[Geology] Planets aggregation ?

[grawl]

Hello,

I'm still developing a small 2D android app displaying a randomly formed Solar system.

My physics engine is now polished enough and I get satisfying random dynamically generated systems. Little objects aggregate with bigger ones to create proper planets, and the collisions impact the way these objects move.

So I'm starting the work on the second part of the project, also known as "Planet Details" !

Therefore I have some questions :

1. Imagine a planet would collide with another planet. What amount of matter from these 2 planets would be aggregating to form the resulting planet ? and what amount of mass would be ejected in deep space ? Is it even predictable ?

I need an approximation, but something like a wild guess would fit me too, to make my game more believable At the moment, 2/3 of the colliding object's mass is transferring to the planet. One third is vanishing in thin air.

2. I need english-spelled names for materials that can be found in space or on planets. I know a bit about geology, but in french, kinda problematic for an international audience

I'm planning to give the user the ability to review a planet's composition, based on the materials it aggregated from.

Something like a density chart for these materials would also be extremely useful for me. It will allow me to create a sliced view of the planet, and define it's external color more accurately.

3. In which conditions does an atmosphere develop? I believe it is dependent on the planet's size and composition. Maybe the distance from the Star too. Am I right ?

How do these parameters influence the probability ?

[edit]

After some thinking I've came to the conclusion that I don't absolutely need real-life material names. Any cool, fun, or plausible name can fit.

My project is aimed at showing how complex stable systems can form from something quite chaotic in the beginning. I don't need too much realism.

[/edit]

Cheers !

Edited June 3, 2013 by grawl
precisions

[magnemoe]

For the impact it will be mostly dependent on the hit angle, hit square on with earth sized bodies and you get very little, hit on the side with not to different speed and you might get lots of the impactor in orbit.

For light bodies most will end up in solar orbit.

[grawl]

OK.

Do you reckon an impact of a small object (less than "a fraction" of the mass?)will only create a thin layer made of the impactor material+a bit of the surface material on the surface of the planet ? And a bigger object (more than "a fraction" of the mass?) will totally remodelate the internal structure of the planet (and eventually create a moon)?

I chose to skip the part when debris go in orbit, then re-aggregate together, it's way easier on the calculations

[ginkaa]

1. It depends on many factors, like the composition (imagine meteoric iron impacting solid rock), angle of impact, speed of impact, mass of the objects, which not only affects inertia but also the strength of their gravitational fields. Overall, its a very difficult thing to simulate and its not just a matter of a fixed amount being ejected into space every single time.

2. If we look at Earth, the most common elements are iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%) (from Wikipedia). Also hydrogen and helium are the most abundant elements in the Universe.

3. For a planet to have an atmosphere it must have a magnetic field (otherwise it will be stripped away by stellar winds) and sufficient gravity (mass) to keep a hold of it. A magnetic field requires a rotating liquid iron core, which means the planet cannot be too close to the star otherwise it will be tidally locked and rotation will be too slow. Gas giants are a little different as their magnetic fields are generated by their liquid hydrogen cores.

[Cryocasm]

So, our given scenario is that a planet is being formed in an accretion disk containing many colliding bodies. Lets have look:

From a game mechanical point of view, you will have to define what metals the colliding bodies are made of (in percentages, or wholesale, whatever fits your needs).

The problem with colliding objects originates from angle of impact, mass and relative velocity (given M2 is always the approaching body):

relative velocity Vr = 5 m/s and angle of impact θ = 0° and both bodies M1 and M2 have 50 kg mass then

Only conservation of momentum will occur, as the angle 0° states the body to becoming from behind and gently pushing the other body. Think of it as billiards.

Vr = 500 m/s and θ = 180° maintaining M1 = M2 = 50 kg then

The bodies will smash into each other in a frontal collision, this results in M3 at a mass of ~ 66 kg and ejected mass M4 of ~33 kg (using your fractions, which are logical and approximate).

Vr = 1000 m/s and θ = 0° at M1 = 100 kg and M2 = 50 kg then

Once again conversation of momentum will occur, however, this time significant mass of M2 will be transferred to M1 (now 125 kg), which ejects mass M4 (~16 kg) creating mass M3 (formerly M1) at 109 kg and mass M5 (formerly M2) of barely 25 kg. M3 will be moving at around 500 m/s faster now.

Vr = 50 m/s and θ = 90° at M1 = M2 = 50 kg then

They are colliding at a right angle, meaning M3 will have a mass of about 33 kg, which is created by the collision of M1 and M2 and flying off at a 45° angle. M4 is the ejected mass consisting of the remaining 66 kg, which wasn't compacted into M3 or launched into its direction.

