Interstellar objects are much in the news these days, as witness the flurry of research on ‘Oumuamua and 2I/Borisov. But we have to be cautious as we look at objects on hyperbolic orbits, avoiding the assumption that any of these are necessarily from another star. Spanish astronomers Carlos and Raúl de la Fuente Marcos dug several years ago into the question of objects on hyperbolic orbits, noting that some of these may well have origins much closer to home. Let me quote their 2018 paper on this:
There are mechanisms capable of generating hyperbolic objects other than interstellar interlopers. They include close encounters with the known planets or the Sun, for objects already traversing the Solar system inside the trans-Neptunian belt; but also secular perturbations induced by the Galactic disc or impulsive interactions with passing stars, for more distant bodies (see e.g. Fouchard et al. 2011, 2017; Królikowska & Dybczy?ski 2017). These last two processes have their sources beyond the Solar system and may routinely affect members of the Oort cloud (Oort 1950), driving them into inbound hyperbolic paths that may cross the inner Solar system, making them detectable from the Earth (see e.g. Stern 1987).
Scholz’s Star Leaves Its Mark
So much is going on in the outer reaches of the Solar System! In the 2018 paper, the two astronomers looked for patterns in how hyperbolic objects move, noting that anything approaching us from the far reaches of the Solar System seems to come from a well-defined location in the sky known as its radiant (also called its antapex). Given the mechanisms for producing objects on hyperbolic orbits, they identify distinctive coordinate and velocity signatures among these radiants.
Work like this relies on the past orbital evolution of hyperbolic objects using computer modeling and statistical analyses of the radiants, and I wouldn’t have dug quite so deeply into this arcane work except that it tells us something about objects that are coming under renewed scrutiny, the stars that occasionally pass close to the Solar System and may disrupt the Oort Cloud. Such passing stars are an intriguing subject in their own right and even factor into studies of galactic diffusion; i.e., how a civilization might begin to explore the galaxy by using close stellar passes as stepping stones.
But more about that in a moment, because I want to wrap up this 2018 paper before moving on to a later paper, likewise from the de la Fuente Marcos team, on close stellar passes and the intriguing Gliese 710. Its close pass is to happen in the distant future, but we have one well characterized pass that the 2018 paper addresses, that of Scholz’s Star, which is known to have made the most recent flyby of the Solar System when it moved through the Oort Cloud 70,000 years ago. In their work on minor objects with long orbital periods and extreme orbital eccentricity, the researchers find a “significant overdensity of high-speed radiants toward the constellation of Gemini” that may be the result of the passage of this star.
This is useful stuff, because as we untangle prior close passes, we learn more about the dynamics of objects in the outer Solar System, which in turn may help us uncover information about still undiscovered objects, including the hypothesized Planet 9, that may lurk in the outer regions and may have caused its own gravitational disruptions.
Before digging into the papers I write about today, I hadn’t realized just how many objects – presumably comets – are known to be on hyperbolic orbits. The astronomers work with the orbits of 339 of these, all with nominal heliocentric eccentricity > 1, using data from JPL’s Solar System Dynamics Group Small-Body Database and the Minor Planet Center Database. For a minor object moving with an inbound velocity of 1 kilometer per second, which is the Solar System escape velocity at about 2000 AU, the de la Fuente Marcos team runs calculations going back 100,000 years to examine the modeled object’s orbital evolution all the way out to 20,000 AU, which is in the outer Oort Cloud.
That overdensity of radiants toward Gemini that I mentioned above does seem to implicate the Scholz’s Star flyby. If so, then a close stellar pass that occurred 70,000 years ago may have left traces we can still see in the orbits of these minor Solar System bodies today. The uncertainties in the analysis of other stellar flybys relate to the fact that past encounters with other stars are not well determined, with Scholz’s Star being the prominent exception. Given the lack of evidence about other close passes, the de la Fuente Marcos team acknowledges the possibility of other perturbers.
