William Borucki’s talk about the early Kepler findings on Monday created the biggest spike in traffic I’ve ever seen on Centauri Dreams, enough to blow through our memory allocation and crash the site for about twenty minutes. I had to reboot the server and up the memory to get back online, a tribute to the interest Kepler continues to generate in our community. I’m also getting plenty of comments from people at the American Astronomical Society meeting in Washington. If you use Twitter, use the hashtag #aas to join the ongoing stream of short updates.
Right now Scott Gaudi’s talk on Tuesday is generating the biggest buzz. Gaudi (Ohio State) reported on a gravitational microlensing effort called MicroFUN (Microlensing Follow-Up Network), one we’ve previously discussed in these pages. The method is well understood: One star occults another as seen from Earth. The light of the more distant star is magnified by the nearer one, and any planets around the lensing star momentarily boost the magnification as well. You find planets this way, though they’re not planets likely to be observed again because of the nature of the method.
I love this Gaudi quote from the talk: “Planetary microlensing basically is looking for planets you can’t see around stars you can’t see.”
Gaudi’s team has concluded that about fifteen percent of the stars in the galaxy are orbited by planetary systems like our own, meaning they have several gas giants in the outer part of the solar system. That fifteen percent is telling. “Solar systems like our own are not rare,” says Gaudi, “but we’re not in a majority, either.” Microlensing is useful for this kind of study because the method does a good job at picking up giant planets far from their primary star, a more difficult task with Doppler methods.
Working with colleague Andrew Gould, Gaudi used four years of MicroFUN data and folded in a statistical analysis based on ‘robust assumptions’ and the earlier work of both men. It turns out that MicroFUN in that period of time has revealed precisely one solar system with two gas giants in roughly the configuration of Jupiter and Saturn. Statistically, if every star had a solar system like ours, we should have found about six such systems by now. The slow discovery rate implies only a small number of systems have our configuration, no more than about fifteen percent. Says Gaudi:
“While it is true that this initial determination is based on just one solar system and our final number could change a lot, this study shows that we can begin to make this measurement with the experiments we are doing today.”
And as Gould notes, given the number of stars in the galaxy, even narrowing the odds down to fifteen percent leaves several hundred million systems that could resemble ours. Nor should we assume that a system necessarily has to mimic our own for life to develop within it. Nonetheless, this is an intriguing result that reinforces our sense that extrasolar planetary systems come in a surprising variety, one we learn more about with every new detection.
What is unstated and completely unknown is what % of this 15% has a terrestrial, rocky planet with water in the HZ. The end # is probably a low single digit %. Rare.
Well that number seems rather higher than the number for the fraction of stars with hot Jupiters that I’ve been able to dredge from a quick Google search. E.g. this gives a value around 1/300. So it would seem that solar system analogues are not the rarest configuration after all.
Was there any information on what is known about the distribution of stellar classes among that 15%? Thanks.
Fifteen percent is actually not bad at all, considering how many variables enter the making of a planetary system. As I said in the H+ magazine contributors’ poll for the best and worst of the decade,
When they say the gas giants are like ours, do they mean they have roughly circular orbits?
Ron S:
Several people told me that Gaudi estimates 1 out of 3 ‘Sun-like stars’ (and here I assume G-class is what he means) have gas giants in Jupiter/Saturn configuration. But I’m not at the meeting and I can’t confirm this — someone else at AAS chime in, please!
Tobias:
We’re working with microlensing here, so the one detection would presumably not allow for orbital data on the gas giants. I think what we can talk about is the presence of two gas giants in the outer reaches of a system.
I am of the opinion that double planets like the Earth/Moon orbiting within the habitable zones of F-G-K class stars are fairly rare. I also believe that technology using life such as ours probably exists only on worlds having active plate tectonics after the technological life evolves into existence. The requirement for continuing plate tectonics restricts technological life to worlds experiencing significant third body gravitational perturbations.
The initial conclusion from these two assumptions would be that technological life is fairly rare in the galaxy. However I am also of the opinion that most technological life in our galaxy does not orbit F-G-K class stars but rather lives on moons orbiting gas giants (Jupiters) orbiting M class stars. M class stars are extremely common compared to F-G-K class stars (almost a 100:1). Also it appears that close orbiting gas giants are fairly common. A moon orbiting a gas giant, orbiting an M class star would escape the problem of tidal locking that prohibits life evolving on such a world if it orbited the star directly. Also the third body gravitational perturbation from the gas giant would assure plate tectonics.
This set of assumptions leads to interesting implications concerning the Fermi Paradox. There should be a thriving interstellar civilisation in our galaxy. The fact that no extraterrestrial artifacts have been detected in our solar system is a genuine paradox. A burned out transfer stage from an old star ship or remnants of von Neuman machines used to rebuild and repair an ancient star ship should have been detected by now. If the overwhelming majority of technological civilisations in the galaxy originate around M class stars, then by definition, the tendency for interstellar contact would be between worlds orbiting M class stars. F-G-K class stars would be regarded as “junk” star systems not worth the expense of sending an interstellar vehicle for exploration or long term communication attempts via a SETI strategy.
One of the things that I’ll be watching very closely with Kepler is the discovery of gas giants orbiting within the habitable zone of M class stars. If Kepler can also detect Earth sized moons orbiting these gas giants then that will be an extremely interesting result.
Which may or may not be elliptical. Can we get any Doppler info?
While 15% is a minority, it’s still a sizable fraction. It’s a very different outlook from past views that our solar system was extremely rare. As time goes on, things look progressively more optimistic for the exoplanet search. We’ve gone from seeing our solar system as a rarity, to finding mostly hot jupiters as exoplanets, to our current situation of finding all kinds of gas giants and terrestrial planets around other stars. I think we still have much to discover.
