Posts by HDE 226868
Use low temperatures. For a given system, we can tell if degeneracy pressure is important by comparing the Fermi energy $E_F$ to the thermal energy $kT$. if $E_F\gg kT$, the gas is fully degenerat...
I agree that a possible solution would be to add in a source of high-energy ambient neutrons. Cosmic rays are a possible neutron source, at least at high enough altitudes and assuming the uranium d...
About 100 trillion years from now. The answer to your question depends on several things: When the final low-mass star forms How long it takes that star to exit the main sequence and become a wh...
You need methane, ammonia and atmospheric temperatures of $∼$150 K. The color of a giant planet depends on the type of clouds dominating its upper atmosphere. These in turn depend on the tempera...
Some simple molecules can exist in stars - but not the right ones. Contrary to popular belief, many different types of molecules can exist in stellar atmospheres, especially cool stars like red d...
The simplest way to achieve this is to have the Moon be on a perfectly circular orbit that lasts twelve months and lies in Earth's orbital plane; this would mean that at each new moon, we would get...
Many stars, including the Sun, periodically display starspots, cooler areas of the surface associated with higher local concentrations of the stellar magnetic field. They can sometimes be a couple ...
It's unlikely, on the whole, for a ring system to maintain a high eccentricity on significant timescales. Dissipative collisions tend to circularize the orbits of individual particles, even if the ...
It's an interesting scenario. The major problem is that ring systems tend to be quite low-mass in comparison to their parent bodies. For example, measurements by Cassini indicate that in the case o...
Handwaving away some of the problems here, one basic one appears insurmountable: Decoherence. This is a process that involves the destruction of the superposition of a quantum system. The loss of q...
We can treat a planet as a magnetic dipole. In this case, the strength of the field scales as an inverse cube law (rather than the more familiar inverse square law), with some angular dependence. A...
No, there's no such element that would justify this sort of attempt. We have data on the composition of the Sun's photosphere, one of its outermost layers. By mass, the solar photosphere is 98.3% ...
This star would not fuse gold. Fusion reactions producing elements beyond zinc-60 are not energetically favorable; they are endothermic, and so consume energy. Several elements heavier than iron a...
I can see four key problems with the system as you've described it: Giant planets. The major thing that concerns me about the system is the presence of at least two gas giants. It's long been tho...
Let's assume that this student wants to begin by understanding the twin pillars of modern physics: quantum mechanics and general relativity. There are several major tools in the toolkit of anyone s...
The technique to do this is similar to that used in constructing stellar models. You know some of the properties of your object - in this case, it look like the mass and radius. You want to figure ...
While thinking about Starfish Prime's answer to the question Algae using UV light from auroras for photosynthesis, I considered the possibility of an alternate Earth which has a normal, Earth-like ...
It might be possible. We've known for around a century (since at least 1933) that ultraviolet light can inhibit photosynthesis and possibly damage photosynthetic mechanisms inside an organism. Phy...
We're talking hours to days. A good deal of work has been done on protoplanet-protoplanet collisions, mainly focused on testing the Giant Impact Hypothesis for the formation of the Moon. A number ...
Stars that become Cepheid variables stay in this phase of their lives for only a short period of time, and after they leave the main sequence. While their properties vary (in particular, Cepheids a...
This scenario is quite problematic for two main reasons: evaporation and peak wavelength. The black hole's lifetime is too short We can make a rough estimate of the properties of the Hawking radi...
As the sphere is self-gravitating, it must be in hydrostatic equilibrium; that is, there must be a non-zero pressure gradient to balance the force of gravity. For a fluid of uniform density, you ca...
I don't have a solution; what I do have is a possible path to a numerical solution. For the sake of simplicity and sanity, I will consider the special case of a non-rotating, chargeless, spherical...
Carbon planets We typically expect a moon's composition to reflect the part of the protoplanetary disk it came from. If it's orbiting a planet close to the star, we'd expect it to be composed larg...
The five primary layers of the atmosphere are, with increasing, altitude, the troposphere, stratosphere, mesosphere, thermosphere, and exosphere. The corresponding boundaries are the tropopause, st...