Image: This is Figure 3 from the paper. Caption: Distribution of radiants of known hyperbolic minor bodies in the sky. The radiant of 1I/2017 U1 (‘Oumuamua) is represented by a pink star, those objects with radiant’s velocity > ?1?km?s?1 are plotted as blue filled circles, the ones in the interval (?1.5, ?1.0) km s?1 are shown as pink triangles, and those < ? 1.5?km?s?1 appear as goldenrod triangles. The current position of the binary star WISE J072003.20-084651.2, also known as Scholz’s star, is represented by a red star, the convergent brown arrows represent its motion and uncertainty as computed by Mamajek et al. (2015). The ecliptic is plotted in green. The Galactic disc, which is arbitrarily defined as the region confined between Galactic latitude ?5° and 5°, is outlined in black, the position of the Galactic Centre is represented by a filled black circle; the region enclosed between Galactic latitude ?30° and 30°? appears in grey. Data source: JPL’s SSDG SBDB. Credit: Carlos and Raúl de la Fuente Marcos.
The Coming of Gliese 710
Let’s now run the clock forward, looking at what we might expect to happen in our next close stellar passage. Gliese 710 is an interesting K7 dwarf in the constellation Serpens Cauda that occasionally pops up in our discussions because of its motion toward the Sun at about 24 kilometers per second. Right now it’s a little over 60 light years away, but give it time – in about 1.3 million years, the star should close to somewhere in the range of 10,000 AU, which is about 1/25th of the current distance between the Sun and Proxima Centauri. As we’re learning, wait long enough and the stars come to us.
Note that 10,000 AU; we’ll tighten it up further in a minute. But notice that it is actually inside the distance between the closest star, Proxima Centauri, and the Centauri A/B binary.
Image: Gleise 710 (center), destined to pass through the inner Oort Cloud in our distant future. Credit: SIMBAD / DSS
An encounter like this is interesting for a number of reasons. Interactions with the Oort Cloud should be significant, although well spread over time. Here I go back to a 1999 study by Joan García-Sánchez and colleagues that made the case that spread over human lifetimes, the effects of such a close passage would not be pronounced. Here’s a snippet from that paper:
For the future passage of Gl 710, the star with the closest approach in our sample, we predict that about 2.4 × 106 new comets will be thrown into Earth-crossing orbits, arriving over a period of about 2 × 106 yr. Many of these comets will return repeatedly to the planetary system, though about one-half will be ejected on the first passage. These comets represent an approximately 50% increase in the flux of long-period comets crossing Earth’s orbit.
As far as I know, the García-Sánchez paper was the first to identify Gliese 710’s flyby possibilities. The work was quickly confirmed in several independent studies before the first Gaia datasets were released, and the parameters of the encounter were then tightened using Gaia’s results, the most recent paper using Gaia’s third data release. Back to Carlos and Raúl de la Fuente Marcos, who tackle the subject in a new paper appearing in Research Notes of the American Astronomical Society.
The researchers have subjected the Gliese 710 flyby to N-body simulations using a suite of software tools that model perturbations from the star and factor in the four massive planets in our own system as well as the barycenter of the Pluto/Charon system. They assume a mass of 0.6 Solar masses for Gliese 710, consistent with previous estimates. In addition to the Gaia data, the authors include the latest ephemerides information for Solar System objects as provided by the Jet Propulsion Laboratory’s Horizons System.
Image: This is Figure 1 from the paper. Caption: Future perihelion passage of Gliese?710 as estimated from Gaia?DR3 input data and the N-body simulations discussed in the text. The distribution of times of perihelion passage is shown in the top-left panel and perihelion distances in the top-right one. The blue vertical lines mark the median values, the red ones show the 5th and 95th percentiles. The bottom panels show the times of perihelion passage (bottom-left) and the distance of closest approach (bottom–right) as a function of the observed values of the radial velocity of Gliese?710 and its distance (randomly generated using the mean values and standard deviations from Gaia?DR3), both as color coded scatter plots of the distribution in the associated top panel. Histograms have been produced using the Matplotlib library (Hunter 2007) with sets of bins computed using Numpy (Harris et al. 2020) by applying the Freedman and Diaconis rule; instead of considering frequency-based histograms, we used counts to form a probability density so the area under the histogram will sum to one. The colormap scatter plot has also been produced using Matplotlib. Credit: Carlos and Raúl de la Fuente Marcos.
The de la Fuente Marcos paper now finds that the close approach of Gliese 710 will take it to within 10635 AU plus or minus 500 AU, putting it inside the inner Oort Cloud in about 1.3 million years – both the distance of the approach and the time of perihelion passage are tightened from earlier estimates. And as we’ve seen, Scholz’s Star passed through part of the Oort Cloud at perhaps 52,000 AU some 70,000 years ago. We thus get a glimpse of the Solar System influenced by passing stars on a time frame that begins to take shape and clearly defines a factor in the evolution of the Solar System.