I tend toward the view that non-human intelligence is rare to non-existent, but here are a couple of interesting solutions to the Fermi Paradox that don’t depend on that:
http://www.rfreitas.com/Astro/ThereIsNoFermiParadox1985.htm
http://www.geoffreylandis.com/percolation.htp
Gary Allen: going to have to disagree with you there. Firstly gas giants appear to be rare around M dwarfs, and those which are located in the inner system appear to be rarer still. Most Jupiter-class worlds around M dwarfs are located in the cold regions beyond the snowline.
The small scale of the system means that the range of stable orbits for moons is going to be very restricted: it doesn’t look particularly good for forming satellites either. Plus you’ve got the issue of whether large enough moons to be habitable can form even under the best conditions. And are you really sure you want to have the “habitable world” rotating with respect to the star? You’d get monstrous tides caused by the star (these are what would cause orbiting planets to get spin-locked in the first place), and that’s before you start to consider whether the star would be able to maintain significant eccentricity in the moon’s orbit, which would result in planet-induced tidal heating.
To make things even more interesting, you’ve also got the issues of the impact of stellar flares on the gas giant’s radiation belts to contend with…
My view is that there is other life in the universe – but the more complex it is, the less common it is.
I would guess that simple forms of life like bacteria or amoebas are fairly common (extremophiles in particular have been found on every habitat on earth, from glaciers to deserts to geysers to nuclear waste sites). Complex fish, animals, plants etc are less common, but theyre around, particularly on more hospitable planets. Intelligent/sentient life is probably rare, although I don’t think we’re the only intelligent species in such a vast universe. Keep in mind that everything on earth developed with the same elements and same laws of physics as anywhere else in the universe.
One-in-six isn’tbad, but I do wonder just how many systems just have rocky planets or one Jovian or one ice giant? A system bare of Jovians might mean the terrestrials are dry due to insufficient mixing of the different formation zones, for example.
Gary Allen, u make an interesting point imho it would make sense that interstellar societies could very well look at our system as a poor investment… Not worth the intergalactic trade, if they were to evaluate our system and the likelihood for advancements, our very environment could be a tell tale sign of a lesser evolved species…We don’t go to primates looking for tech advances…we don’t let monkeys drive cars. Ants can communicate. Or maybe its something we don’t know… Maybe they can tell when a black whole is about to devour a system and they know we aren’t going to survive and they can’t get here quick enough… And though Star Trek is a television show they could be on to something… There could be a galactic law prohibiting first contact. Could be that “they” know what rudimentary communications we have and sent us a message that way… Knowing that it would take millenia to get here but hoping we will evolve sooner… Information may be the only means of contact. Whatever it is, it seems that only people who have the imagination and intelligence to work together and dedicate their lives to mankinds greatest adventure have the chance at ensuring the survival of our species. Because no matter what eventually we are going to have to leave.
The person who invents a means for interstellar travel will have simultaneously saved their species from extinction.
NS: The Geoffrey Landis paper is of interest. I’ve long wanted to write a Monte-Carlo program simulating interstellar colonization. The program would be a variation of Conway’s Game of Life where I simulated a volume populated with stars based upon the Hipparcos star catalogue and set rules for propagating from one star system to another. It would be assumed that the starship was a von Neumann self-replicating machine. The starship would enter into a new star system, replicate itself and then propagate to the nearest surrounding star systems. The starship’s ability to replicate would be a function of the star system’s spectral class, e.g. if the star system was metal poor then the starship would be unable to replicate and “die” in that star system. There would be other rules governing the maximum distance that the starship could travel before it broke down. It would be assumed that the starship was controlled by an artificial intelligence and had the human genome stored in memory. The starship would seed habitable Earth-like planets with “people” having genomes modified for compatibility with the planet’s pre-existing biology. The pay off from the simulation would be in determining the set of parameters enabling complete colonization of the galaxy in less than a hundred million years. Just as Landis implies, I suspect there would be a significant set of parameters where colonization became arrested before spreading through out the galaxy.
Andy said:
“.. have to disagree with you there. Firstly gas giants appear to be rare around M dwarfs, and those which are located in the inner system appear to be rarer still… ”
I’m sceptical. An M class star with a gas giant planet is almost a binary star. Those should be very common. The results from Kepler will probably provide statistics about M stars with companions in the next couple of years. Can you reference a paper claiming that M class star binaries are rare?
Andy also said:
“The small scale of the system means that the range of stable orbits for moons is going to be very restricted: it doesn’t look particularly good for forming satellites either. Plus you’ve got the issue of whether large enough moons to be habitable can form even under the best conditions.”
For sure there would be a narrow range of stable orbits for a moon orbiting a gas giant that was orbiting an M-class star. Likewise given the requirement that a viable planet needs to have plate tectonics, there is a narrow range of allowable mass for a moon orbiting an earth-like planet orbiting a sun-like star. If you buy into the “Rare Earth Hypothesis”, it borders on miraculous that we exist. As I earlier speculated, I suspect it is much less miraculous that “Earths” exist in M-class star systems orbiting gas giants. Again, the nice thing about this line of speculation is in it soon being testable. Right now we’re arguing about angels dancing on the heads of pins but in a couple years time, we’ll have the data from Kepler.
Gary Allen: like andy, I also disagree with you, for rather simple and numeric reasons.
Besides the facts mentioned by andy (partic. low occurrence of planets and especially gas giants in close orbit around M dwarfs), the following facts:
– the ratio of M : F+G+K is not 100:1, but about 70:20, as can be verified at NStars and RECONS, among others.
Even when limiting ourselves to the more solar type spectra, say from F7 through K2 and only main sequence (V), the ratio M : solar type is about 70:15.