Vr = 1000 m/s and θ = 90° at M1 = 1000 kg and M2 = 100 kg then

They are colliding at a right angle, and M2 is completely consumed forming M3 (M4 is negligible this time), which is however flying off from its original trajectory by ~9° due to the impacting force.

Given you can extract this information from the simulation itself, you only need to do some math (I could help with it).

English Geology/Planetology:

A rocky planetoid consists of several layers, namely crust, mantle, and the core.

This can be differentiated into multiple different sub-layers:

Earth's core consists of the solid inner core and the molten outer core.

The Moon's core consists of only the solid cold core, not molten.

The crust is usually defined as the region on the surface of the planet, Earth's being around 75 km deep. This surface is the most exposed to the cosmos. The crust can be reshaping constantly: Earth's crust is recycled in a 4 billion year cycle due to tectonic movement, causing earthquakes and volcanic eruptions.

The mantle is the region between the crust and the core, and in the case of the Earth, the mantle is mostly solid and the place where tectonic plates are molten and born (being consumed by the mantle or pushed out of the mantle).

In contrast, the Moon's mantle is solid and cold.

Adding on to this, many rocky worlds with significant gravity and (usually) a magnetic field an posses a gaseous layer, the atmosphere. Earth is able to do this despite its proximity to the Sun (magnetic field and high gravity). Venus also has an atmosphere, despite it being closer to the Sun and having a lower gravity. Venus only manages to retain this atmosphere because it consists of 96% carbon dioxide, a gas too heavy for the solar wind to effectively sweep away into space. Mars, however, also has a mainly carbon dioxide atmosphere, but due to its low gravity (38% of Earth's), the solar wind doesn't have to work hard to strip away Mars' atmosphere.

On the contrary, gaseous worlds (like Jupiter), accreted more hydrogen and helium than heavier elements, resulting in them having huge atmospheres when compared to their solid cores. Jupiter consists mainly of hydrogen 75% and helium 24%. While this results in a much lower density than Earth's, the gravity is still higher due to the mass. Gaseous worlds still feature a mantle and core, however, usually the mantle and the core are the same thing, meaning they have a solid core simply due to the atmospheric pressure.

Atmospheric development can be triggered by a variety of conditions. Earth and Venus contrast very well here:

Earth used to have an atmosphere of mainly carbon dioxide, however, once life evolved due to thunderstorms and hydrocarbons (http://en.wikipedia.org/wiki/Miller%E2%80%93Urey_experiment), it used its surroundings to benefit itself:

As we know, plants absorb CO2 and H2O (carbon dioxide and water) as well as sunlight in order to produce molecular oxygen. This is one fundamental building block for any planet to sustain animals, which do not produce O2 anymore but consume O2, producing CO2, creating a closed carbon cycle.

Before plants however, chemoautotrophs ruled the planet, which don't require sunlight in order to produce O2 as a by-product. These organisms (now rare and located at deep sea vents, highly toxic to most organisms, but not these microbes) are the root for all life on Earth, being not only the first, but also those to set the stage for later organisms. Through billions of years time, the Earths atmosphere went from being highly toxic (containing CO2 and H2S) to containing more and more oxygen, which eventually made it safe to populate the continents with life (as water is a very good radiation shield, and before 3.5 billion years ago, the Earth had no magnetosphere and hence the continents were all radioactive hells which could kill you fairly quickly, not to mention the temperature.) The evolution into plants paved the way for animals to live without having chlorophyll themselves (some microbes were mobile, possessing flagella, but retaining chlorophyll despite their heterotrophic nature.)

Earth's CO2 accreted with the planet, similar to Venus'. However, on Venus, a runaway greenhouse effect was produced, which resulted in the water there being vaporized and stripped away by the solar wind. Venus has always had a surface temperature too high to sustain life, which contributed to the runaway greenhouse.

[falofonos]

elements in Earth's crust

http://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust

minerals in Earth's crust

http://www.rsc.org/education/teachers/resources/jesei/minerals/students.htm

[grawl]

Thank you for your replies !

I've decided, as I am running low on time (2 weeks left ) to keep it simple.

So I will keep my accretion rate at a constant 2/3 of the mass, maybe a bit less, it's working well for me after the tests.

I will have all the starting objects formed by only one element.

On the list :

- Oxygen

- Silicium

- Aluminium

- Iron

- Calcium

- Sodium

- Potassium

- Magnesium

- Carbon

- Frozen Carbon Dioxide

- Frozen water

The mechanics will be :

Solid materials will create the planet itself, with the materials dispatched as layers, from the heavier (center) to the lighter (border).

Frozen materials will, or will not, depending on the parameters, form an atmosphere around the planet.

I've managed to take some screenshots in the eclipse emulator some time ago. It's not exactly beautiful but it gives you an idea.

Sometime after the start.

The system is settling down...

What do you think?

Edited June 4, 2013 by grawl