What Gaia Can Tell Us
We can now back out further again to a 2018 paper from Coryn Bailer-Jones (Max Planck Institute for Astronomy, Heidelberg), which examines not just two stars with direct implications for our Solar System, but Gaia data (using the Gaia DR2 dataset) on 7.2 million stars to look for further evidence for close stellar encounters. Here we begin to see the broader picture. Bailer-Jones and team find 26 stars that have or will approach within 1 parsec, 7 that will close to 0.5 parsecs, and 3 that will pass within 0.25 parsecs of the Sun. Interestingly, the closest encounter is with our friend Gliese 710.
How often can these encounters be expected to occur? The authors estimate about 20 encounters per million years within a range of one parsec. Greg Matloff has used these data to infer roughly 2.5 encounters within 0.5 parsecs per million years. Perhaps 400,000 to 500,000 years should separate close stellar encounters as found in the Gaia DR2 data. We should keep in mind here what Bailer-Jones and team say about the current state of this research, especially given subsequent results from Gaia: “There are no doubt many more close – and probably closer – encounters to be discovered in future Gaia data releases.” But at least we’re getting a feel for the time spans involved.
So given the distribution of stars in our neighborhood of the galaxy, our Sun should have a close encounter every half million years or so. Such encounters between stars dramatically reduce the distance for any would be travelers. In the case of Scholz’s Star, for instance, the distances involved cut the current distance to the nearest star by a factor of 5, while Gliese 710 is even more provocative, for as I mentioned, it will close to a distance not all that far off Proxima Centauri’s own distance from Centauri A/B.
A good time for interstellar migration? We’ve considered the possibilities in the past, but as new data accumulate, we have to keep asking how big a factor stellar passages like these may play in helping a technological civilization spread throughout the galaxy.
The earlier de la Fuente Marcos paper is “Where the Solar system meets the solar neighbourhood: patterns in the distribution of radiants of observed hyperbolic minor bodies,” Monthly Notices of the Royal Astronomical Society Letters Vol. 476, Issue 1 (May 2018) L1-L5 (abstract). The later de la Fuente Marcos paper is “An Update on the Future Flyby of Gliese 710 to the Solar System Using Gaia DR3: Flyby Parameters Reproduced, Uncertainties Reduced,” Research Notes of the AAS Vol. 6, No. 6 (June, 2022) 136 (full text). The García-Sánchez et al. paper is “Stellar Encounters with the Oort Cloud Based on Hipparcos Data,” Astronomical Journal 117 (February, 1999), 1042-1055 (full text). The Bailer-Jones paper is “New stellar encounters discovered in the second Gaia data release,” Astronomy & Astrophysics Vol. 616, A37 (13 August 2018). Abstract.
Super interesting article as usual! Puts a lot of the speculation about ‘Oumuamua possibly being an interstellar spaceship into context.
Given the known impact of the KT event, I would be interested in what the possible effect of increased comet encounters would be (notwithstanding Loeb’s controversial idea that the KT event was a comet, not an asteroid).
Could comet impacts have a significant impact on the biosphere, causing evolutionary jumps through extinctions and new species radiation, locally or globally? A comet the size of Hale-Bopp (40-80 km) would cause quite an impact, even if made mainly of ices.
Are there estimates of comet vs asteroid impact frequencies, their energy releases, and possible effects. A comet, unlike an asteroid, would dump a lot of H2O, CO2, and CH4 into the atmosphere. While the energy released might be less, the effect of global heating could be far higher, with a pulse warming, ocean acidification, and subsequently increased weathering. A rough calculation suggests that a comet of Hale-Bopp’s size would raise the sea level by 70 cm from the water alone, and before any warming added to that from melting ice caps, had there been any when the impact occurred.
Scholz’s Star may only now be a threat…though the pass was a long time ago—-it may only be just now that anything it perturbed gets closer to the inner solar system.
Every time Gl 710 gets looked at—the flyby gets closer:
https://forum.cosmoquest.org/forum/science-and-space/astronomy/149381-
The Starflight Handbook said DM 61 366 was to make a close pass. This the same thing? Or maybe a smaller object closer in?