And when we also incorporate the relative width of the habitable zone (HZ), the picture becomes even more favorable for the solar types:
if we reasonably assume that the ‘average’ M dwarf has 1% of solar luminosity and the ‘average’ solar type star (around G5/G6) 80% of luminosity, we find that the HZ of our solar star is about 9 times as wide as that of our M dwarf.
So, purely statistically, the chances of a planet, any planet, to be situated in the HZ of either an M dwarf, or a solar type star, are then about 70:135. In other words, all the solar type stars in our MW galaxy together possess almost twice as much ‘HZ territory’ as all M dwarfs together.
If also taking into account the relative rarity of (gas giant) planets near M dwarfs and the issue of inward migration of giant planets, it is not so surprising that we orbit a G star.
I still firmly put my money on the solar types.
“An M class star with a gas giant planet is almost a binary star. Those should be very common. ”
No. The mechanisms for forming a binary star appear to be very different from the mechanisms for forming planets around a star. Binaries form at the same time, out of the prestellar nebula; planets form later, after most of the system’s mass has already accreted into the central star.
The cutoff point for “star” formation seems to be somewhere in the brown dwarf range, about an order of magnitude lower than the cutoff for fusion ignition.
This in turn suggests that there are two sorts of brown dwarves — low and medium mass ones that formed as planets, and bigger ones that form as binary stars. Wemay actually know the answer to this within a year, as WISE is about to start imaging the hell out of the local brown dwarves in the infrared.
But anyway: no, an M class star with a gas giant is not “almost a binary”, any more than a parent with a tall child is “almost a sibling”.
Doug M.
Ronald writes, “limiting ourselves to the more solar type spectra, say from F7 through K2 and only main sequence (V), the ratio M : solar type is about 70:15. And when we also incorporate the relative width of the habitable zone (HZ), the picture becomes even more favorable for the solar types:
if we reasonably assume that the ‘average’ M dwarf has 1% of solar luminosity and the ‘average’ solar type star (around G5/G6) 80% of luminosity, we find that the HZ of our solar star is about 9 times as wide as that of our M dwarf.”
Excellent analysis. The trendy M star case for habitable worlds has been overstated. The HZs are very narrow with most M stars much less luminous than 1% sol. Large moons of hypothetical gas giants in M HZs would be subjected to extreme tidal stress by the “near by” M star. Excessive volcanism in the cases of the most numerous really dim (and therefore close) M5 and later stars. Worse yet, now we have some M star data but we have NOT observed commonality of gas giants in Mstar HZs. Worse again, many models don’t posit the formation of large enough moons around the hypothetical gas giants. You need a strong gravitational field to hold an atmosphere in the warm HZ. No Titans need apply.
Gary Allen,
As the others have pointed out, giant planets around M dwarfs are rare.
A few years ago, GJ 876 was the only M dwarf known to have giant planets of the 100 to 130 that were then searched. A few more M dwarfs have since been found to have giant planets,
but the overall percentage still remains at something like 1 percent. A paper explaining why can be found at:
http://www3.interscience.wiley.com/journal/112210517/abstract?CRETRY=1&SRETRY=0
Actually, M dwarfs do seem to do badly on the binarity fraction… the often-repeated claim that most stars are in binary systems is in fact not true: most stars are M dwarfs and most M dwarfs are not in binary systems. Then you have to consider the observation that the binary star formation process is apparently biased towards mass ratios near unity anyway. Essentially you are looking for the extreme-mass-ratio tail of the binary star distribution around the stars for which binary occurrence is low anyway.
In any case, we should have found a lot more examples of M dwarfs with inner system gas giants by now if they were at all common. Given the low stellar masses, Jupiter-class worlds in the inner system of an M dwarf should produce very large velocity variations. It isn’t as though people haven’t looked: the radial velocity campaigns are producing a sample of long-period giant planets in such systems, but the inner systems are largely devoid of Jupiters, and indeed no example of a hot Jupiter (roughly 3 days orbital period) has been found orbiting an M dwarf. Remember that radial velocity surveys are biased towards massive planets in short-period orbits: this is not a poorly-sampled region of parameter space.
Gliese 876 is one of the very rare exceptions to the rule that Jupiters around M dwarfs lie well beyond the habitable zone. The planet formation process around M dwarfs is apparently not only inefficient at forming gas giants, it also doesn’t seem to be very good at migrating them into the inner system either.
Here are some M-class stars that are believed to have gas giants orbiting them:
Gliese-581 has a Neptune-sized gas giant along with three other known planets
Gliese 649 has a gas giant 1/3 the mass of Jupiter.
Gliese-876 has a planet 2.6 times the mass of Jupiter along with two other known planets
Supposedly two of the planets orbiting Gliese-581 are within its habitable zone. It’s conceivable that an Earth-sized moon orbiting Gliese-581d (half the mass of Uranus) could be viable. I suspect there would be orbit stability issues for such a scenario because Gliese-581d is insufficiently massive.
Note that my examples are all from the Gliese catalogue, i.e. they’re within 22 parsecs of Earth. M class stars are not very bright so the star needs to be nearby for planetary detection to be possible (drunk searching under a lamppost scenario).
This situation changes with Kepler which is a much more sensitive instrument for planetary detection. Again, in a couple years we’ll know whether or not there are many potentially viable planets orbiting M-class stars.
“Here are some M-class stars that are believed to have gas giants orbiting them:
Gliese-581 has a Neptune-sized gas giant along with three other known planets
Gliese 649 has a gas giant 1/3 the mass of Jupiter.
Gliese-876 has a planet 2.6 times the mass of Jupiter along with two other known planets”
And how many of those gas giants are in the habitable zone? Also, as has already been pointed out, they aren’t big enough in most cases to form Terran mass moons. Interestingly, you appear to need brown dwarf sizes…
The overall percentage of gas giants in M systems is quite low, around 1 percent. Given how many more F-G-K type stars there are for every M class star with a gas giant…
Gary,
of the M stars you mention, there is indeed one with a true giant approx. in the HZ:
Gl 876b.
