# Tag Info

1

Zeng et al. (2015) "Mass-Radius Relation for Rocky Planets based on PREM" might be useful for you. They give the following equation: $$\frac{R}{R_\oplus} = \left(1.07 - 0.21 \cdot \mathrm{CMF}\right) \cdot \left(\frac{M}{M_\oplus}\right)^{1/3.7}$$ Where $R$ and $M$ are the planetary radius and mass respectively, $R_\oplus$ and $M_\oplus$ are the radius ...

3

Alot of people assume that the magnetosphere of a planet is the main factor determining whether it can retain an atmosphere. Long ago it was calculated that the escape velocity (not the surface gravity, the escape velocity) of a object was vital to how long it could retain an atmosphere. As I remember, if a planet, moon, or other astronomical body has an ...

0

Simpler Approach (no 𝜋 for you) Assume the density of silica is 1, and the density of iron is 3: The second planet's density will be 1*50% + 3*50% = 2.0 The first planet's density will be 1*70% + 3*30% = 1.6 The ratio of their densities will be 2.0 / 1.6 = 1.25 The ratio of their volumes will be 1 / 1.25 = .8 The ratio of their radii will be the cube root ...

2

Short version : the second planet (same total mass) will have a radius that is larger than the first unless the second planet's core is larger (in mass) than the first. This makes perfect sense if you think about it. The smaller core has to have much more of the lighter exterior material to make up the total mass. The larger core needs less to make the ...

2

Interstellar methanol clouds! I read up on methanol, I was surprised to learn that methanol is one of the most common molecules in interstellar space! https://web.archive.org/web/20110720152236/http://www.jodrellbank.manchester.ac.uk/news/2006/cloud/ Upgraded MERLIN spies cloud of alcohol spanning 288 billion miles Astronomers based at Jodrell Bank ...

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It depends on what molecules are most stable/lowest energy in given environment. I am not a chemist, so can't say for sure, but methanol probably isn't, see Wikipedia: It does not persist in either aerobic (oxygen-present) or anaerobic (oxygen-absent) environments. The half-life for methanol in groundwater is just one to seven days, while many common ...

5

I noticed you had a question about whether a carbon planet was possible earlier also. I don't remember the answer given, but what you're looking for is effectively a hydrocarbon cycle. For more real-world research on this matter, look up the moon Titan in our solar system - it's the only moon we know of with an atmosphere, and it has rivers and seas of ...

1

Short version: It'll be heavier than an Earth-like world the same size but we can't actually work out how heavy. Long version: Carbon Planets aren't really made of carbon, they just have enough carbon, as a molar fraction, that it can't all react with the available oxygen and hydrogen so you can get pure carbon that can't be oxidised into CO, CO2 or the ...

1

It was always your second choice Your scientists already had scans of Coruscant (somehow). These scans show it as developing as a paradise world - in fact, due to light-lag, it probably already is. By comparison, Nu Terra is awful. Humanity can just about eke out a living, but it's hard going. On the other hand, the time and effort required to reach ...

1

It was an unexpected move. Someone stored the crystals abit too close to the main power lines on their ship. When they turned their ship on up for a sub-orbital hop around the planet the crystal was powered up and activated. It then sent then ship though hyperspace to their destination.

2

Could it just be that Nu Terra is an awful place to live, but at least it's better than Earth? i.e. Earth has been taken over by the Plague, has an imminent gamma-ray-burst / solar flare, is about to be demolished to make way for an interstellar motorway, or for whatever reason they've left for the only other known planet that could possibly support life, ...

1

If it is Star Wars universe, than the answer is obvious. The Force. The Dark Side of It. Nu Terra has a huge lot of those "force crystals" and is evercorrupted with Dark and slowly corrupts everyone who lives there. It can even have evil "force specter"'s civilisation hidden on it! A huge plot engine!

2

Relics of an ancient civilization. Think of the Reapers & Protheans from the Mass Effect universe. They land, all seems well. Ruins are eventually found, once activated it displays a message of inpending doom. The galaxy cleaning squad is coming to town really soon. Leaders keep it under wraps, scientist panic and go public. Civilization panics. One ...

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Very alien aliens The planet looked unoccupied during the first scouting missions, but there was a previous owner and he attacked them after while or send an ultimatum. Maybe its an AI or hivemind which has merged itself with the biosphere. Or some ancient sleepers like the Necrons or Cthulhu, whose vault were hard to spot in the beginning. Maybe those ...

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Economics There is no valuable resources on Nu Terra, but plenty on Coruscant. Once the crystals were discovered and enabled the humans to travel to and from Coruscant, the first to go there and return returned with unimaginable riches in gemstones, minerals, precious metals or other things that are highly valuable (or useful). The local environment is ...

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Pollen. This is produced by plants seasonally of-course, usually once a year for a short period, sometimes only during the heat of the day when a specific temperature is hit. The effects of this particular pollen are profound, hallucinations, visions and reckless behaviour in the vast percentage of the population. The effect is indiscreet sexual ...

