Activity for HDE 226868
| Type | On... | Excerpt | Status | Date |
|---|---|---|---|---|
| Question | — |
Can a planet survive a supernova? The Sun has nowhere near enough mass to enter the branch of stellar evolution that would lead to a supernova, fortunately for us. However, there are planets that orbit stars that are destined to go supernova. These planets might not be habitable, because such massive stars live and die within short p... (more) |
— | over 9 years ago |
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Making the Marauder's Map: Can I make a map that changes? Those familiar with the Harry Potter series may be familiar with the Marauder's Map, a map that allows the holder to see where people are at any given time. It displays a person as a set of footprints with a label next to them. The footprints appear and then fade as a person walks along. For all int... (more) |
— | over 9 years ago |
| Answer | — |
A: How could bird people map the air? Maps I made a partial example map for the birds of a land called Tjerokya. It uses (crude) arrows to show the path of currents traveling across the land and sea. Indicating changes in three dimensions is harder, so I used colors to describe the changes. Redder colors mean rising currents, and bluer ... (more) |
— | over 9 years ago |
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A: What would an Antarctica without ice look like compared to other continents? A 3D map showing the topography of the area was created by NASA and the British Antarctic Survey: This is what the continent would look like if you instantly removed all the ice and snow. A map indicating elevation in color was created by the same team (from here) : Note that it's far from flat... (more) |
— | over 9 years ago |
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How can I indicate a third dimension on a map of outer space? I'm working on a map of several star systems (with the stars, planets, etc. not to scale with the map), and I'd like to show that they don't all lie in the same plane. Some orbits are perpendicular to the plane of the viewer, while others are flat, and still others are at odd angles. In short, I'd l... (more) |
— | over 9 years ago |
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Building Noah's Ark The current topic challenge is apocalypse, so I figured I might as well come up with a question about surviving one. A man named Noah somehow learns that there will be a large flood within one year, which will cover most of the world. He also learns that it is - for some reason - his task to load on... (more) |
— | over 9 years ago |
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A: A planet ringed by stars Jim2B beat me to the best answer, but there are more solutions. Analyzing a system like this is called the three-body problem, a case of the n-body problem. There are not many stable solutions to it, which kind of stinks for anyone wanting more exotic setups, like you. In most cases, it's best if tw... (more) |
— | over 9 years ago |
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Genetically preventing a rebellion on a generation ship In the year 21--, a crew of 100 sets out from Earth on the good ship Tenzing Norgay, bound for Epsilon Eridani. The journey is estimated to take . . . well, quite some time, given that it was calculated that the time spent to engineer a significantly faster propulsion system (compared to the technolo... (more) |
— | over 9 years ago |
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A: How could events triggered by a supernova accelerate the death of a main sequence star? They're fine. Here, I discussed the effects of a supernova on life on Earth. Note that a supernova would have to be within about ten parsecs (33 light-years) to have harmful effects on life on Earth. Furthermore, the effects would be indirect, destroying the ozone layer (partially or in full) rather... (more) |
— | over 9 years ago |
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A: What if two planets orbited each other and also a star? The tidal forces would be the main gravitational effects that would change. Tidal forces cause, among other things, tides, and are the result of another object's gravitational pull. The Moon is influential enough. Put the mass of Earth there and the tidal force will increase by a factor of $M{\oplus}... (more) |
— | over 9 years ago |
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A: Larger moon = Larger Tides = No oceanic ships? If you want a detailed analysis, simply solve Laplace's tidal equations. These are not easy to do. If you're curious, I can get you part of the way to what might be an answer. Also, I'm curious as to what the math will turn up. Achille Hui has a very helpful spoiler (regular ones don't work for $\La... (more) |
— | over 9 years ago |
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A: Can a planet hit by a meteor shatter into two pieces? Alternately, if not a meteor, an advanced interstellar weapon? I like TimB's answer discussing the Giant Impact Hypothesis. I see that in a comment on his answer, you wrote Thank you! I actually had this Moon origin theory in mind. But I'm actually wondering about an inhabited planet, in the immediate run. Is there any possibility of survivors, say, after th... (more) |
— | over 9 years ago |
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How can I explain a planet with perpetual rain? I was planning a short story that focuses on a rainy day in a city, and I realized that there's one interesting feature of it: Even though the weather seems bleak, and it affects the actions of those in the story, anyone reading it knows that the next day will be, in all probability, sunny, bringing ... (more) |
