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What is already scientifically correct?
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| NeapolitanBoy | Date: Tuesday, 23.09.2014, 15:47 | Message # 1 |
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Space Tourist
Group: Users
Italy
Messages: 34
Status: Offline
| Hello, friends.
I adore SpaceEngine and the beautiful community around it. Unfortunately, because of some time restrictions, I don't usually have the possibility to partecipate the way I'd like to.
I appreciate your passion and competence for stars and planets, and I am very happy that SpaceEngineer is both a great programmer and an expert in astronomy!
I remember I had a short message exchange with SpaceEngineer about what physical laws had already been implemented in the program and the laws that still needed to be considered.
I noticed that some tidally locked planets had water near the hot pole and SpaceEnginer told me it was not realistic because the system required more sophisticated algorhythms.
Now, I would be very very happy if someone of you colud help me understand, more or less, what is already accurate from a physical point of view and what is not so accurate.
Thank you very much.
Edited by NeapolitanBoy - Tuesday, 23.09.2014, 19:33 |
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| Watsisname | Date: Wednesday, 24.09.2014, 00:38 | Message # 2 |
 Galaxy Architect
Group: Global Moderators
United States
Messages: 2613
Status: Offline
| Space Engine doesn't really implement physical laws. To do physics is to take the state variables of a system, then apply some equations to predict its future behavior. To simulate a universe in this way is virtually impossible. The closest thing Space Engine does is calculate orbits via a 2-body approximation. Otherwise, Space Engine tries to emulate a universe consistent with one that does operate under these laws. So we can ask how well does Space Engine emulate such a universe, what objects and phenomena does it represent faithfully, what needs more work, and what things remain to be shown?
I think the best first step in addressing these questions would be to review SpaceEngineer's TODO list. Almost everything regarding future work that we could discuss here is already listed there. As for what things which are already shown are physically accurate or not so much, well that's a lot to go over! 
Regarding water near the sub solar point on tidally locked planets, whether this is realistic depends on
(i) Is water present there in the first place?
(ii) Is the surface pressure and temperature consistent with liquid water on the phase diagram?
(ii) is the hard part, because answering it requires using global climate models for tidally locked planets, which we don't have in SE. Realistic portrayal of these worlds is much more general than that. For instance, SE calculates their temperature using solar irradiance and general properties of atmosphere only. (It doesn't calculate heat flow via ocean currents. These would be important on a tidally locked world with global oceans like Earth's.)
The cyclonic systems SE shows over the sub-solar point are probably realistic in the general case, as atmospheric models often produce such features.
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| FastFourierTransform | Date: Wednesday, 24.09.2014, 11:53 | Message # 3 |
 Pioneer
Group: Local Moderators
Spain
Messages: 542
Status: Offline
| I was thinking about something like that. In the credits part of the game we could put all the scientific papers where SE relies to make Scientific Community part of the progress of the software. For example, a reference to the paper where we have taken the frequency of planetary nebulas in the galaxy or those papers where they have simulated numeriacally the shape of red giant stars to make people aware of the accuracy of the program. This also could lead to changes in future if some scientific research debukns an older one included in the SE credits.
Space Engine: Created by Vladimir and the modern Science (citating all the texts)
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| NeapolitanBoy | Date: Wednesday, 24.09.2014, 13:23 | Message # 4 |
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Space Tourist
Group: Users
Italy
Messages: 34
Status: Offline
| Thank you, Watsisname, for your long reply: I really appreciate it.
I want to be clear: I’d like to write a science fiction novel. I am a young doctor and I’ve already written a little book. I studied Physics, Chemistry and Biology when I attended university, and Astronomic geography only when I was at school.
After deciding to write this novel, I started to study these subjects again: I read books, articles, I asked many questions to an astronomy professor, watched documentaries and I am still in the process of learning.
I take these things seriously, because I think that even the most unrealistic story should have a solid base or an almost solid base, at least.