All the other planets mentioned are either outside the HZ and/or too small for real gas giants.
Gary Allen: Sure you are correct that Neptune-class planets are indeed found in red dwarf inner systems (red dwarf systems don’t seem to have nearly so much of a problem forming them). On the other hand, the lower masses compared to Jovian planets result in a much smaller region for stable satellites. Plus you’ve got the issue that at least in our solar system, Uranus and Neptune appear to follow the scaling law between the planetary mass and the mass of the satellite system despite being much less massive than Jupiter and Saturn, so we’d expect the formation of moons massive enough to be habitable to be very unlikely around such worlds.
In fact, for a Neptune-sized planet in the habitable zone of Gliese 581 (orbital radius 0.12 AU), and plugging in the relevant values into equation 7 in this paper about the survival of satellites around inner system giant planets, I get maximum satellite survival timescales of the order of tens to hundreds of millions of years for Earthlike moons, using various sets of estimated tidal parameters for Neptune. Ok, such a system does violate some of the assumptions being made in the model (particularly regarding synchronisation of the planet), but this shouldn’t change too much the overall conclusion that the tidal evolution of such planet+moon systems would occur extremely rapidly.
Neptune-class planets around M dwarfs therefore do not seem to be good candidates for habitable moons. You really need Jupiter-class planets for the moons to stand a chance of surviving for billions of years in the habitable zone, and only in very rare cases do you get a Jupiter that close to an M dwarf star. Take a look at table 1 in the Gliese 649b discovery paper, which lists the known Jupiter-class planets around M dwarfs. Aside from one of the giant planets around Gliese 876, they are all located too far from the star to be habitable (habitable zones for these stars are at ~0.1 AU)… and this paper does not list the hundreds of M dwarfs surveyed which show no signs of Jupiter-class planets at all.
Ronald said:
“Besides the facts mentioned by andy … the following facts: – the ratio of M : F+G+K is not 100:1, but about 70:20, as can be verified at NStars and RECONS, among others.”
If one goes to http://www.recons.org/census.posted.htm , one can find:
For 2000:
F+G+K 71
M 199
M/[F+G+K] 2.8
For 2009:
F+G+K 71
M 239
M/[F+G+K] 3.4
The ratio of M class stars to F+G+K class stars is increasing as a function of time.
Why? Because M class stars include both red dwarfs and brown dwarfs. Brown dwarfs are difficult to detect because of their low magnitude and color that can be down in the infrared. We are discovering new brown dwarfs as bigger and better infrared telescopes go on orbit. I have read some astronomers speculate that the true ratio could be a 100:1 but the truth is that no one really knows. Also I should add that the really low temperature brown dwarfs are not germane to this discussion since it’s difficult to imagine photosynthesis occurring on a world orbiting such a star.
Another aspect about a moon orbiting a gas giant that I did not earlier mention was the gas giant acting as a “garbage man”. An important part of the “Rare Earth Hypothesis” is that our moon and the planet Jupiter act as garbage men protecting the Earth from asteroids and comets. One can see from the many huge impact craters on the Moon, that the Moon has shielded us from many asteroid impacts that could have wiped out life on our planet. However despite the shielding of the Moon and Jupiter, evolution on our Earth has always been a “three steps forward, one step backwards process” as our biological evolution kept being knocked back by asteroid impacts. Now imagine biological evolution on an earth-sized moon orbiting a gas giant. The gas giant would be a far more efficient garbage man than our Moon and Jupiter. Consequently biological evolution on this gas giant moon would be more rapid than on our Earth due to fewer asteroid impacts. I would dare say that technological life could have evolved into existence a hundred million years prior to ours on such a moon. A hundred million years would be more than ample time for self-replicating von Neumann machine / star ships to have spread from one of these worlds and explored the entire galaxy. It’s quite possible that our own solar system was investigated by one of these machines when the Earth’s continents were mostly populated with ferns, dragonflies and cockroaches. I can imagine that we’ve rated a one line entry in a thousand volume galactic star catalog listing us as a boring planet only inhabited by bugs and primitive plants.
Gl 876c it’s habitable zone too… the 2 gas giant in Gl 876 system it’s in the star habitable zone.
the planets on this system maybe could have Earth-size moons with magnetic field to protect the moon atmophere against the M dwarf star flare and the radiation field like jupiter have in our solar system,and moons can have magnetic field like Ganymede the jupiter moon have
however look like the system like Gl876 are very rare,but we can’t be right about it yet,the infrared radial velocity program start too recentily,and there lot of M stars out 22 pc out there still wait for big Telescope be build, like E-ELT with the primary mirror of 42 m, and with high precision radial velocity
Don’t hatchet your counts before they chicken, people. We don’t necessarily want gas giants around M type suns to be in their stars’ habitable zone. That would leave no orbits available for smaller rocky planets (aka earths).
Athena Andreadis said:
“We don’t necessarily want gas giants around M type suns to be in their stars’ habitable zone. That would leave no orbits available for smaller rocky planets (aka earths).”
An ordinary Earth-like planet orbiting an M class star is not interesting as a biologically viable planet. The planet would have to be so close to the star that it would become tidally locked with one face always facing the star (like the Moon’s near side always facing the Earth). However if the Earth-like planet is orbiting a gas giant then the problem goes away. The moon’s sidereal rotation would be some resonance of its orbital period around the gas giant and the gas giant’s orbital period around the star.
Hi Folks;
I would really like to know what planets if any exist in the Proxima Centauri System.
Having seen Avatar, even though science fiction, my interest in any existent ETI peoples that might exist on habitable moons orbiting gas giants has been picced.
If we can find biospheres within the Proxima Centauri System, Barnard’s Star, and other locals, I think the race will heat up to build star ships to get us there.