— | over 9 years ago |
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A: Space cataclysm that can slowly cook the Earth around Gamma-ray bursts Let's not give up on the gamma-ray burst (GRB) idea so quickly. Sure, most GRBs are quite short, but there are exceptions: ultra-long gamma-ray bursts. While normal GRBs last on the order of seconds - with some lasting for minutes - ultra-long GRBs can last for hours. Frostfyre cit... (more) |
— | over 9 years ago |
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A: What would happen if Earth's oxygen reached the Sun? Let's calculate the mass of this huge oxygen atmosphere, shall we? I can use a modified version of the barometric formula to calculate the density at any altitude $h$ above a reference point - in this case, at Earth's surface: $$\rho=\rho0 \exp \left[\frac{-g0M(h-h0)}{RT} \right]$$ where $0$ denotes... (more) |
— | over 9 years ago |
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A: What would the orbit of the Earth be like if we constantly sent our waste to the Sun? What Shihab Dider said. The Earth is monstrously massive compared to everything humans have ever built, and the Sun is monstrously massive compared to the Earth. How monstrously massive are we talking about here? The mass of the Sun is about 1.99 $\times$ 1030 kilograms. The mass of the Earth is abo... (more) |
— | over 9 years ago |
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A: What is the minimum planetary mass to hold an atmosphere over geologic time scales? First, kudos to you for realizing that planetary mass is not the only thing influencing how a planet (or even if!) a planet holds on to its atmosphere. Distance is also an important factor. Thanks for not putting it too close to the central star. I know that this is a terrestrial planet, so it wouldn... (more) |
— | over 9 years ago |
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How can I set a moon on fire? So, for reasons which may or may not pop up in a later question of mine, I need to light a small Moon-like moon on fire. Well, sort of. See, I need a small object capable of emitting a lot of light - i.e. with a high luminosity. That could either be a large ball of gas on fire, or it could be someth... (more) |
— | over 9 years ago |
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How could a dust cloud form around a middle-aged star? I bring you all to the planet Krikkit, stuck in a star system enshrouded by a large dust cloud which prevents the Krikkiters from seeing the rest of the galaxy - and, by extension, the universe. The planet is a solitary, Earth-like one, orbiting a solitary, Sun-like star. But the dust cloud wasn't a... (more) |
— | over 9 years ago |
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How large can a volcano be? A key part of the plot in a story I'm working on revolves around the main region being on top of volcano that is set to erupt. The trouble is that the region in question in my setting is roughly the size of Wyoming. It's on an Earth-like planet. Clearly, the volcano needs to be a supervolcano. Howev... (more) |
— | over 9 years ago |
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A: Celestial bodies and gravitational effects on the Earth A few scenarios could occur. A near miss If the object is from outside the Solar System, then its velocity may be greater than the Solar System's escape velocity, which could mean that its velocity is greater than Earth's escape velocity. In this case, a close encounter could perturb Earth's orbit,... (more) |
— | over 9 years ago |
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What are the advantages of four wings over two wings? On a certain planet, there is a large population of falcon-like birds. They dominate the avian ecosystem. However, a population of nearly-identical birds soon finds its way in. The only difference between the two species is that members of the new population have four wings instead of two. What adva... (more) |
— | over 9 years ago |
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A: Cosmic Background Radiation in the past Gawiser & Silk (2000) provide a nice overview of the CMB (possibly better than Wikipedia). The paper is a bit outdated - after all, they use a figure of 15 billion years as the age of the universe! - but the rest of the information conforms with recent measurements . . . sort of. They give the date o... (more) |
— | over 9 years ago |
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Asteroid flux or: How to make a planet perfect for mining One of the cool things about the Moon is that the far side has a thicker crust that the near side.1 One theory explaining this is that the Moon was hit by an object, possibly a moonlet created by the remains of Theia as per the Giant Impact Hypothesis (while the Moon was still forming). The object hi... (more) |
— | over 9 years ago |
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How can a Type II civilization influence accretion rates from a debris disk to a passing star? A young B-type star (with a mass of about 10 M${\odot}$) is surrounded by a debris disk extending from about 2 AU to 1000 AU away. The disk has a mass of about 300 Earth masses - enough to form quite a lot of planetesimals. There is also an outer cloud of icy, comet-like bodies extending from 750 AU ... (more) |