Because of time restrictions, my dedication to medicine, music and so on, I doubt I’ll be able to acquire such a level of information to the point of writing a credible novel: I would need a constant guide.
When I discovered Space Engine, I was happy: I thought that someone else had already done the job for me, that I could instantly “put” whatever character on a SE planet to know exactly what was realistically happening on its surface: is there a lake? Wonderful, it means it can be there; is the sky red? Wonderful, it means it can be red.
The reader should be immersed in the story, and you can immerge the reader only if you describe accurately the world around the protagonists: at the moment, I risk to write stupid things even in an simple sentence like: “The wind was blowing…”
The TODO list seems focused more on graphical and technical aspects than on creating a credible atmosphere model or similar things.
If you want to help me, tell me just a pair of things I can’t rely on.
I’ll guide you with a pair of questions:
1) Is the atmosphere pressure on the procedurally generated planets realistic in relation to their mass, their collocation in the system, their gravity?
2) We can notice methane lakes on Titans, but on every Titan are the temperature and atm pressure plausible to justify the presence of liquid methane?
3) In the aspect of planets and their surface, what is usually plausible and what is almost always not?
4) What should I be particularly aware of when I try to figure out the important differences between how the planet is on SE and how it could be in reality?
Thanks.
Edited by NeapolitanBoy - Wednesday, 24.09.2014, 13:25 |
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| Destructor1701 | Date: Thursday, 25.09.2014, 00:42 | Message # 5 |
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Pioneer
Group: Users
Ireland
Messages: 533
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| This is a great question.
I think the answers are getting tied up with the degree to which physical processes are correctly simulated. That's a worthy goal, and I'm not knocking it, but it's obviously not going to be possible to simulate reality on any scale dealt with in SE.
I think a better wording of effectively the same question - the question whose answers will help us in talking to the uninitiated masses about the awesomeness of Space Engine is:
"What aspects of Space Engine superficially approximate the scientific reality (or current consensus) well?"
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| Watsisname | Date: Thursday, 25.09.2014, 11:28 | Message # 6 |
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Galaxy Architect
Group: Global Moderators
United States
Messages: 2613
Status: Offline
| Sure thing, Neapolitan. I admire your desire for hardness in your sic-fi. For your questions, I might not be the best person to answer them, as I don't know all the details behind SE's planet/atmo generation. SpaceEngineer may be able to explain better if he is not too busy.
(1) The pressure calculation does consider thermal escape so that the atmosphere is thin or nonexistent for worlds that couldn't retain them, but I'm not sure if/how the distribution considers mass and so forth.
(2) This would require implementing phase diagrams for these substances to determine when to allow or forbid those lakes. I don't know if SE does this already, or just approximates it, or if it's intended for future development.
(3) I'd say that the planets whose surfaces are most easy to represent realistically are the ones with the least amount of surface processes, which generally scales with mass. So it would favor small, airless bodies. Atmospheres add a layer of complexity, and then liquids/hydrologic processes, volcanism, tectonics, glaciation, etc. Temperate terras may very well be the most complex, but then again we have a lot of familiarity from the study of our own planet. So we can make ones that look convincing. Ones with lots of unknowns would be large terrestrial planets (super-Earth's), because we've never seen one up close. There aren't any in our solar system. Everything we know about them comes from modeling.
As for specific surface features, perhaps mountain generation is sometimes too tall. In reality the height is limited by the strength of the rock. And without simulating tectonics, the topography itself is completely artificial (e.g. no underlying connection to the continents, because there are no plates.) And without global climate models, biomes don't reflect this topography beyond just the altitude (e.g. no shadow deserts).
(4) Ask yourself how well we understand the type of planet in question (is there a close solar system analogue?), and how complex the planet would be in terms of atmospheric dynamics and geophysics.
I hope that helps a bit more at least. These are great questions but are not easy to answer.
