Hundreds of Nomadic Worlds Within 4 Light Years

New research indicates that tens to hundreds of planet-sized nomadic worlds may populate the spherical volume centered on Earth and circumscribed by Proxima Centauri, and thus may comprise closer interstellar targets than any stellar planetary system. For the first time, there is systematic analysis of the feasibility of exploring these unbounded celestial bodies via deep space missions.

They published several papers and discussed the work at Centauri Dreams. They talk about what propulsion would be needed to reach the nomadic objects when we find them.

Near-future propulsion systems could theoretically enable us to reach nomadic worlds (of radius > R) on a 50-year timescale. Objects with R ∼ 100 km are within the purview of multiple propulsion methods such as electric sails, laser electric propulsion, and solar sails. In contrast, nomadic worlds with R ≳ 1000 km are accessible by laser sails (and perhaps nuclear fusion).

It is fairly challenging to distinguish between interstellar dust and interplanetary dust but we have now captured such dust grains in space for the first time and returned them to Earth.

The existence of interstellar dust is well-known, however, the existence of larger objects has only been hypothesized for a long time. The arrival of 1I/’Oumuamua in 2017 in our solar system changed that. We now know that these larger objects, some of them stranger than anything we have seen, are roaming interstellar space.

We know from gravitational lensing studies that there are gas planet-sized objects flying on their lonely trajectories through the void. Such planets, unbound to a host star, are called rogue planets, free-floating planets, nomads, unbound, or wandering planets. They have been discovered using a technique called gravitational microlensing. Planets have enough gravity to “bend” the light coming from stars in the background, focusing the light, brightening the background star, and enabling the detection even of unbound planets.

~100 km-sized objects have an average distance of about 2000 times the distance between the Sun and the Earth (known to astronomers as the astronomical unit, or AU).

Until now, about two hundred of these planets (we will call them nomadic worlds in the following) have been discovered through microlensing. This is a rough statistical estimate for the average distance, meaning that the ~100 km-sized objects might be discovered much closer or farther away than the estimate.

29 thoughts on “Hundreds of Nomadic Worlds Within 4 Light Years”

  1. So we forget about immediately going to the stars, because the real action may be happening in the space between the stars.

    Difficult to see due to their lack of self illumination, brown dwarfs are being discovered using infrared telescopes and their masses accurately measured for the first time. They may account for the universe’s missing mass, the dark matter needed to explain the gravitational models of the universe’s expansion. Since 90% of the universe’s mass is unseen, there may be vastly more brown dwarfs than stars. What if space is littered with these failed stars, scattered between the bright ones like an interstellar Polynesia, making interstellar travel a series of short hops, rather than a single gigantic one?

    Instead of just being convenient refueling stations for voyages to other solar systems, brown dwarfs could be the hubs of mini-solar systems of their own. The first picture of an extrasolar planet is of a planet orbiting a brown dwarf. While brown dwarfs give off little in the way of light, they do generate heat. Enough heat to make life possible on the planets orbiting them.

    In addition to the Oort Cloud, there is the Kuiper Belt the home of Sedna, Quaoar, and Pluto. There may be dozens or hundreds of mini-solar systems between Sol and Alpha Centauri. With the discovery of brown dwarfs, free floating planets between the stars, and extrasolar planetoids like Sedna, future space explorers may find plenty to keep them occupied in our own solar neighborhood for centuries to come. While not the galaxy spanning empires and federations of science fiction, it would be enough for our species to explore far into the future without the need for exotic starflight technologies.

    There are certain organisms that use infrared here on Earth for photosynthesis (like purple and green bacteria that contain bacteriochlorophyll that absorbs in the infrared). Absent competition from other forms of photosynthesis, there probably isn’t any major obstacles to life derived from infrared instead of the visible spectrum. In fact, we may find one day that life based on visible light photosynthesis is the exception rather than the rule and infra red based life dominates the galaxy. Perhaps we’ll find that our kind of life, based on visible light spectrum photosynthesis, is the rare oddity and infrared based life far more common.

    Now if Brown Dwarfs turn out to be scattered by the dozens or hundreds in the space between the stars (and if most of them have mini solar systems capable of supporting life because enough heat is generated by the BD to allow liquid water and photosynthesis based on infrared frequencies), then the old galactic space operas become as obsolete as dinosaurs on Venus.