“Such passing stars are an intriguing subject in their own right and even factor into studies of galactic diffusion; i.e., how a civilization might begin to explore the galaxy by using close stellar passes as stepping stones.”
Maybe I am missing something, but I don’t understand this concept of “hitching a ride” on some passing star.
To begin with, that star may not particularly be going anywhere we might want to go.
Secondly, the nearby stars will be traveling at relatively slow speeds in relation to the LSR and to us. Its not like they will give us any advantage in speed. Consider an insect floating down a river on a log. Swimming across to another log floating nearby won’t get it down the river any faster.
Third, it makes no sense energetically. We may be able to generate enough velocity (relative to us) to rendezvous with a passing star, but as we approach it we will have to use a lot of energy to match velocities with it, go into orbit around, or land on it. This is energy which we will not be able to utilize for just going faster. If we are willing to settle for a close fly-by, or an outright collision, we will still not be able to use it to drag us somewhere else. In six dimensional phase space, we not only have to travel to another ( x,y,z) location, we must match its (px,py,pz) momentum vector as well.
I understand that the nearby passage of another star might cause all sorts of havoc in our Oort Cloud, but the idea of using these interlopers as a means of transport eludes me.
I think the reasoning is analogous to the island-hopping of the Polynesians. Each star system becomes the next island to hop to and establish a new civilization before hopping to the next star.
Having said that, I agree with you. Worldships are not small boats, and target destinations are unlikely to be suitable for the encountering star. Far more likely the ship will head for a star that is far more suited to the needs of the ship and crew, whatever those needs may be – a world to live on, a system to mine for resources, etc. It seems to me that the infrequency of encounters makes no sense for the time frame of a civilization expanding into the galaxy. Using James’ value of a 10 ly encounter every 5000 years, even this seems like a very slow way to colonize, given ships that can travel at a modest 0.01 c (3000 km/s). It seems to me this approach is rife with the problem of ship velocity. If you get a chance every 5000 years on average to take a 1000-year journey to that star, wouldn’t it make more sense to increase velocity to 0.02 c to catch that star further away and colonize it first before the slower ship has even sets off? At 0.1-0.2 c, the 10 ly journey takes 50-100 years. Then you have to wait another 5000 years for the next encounter? Why? Why not just head out into the galaxy at that higher velocity, and in 500-1000 years you can reach stars 100 ly away, and 10x further if you want to travel with the same frequency as you would have to wait for 10 ly encounters.
Star hopping or probe incursions at the star encounter rates seem absurdly slow to me.
The advantage of hitching a ride on a passing stellar system would be that it would provide immense resources already escaped from the Solar System. Granted we would not control the direction or velocity but by that time we would have a lot of experience living on the resources of asteroids and probably planets and moons so if we examined a passing system and it was not a total loss surely some group of people would choose to hop aboard and develop a civilization in this new system while traveling to yet another system.
The dynamics of space travel dictate that how close a destination is to you has little to do with how easy it is to get there. Everything is in motion, and braking is just as expensive as accelerating. For the Polynesian seafarers, a nearby island provided a place to rest, refit, or even settle. But the new island was not moving and stopping there would not require an amount of energy comparable to how much it took to get there.
Even in our solar system, sheer distance is not what dictates travel time and cost, its the delta-v you need to reach your destination in a reasonable time PLUS the delta-v you need to match speeds when you get there.
Of course, if your technology allows you to generate ship velocities much greater than that of the drift relative to the LSR, then distance alone becomes a factor in whether or not you choose temporarily nearby destinations.
This was the second objection in my original post.
The desirability of doing this would vary with the technology available. If you have a technology that allows you to build up significant fractions of c And protect yourselves against all the interstellar cosmic rays And against whatever dust or gas you may run into at those speeds And haul along whatever resources you are likely to need on the trip and on arrival And almost everyone is satisfied with life in the Solar System, then people might not choose to jump aboard a passing stellar system.
But if the technology is there to take several people and some technology and a few materials the relatively short distance to the passing system and brake, perhaps using multiple planetary flybys in the process, but that’s about the limit of our tech then I claim this could be appealing.
“Swimming across to another log floating nearby won’t get it down the river any faster.”
Quite a valid point as the logs in proximity approximate each other in forward motion. Lateral drift may result in wide enough separation to be in different streams in the same flow with different rates of forward (and lateral) motion.