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| NeapolitanBoy | Date: Saturday, 27.09.2014, 11:19 | Message # 7 |
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Space Tourist
Group: Users
Italy
Messages: 34
Status: Offline
| Thank you again, Watsisname.
You have the rare quality of perfectly understanding the doubts and questions people have and ask, and this means great teaching skills.
Your answers helped me.
I have just read your previous message for the fourth time. In it, you underline the three important steps required to have a plausible idea about the presence of water on a planet.
The first step catches my attention now: “Is water present there in the first place?”
In your opinion, what approximate trick could I use to determine if a particular planet on SE is supposed to have water in the first place?
Remember that my objective is to use SE for my novel: basically, if SE can’t give me realism in the geological, atmospheric and meteorological fields, I’ll use it only for relying on system structure (orbital relationships among planets and stars) and general planet data.
Other questions (related to your second step):
When you open a book or a Wikipedia page about a planet of our solar system, you can find the values of various important parameters. Among these parameters, there’s always this one: Superficial Mean Temperature.
Does this parameter (Superficial Mean Temperature) consider only solar irradiance (properties of the sun and distance planet-sun) and albedo or does it keep into account every possible element, such as greenhouse effect, heat flow via ocean currents, etc?
And, in your opinion, do the mean temperatures indicated in SE only consider solar irradiance, or also greenhouse effect? For example, if a planet in SE has a very dense atmosphere (high atmospheric pressure), does the software consider such an element in approximately establishing the mean temperature of the planet?
Last question (then I won’t bother you for a long time!  ): with only the SE parameters atmospheric pressure and mean temperature, plus a phase diagram, can I establish with a decent degree of plausibility if liquid water or liquid methane that I find on a SE planet are quite realistic?
Thanks.
P.S.: I’ve bought two Astronomy books, two Earth Sciences books and one Astrobiology book. I hope that, at the end of my study, I’ll write a novel with MANY mistakes instead of a novel with ONLY mistakes. A person can’t become a physician or an astronomer with a pair of books that are studied as hobby, but maybe being in the scientific field as a doctor and writing something that allows a lot of fantasy will permit me to reach decency
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| Watsisname | Date: Sunday, 28.09.2014, 05:07 | Message # 8 |
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Galaxy Architect
Group: Global Moderators
United States
Messages: 2613
Status: Offline
| Thanks for the kind words, and sure, I can do another post for you:
Quote NeapolitanBoy (  ) In your opinion, what approximate trick could I use to determine if a particular planet on SE is supposed to have water in the first place?
Check if it has water on it now.
What I mean is that the existence of water is obviously a pre-requisite to the existence of liquid water. In reality, water is very common in protoplanetary disks. But how frequently is that water incorporated directly into the formation of terrestrial planets, or else delivered later by comets? In our own solar system, pretty much all the planets succeeded here, but how typical is this in general? We don't know.
Once supplied with water, the retaining of it and having it on the surface in liquid form then depends on the planet's subsequent evolution. SpaceEngine does not model this. What it does is flip a virtual coin during planet generation, the result of which chooses whether to designate that planet as a Terra or Oceania, or something else. It also checks that the planet has the right surface temperature (not putting them where it is very clearly too hot or too cold).
So what trick should you use? None -- SE already did it for you. If you find a terra/oceania, consider it a veritable planet with water. Unless you can retrace the evolution of that planet and its host star system, you can't do any better.
Quote NeapolitanBoy ( ) Does this parameter (Superficial Mean Temperature) consider only solar irradiance (properties of the sun and distance planet-sun) and albedo or does it keep into account every possible element, such as greenhouse effect, heat flow via ocean currents, etc?
For known exoplanets, take all of these figures with a huge grain of salt. It's a very simple calculation which only considers the sun's luminosity and the planet's distance, and perhaps some standard value for albedo. Since we don't have good data on their atmospheres or surfaces, we don't actually know what their albedo or greenhouse effect contribution, etc, may be. For example, if we were astronomers in another star system looking at Sol, we would vastly underestimate the temperature of Venus.