    Since these solar systems are a stone’s throw away, they can be reached without exotic warp drives or hyperspace. Simple laser sails or nuclear rockets will do just fine. Exploration missions can visit and return in a matter of years, instead of centuries or millennium.

    Interstellar “empires” and “federations” can be created using slower than light space travel. Maybe Capt. Kirk and Obi Wan Kenobi wouldn’t be impressed, but a BD federation would consider Alpha Centauri to be as far away as Capt. Kirk considered the Andromeda Galaxy.

    P.S. In addition to infrared based life, Cornell researchers have modeled methane based life forms that don’t use water and could live in the liquid methane seas of Titan. Methane based life forms by themselves are a fascinating concept. But ironically the potential “Goldilocks” zone for such life is far greater (extending across the range of Jovian worlds out to the Kuiper belt) than our narrow zone for water based life forms. However, the slow chemical reactions of such cryo-life forms may be such that an intelligent species may take thousands of years to finish a single thought.

    So “life as we know it” based on water and the visible light spectrum photosynthesis may be the rare exception in a universe dominated by methane based life and life that utilizes infrared photosynthesis.

    • I think brown dwarfs are still pretty detectable by IR, but the latest IR survey results have been rather poor.

      No brown dwarf has been found to be closer than Proxima, for example.

      Those results along the results in this topic, place the detectable (and meaningful) rogue body masses between those of dwarf planets and gas giants, but not a lot of stellar brown dwarf masses.

      That’s still a lot of potential real estate, and a chance for a feasible expansion into the cosmos.

  2. I wonder when humanity will realize they live on a ‘world ship’ and there is simply no being-scale propulsion device that will permit interstellar travel on a time scale reasonable to metabolic life. Simple math will show that the complete fission of 1kg of 235U yields only enough energy to accelerate 1kg to ~4% of the speed of light. The Fermi paradox isn’t a paradox – it is an illustration of a very steep potential well or barrier.

    • I suspect that ‘metabolic’ humanity in its current form is a very primitive, fragile, and early state of ‘cosmic’ evolution that will likely be superseded by some type of hybrid, robust, inorganic container, sensory apparaus, and somewhat organic-ish memory/controller construct (read: mind-personality) species. Functional immortality will have its privileges, it just refuses to seek out, become known to, and take an interest (Fermi solution) in its recently-tree-hanging forebears, many 1,000s of pcs off the galactic backwater of Milky Way’s Sagittarius Arm.

    • I agree with you, that life is only possible in a system rich and complex enough to provide the necessities and pleasures of life. 1g gravity, 1 atmosphere, warmth, water, food, living space, company, opportunities to pass your whole life entertained and be as happy as humanly possible.

      So far, only Earth can provide us that.

      But not for long. Humanity will soon have technologies allowing the creation of such world-systems. Relatively soon in historical terms, of course.

      Let’s look at the big picture, and we can notice that humanity no longer has the monopoly of intelligence (which is different of sentience) and technical ability. We are creating machines that are increasingly capable to do what humans do, without weariness nor boredom. Nowadays even making us question the need of some intellectually creative and not-so-creative manual jobs.

      And that such systems have been developed in what amounts to the blink of an eye in historical terms. A century more, and they could be as capable as the mass of humanity to produce the things we need for living, both on Earth and in space.

      Including artificial structures we could inhabit, providing us with the same quality of life we need and enjoy on Earth, and also be sustainable by self monitoring and reparation. What then?

      When Earth ceases being the only ‘world ship’, we could take the new ones anywhere.

      • Lots of people live most of their lives above 16000 feet of altitude(where atmospheric pressure is half of sea level) in the Andes, and the Himalayas. Given time, most people in the world can acclimate to 16000 feet. Of course the same partial pressure of oxygen as on earth is possible at much lower atmospheric pressure.

        It’s not known what gravitational acceleration is needed for long term habitation. Some gravity is certainly needed, but it’s likely that one gee is more than that. Sleeping, doing leisure activity, and desk, and tabletop work in a large centrifuge yielding 1 gee, on a bank relative to local gravity would likely enable extensive activity in say a 0.1 gee environment.

        Such centrifuges may be necessary on Mars, and the moon for long term habitation.