If we survive global warming and who knows what after it we should be, by that time, well able to swat away a swarm of incoming comets and asteroids. If we do not survive some great filter whatever’s living on earth then is going to have a very bad time of it. Let’s smarten up and elect more people who will deal with global warming.
“well able to swat away a swarm of incoming comets and asteroids”
Let’s hope so!
Something I wonder about the close stellar passes: how often does a bright star come close enough to outshine the Moon or disturb animal behavior? Humans have created a tremendous amount of light pollution, and while it surely has harmful effects, they’re nowhere near as dramatic as we might have expected from first principles. Did previous encounters with passing stars prepare animals to deal with today’s city lights?
My first “encounter” with this subject was several years ago with a Wikipedia diagram showing how the nearest stars would change their relative position with respect to the sun over about 100K years – and then gradually coming to understand the extent of the Oort Cloud, whether “empty” or “full” of objects waiting to turn into comets. Since then we’ve had a couple of objects with eccentricity significantly higher than 1.0 – and some further integration to identify other past or future encounters, Scholz’s star, say, penetrating the Oort Cloud within less
than 50K AU of the sun.
Now the Oort Cloud’s bounds are arbitrary since it is difficult to map as yet. it’s more inference from constituents dropping in on us – and the perturbing effects are only becoming understood slowly, And when you find the Oort Cloud illustrated, in a local interstellar frame, the nearby stars are not assumed to have similar surroundings. E.g., an astronomy textbook I use showed an Oort Cloud around Sol, but not around its neighbors.
Well, confronted with this illustration, one could
1. take the publishers to task and say fill them all in;
2. assume that the Oort Cloud around sol is an exception
3. wonder about the frequency of Oort Clouds among star and star systems.
As pointed out here, Stolz’s star moved through our system at a distance equivalent to Proxima’s from A& B Centauri. One could well wonder if A &B plus Proxima had stirred up the original system so much that it is now depleted. But then there will be encounters with stars older than ours and some younger. And the younger, single stars have got to have some debris surrounding them. Tau Ceti and Epsilon Eridani both have planets and dust disks. Would it be a wild extrapolation to think that they have Oort Cloud equivalents?
So, while this exposition might be a little tedious, I think it worth considering that encounters with other stars, practically of any type, potentially involves their Oort Clouds as well as ours. And the likelihood of hyperbolic passage would be higher for exo-Oort Cloud components than local ones.
Moreover, if this is the case and Oort Cloud components are similar to what were observed with Kuiper Belt object viewed by the New Horizons spacecraft ( Ultima Thule or Arrokoth), the organic chemistry constituents of comets would not simply be examples of solar nebula material being folded back in. Some fraction of the infall would be from systems outside of the Solar.
Fermi’s argument about “where is everybody?” addresses the diffusion of intelligent life through the galaxy and assumes that if there were any with staying power, it would have arrived at “here” by now – and about all over as well. But the diffusion concept could just as well be applied to building blocks of life, what with encounters as under discussion.
Maybe more than building blocks.
Regarding the case of Scholtz’s star, Thought I should review a couple of its features. Beside penetrating into the Oort Cloud tens of millenia ago, it was also something of a binary system.
Scholtz is small red dwarf, but it travels with a brown dwarf. A more precise description from Wikipedia:
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The primary is a red dwarf with a stellar classification of M9±1 and 86±2 Jupiter masses. The secondary is probably a T5 brown dwarf with 65±12 Jupiter masses. The system has 0.15 solar masses. The pair orbit at a distance of about 0.8 astronomical units (120 million kilometres; 74 million miles) with a period of roughly 4 years. The system has an apparent magnitude of 18.3, and is estimated to be between 3 and 10 billion years old. With a parallax of 166 mas (0.166 arcseconds), about 80 star systems are known to be closer to the Sun. It is a late discovery, as far as nearby stars go, because past efforts concentrated on high-proper-motion objects…
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Being a binary such as it is, I would maintain that it is even more of
a perturber than a single body of about the same mass. And it is also a significant standout to the statistical model of our neighborhood.
Maybe a few more objects out there with a low proper motion are either clearing out of our neighborhood – or headed our way.
It might be easier to address such a study with an example like Mars.