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Disease It's been wiping out lifeforms for millions of years. It can be frozen in glaciers and permafrost. It could wipe out humanity and then die out leaving no trace except for more frozen sources preserving it. Currently humanity is finding new viruses still viable in the melting permafrost due to global warming. A disease that is fast spreading and ...

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Your planet will either be incredibly cold, or have no heavy elements. Krypton is a fairly light noble gas, it boils at 119K, and it's fairly rare. Naturally, such an element would never form the core of a planet. Even for planets where krypton occurs as a solid, heavier, denser materials will sink and form the core of the planet, especially when the ...

1

Impactite--desert glass, is actually not that rare or difficult to find, and they are quite transparent as well. For your desert, because the atmosphere were significantly denser, there could by significant past bolide impact above that desert, of which explode d in an airburst that is much larger than that of anything on earth. At a very high impact yield,...

-1

I think natural marble balls could become possible by long term accumulation of sand in very desert areas over many hundreds of years. The strong winds of deserts could make the sand grams accumulate at different rates making marble balls to form and have different shapes and sizes.

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If temperature in the mantle of your planet is very high, one can have geysers erupting with quartz lava turned into vapor. It would then condensate in form of spherical droplets.

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The glass balls are fossilized honeydew. The volcanoes in the desert were originally islands. The aphids that lived there were huge due to insular gigantism. Now since they are insects, they don't fossilise as well. When tectonic activity cause the island to connect to the mainland, and then dried the ocean to one side of it, all that was left was the ...

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Bring in a desert-dwelling animal or insect. There can be two ways to do this. One is have an animal/insect attracted to the glass itself. Depending on what it's made of, there could be minerals in it the animal needs, but the rest of the glass is useless or even poison. So the animal breaks off the glass and swallows it, leeching out the appropriate ...

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Your desert glass pebbles are volcanic glass. In the US they are called Apache Tears. source These are unpolished, as found in the desert. When polished they are a very beautiful deep black and suitable for use in jewelry. Some of the round ones in this image ones look pretty close to that without polishing. https://en.wikipedia.org/wiki/Apache_tears ...

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If you don't insist they be glass, then sure. Cave pearls are little spheres of calcium salts that form due to successive periods of wet followed by drying. Each dry period deposits another layer. They can be quite regular shaped. The shape arises due to the regularity of growth, and due to the fact a sphere is the most mass per surface area you can get. ...

4

People can survive in hostile environments. In Australia, plenty of things can kill or poison you, including koalas and some plants. In Africa, plenty of western explorers died from yellow fever, but they pushed on. With proper discipline and scientific methods, it is a simple matter of identifying the hazards, finding ways to protect against them, and then ...

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There are 3 types of natural glass: obsidian (volcanic glass), impactite (meteor glass), and fulgurite (lightning glass). Naturally round impactite is virtually unheard of. Impactite tends to have strong striations in the direction of impact that gives it more of a cleaved shape. It is also very rare for it to be transparent. Technically, a round ...

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The following steps, inspired by the process used for manufacturing lead bullets in the past, can determine the formation of spheroidal glassy agglomerates: take a sandy surface let a meteor hit that surface the impact will melt and splash material (sand) around during its ballistic trajectory, the molten material will solidify in free fall the solid shape ...

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Sorry no, at least not as a purely, earthbound, geological process, the environment doesn't allow for the amount of multi-directional rolling you would need to round glass into a ball. Glass yes, probably in the form of fulgerites like the Mauritanian example shown below: Smooth wind sculpted surfaces yes, the below is a purely wind polished piece of ...

0

Some nice answers already. If you don't mind doing some math, look up effective temperature of a planet. You can design the star size, the planet's albedo and calculate the effective temperature. Earth's effective temperature isn't too far off from -20 degrees C, in fact it's -21 C. https://en.wikipedia.org/wiki/Effective_temperature#...

0

Global Cooling Reduce the amount of carbon dioxide in the atmosphere. The planet goes into a "snowball earth" global cooling episode where the whole planet is covered in a miles thick layer of ice. Given the current level of hysteria over global warming it would not be difficult to convince humanity to participate in this. "Hey our carbon sequestration ...

2

If you are talking about low light problems in the sense of people not being able to see well, you should be fine. The human eye can adapt to massive changes in light level. For example, even though Pluto receives about 1/1000 of the light as does the Earth, if you were standing on Pluto at noon you could read a book by sunlight. To get a -20c ...

3

Global Warming Pump extra CO2 into the atmosphere, and seed some ideas into anti-capitalist intellectuals that man is causing all the global warming. No matter what we do, the temperature keeps on warming and blaming each other for the problem. Sooner than later, food production will start to fail, wars for resources will happen, nukes go off and ...