    • “interstellar travel on a time scale reasonable to metabolic life”

      Trees and Fungi can live for thousand of years. The Fermi paradox means (among other things) that no tech species has a lifespan, or even better a dormancy period, that we know is biologically possible.

      It’ll be REALLY embarrassing if we get high C fraction starships, visit other systems, and find they were all settled by someone with ~ 1950s tech, but a really long hibernation period.

      • I don’t quite remember who coined the idea, but it can be paraphrased along the lines of “if there is extraterrestrial intelligence, it most certainly already knows we’re here, and moreover, what we are developing into”.

        Its part of what I believe is the Sobering Reality … that spacefaring intelligences are quite rare (yay!), and quite disinterested (yay!) in a bunch of monkeys that’ve barely learned to wash our privates and keep dirt out of our pounded root porridge. We haven’t invented competent flying cars, subspace radios or even beta tested Star Trek’s warp drives.

        Lets face it… (channeling Bradbury) we’re meat. Meat critters that’ve gotten a good start in Science, and gotten through the all too predictable first baby steps of every nascent starfaring civilization. Blaring radios for a few rotations, blasting out beams of microwaves for awhile, encircling the home planet with an endless succession of working-for-a-few-years then left-for-junk satellites. Just as every other civ does. BORING.

        At least that’s my hope.
        They’re not remotely interested in us … because we’re still terribly boring.


  3. I always had this idea that some of these objects retain an active core from which to extract energy, on top of fuel in the form of hydrogen or water.
    Effectively, we island hop from one object to the other over thousands of years until we reach Alpha Centauri, with one colony giving rise to the subsequent colony or a network of them expanding outward.

  4. I imagine that a far future civilization, after filling up and nimby-fying the worlds and worldlets of the Solar System (that is, reaching the point where development and change slow down and eventually stop), will have parties interested in finding these worlds to make an empire of their own.

    An army of automatically built space telescopes can explore different parts of the sky permanently, looking for the ephemeral signature of a distorted star, pinpointing the location of a future El Dorado.

    At that point, making the effort of going there (they can be decades of travel away) and lighting an artificial sun fed with ice could look as a good investment. It’s a figure of speech, of course, at that point, the construction of most of these new settlements in space ought to be automated, with people or whomever they are just going there for claiming it.

    • Perhaps easier to make these into worldships by burrowing and nudging them to eventually be on gravity-assist sling trajectories, forever travelling the ISM.

    • Gravitational lensing works best for massive, small objects. The less massive the object, the further away you have to be to use it as a gravitational lens. But also, the larger the diameter the further away, because too close and the light it would focus on you is blocked by the body.

      For the Sun, 550 AU.
      For Jupiter mass, 6100 AU. 1/10th light year. Which, incidentally, is about the distance the nearest Jupiter sized object is expected to be.
      Neptune, 13,525 AU
      Saturn, 14,425 AU
      Earth sized? 15,375 AU, because Earth, though much less massive, is a lot more dense.
      Venus? 17,000 AU, a quarter light year.
      Ceres? 9 light years.

      So, gravitational lensing is probably useful for finding objects as small as planets but still close enough to reach, but any asteroid sized bodies it could detect would be too far away to bother with.

      Well, rogue planets must be common enough, and are in a useable size range. If you wanted to hunt for ones within reach, you’d launch your telescopes away from Earth, similar to a Sun gravitational lens mission, and they just look for micro-lensing events on the FAR side of the Sun. Because there are probably several too close to earth to see by gravitational lensing.

      • I find this development of rogue planet detection and the first measured statistics of them very exciting. When I first saw the idea of Polynesian-like island hopping, it was imagined like finding these bodies by sheer luck in the depths of space, by stumbling into them or by their faint IR glow of a few degrees above absolute zero, fortuitously captured from a telescope or robotic spaceship in the Oort cloud.

        Seems these worlds, up to really big sizes, could be pervasive in the depths of galactic space, making a lot more destinations that could be reached faster than the nearest star.

        Even Jupiter like systems with moons are possible, meaning whole chapters of history for some branch of humankind.

        A pity all these things are in the far future us alive won’t live to see. But we could at least be around to see the start of it, and maybe more if there are some surprising developments accelerating things up, who knows?

