can keep water liquid. There might have to be multiple moons for it to work. The outer moon keeps making sure the inner moon has an elliptical orbit, and as the ...


3

Our knowledge of planet formation processes comes from theoretical work and is supported by observations. I'm going to give it my take based on that. On the lower mass end of the planet distribution, starting from comets up to Super-Earths/Mini-Neptunes one needs a high number of rock-forming elements in order to build rocky worlds. Without high ...


1

It is a mistake to assume that the cores of the gas and ice giants are solid, just because they are thought to be "rocky". Temperatures deep inside these planets are very high - I remember reading a figure of 25,000 Kelvins for Jupiter. Pressures are very high too, and the way materials behave under these conditions is not well understood. So there could be ...


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