SpaceEngine does consider the greenhouse effect. You can see its contribution to planet temperature listed in the info tab.
Quote NeapolitanBoy ( ) with only the SE parameters atmospheric pressure and mean temperature, plus a phase diagram, can I establish with a decent degree of plausibility if liquid water or liquid methane that I find on a SE planet are quite realistic?
To a very good degree, yes! In physics, the phase of a substance is uniquely determined by temperature and pressure (phase diagram). SE supplies you with both of those, so that's all you need. I think you will find that the vast majority of worlds in SE will be accurate in this sense. I only recall a few instances of planets with liquid water for which the phase diagram indicated it shouldn't, and it generally involved worlds with extremely high surface pressure (so the water should be ice). I'm not sure how common that would be in your sci-fi settings, but I guess it wouldn't hurt to know.
Which books did you get by the way?
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| NeapolitanBoy | Date: Monday, 29.09.2014, 17:05 | Message # 9 |
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Space Tourist
Group: Users
Italy
Messages: 34
Status: Offline
| Thank you for the precise reply. This is what I’ve understood:
1. I’ll let SE decide if a particular planet has water or not.
2. We can’t directly measure the mean temperature of an exoplanet, so, when we want to esteem it, we only use the basic information that we have and the only parameters we can precisely calculate. On the other hand, the mean temperature of the Earth can be measured more directly, so, of course, the number 286 K that we register is the result of every possible element influencing temperatures, from atmosphere, to seasons, to volcanic activity, etc. And the greenhouse effect, that 35 K, is a number “incorporated” in the 286. I imagine that for Venus and other planets of our system the temperature determination is closer to the one of the Earth (more precise, more direct). In SE we pretend to know in detail every planet, so, in theory, every mean temperature is the result of greenhouse effect + every other pertinent physical or astronomical element (that SE has not implemented every element yet it’s another story).
3. Phase diagram and the two parameters mentioned are enough, and SE is accurate in determining the state (solid, liquid, vapour) of water and other substances on most planets. At this point, I’d like an opinion about tidally locked planets and hot oceanias: there are a lot of amazing tidally locked terras in the game, but I am surprised that many of them have liquid water near the hot pole; as for hot oceanias and their liquid water, SpaceEngineer gives an explanation about liquid state in very hot conditions, but I’d like to understand it better.
My books:
Margherita Hack – Tutto comincia dalle stelle;
Astrophysics is easy! – Mike Inglis;
Illustrated encyclopedia of the universe;
Earth science – Tarbuck;
Cosmic biology – Irwin & Schulze-Makuch;
Other books from school.
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| NeapolitanBoy | Date: Friday, 31.07.2015, 16:17 | Message # 10 |
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Space Tourist
Group: Users
Italy
Messages: 34
Status: Offline
| Hi, guys.
I've found an interesting planet in SE 0971: it is tidally locked to a brown dwarf, so it should have one face always immersed in the dark. The particular thing is that, since the system is binary, there's a red dwarf which gives light to that face for prolonged periods of time.
The planet rotates only around the brown dwarf, but the presence of the red dwarf is relevant.
My question is: in determining the planet's temperature, does SE take that red dwarf into consideration?
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| Watsisname | Date: Saturday, 01.08.2015, 07:37 | Message # 11 |
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Galaxy Architect
Group: Global Moderators
United States
Messages: 2613
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| Yes. The temperature calculation for a planet will consider all stars within the system, even if it is a separate component of the binary which the planet does not orbit directly.
This will be apparent as an overall shift in the temperature range seen on the planet over the course of the stars' orbits, though the effect is often pretty small, sometimes just a few hundredths of a degree. It's more obvious in highly eccentric binaries.