5

Here's a new and really insidious one: Approach them with big smile and offer them a "happy-machine". It hooks up directly to their brains and stimulates all the pleasure centers and whatnot. Along the way, cure mental diseases with the same tech. Instant happiness for everyone who wants it, for as long as they want it. Purely voluntarily, of course. And no ...

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Destroying all life is easy - slowly crank up the sun's temperature until you bake the planet. Destroying complex life, while allowing bacteria to survive, is also doable. Destroying intelligent life, while leaving other life alone? That's hard. Really hard. Adapting to new circumstances is what intelligence excels at - it's pretty much the whole point of ...

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Ways to destroy sentient life on a planet: Upset the ecosystem. Introduce animals into places they shouldn't be (the poison frogs or cats of Australia), or destroy ones that should be there (see just about any extinction and the results). Move some plants into the wrong ecosystem (think the devouring capabilities of kudzu outside it's natural environment). ...

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Infiltrate the planet's early societies and teach them about money. Steer the societies into loving it. Change their genes to make them hoarders and cheaters. As soon as those societies reach the industrial age they will start destroying their own ecossystems in search of profit. Just chillax and watch for a handful centuries. They'll live their last ...

2

The answers you've received are great! I'd like to piggy-back off of them - specifically L.Dutch's: We can add to this answer by incorporating volcanic activity. A decent supervolcano will start a nuclear winter. An overactive, planet-wide 'ring of fire' with many small volcanoes could potentially prevent a forever-cold feedback loop. I could have mentioned ...

5

Our planet is just a few thousand years out of an ice age. To get a habitable planet covered in ice (or mostly covered in ice): Make the sun slightly dimmer (less radiated heat) Make the planet slightly further from the sun (less intercepted heat) Make the planet have slightly less green house gas (less retained heat) Be at an extreme cold point in a planet'...

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Just remove greenhouse gases from the atmosphere: CO2, H2O, CH4, for example. This would lower the amount of infrared radiation trapped by atmosphere, lowering as a consequence the temperature. Keep in mind that since the climate is a complex system with several feed-back and feed-forward, a snowball planet would reinforce its conditions: more water ...

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The arrangement you wish does not seem feasible. If by "dim" star you mean a star that is dimmer than our sun, you are probably thinking of a red dwarf. Such stars are thought to be far from habitable, because: The habitable zone around them requires a tidal lock; They are usually flare stars, which means the star facing side of planets in the habitable is ...

11

Better than that; there's a game that will do it. Steam has a game called Universe Sandbox where you can line up different planets, stars, et al with different masses and trajectories. I've never tried it but as I understand it the game is capable of simulating the orbits of planets, stars and the like in a way that you can graphically see the results. In ...

1

Other answers have discussed the methods used by ancient, medieval, and modern pre-spaceflight astronomers to discover the distances, sizes, and masses of various astronomical bodies, from which the surface gravity and escape velocity of those bodies could be calculated once Newton published his laws of physics. Here is another type of answer. Any large ...

0

The planet's inhabitants are going to need, at minimum, to understand Newton's law of gravitation. Once they have that, there are many viable ways to calculate the mass of the moon. Here's one involving pendulums: First, measure the distance to the moon using lunar parallax. Then, set up identical pendulums at 2 points on the planet's surface and record the ...

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"Can early astronomers determine the gravity of their planet's “moon” without ever going there?" Of course they can. Our Earth-bound astronomers did, and we know how they did it. The distance from the Earth to the Moon and the size of the Moon were known since the Antiquity. The Moon is close enough that the parallax method works well enough with the naked ...

0

Distance and size to our own moon were calculated with a surprising accuracy by the old greeks. That should make it fairly simple to calculate gravity relative to your own planet assuming the same density. It should be noted that the moon is tidally locked to us because it has a bulge on one side, that caused it to slow it's rotation (by interaction with ...

4

1. Tides the moon would not move in the sky and there would be no tides Wrong. The sun provides tides too (albeit smaller ones than our moon), so the sea still rises and falls on a regular cycle. You'll even get variations in tide height depending on the relative angles of the sun and your "moon", though not to the same extent as spring tides on earth. ...

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The way I would do it is have your moon orbiting a gas giant which itself is in a P-type orbit in a binary star system. Your gas giant orbits a small, dim star which is a binary companion with a much larger, much brighter star. The primary energy source for your moon is the more distant of the two. The shadow period would occur when the bright companion is ...

3

Our asteroid belt is so thin that we send spacecraft through it withiut fear of a collision. It won't overshadow anything. An orbital arrangement where a planet is eclipsed for a quarter of its orbit is very unlikely. I can think of two situations in which it can work: If your planet is orbiting a relatively dark body, such as a black hole or a pulsar, and ...

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This is a surprisingly difficult question to answer... related ones have been asked elsewhere, with few satisfactory answers. Turns out that simple questions like "what is the stellar density in such-and-such a region of space" doesn't often have a very good answer (multiple answers may exist, differing by at least an order of magnitude) let alone more ...

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