Configuration of Planetary Systems

[Prime_Evil]

There's a great article published by the Proceedings of the National Academy of Sciences of the United States of America (PNAS) on 26 March 2014 attempting to sort the various solar systems discovered on ever the past decade into a number of distinct families based upon their internal configuration. The author believes that we are starting to get enough evidence to group the known planetary systems into several distinct types. He argues that same patterns are starting to emerge again and again from the data. He suggests that we may discover additional architectures or configurations as the number of confirmed exoplanets grows, but feels that we already have enough data to start drawing some preliminary conclusions about what the dominant types of planetary systems are. Based upon his analysis, it turns out that our own solar system is not the most common configuration - but neither is it as rare as people thought in the early days of exoplanet discovery when observational biases created by the nature of the techniques used led us to assume that hot Jupiters were far more common than they actually are. According to this study, it looks like our solar system isn't typical, but neither is it particularly unusual.

Here's a link to the relevant page where you can download a PDF copy of the article:

Architectures of planetary systems and implications for their formation -- Eric B Ford

Also, another recent academic article evaluates the Kepler data and also finds that small planets appear to be far more common around stars similar to our sun than originally thought:

Occurrence and core-envelope structure of 1--4x Earth-size planets around Sun-like stars - Geoffrey W. Marcy, Lauren M. Weiss, Erik A. Petigura, Howard Isaacson, Andrew W. Howard, Lars A. Buchhave

It looks like statistically, these planets consistently appear to be 1 to 4 times the size of earth and their density suggests that they have a rocky composition.

 

[sideranautae]

Thank you VERY much for posting this.

 

[Prime_Evil]

You're welcome

It's fascinating stuff.

 

[Reynard]

*Sigh* Still isn't looking good for the shirtsleeve worlds of science fiction.

Problem is we still only see the macro scale for other system and need to fine tune someday. It could be the Traveller system gen will need to feature more GGs and uber-terrestrials and far fewer habitable worlds but we won't know probably for a long time. The game might become more about way stations in systems on the extreme ends of the UPP curve leading to the rare habitable system. Interesting.

 

[sideranautae]

*Sigh* Still isn't looking good for the shirtsleeve worlds of science fiction.

Oh yes it is. With that average distribution (Earth sized planets are much harder to locate) there will be MANY.

 

[Rikki Tikki Traveller]

Thanks for the Link.

VERY interesting - ANOTHER 2D table to create!

 

[sideranautae]

Thanks for the Link.

VERY interesting - ANOTHER 2D table to create!

You making distribution table(s)? If so can you post when done?

 

[Reynard]

We need to boil down the numbers in those two articles to some dice rolls then add a big smidgen of speculate.

 

[Prime_Evil]

*Sigh* Still isn't looking good for the shirtsleeve worlds of science fiction.

This is hardly surprising - humans evolved to fill a particular ecological niche on Earth at a particular stage of its geological history. There are plent of environments right here on earth that are challenging for us, from the depths of the oceans to the upper stratosphere where the air is thin. And we wouldn't fare too well at different stages of the earth's geological history as well - go back before cyanobacteria oxygenated the atmosphere and we'd suffocate and go forward a few billion years when the sun starts to leave the current stage of its life. Like all other organisms, we are specialised for a particular environment and cannot exist without it (even if it is 'simulated' using life support technologies).

If terraforming is possible, then it may be possible to convert marginal planets into something comfortable for humans - but the time scales involved in making a world habitable are likely to be far greater than any other engineering project that humans have attempted.

Maybe sending canned primates into space is NOT the best way to explore the galaxy - perhaps it will be our robotic descendents that colonize the stars.

Problem is we still only see the macro scale for other system and need to fine tune someday. It could be the Traveller system gen will need to feature more GGs and uber-terrestrials and far fewer habitable worlds but we won't know probably for a long time. The game might become more about way stations in systems on the extreme ends of the UPP curve leading to the rare habitable system. Interesting.