To that end, one can imagine a sail made of graphene that is 99 percent empty space in the form of a cross woven net where the nets strings are 1 nanometer wide strips of graphene separated by 200 nm. Note that graphene is a one atom thick membranous sheet of carbon and as such is about 0.1 nanometers thick with a density roughly equal to that of water. Graphene has also been measured to be 200 times stronger that structural steel. Too bad only tiny sample have thus far been able to be manufactured.
The equation of motion for a dive and fry relativistic solar sail is:
B[(1 + (B EXP 2)]dB/[(1 ? B)EXP 2] {[1 ? (B EXP2)] EXP 3/2} = p [(R0/x) EXP 2](dx/Ro), where B = v/c, v is the speed of the sail, x is the distance from the star, R0 is the initial distance from the star,
P = 2fA(u0)R0/[Mo(C EXP 2)] where A is the area of the sail, m0 is its rest mass, and u0 is the energy density of starlight at x = R0; thus, u(x) = (u0)[(R0/x) EXP 2].
Adopting the above graphene sail as an example of extreme dive and fry solar sails, assuming f = 1, a value of M0/A = (10 EXP ?9) kg/(meter EXP 2) = the effective mass specific reflecting area of the sail craft, and u0 ~ L/[4(pi)(Ro EXP 2)C] with L the Sun’s luminosity and R0 = .006AU, I find P = 2.3578. Note also that the equation of motion can be integrated analytically to find the terminal speed.
Just integrate B from zero to its terminal value and x from R0 to infinity. This yields for the terminal velocity:
{[(1 ? (B EXP 2)] EXP (1/2)} [7 ? 14B + 11 (B EXP 2) + 2(B EXP 3)]/[(1 ? B ) EXP3](1 + B) = 7 + 15p = 42.367 ~ 42.37
With p = 2.3578, the terminal velocity = 0.6795 C. This corresponds to a gamma factor of 1/{[1 – [(v/C) EXP 2]] EXP (1/2)} = 1/{[1 – [(0.6795C/C) EXP 2]] EXP (1/2)} = 1.363.
Such a sun diver mission could be augmented with maximally efficient fusion powered propulsion systems to get us up to the 0.7 C in Avatar. Antimatter rockets could best number but producing and storing stabilized antimatter that is effectively electrically neutral will take some doing.
However, if Kepler or future observatories find biospheres, the race to get to these star systems will heat up. Even with star diver moderate gamma factor craft augmented by nuclear fusion rockets, we could hop from star to star, colonizing as we go or perhaps terraforming associated moons and planets.
I would not advocate blowing up any huge trees that house native peoples settlements however.
By the way, for those of you who have not yet seen the movie Avatar, this movie is a stellar (no pun intended) work of art. I just cannot stop thinking about it as I periodically scroll through Paul’s latest threads.
Gary,
while you are right that M dwarfs may have been omitted because of observational bias (i.e. harder detectability) and are now turning up with improving technology, in my above estimate I have used recent (2009) data from both RECONS and NStars, the latter up to 50 ly (15.33 parsec) and not 70 ly (I have those data as well) to be representative, because indeed the farther one goes the more observational bias one gets against M dwarfs, and brighter stars then seem overrepresented.
To be more precise, my data analysis points to a % ratio of M/(F+G+K) = 72 : 21 = 3.4 : 1 for RECONS, which is exactly what you also indicate (and in fact a fraction lower than the rounded off 70 : 20 = 3.5 : 1 that I mentioned above) and a % ratio of 69 : 23 = 3.0 : 1 for NStars up to 50 ly.
So, even taking the highest ratio, allowing for additional M dwarfs to be discovered, this ratio does not go up spectacularly (both in increasing survey time and decreasing survey radius). It will never go anywhere in the direction of 10:1, let alone 100:1.
I will even go a step further: even if we consider only the ‘real’ solar type stars, F9 through K2, main sequence (V), between 0.2 to 1.5 times solar luminosity, but allow *all* M dwarfs, we get a % ratio of 72 : 11 = 6.5 : 1. And if we take a modest G8 star, 0.45 solar lum, as an average solar type (while retaining the optimistic 1% lum as an average M dwarf), the HZ of solar : M dwarf is still almost 7:1.
In other words, even being this strict with solar type stars and permissive with M dwarfs, ‘total HZ territory’ of M dwarfs : solar types is still only about 6.5 : 7, hardly equal. Taking into account low occurrence of (giant) planets, and the rest of andy’s objections, etc., this still does not bode well for M dwarfs. The only factor that seems to be in favor of M dwarfs is their amazingly long lifespan, so if and when you get a planet (or exomoon) with life, you are set almost for ever (at least as far as the star is concerned, geological lifespan of the planet is an entirely different matter).
And with regard to brown dwarfs, apart from the fact that there is no indication that their abundance, though significant, is anywhere near what you speculate, what gives you any hope regarding their prospects for planets and life? If M dwarfs are already characterized by paucity of (giant) planets and small HZ, this will be even much more true for BDs! Their HZ will inevitably be very close to non-existent if not totally so.
“If M dwarfs are already characterized by paucity of (giant) planets and small HZ, this will be even much more true for BDs! Their HZ will inevitably be very close to non-existent if not totally so.”
However, as a rule, the smaller the primary is the closer any moons/planets will orbit, so any planets around brown dwarfs will be closer to the habitable zone than you seem to be indicating. For example, M dwarfs appear to have their planets orbiting closer in than more massive stars.
I know all about tidal locking and the thin HZ sphere of M class suns, Gary. Such a planet may be able to support life on the twilight ring. We have a single life sample and cannot generalize until we find another.
