52
Gravity isn't going to let that happen
I'm not the resident orbital mechanics specialist so I don't have specific figures in front of me but as I understand it, there's no way that two planets, both of Earth mass, are going to collide slowly. The reason for that is that they're going to be attracted to each other by gravity. Even if they could collide ...
39
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
...
34
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 ...
26
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 of fluid simulations (many smoothed-particle hydrodynamics) have been performed, for varying angles of attack and initial relative velocities (see e.g. Canup 2012, ...
23
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 ...
19
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). ...
19
why invade at all? Most structures of a civilisation are probably going to be on a surface. It is, after all, more difficult to build underground than on a surface. That means that most items of value can be simply blasted from above.
But you might not want to blast them from orbit because these items might also be of value to you.
You might want to avoid ...
16
"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 ...
15
This scenario results in the sterilization of both planets even if they don't collide in any situation that you could reasonably call a "near miss."
No matter how slowly the planets collide, tidal effects will cause massive heating and disruption of their crusts. These effects come into play long before the planets even touch, and by the time they do touch, ...
15
I think your best bet is speed, and lots of it.
If you look at pictures of Jupiter and Saturn (and, to a lesser extent, Uranus and Neptune), you would notice belts and zones across the surface. On Jupiter, these are especially prominent because the belts (the dark bands, which fall) and the zones (the light bands, which rise) are composed of different ...
15
Not Survivable.
I am going to ignore gravity's demand of 2 planet masses becoming 1 sphere - Tim B II covered that. And I am ignoring the energy requirements and the resulting lash-back of getting 2 planets close enough together to do 'peanut' that Ryan_L covered.
Even considering that, 'peanut' would not be survivable due to earth is rotating around its ...
15
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 ...
15
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 ...
13
These gasses you seek will naturally mix, if given the chance. Their unforced steady-state behavior is always a homogeneous mixing. This means that you need something which forces them.
- Wikipedia
Quite the stark contrast between the air around Almaty, Kazakhstan and the mountains above is it not? This is caused by an inversion layer. A warm layer of ...
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 ...
11
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 ...
9
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 ...
9
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 ...
7
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 ...
7
Tim B II's answer is really good, but I have another, different reason it can't happen. Let's say you do have some way to slow the planets down so they don't collide at escape velocity. Let's also say your planets are mostly made of some fictional material that actually is strong enough to stay a contact binary planet, a "Peanut planet" as Tim put it. So ...
7
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 ...
7
A lot 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 ...
6
Your planet is traversing an emission nebula. Here is the Orion nebula.
By ESO/Igor Chekalin - http://www.eso.org/public/images/eso1103a/, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=27880539
Nebulae are interstellar clouds of gas. Some are bright and give off light; these are emission nebula. Orion is a big one; 22 light years across ...
6
Please check out this link in case you find it interesting. It's about how the moon formed from a similar impact.
In the link above, it is assumed that there was an explosive collision (moderate at celestial standards) between Earth and Theia at an oblique angle. Despite such a collision, it is thought that it took surprisingly little time to form the moon, ...
6
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.
...
6
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 ...
6
If you wish for more UV light to reach the poles, you can deplete the ozone layer over them. This is exactly what happened on our world - ozone depleting chemicals reached the upper layer of the atmosphere and due to wind currents they concentrated over pole over the decades, specially the south pole.
The hole over the south pole is shown as the blue-ish ...
6
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 out the internal structure of the planet, including the central density and pressure, as well as the density and pressure profiles as functions of radius. The best ...
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'...
5
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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