        • Expecting to see the smaller ones in IR is unrealistic. Brown dwarfs, maybe, but at that point you’re talking pretty distant, and easy to detect by lensing or occultation.

          Occultation and lensing complement each other; Occultation works closer, lensing further away. Both can be done massively in parallel, and by the same equipment at the same time. Technologically, finding these bodies is easier than reaching them; I expect that by the time we’re up to mounting such a mission, we won’t lack for candidates.

          “A pity all these things are in the far future us alive won’t live to see.”

          I know what you mean: As a child I watched the Apollo astronauts walk on the Moon, I grew up thinking I’d end up in space, and then it all just… stalled. For decades. It’s frustrating at times that it’s finally happening as I’m too old.

          Well, we can always hope for some big breakthrough in gerontology or cryonics. But it better come soon.

    • I suspect that colonization of the outer solar system and Kuiper belt will start long before the “nimbification” of the inner solar system. The driving factor will be people wanting to explore social and technological developments that might be unpopular with the powers that be. Cults, religious and otherwise, essentially. Groups that would be characterized as such, anyway.

      Out of sight, out of mind, and just enough distance that checking up on you isn’t worth the trouble.

      Such colonization will start shortly after, or maybe tragically before, the technology is available. Key to enabling it will be some kind of self-reproducing machinery, because outer system colonies pretty much have to be self-sufficient, and the minimum colony size without some kind of replicator is just too large.

      • I presume successful colonization will be all about (read: bottleneck) getting an intelligent entity/ group out there and maintained ‘in a sustainably healthy’ functional state.

      • Agreed. In my comment, I’m assuming propulsion technology develops much more slowly than automation.

        That is, I’m assuming we would have industrial self replication capabilities (with whatever degree of automation) way before having any rocket taking us to a decent fraction of c. And that these capabilities will be used for making fully human compatible environments, for example, smaller rotating habs near our mining outposts, a bit more on planets.

        That means progression would go in waves, filling up places we can go in the short term (1-2 years of travel tops). Ergo first the triad Earth, Moon and Mars and the space around them, then the asteroids and later the outer solar system, in big hops taking decades.

        These places would become “settled” relatively soon in historical terms, though, and the rate of change in them would follow a S-curve, eventually reaching a plateau.

        In that way, a rotating colony produced in space would be relatively cheap for some groups, and if placed conveniently away, it would be not worth the hassle to visit to impose our sanctified laws and rules. At that point, the diaspora could really occur. Probably fed by the earlier space settlers, now fed up with the cancerous growth of regulation and rent-seeking of Earth and the older settled worlds.

        • The thing is, if you’re not in a hurry, and have no particular plans of coming back, propulsion techniques not much more impressive than we use now would suffice for taking you out to the Kuiper belt. Solar or nuclear powered ion engines would do the job just fine, if you’re already in a habitat suitable for long term habitation.

          Or maybe you could rendezvous with a long period comet, with just enough equipment to homestead it, instead of having to accelerate your whole habitat.

          The biggest threat here is the “Far Centaurus” problem: Propulsion advances after you left that were enough to get people to your destination before you.

          The issue is not getting there, it’s getting there FIRST.

  5. Terribly interesting to consider those objects beyond the Heliopause, especially to size, locate, and assess their constituents; but, to assess the interstellar matter/ debris/ leavings amongst the plasma on the leading edge of our heliosphere-as we glide through the galaxyISM- the ultimate of all exo-solar-archeological digs (or filtering exercises as the case may be). To trawl and dredge the various regions outboard of the termination shock, sampling all within the likely zones of stagnation for all means interstellar evidence.
    I, for one, embrace the need to journey and view beyond our voyaging shell, but what better way to truly understand the actual substances beyond than to feature a mission that ‘drags’ over a great area, while ‘surfing’ the leading edge of the sheath.

    • It might sound strange or sifi to some people but Nomadic worlds have always been a part of the universe, I don’t know how many people ever looked at a bible or listen to anything biblical but it has things that pertain to the future, or light years. Example: In my father’s house there are many mansions if it were not so I would have told you. ( What I take from this is, it’s the universe that’s being talked about, because where else could be so massive as to hold such worlds, open your minds and think about it,?And the mansions are the Nomadic Worlds that are light years away. I would like to have feedback about what your thoughts are about this?

Comments are closed.