Gary Allen said:
“A hundred million years would be more than ample time for self-replicating von Neumann machine / star ships to have spread from one of these worlds and explored the entire galaxy. It’s quite possible that our own solar system was investigated by one of these machines when the Earth’s continents were mostly populated with ferns, dragonflies and cockroaches. I can imagine that we’ve rated a one line entry in a thousand volume galactic star catalog listing us as a boring planet only inhabited by bugs and primitive plants.”
von Neumann machine / star ships ???????
sorry for people the believe in such machines but i don’t buy it!! that sounds more science fiction that truly science!
there not such evidence,the alien use von Neumann machine to explore and colonize the galaxy
well believe for believe, for me make more logical sense the opinion of drpayton
drpayton said:
“Gary Allen, u make an interesting point imho it would make sense that interstellar societies could very well look at our system as a poor investment… Not worth the intergalactic trade, if they were to evaluate our system and the likelihood for advancements, our very environment could be a tell tale sign of a lesser evolved species…We don’t go to primates looking for tech advances…we don’t let monkeys drive cars. Ants can communicate. Or maybe its something we don’t know… Maybe they can tell when a black whole is about to devour a system and they know we aren’t going to survive and they can’t get here quick enough… And though Star Trek is a television show they could be on to something… There could be a galactic law prohibiting first contact. Could be that “they” know what rudimentary communications we have and sent us a message that way… Knowing that it would take millenia to get here but hoping we will evolve sooner… Information may be the only means of contact. Whatever it is, it seems that only people who have the imagination and intelligence to work together and dedicate their lives to mankinds greatest adventure have the chance at ensuring the survival of our species. Because no matter what eventually we are going to have to leave.”
i don’t think mankind it’s ready to live a in interstellar society,we don’t ever such tecnology to build starships !
and about this von Neumann machines need have artificial intelligence who can guarantee what it’s better to build starship or this kind of machine?
and when people talk about this von Neumann machine,they talk like that this von Neumann machine are real!
sorry i don’t buy it,i prefer stay with the starship with a crew that for me make much more sense,i think that von Neumann machine would be much more complex to build, that build starship if not nearly impossible!
Tidal locking does not appear to be a showstopper for maintaining potentially habitable conditions on a terrestrial planet… fairly modest atmospheres should be able to carry enough heat to the nightside of the planet to prevent collapse of the atmosphere/ocean system into a darkside ice cap. Sure it will be very different to conditions on Earth, but not necessarily hostile to biology.
Re. habitability of brown dwarfs – http://www.iac.es/proyecto/nahual/FirstMeeting/Contributions/caballero_nahual04.PPT
“There could be a galactic law prohibiting first contact.”
Which assumes that all alien socieites are monolithic, and can agree on not contacting primitives – very unlikely.
Daniel said:
“i don’t buy it,i prefer stay with the starship with a crew that for me make much more sense,i think that von Neumann machine would be much more complex to build, that build starship if not nearly impossible!”
The physical limitations imposed by relativity and cosmic radiation makes interstellar travel by DNA based life impossible (“Star Trek” is fantasy) . You can still travel to the stars but you are required to leave your biological body behind. The way you achieve this apparent contradiction is by up-loading your consciousness and genome into a machine that is radiation resistant (the star ship’s autopilot computer). After you arrive in the new star system, your body is reconstituted from the machine stored genetic information and your consciousness down-loaded into the newly made body.
The expression “von Neumann self replicating machine” can have rather broad meaning. A fertile man and woman working in a machine shop are effectively a von Neumann self replicating machine, i.e. the man and woman can reproduce themselves sexually and operate the lathes and mills in the machine shop to reproduce the machines. In the context of interstellar travel, the star ship would have an artificial intelligence acting as its autopilot that was very hard against radiation. The star ship would have an extensive machine shop manned with puppets controlled by the artificial intelligence. If something broke on the star ship, it would respond by acquiring raw materials from local asteroids and then fabricate replacement parts in its machine shop. When the star ship entered a new star system, it’s first task would be a preliminary exploration followed by down linking its discoveries back to the home planet. The star ship would then proceed to repair itself by fabricating von Neumann machines. By definition, star ships are huge, massive and complex. The self replicating von Neumann machines would have to replicate geometrically until a significant network of manufacturing capability was recreated. Then the network of von Neumann machines would first repair the original ship and then begin fabricating new star ships. This process would continue enough star ships were built to send off to all nearby star systems. While building this fleet a star ships, local exploration vehicles would also be constructed and the local star system extensively explored. If there was an Earth-like world in-system then “people” would be reconstituted from genomes stored in the auto-pilot. The genetic structure of these people would be edited to match pre-existing conditions on the new “Earth”. Any conscious minds functioning within the auto-pilot would be polled about the new world and given the opportunity to resume living as autonomous beings. The minimum number of people necessary for the new colony could be supplemented with children raised by autopilot puppets and/or reconstituted people. After the new-Earth was seeded and all newly fabricated star ships launched. the von Neumann machine network could either go into idle and allow itself to be dissolved by micrometeorite erosion or actively disassemble itself. Whether or not an extraterrestrial von Neumann machine network would be ethically compelled to actively disassemble itself is a $64,000 question. If the answer is “No” then there should be relics of such a network in our Solar System, i.e. there should be semi-wrecked hardware floating around in the Saturn system in plain view of the Cassini spacecraft. The equatorial ridge on the moon Iapetus is suspicious in that regard but it’s probably too big to be an artifact.
Andy said:
“Tidal locking does not appear to be a showstopper for maintaining potentially habitable conditions on a terrestrial planet… ”
I disagree. The sidereal day of the planet Venus is of long duration, i.e. -243 day. The Venusian atmosphere is essentially a giant hurricane. Nobody really knows what caused Venus to go into thermal runaway. It is believed that Venus once had oceans and a relatively temperate climate (two billion years ago, the Sun was less luminous). However I suspect it was a combination of being almost tide locked and having an inactive mantle (no surface crust recycling) that killed Venus. It is my belief that most (all?) Earth-like tide locked planets within a habitable zone will turn into worlds like Venus before having opportunity to evolve technological life.