Keep in mind that the Kepler data is still coming in and there is already a huge backlog of potential exoplanets to be confirmed by ground-based telescopes. And there is a known bias in the data due to the observation methods used - because you need to observe a planet transit its star several times before you can be certain that it really is a planet, the amount of time required to detect distant planets is a function of their orbital period (unless they are massive enough to be detected by their gravitational effects on the parent star). This means that we are starting to find small, rocky planets close to their parent star, but more distant planets of this type may not be confirmed for another 4-5 years. Put it this way - if you were detecting earth's orbit around the sun from a distant star system, you would need to observe the sun for at least four years before you could be certain that the earth existed...

One of the most interesting things from the data for me is the discovery that there appears to be a transition in composition of planets at about 1.5 earth masses. Smaller worlds appear to be solid, but above this limit their density drops - suggesting that they are either ocean planets or gaseous in nature. Fascinating...

 

[Tom Kalbfus]

*Sigh* Still isn't looking good for the shirtsleeve worlds of science fiction.

This is hardly surprising - humans evolved to fill a particular ecological niche on Earth at a particular stage of its geological history. There are plent of environments right here on earth that are challenging for us, from the depths of the oceans to the upper stratosphere where the air is thin. And we wouldn't fare too well at different stages of the earth's geological history as well - go back before cyanobacteria oxygenated the atmosphere and we'd suffocate and go forward a few billion years when the sun starts to leave the current stage of its life. Like all other organisms, we are specialised for a particular environment and cannot exist without it (even if it is 'simulated' using life support technologies).

If terraforming is possible, then it may be possible to convert marginal planets into something comfortable for humans - but the time scales involved in making a world habitable are likely to be far greater than any other engineering project that humans have attempted.

Maybe sending canned primates into space is NOT the best way to explore the galaxy - perhaps it will be our robotic descendents that colonize the stars.

Lets see, how long would it literally take to explore the Galaxy? The Galaxy has 200 billion stars and is 100,000 light years across. Lets assume the average velocity is 0.5 times the speed of light and the average distance to be crossed is 5 light years. 10 years for a one way journey from one star to the next. Once a probe arrives within a system, it explores the system for 5 years and spends the other 5 years building a duplicate of itself, the ships then take of for two other star systems.

20 years 1 star system explored
40 years 3 star systems explored Exploration sphere 20 light years 100 star systems
60 years 7 star systems explored
80 years 15 star systems explored 40 light years 800 star systems
100 years 31 star systems explored
120 years 63 star systems explored
140 years 127 star systems explored
160 years 255 star systems explored 80 light years 6400 star systems
180 years 511 star systems explored
200 years 1023 star systems explored
220 years 2047 star systems explored
240 years 4095 star systems explored
260 years 8191 star systems explored
280 years 16383 star systems explored
300 years 32767 star systems explored
320 years 65535 star systems explored 160 light years 51200 star systems within range
640 years, 320 light years 409600 star systems explored
1280 years, 640 light years 3,276,800 star systems explored

From this point its just a matter of how far away each star is. Since our position in the galaxy is about 30,000 light years from the Galactic core the furthest stars will be about 80,000 light years away, since it takes 20 years to explore every 5 light year increment, it should take 320,000 years to explore the entire galaxy with self replicating space probes, ad it would take a total of 400,000 years to do that and receive all the data heading back to Earth at he speed of light. Do you really think humans will just sit on Earth for 400,000 years to wait from all the data of every star system in the Galaxy to come in? Might it not be better to travel with the star probes? Imagine an O'Neill cylinder traveling at 0.25 times the speed of light following the expanding wave of self-reproducing probes. The first probe is launched from the Solar System 20 years prior to th departure of the manned starship the probes travel twice as fast, but they stop and linger in each system doing exploration and reproduction while the manned starship follows behind at a constant velocity of 0.25 times the speed of light. As the probes ahead multiply, the chances increase that an interesting planet will be found, and if one is found, the manned starship diverts its course toward that planet. Probably after 320 years their will be enough probes ahead of the colony ship to find a suitable world for colonization, perhaps by lagging behind the probe front by 80 years their will be enough time for the exploration probes to self-replicate into terraforming machinery, maybe taking an extra 5 years to do so and then continuing their exploration wave. The self-replicating terraforming machinery will then do its work to get the planet ready for human habitation. This is a lot better than all of humanity sitting on Earth for 400,000 years waiting for all of the results to come it. But tell me what you think of this.