— | over 9 years ago |
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A: What gravitational impact would moving Jupiter to the inner solar system have on the outer? In Real Life Awesome question, because A) It's a cool idea and B) We know just what will happen. The principle here is planetary migration. This phenomenon is common in many planetary systems. During planetary migration, a planet interacts with either a protoplanetary disk or planeteimsals. There a... (more) |
— | over 9 years ago |
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A: How deep can underground tunnels be within the scope of science? Problems for humans The deepest tunnel-like structure created so far is the TauTona Mine in South Africa. The bottom of it is 2.4 miles below the surface. Temperatures there can reach 131°F, which has proven deadly many times in the past. The temperature can be lowered to more pleasant levels, but ... (more) |
— | over 9 years ago |
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A: Could air gas giants exist? There are two parts to this question: Could a massive planet amass large quantities of nitrogen and oxygen? Could these gases be the main ones the planet is composed of? Giant planets relatively close to the central star (but beyond the frost line) will accrete large quantities of hydrogen and he... (more) |
— | over 9 years ago |
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A: Are lithotrophic animals possible and if so how? I've been slacking lately on biology questions, so I'll try my luck on this one. Good news! These things aren't so far-fetched! Meet the giant tube worm (see also here). (Original image source: http://deepseacreatures.org) These things are, believe it or not, animals. Not plants. Not fungi. Ani... (more) |
— | over 9 years ago |
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A: Alternative atmosphere plantlife Yes, there's an alternative. Plants using chlorophyll must, to the best of my knowledge, take in CO2 and put out oxygen. So chlorophyll is a no-no. Fortunately, not all photoautotrophs use chlorophyll. A select few use a substance called bacteriochlorophyll (see also here). Here's its structure: ... (more) |
— | over 9 years ago |
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A: Could there be a planet bigger than Earth, but with less gravity? Bigger planets don't always have greater masses. Remember, mass and volume are related by $$M=\rho \frac{4}{3} \pi R^3$$ where $\rho$ is density. Make $\rho$ small enough and the gravity and be as weak as you like. So the answer to the title question is a firm "yes." I did some playing around with th... (more) |
— | almost 10 years ago |
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A: Physical laws for a matter-filled universe Let's build a universe. To describe this universe, we need a metric. I won't go into details about the precise definition - for more, see Wikipedia, as well as Physics and Mathematics. In this case, we need a metric of dimension (4 + 2) (i.e. four dimensions of space and two of time). This will be r... (more) |
— | almost 10 years ago |
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A: Making a planet habitable for humanoids: The planet Special cases Tectonically-locked Mostly Frozen Surface Water-free (Dune) Or, no/very-little free water. All Water (Europa) Currently, by question definition, this is non-habitable. (Original source for this image: http://i.livescience.com/images/i/000/049/907/i02/human-survival-limits-1208... (more) |
— | almost 10 years ago |
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A: Making a planet habitable for humanoids: The planet Atmosphere, surface temperature and other properties directly related to life Magnetosphere: Magnetospheres are thought to be driven by a dynamo process driven by internal circulation in the molten core of the planet, are are very useful in protecting the planet from DNA-damaging ionic particle... (more) |
— | almost 10 years ago |
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A: Likely orbital period of a moon around an earth-like planet The important thing here is how the moon formed. Earth's moon formed in a scenario explained by the Giant Impact Hypothesis: Earth, the inner planets and other small bodies coalesce in the Sun's protoplanetary disk. Over the years, they grow from their diminutive initial states to more planet-like... (more) |
— | almost 10 years ago |
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A: Multi-planar planetary rings How long does this process take? We don't know. As I discussed here1, Saturn's rings could have formed billions of years ago or only a few hundred million years ago. Wikipedia and NASA each explain the two different sides; the other links in my answer are also informative2. I like the 4-billion-... (more) |
— | almost 10 years ago |
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A: Can a planet with 2/3 Orbital eccentricity sustain life? The eccentricity of an orbit is defined as $$e=\frac{ra-rp}{ra+rp}$$ where $ra$ and $rp$ are the distances to the farthest and closest points of the planet's orbit from the star. If $e=2/3$, then $ra=5rp$, which is quite significant. It seems that the planet will not remain in the habitable zone for ... (more) |
— | almost 10 years ago |
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A: How would interplanetary transits take place with a "space compressing" system? Here's a starting point: the Interplanetary Transport Network (ITN): Artistically gratuitous representation. Not to be taken literally. The green swoops are odd and potentially unimportant. The ITN is a series of "pathways" throughout the solar system emanating from and disappearing into the Lagra... (more) |