All neatly tied up (or down), Gary — but some of your concepts are as fantastic as the Star Trek ones. Computers are as susceptible to long-term hard radiation as other constructs. Also, a body forms with a brain which comes with a mind. You don’t “load” a mind into a body the way you lower an engine into a car chassis, or add programming to a blank computer box. More on this here:
Ghost in the Shell: Why Our Brains Will Never Live in the Matrix
“there should be relics of such a network in our Solar System, i.e. there should be semi-wrecked hardware floating around in the Saturn system in plain view of the Cassini spacecraft”
O-k…. so first you claim that interstellar travel by biological beings is ‘impossible (be careful with terms like impossible), then you claim that the solar system should have alien artifacts floating around, because you assume aliens have visited here.
The surface crust recycling is probably related to the lack of water under present-day conditions. Subduction processes on Earth rely on water to lubricate the process, on Venus this is not possible because the crust is very dry. The high surface temperatures don’t help either: this means you don’t get such a large thermal gradient. The lack of subduction on Venus is likely to some extent caused by the runaway greenhouse conditions, not necessarily a cause of those conditions.
In any case, the overwhelmingly likely culprit for Venus going runaway greenhouse is the location of the planet being too close to the Sun. For a planet with oceans this would lead to higher amounts of water vapour in the atmosphere and hence a stronger greenhouse effect. And once you get temperatures sufficiently hot to shift the equilibrium of the carbonate-silicate cycle so that carbonate rocks break down into carbon dioxide, you’re in real trouble, as the greenhouse effect gets much worse. (Plus you have the subduction zones seizing up as the crust dries out, preventing recycling of atmospheric carbon dioxide back into the interior just to make things worse)
Venus is not a good reason to rule out habitability of tidally-locked planets with more Earthlike insolations.
Gary Allen said:
“The physical limitations imposed by relativity and cosmic radiation makes interstellar travel by DNA based life impossible (“Star Trek” is fantasy)”
mankind still don’t have the science knowledge enough to to prove or disprove tecnology to build starship like in Star Trek, i won’t say that star trek is real, but our Physics still on the infancy,in quantun gravity,casimi efect,dark energy,a “theory of everything” wornhole,etc…
and Gary Allen said:
“The expression “von Neumann self replicating machine” can have rather broad meaning. A fertile man and woman working in a machine shop are effectively a von Neumann self replicating machine, i.e. the man and woman can reproduce themselves sexually and operate the lathes and mills in the machine shop to reproduce the machines. In the context of interstellar travel, the star ship would have an artificial intelligence acting as its autopilot that was very hard against radiation”
“The star ship would then proceed to repair itself by fabricating von Neumann machines. ”
“By definition, star ships are huge, massive and complex”
“If there was an Earth-like world in-system then “people” would be reconstituted from genomes stored in the auto-pilot. The genetic structure of these people would be edited to match pre-existing conditions on the new “Earth”. Any conscious minds functioning within the auto-pilot would be polled about the new world and given the opportunity to resume living as autonomous beings”
sorry this is pure Fantasy!
artificial intelligence?????
the brain it’s complex thing that we know in the universe, and for build such “von Neumann machine” we go to need first understand,what is mind,what is feeling,and all mistery in our brain,maybe this go to be ever more complex,that build wornhole or starship,etc…
then i believe that ” von Neumann machine” it’s a pure fantasy too
“After the new-Earth was seeded and all newly fabricated star ships launched. the von Neumann machine network could either go into idle and allow itself to be dissolved by micrometeorite erosion or actively disassemble itself”
why such artificial intelligence machine would allow itself be self-destroyed?
because that machine need a least human intelligence,then go to be a being with mind,and need to survive like humans,do you really think just go to accept the human order of self-destroy?
sorry but look like that this “von Neumann machines” are more fantasy that star trek,a least warp drive,(ok maybe not work for space travel) have already physics theoric scientific papers, same for wornholes
If the answer is “No” then there should be relics of such a network in our Solar System, i.e. there should be semi-wrecked hardware floating around in the Saturn system in plain view of the Cassini spacecraft. The equatorial ridge on the moon Iapetus is suspicious in that regard but it’s probably too big to be an artifact.
then same theory must be valid to UFOs too, if something on this “von Neumann machines” are serious,probabily UFOs it’s much more serious for science that “von Neumann machines”
a least UFOs people see ,and “von Neumann machines” not one see that
that is pure fantasy more fantasy that star trek
a least the Teleportation in some way it’s been prove for science
Terraformer (a.k.a Tobias Holbrook) said:
“There could be a galactic law prohibiting first contact.”
Which assumes that all alien socieites are monolithic, and can agree on not contacting primitives – very unlikely.
i wouldn’t say some kind of law, but maybe something more like, we are too primitive yet for first contact,why the alien should have interest in make direct contact with such civilization that don’t ever have the capability of interstellar space travel? with such tecnology of travel among the stars,they don’t care for our bissunes here on earth,they have every resources and everything in space with that kind of tecnology!
they maybe have just the interest of study ours from out there,like in a laboratory,and see what we can accomplish.
well still just a speculation…
Athena said:
“some of your concepts are as fantastic as the Star Trek ones. Computers are as susceptible to long-term hard radiation as other constructs. Also, a body forms with a brain which comes with a mind. You don’t “load” a mind into a body the way you lower an engine into a car chassis, or add programming to a blank computer box. ”
Computers as in servers have ECC memory with parity bits to correct actual data bits that were randomly flipped by cosmic radiation. I’m an aeronautical engineer by profession (Stanford University Ph.D, 1984). My job involves designing thermal protection systems (aeroshells) for spacecraft entering planetary atmospheres. The two rovers on Mars (MER A & B) entered the martian atmosphere inside aeroshells that I helped design. I do not trust the results of a scientific program running on a machine without ECC memory. I do all my professional work on machines with ECC memory and all my computers at home have ECC memory. I’m paranoid about stuck bits.