The crater record is longer standing and the poles have elaborate
traces for climate changers. Some likely are associated with the equivalent Milankovich cycles ( perihelion precession and eccentricity),
but some climate events could be disruptions associated with identifiable impact craters. Thus far, the presumed perma frost surround the impact craters are what we associated fluid flows with.
Or, in other words, water and other volatiles already deposited and frozen in. But there might be a way to spot an outlier or two associated with a cometary hit.
The Mars impact study suggestion posted above was intended as a response to Alex Tolley’s consideration of the KT or other impact events here on Earth.
The response landed in the wrong place.
WDK
If close stellar flybys are a common feature, how frequent is stellar capture to form binaries, and perhaps even stellar mergers?
Stellar captures are highly unlikely, probably impossible. Two bodies approaching from “infinite” distances would trade potential for kinetic energy, and would either slingshot by one another, or collide catastrophically. The interaction of a third body to absorb excess energy is required for any capture to take place. Binaries are formed during the star-making process, not later during chance encounters.
For the same reason, ejections from gravitationally bound systems do not occur unless a third body is present to help balance the dynamical books. Ejections and captures occur in crowded, multi-member systems, like solar systems or star clusters.
Statistically speaking stellar mergers or collisions are incredibly rare: so rare that one has probably never happened in our galaxy. That’s a simple consequence of the vast size of the galaxy and the insignificant (in comparison) size of the stars within it. Even during galactic collisions it is almost impossible for two stars to merge.
Blue stragglers are an example of stellar mergers.
Bailer-Jones et al., showed that the number of stars passing within a given distance R, the number of stars passing within a given distance N (R), scales as the square of that distance. This comes about because Earth is in a flow of stars circling the galactic center, so the cross-sectional area is what matters, which gives an R^2 scaling, rather than the volume, ~ R^3. Using accurate 3D spatial and 3D velocity data for millions of stars from the Second Gaia Data Release they showed that a new passing star comes within one light year of our Sun every half million years, 100 within 10 light years.
In my paper of last year, [“How Many Alien Probes Could Have Come From Stars Passing By Earth?”, J. Benford, JBIS 74 76-80, (2021)], I derived a simple expression for this: With N(R) the number of stars passing within a given distance, and R the distance of the star from the Sun in light years, the rate of passing stars is:
dNS(R)/dt = = 2 R^2 (ly^2) stars/Myear
From this, a new star comes within 10 ly every 5,000 years: during our 10,000-year agricultural civilization, two new stars have come within 10 ly.
Given the velocity of the encouter, if the star is bright enough. have any of those stars been tracked by Chinese and other early astronomers? Would not the Gaia data indicate which stars have rapidly become brighter and moved in the sky over say 500-1000 years, and those stars checked against the early observations?
As regards a visiting probe from a stellar encounter, is there some reason that 10 ly is some important distance that is used to suggest we may have been visited by 2 probes since civilizations started? Why not more probes within 20 ly, or fewer in 5 ly? If 1 probe arrives from a star encounter at 1 ly every 500,000 years, isn’t that a possible uplift machine for a tribe of one of our hominid ancestors?
Just pointing out that you can equally well say that our Sun is moving towards Gliese 710 and will pass through its system and its equivalent of the Oort Cloud. It could potentially pass much closer to many smaller bodies than it will do to the parent star itself. Is that something that needs taking into consideration?
And of rogue brown dwarfs and rogue planets we know nothing, many must have drifted through our system much closer as well.
Alex: No reason to choose 10 ly, it’s just a round number. Influence of interstellar probe on hominid ancestors? To quote 2001: ‘…its origin and purpose still a total mystery’.