 

[Reynard]

Sounds like the makings of a new game without any Traveller science or technology featuring macro robotics and an entirely new transport system. Interesting idea is the probes and colony ships are subject to relative time.

Where's that old formula for determining possibly terrestrial worlds and sentients in the galaxy? That could be used to determine how many planets the probes find suitable plus life forms and other civilizations in this expanding sphere. Add new and maturing human colonies behind the expansion. Pick a snapshot period after first probe launch to know the size of the sphere centered on Earth, take all the systems in that sphere and use a table to know how many should have habitable worlds. Next determine how long it would take from the distance to that system to rely the discovery and build, stock and launch a colony ship then its arrival time, set up and development of each colony. The time factors for distance will determine the maturity of each colony and their relation in the community.

 

[AndrewW]

Sounds like the makings of a new game without any Traveller science or technology featuring macro robotics and an entirely new transport system. Interesting idea is the probes and colony ships are subject to relative time.

The Drake Equation?

The Drake equation is:

N = R_{\ast} \cdot f_p \cdot n_e \cdot f_{\ell} \cdot f_i \cdot f_c \cdot L

where:

N = the number of civilizations in our galaxy with which radio-communication might be possible (i.e. which are on our current past light cone);

and

R* = the average rate of star formation in our galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fl = the fraction of planets that could support life that actually develop life at some point
fi = the fraction of planets with life that actually go on to develop intelligent life (civilizations)
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space[8]

http://www.seti.org/drakeequation

 

[Reynard]

I assume some civilizations haven't yet invented even simple radio while other civilizations can be using energy forms we haven't invented detectors for. Of course there can be signals too weak to survive the travel. Some civilizations may have been broadcasting for centuries but... something happened and no more signals reach us before we have the tech to receive. In between, if there are detectable civilizations out there, where are their signals? The energy can travel incredible distances for a LONG time and yet, for about a century, we have not found one.

That's lonely.

It just means the galaxy belongs to us. A purely homocentric universe. A non-alien Traveller campaign and the enemy is us.

 

[dragoner]

IIRC, signals attenuate so that there is adequate resolution; not there can never be, but we don't have anything like it now, or maybe not looking.

 

[sideranautae]

That's lonely.

It just means the galaxy belongs to us. A purely homocentric universe. A non-alien Traveller campaign and the enemy is us.

Or, they use meson communicators. :lol:

 

[Tom Kalbfus]

I assume some civilizations haven't yet invented even simple radio while other civilizations can be using energy forms we haven't invented detectors for. Of course there can be signals too weak to survive the travel. Some civilizations may have been broadcasting for centuries but... something happened and no more signals reach us before we have the tech to receive. In between, if there are detectable civilizations out there, where are their signals? The energy can travel incredible distances for a LONG time and yet, for about a century, we have not found one.

That's lonely.

It just means the galaxy belongs to us. A purely homocentric universe. A non-alien Traveller campaign and the enemy is us.

Don't be so sure, the planets we terraform will all eventually evolve in their own direction producing widely divergent live forms, of course all based on DNA and we can eat them and they can eat us! Much of the life in a science fictional galaxy, read Vargr and Aslan, are not so different from us. I could imagine a setting not so different from Traveller with all sorts of "alien" species, yet all of them are descended from Earth life. Come back to the Milky Way after 400,000 years and the Star Wars Cantina scene is entirely possible.