Posts by HDE 226868
You want a cold disk. Mercury is an example of a volatile, which, for our purposes, means that it exists as a solid only at very low temperatures. One thesis (Funk (2015)) classifies it as "modera...
Short answer You have the two equations you need on the linked page under the heading "Stage two": $$r_i=\sqrt{\frac{L_{\text{star}}}{1.1}},\quad r_o=\sqrt{\frac{L_{\text{star}}}{0.53}}$$ where $r...
Let's assume that the Moon is roughly a black body. Therefore, its luminosity can be approximated by the Stefan-Boltzmann law: $$L=4\pi\sigma R^2T^4$$ As you've said, $T=1100^\circ\text{ C}=1373\te...
On Earth, escape velocity is about 11 km/s, or 11,000 m/s. Assuming the opponent weighs around 70 kg (maybe more), that's a kinetic energy of at least $$\text{KE}=\frac{1}{2}mv^2=\frac{1}{2}\cdot70...
I wrote an answer on Physics Stack Exchange that discussed this a bit. I'll present a shorter and more focused version here. There are two main processes by which a planet can lose atmosphere: Jea...
A couple hundred years. In 2013, the Inter-Agency Space Debris Coordination Committee (IASDCC) published a report detailing comparisons of several independent models (one each from ASI, ESA, ISRO,...
Fire the engines closer to the Sun for maximum efficiency. This is due to the Oberth effect. Assume the spacecraft undergoes a burn when it is farther away from the Sun. The expelled propellant wi...
Let's think about this in terms of peak emission. Wien's displacement law tells us that the peak emission wavelength of a black body, $\lambda_{\text{max}}$, is inversely proportional to its temper...
I was rereading The Restaurant at the End of the Universe, the sequel to The Hitchhiker's Guide to the Galaxy, and I came across an interesting passage: Flare riding is one of the most exotic a...
That's no planet! Let's say that the radius is $18R_{\oplus}$, where $R_{\oplus}$ is Earth's radius. The volume will then be $$\frac{4}{3}\pi(18R_{\oplus})^3\bar{\rho}=5832\left(\frac{4}{3}\pi R_{...
So . . . modeling the space near two close black holes is actually a really, really tough task. Numerical relativity is extremely challenging; a good example is the intense computations it took to ...
Consider a short-period comet (specifically, Comet Encke). Pros: Very short-period comets can have orbital periods of only a few years, with approaches relatively close to Earth ($\sim0.1\text{ ...
I can give you a Newtonian analysis of the situation, which may or may not be correct. If you want a Newtonian universe, then great. If you want a general relativistic one, you'll need something mo...
The best way to study water waves of many sizes is to use Airy wave theory (see also here), a mathematical model using several simplifications that nonetheless produces reasonable results. The line...
Let's look at the two extremes: $\Delta T=15^{\circ}\text{F}$ and $\Delta T=40^{\circ}\text{F}$. In the first case, I'll say $T_{\text{min}}=50^{\circ}\text{F}$ ($283.2\text{ K}$) and $T_{\text{max...
Have you ever heard of the Einstein-de Haas effect? Take a large piece of iron, cylindrically shaped. Now, put it in an external magnetic field. The bar should become magnetized. Given that magnet...
Although astronomers have considered this phenomenon in the past, the data indicates that this isn't how stars are born. That said, yes, your premise works. Here's how you make a star, in a nutshe...
As I'm sure you know, four more exoplanets were recently discovered around TRAPPIST-1 (Gillon et al. (2017)), bringing the total to seven "” all, amazingly, presumably rocky and near the star's hab...
I'm considering a story where an exploration is devised to explore a binary system containing a black hole; the choice is Cygnus X-1, with its companion supergiant star HDE 226868. It would likely ...
Asimov's laws of robotics are not technical laws; they're societal laws, imposed by humans to ensure that robots don't destroy mankind. You can make a robot that breaks any of them, still using or...
This has indeed been investigated. I found a thesis by Daniel Jontof-Hutter (2012) that did a stability analysis of particles in rings orbiting, among other bodies, Saturn. One important quantity h...
How far and how well will sound travel through the sea? First, we need to figure out exactly what the sea is made out of. You've indicated that it's sulfur, but what kind of sulfur? Lopes & Wi...
I decided to start answering this question by building a galaxy (well, a model of a galaxy, but it sounds cooler the first way). A lot of research has already been done in this area, specifically, ...
I recently finished reading the Kim Stanley Robinson novel 2312 - set, of course, in the year 2312. Part of the background to the political negotiations and ongoing terraforming in the outer Solar ...
The change in pressure below the ocean is approximately $$\frac{dp}{dz}=\frac{1\text{ atm}}{10\text{ m}}$$ where $z$ is measured from the surface of the water downwards. We also have to add in the ...