— | almost 10 years ago |
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A: How far could life develop inside a black hole before it explodes? Original answer, preserved for posterity Here's the paper. First, there are some important assumptions that the author - Vyacheslav Dokuchaev - made. Specifically, there are two scenarios: The particles are charged and the black hole is not rotating. This is not helpful, because all the particle... (more) |
— | almost 10 years ago |
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A: What if Jupiter's rotational period was equal to that of the Earth? I have one major point to make: A good portion of Jupiter does not complete one rotation in 9.8 hours. Jupiter isn't like a giant ball of rock. It's called as "gas giant" for a reason, which is that it has a large, massive, turbulent atmosphere that's constantly moving and changing. This means that ... (more) |
— | almost 10 years ago |
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A: Is there a theoretical maximum size for rocky planets? Estimates vary, but I'll be cautious and say that a radius of roughly two Earth radii is most likely the upper limit for rocky planets. There are many studies, both theoretical and empirical, that have tried to attack the problem. I'll attempt to summarize the results of a few of them: Lammer et a... (more) |
— | almost 10 years ago |
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A: Making a planet habitable for humanoids: The planet Orbit, rotation, mass and other properties not directly related to life A planet is a rotating mass (larger than 500km in diameter) in orbit around the star of normal material becomes an oblate spheroid due to gravity (no cubes, or other shapes). The IAU also defines a planet as having cleared its n... (more) |
— | almost 10 years ago |
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Making a planet habitable for humanoids: The planet The question: What characteristics are necessary for a planet to be habitable for humans? What should the generic star and planet be like? The life forms are human, so they Need to have access to water (they can melt snow or ice in their mouths, given sufficient surplus metabolic energy). Breathe... (more) |
— | almost 10 years ago |
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A: Making a planet habitable for humanoids: The star Age: The time a star spends on the main sequence is roughly inversely proportional to the luminosity, as given by the formula $$T \approx \ 10^{10} \text{years} \cdot \left[ \frac{M}{M{\bigodot}} \right] \cdot \left[ \frac{L{\bigodot}}{L} \right] =10^{10} \text{ years} \times \left[\frac{M}{M{\odot... (more) |
— | almost 10 years ago |
| Question | — |
Making a planet habitable for humanoids: The star The question: What characteristics are necessary for a planet to be habitable for humans? What should the generic star and planet be like? The life forms are human, so they Need to have access to water (they can melt snow or ice in their mouths, given sufficient surplus metabolic energy). Breathe... (more) |
— | almost 10 years ago |
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A: Habitable zone around a Class O hypergiant Oh, good, a planet habitability question. I love these. What would be the habitable zone (capable of supporting liquid water) for a planet with an atmosphere and size similar to Earth, but several times more dense? I recently wrote an answer on Worldbuilding referencing an answer I wrote on Ear... (more) |
— | almost 10 years ago |
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A: How can my accidental time travelers determine the year using star/stars? The technique should work. I can't really say much besides that. There are other things they could do, too. They might not be easier than tracking the proper motion of a star, but they'll work: Use variable stars. Most variables stars have regular periods hat can (and have been, in many cases) det... (more) |
— | almost 10 years ago |
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A: What would a binary black hole look like from the surface of a planet orbiting that system These black holes are going to emit Hawking radiation. Not a lot, but a bit. The power emitted by a black hole with mass $M$ is $$P=\frac{\hbar c^6}{15360 \pi G^2M^2}$$ Each black hole will emit that amount of power, so - not accounting for the fact that they may eclipse each other (from the view of ... (more) |
— | almost 10 years ago |
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A: Life on a Venusian world? Here's some information about Venus: Surface gravity: $8.87 \text{ m/s}^2$ Surface temperature: $737 \text{ K}$ Surface pressure: $\approx$ $92 \text{ atm}$ So no liquid water on the surface. Wikipedia also mentions later on that you have to get 50,000 meters in the air before conditions become ... (more) |
— | almost 10 years ago |
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How could a civilization trigger star formation? I'm going for the ultimate in world building here: Creating a whole new star. I have a race that's about a Type II civilization (as per the Kardashev scale). The important thing here is that they're capable of building megastructures, such as a Death Star. They could build a Dyson Sphere or somethin... (more) |
— | almost 10 years ago |