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| NeapolitanBoy | Date: Saturday, 01.08.2015, 17:45 | Message # 12 |
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Space Tourist
Group: Users
Italy
Messages: 34
Status: Offline
| Thanks for your help, Watsisname
I am continuing to study a way to use SE as a base for my sci-fi. But I’m having a lot of difficulties: I haven’t already found a method to obtain plausible information from unrealistic planets.
In other terms, what I want to do is analyze the properties of a particular in-game planet and then understand what characteristics are plausible and what are not in order to deduce how that planet would be in reality. In doing that I am conscious that Planetology is such a difficult and still mysterious science, so I welcome approximation. But why such a laborious procedure? Well, you perfectly know that writing an interesting, well done novel in this genre is something complicated: however, the more realism is in it, the higher the probability to be appreciated.
I don’t know if you use SE 0971 (I am using it because the new versions are much slower on my PC). In SE 0971 I found a planet called “8 and 2”. This planet is shown as a warm Terra: there’s a lot of water and an arid dry land.
If I had the desire to adopt this planet for my sci-fi, I would encounter a lot of difficulties in the determination of its realistic properties.
Its temperature is 384 K and its atmospheric pressure is 0,45 atm. The first thing that emerges when looking at the phase diagram of water is the difficulty in having liquid water on the surface (if I am not wrong).
So I suppose that, first, this planet has a different aspect from the one showed.
Second: if one of my characters decided to indicate the value of the mean atmospheric pressure of “8 and 2”, I doubt he could say “0,45”, because, as I’ve said previously, that liquid water should have evaporated, increasing that value.
This analysis underlines another problem: what comes first? SE’s value of 0,45 or my evaporation event?
And I’ve only scratched the surface
I’ve written all this to have suggestions from this community: what methodology would you suggest for “extrapolating” a real planet from a SE planet?
There’s a general, comprehensive enthusiasm related to the possibility of making SE a game with spaceships, adventures, galactic wars, etc.
I like the idea, but I think that scientific accuracy should come first. SpaceEngineer has already created amazing realistic dynamics; nobody has ever reached this kind of accuracy (think at the movement of every planet, every star, the way things are visible in the sky – wonderful!). He is close to the creation of the perfect simulation, closer than anybody else in the world, while, on the other side, there are a lot of great videogames with space heroes.
Thanks for reading.
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| Idgelios | Date: Tuesday, 04.08.2015, 18:22 | Message # 13 |
 Astronaut
Group: Users
United States
Messages: 77
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| In terms of scientific correctness i'd say that the world types are all accurate. All of them are based on actually existing exoplanet classes and the way the game simulates world sizes and is able to make (from time to time) worlds that blur the line between jovian and terrestrial has been a pleasant surprise.
What worries me with space engine however, is that the engine limitations may keep getting in the way. For instance engine limitations is why stars with exoplanets have no procedural planets outside of detected ones (so no hypothetical worlds) or even procedural asteroids/moons. I do worry at times how much these engine limitations will crop up and put a cap on how "accurate" space engine can get. Like, will engine limits make humidity simulations impossible?
Currently space engine's universe is rather static outside of rotations, orbits and what-not. I don't know if space engine can simulate wave size on planets or tides yet and if the engine is too limited where tide simulation is impossible dynamics like seasons or dynamic weather simulations (for instance gas giants with dynamic storms) may also prove extremely difficult.
Simulating a universe with scientific accuracy in short, is extremely hard and I am not sure if current software is capable of it. Simulating billions of dynamic particles in a universe simulating super computer is one thing, having a dynamic universe for free on any computer up to specs may simply not be a realistic prospect this decade. Algorithmic and procedural generation can generate environments on galactic/universal sizes, but they're often static and populating all this space with interesting content will be anything but easy. I'm surprised how diverse space engine can be as is, to be honest. Many other generators tend to be very repetitive, but space engine creates all sorts of worlds it's mind boggling at times.
Edited by Idgelios - Tuesday, 04.08.2015, 18:25 |
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