I agree with your statement that a body forms with a brain which comes with a mind. However I see the brain as essentially a vessel holding the human consciousness much like a bottle holding a liquid. If one could attach artificial memory to a human brain much like adding sticks of RAM to a computer then the consciousness could drift into this artificial memory. If through an advanced technology this artificial memory had greater storage capacity than the memory capacity of a living brain then (by definition) most of the consciousness could exist within the artificial memory. This process of memory augmentation could go on for many decades, with a person’s memories and behaviors slowly diffusing into the artificial memory. During this process, natural aging would cause the death of neurons and loss of capacity in the original biological brain. Eventually the original brain would be effectively dead and consciousness would exist entirely in the artificial memory. In essence, I’m describing the process that the Tin Man went through in “The Wizard of Oz”. Now we could go completely off-topic and have a long discussion about whether or not the consciousness inside the machine was the same one originally inside the organic brain. Supposedly our body is constantly replacing itself with new material and it only requires a few years before we’re a “new person”. I find that sort of argument a little bit suspect because I have fillings in my teeth that are over 25 years old. However it is credible that the organic parts of my brain are being continually replaced with fresh organic material.
Terraformer said:
“so first you claim that interstellar travel by biological beings is ‘impossible (be careful with terms like impossible), then you claim that the solar system should have alien artifacts floating around, because you assume aliens have visited here.”
I assumed the Solar System has been visited by starships controlled by artificial intelligence hardened against radiation. There is no contradiction here against the assertion that interstellar travel by DNA based life is impossible. Cosmic radiation in space is like death and taxes (you can’t get away from it). Shielding against cosmic radiation on a star ship is out of the question (it requires walls of concrete 20 feet thick). Simply getting people to Mars is difficult due to cosmic radiation. The longest you want to expose a person to cosmic radiation is about 200 days. Fortunately we can get a person to Mars and back in about that length of time (he’d spend his time on Mars in a habitat regolith shielded against radiation). I design spacecraft for living. The old bit about “never say impossible” is baloney. I encounter impossible problems all the time. It’s part of an engineer’s job to recognize when something is impossible or impractical and design around it. “Impossible” is NASA-Speak is TRL=0 (Technology Readiness Level).
sorry Gary Allen still to much science fiction and less science i don’t buy it
this is your believe and not science, no matter if you are engineer from NASA,” von Neumann machines” fantasy same as star trek
in my believe of something exotic that could turn up is wormholes.wormholes still under study by theoric physiscs and there lot scientific paper of wormhole eveyday, and there a lot things in Physics that we still don’t understand.
Gary, I address all your points in the link I gave earlier, which is the reason I gave it. I’m a research molecular biologist working on brain regulation and function, Harvard ’77, MIT ’84 (since we’re comparing lengths of belts) and I’m as good in my domain as you are in yours. The brain is not a passive vessel, that concept could not be further from the truth. With tiny exceptions, all the central nervous system neurons never get replaced, though their connections (synapses) remain plastic. The details of the connections make and define you as a individual person. That’s your sense of self. When you lose enough neurons from stroke, trauma or dementia, you’re not “you” any more. Here’s the link again, long hand this time:
Ghost in the Shell: Why Our Brains Will Never Live in the Matrix
http://hplusmagazine.com/articles/ai/ghost-shell-why-our-brains-will-never-live-matrix
Gary Allen said:
I agree with your statement that a body forms with a brain which comes with a mind. However I see the brain as essentially a vessel holding the human consciousness much like a bottle holding a liquid. If one could attach artificial memory to a human brain much like adding sticks of RAM to a computer then the consciousness could drift into this artificial memory
this need to be prove by science, it’s much science fiction here ,how could you said that could attach a human brain the complex thing that we know in universe with some machine, it’s not that simple, that maybe it’s so complex that build starship… no way!
Some comments:
While there may be reasons the moon helped development of life on Earth, I do not think it is through tidal effects, much less through their influence (highly hypothetical and much disputed) on plate tectonics. For one, the tidal effects of the sun are roughly equal to those of the moon, making it hard to see why the moon’s would be necessary, somehow.
Even more absurd is the notion that the craters on the moon somehow show that the moon protects us from bombardments. Practically none of the rocks hitting the moon would have hit Earth, and extremely few that would have hit Earth could have been “shielded” by the moon. Why did the Earth not protect the moon?
Another misguided notion that has been left unchallenged is that von Neumann machines require any sort of intelligence. A bacterium is a von Neumann machine, and it has no intelligence whatsoever. Building a technological von Neumann machine from scratch is a colossal undertaking, but it can be done. I believe it can be done today, given sufficient effort. The greatest challenge is the sheer creative manpower needed to design, develop and integrate the many thousands of processes that are required for a machine to assemble itself from raw materials. The technology is there, exemplified by our existing technological economy, but the design task is monumental and for reasons not clear to me almost no work is being done on it. The benefits for humanity would be boundless. Think large, self-maintaining solar-powered factory complexes providing limitless energy and ANY kind of manufactured goods for free. On Earth, and also in space. Anywhere there is metal, oxygen and silicon, which is a lot of places.
xkcd nailed the human von Neumann analaogy:
http://xkcd.com/387/
The alt-text reads “We are sexy, sexy Von Neumann machines.” :-)
A quick semantic point:
“By definition, star ships are huge, massive and complex.”
I disagree that this is true by definition. I think it’s probably true as a matter of physics (as far as we understand it at the moment), but there is nothing inherent in the definition of the concept of a star ship that means it must have these attributes.