Gliese 710 will intercept our Oort cloud in 1+ million years. It will have no import for any humans if we are not extinct by then. Either we [humans/post-humans/machine descendants] will have managed to settle the galaxy by then, or are still planet-bound in a likely limited state that will make our current period seem like a vanished, Atlantean golden age. Within the next millennium (probably at the front end) we will have launched probes of various sizes to the stars, maybe even starships. If we haven’t, then we may never do so. Unlike the end of the Roman empire in Europe, there will not be the resources to fully recover and extend our physical technology. [ I don’t care for the hippy-dippy, AI-run society depicted on the Moon in the new tv series “Moonhaven”, a society that still needs regular shipments from a poisoned Earth. I tend to be more in the Cabal camp of Things to Come: “All the universe or nothingness? Which shall it be, Passworthy? Which shall it be? …” ]
All of which is to say that “star-hopping by close encounters” seems to me to be an irrelevance. The time frames are far too long for human cultures. Modern humans in the sense of rapid culture change have only been around for 40-80,000 years. Our modern, post-Malthusian technological world is less than 250 years. Either it continues to flower or we fall back, and with it, the likely end of biological, human, high-tech civilization. Maybe a machine civilization could emerge that has very slow cultural change like the social insects, but I suspect it will be as dynamic as ours, being based on human-designed AI thinking and motivations. If it does emerge, it will be while our civilization is still flowering, and will be given the banner to explore (and exploit?) the galaxy. Similarly, if there are other civilizations out there, they will send their emissaries here regardless of distance, as the travel time will be far shorter than any random stellar encounter. If we do become a post-KII civilization, then we may even be moving the stars themselves.
There is a lot of discussion about how stable our current civilization is and what threats we face. If the modern version of us is about 250 years old it seems obvious that the current level of environmental damage and climate change is a non-linear process, and that the majority of the damage has been done in the last fifty years or so. These effects are rapidly increasing and the rate of increase is increasing (that’s what non-linear means) so to discuss possible human accomplishments (or even survival as a technological society) extending hundreds or even thousands of years into the future seems fraught with peril to me. Planning to take advantage of passing stars as Alex says is a ludicrous idea. Smug self assurance that everything is going well here on Earth and that we have a future of plentiful resources and a well functioning planet also seems extremely dangerous. Actions are required for even short term survival. I won’t bother with any more examples of ecological damage occurring around the entire globe. There are thousands of such events documented and easily accessible on the web. Investigate the works of Jared Diamond or Kim Stanley Robinson or hundreds of other scientists/authors in many fields. Speak out and vote according to your conscience. Every individual matters.
“Planning to take advantage of passing stars as Alex says is a ludicrous idea.” This is why the website is called Centauri DREAMS, as opposed to Centauri mission, project, etc. Basically you have to have faith, sort of like the cathedral builders of the middle ages who seldom lived long enough to see the completed work.
The Catholic Church at least was practical and drew up plans and got building. They weren’t waiting for some distant future event to occur before getting started. Waiting a million years before hoping to fulfill the dream of interstellar flight isn’t quite how I envisage human agency in this endeavor.
OK. While waiting half a million years to hitch a ride on a star that isn’t even passing that close, seems ludicrous, there are other things to consider.
Since there seems to be a “significant overdensity of high-speed radiants toward the constellation of Gemini” that would seem to indicate that Oort cloud objects perturbed by the passing Scholtz star 70k years ago, seems to be arriving here now.
Which means they were perturbed in such a way that they travelled here at a speed that would bring them here in 70k years.
It would seem that there would be other objects which would be perturbed in such a way that they would travel at different speeds. Those traveling faster would have passed through here already, those traveling slower are still coming.
So if we were to slow-boat our way out of here by hopping onto passing Oort Cloud Object (instead of a passing star) , i.e. landing on a passing OCO with a relatively small spacecraft and mining it to al produce more spacecraft to hop onto the next OCO with and b) hollow it out and convert it into a worldship, then we would probably find faster moving OCOs to hop onto further away in the direction which our OCO is traveling in.
Which means that the passage of Scholtz’s star 70k years ago, is now offering us, at this juncture in our technological advamcement, the opportunity to hop onto some logs in the stream and slow-boat our way to other stars which are passing by us further away but at a slower relative speed than Scholtz’s star did.
But still, I’d say in a couple of centuries we’ll have fusion powered starships leaving these slow boats in their dust, so to speak. Which doesn’t mean that we shouldn’t build these slow boats, as they would give us a better understanding of our interstellar surroundings and also give us infrasteucture which would support our endeavours to travel outwards at ever increasing speeds.
So no, we will not wait 1.3 million years for Gliese what-what to pass by us before we hop onto another star, but we do have the opportunity now to start swimming from log to log, presented to us by a star that did pass here 70k years ago. An opportunity we would arguably not have had, had we reached our current technological advancement 10k or 20k earlier or later.
August 2, 2022 at 3:30 PM
THE ALPHA CENTAURI SYSTEM: A BECKONING NEIGHBOR (DL07) – SIMON PETER WORDEN
https://www.youtube.com/watch?v=fkYQ3UVipy8