Centauri Dreams
Imagining and Planning Interstellar Exploration
Catches, Comets and Europa
If the public seems more interested in spaceflight as a vehicle for streaming TV dramas, the reality of both the Europa Clipper liftoff and the astounding ‘catch’ of SpaceX’s Starship booster may kindle a bit more interest in exploring nearby space. When I say ‘nearby,’ bear in mind that on this site the term refers to the entire Solar System, as we routinely discuss technologies that may one day make travel to far more distant targets possible. But to get there, we need public engagement, and who could fail to be thrilled by a returning space booster landing as if in a 1950’s SF movie?
Europa may itself offer another boost if Europa Clipper’s science return is anything like what it promises to be. Closing to 15 kilometers from the surface and making 49 passes over the icy ocean world, the spacecraft may give us further evidence that outer system moons can be venues for life. We also have the European Space Agency’s Jupiter Icy Moons Explorer (JUICE), which will study Europa, Callisto and, in a spectacular move, end up orbiting Ganymede for extended close-up observations.
Image: Europa Clipper begins its journey. Credit: SpaceX.
JUICE gets to Jupiter in July of 2031, while Europa Clipper starts its flybys in the same year, though arriving in 2030. As a measure of how tricky it can be to get to these destinations, both craft make flybys of other worlds, returning in fact to the Earth for some of these. Europa Clipper’s journey will be marked by gravity assists from Mars in February of 2025 and Earth in December 2026. JUICE has already performed one Earth/Moon flyby and will make a flyby of Venus (August, 2025) followed by two Earth flybys (September 2026 and January 2029). A long and winding road indeed!
Speaking of flybys, it’s interesting to note that we have two cometary appearances this month. Comet C/2023 A3 (Tsuchinshan-ATLAS) and C/2024 S1 (ATLAS) are both likely to be visible in October, with the latter closest to Earth on October 24 as it swings toward Sol where it will likely disintegrate. The former should make an appearance in the western sky just after sunset before growing fainter in the latter part of the month. C/2023 A3 appears to be an Oort Cloud object, or long period comet, with an orbital period of some 80,000 years. Short-period comets (Halley’s Comet is one of these) have much shorter orbits, with Halley’s showing up every 76 years.
I find the Oort Cloud a fascinating subject, for it’s based on deduction and not observation. Astronomer James Wray (Georgia Tech), writing in The Conversation, makes the point that while we can’t directly image this vast collection of comets, likely numbering in the hundreds of billions, we can estimate that it extends possibly as far as halfway to the Alpha Centauri system. That’s an intriguing thought, for it means our cometary cloud may intermingle with an equivalent cloud (if one exists) from the Centauri stars. The space covered by our first interstellar probes is not vacant, though the distances between individual objects would still be vast. On the other hand, if the theory that the Oort Cloud formed because of interactions with the giant planets, it’s possible that in the absence of such planets (still not demonstrated), Centauri A and B may not have formed such a cloud.
Wray makes the case that long-period comets are conceivably our greatest planetary threat, outranking near Earth asteroids in degree of danger since an incoming Oort object would likely not be spotted until well inside the planetary system, giving us little time to react. ‘Oumuamua, after all (not an Oort object) was discovered after its closest approach to Earth.
Cometary flybys of our Sun will always be cherished for their visual appeal as ices evaporate and a tail forms, and a collision course with Earth is a highly unlikely scenario, but it’s always best to consider the prospects. Wray puts it this way:
One way to prepare for these objects is to better understand their basic properties, including their size and composition. Toward this end, my colleagues and I work to characterize new long-period comets. The largest known one, Bernardinelli–Bernstein, discovered just three years ago, is roughly 75 miles (120 kilometers) across. Most known comets are much smaller, from one to a few miles, and some smaller ones are too faint for us to see. But newer telescopes are helping. In particular, the Rubin Observatory’s decade-long Legacy Survey of Space and Time, starting up in 2025, may double the list of known Oort Cloud comets, which now stands at about 4,500.
The European Space Agency’s Comet Interceptor mission, scheduled for launch later in this decade, should offer an option for intercepting an Oort Cloud comet when one appears, making it possible to learn more about these objects in terms of their composition and possible role in the delivery of volatiles to the inner system. Oort comets are tricky because their wide orbits mean gravitational influences from other stars can nudge one into a solar close pass without any prior warning. An incoming long-period comet, writes Wray, might offer mere weeks or days to prepare any defense measures we have in place. Even so, the odds of an impact are extremely low.
Image: A stunning return. The Starship booster comes home. Credit: SpaceX.
All this is by way of hoping public interest in space will be quickened both by recent mission successes, ongoing exploration of possible sources of life, and the appearance of the occasional comet. The startling SpaceX success with Starship’s ‘catch’ underlines that technological advances, like comets, can seem to come out of nowhere when we’re not paying attention. I’m thinking back to the science fiction I read as a kid and realizing that watching Starship’s booster descend was right out of Astounding Stories. Heinlein would have loved it, and indeed foreshadowed what unfolded on Sunday.
As SpaceX communications manager Dan Huot put it: “What we just saw, that looked like magic.”
Go Clipper
Is this not a beautiful sight? Europa Clipper sits atop a Falcon Heavy awaiting liftoff at launch complex 39A at Kennedy Space Center. Launch is set for 1206 EDT (1606 UTC) October 14. Clipper is the largest spacecraft NASA has ever built for a planetary mission, 30.5 meters tip to tip when its solar arrays are extended. Orbital operations at Jupiter are to begin in April of 2030, with the first of 49 Europa flybys occurring the following year. The closest flyby will take the spacecraft to within 25 kilometers of the surface. Go Europa Clipper!
Photo Credit: NASA.
In less than 24 hours, NASA's @EuropaClipper spacecraft is slated to launch from @NASAKennedy in Florida aboard a @SpaceX Falcon Heavy rocket.
Tune in at 2pm PT / 5pm ET as experts discuss the prelaunch status of the mission. https://t.co/Nq36BeKieX
— NASA JPL (@NASAJPL) October 13, 2024
Is Dark Energy Truly a Constant?
In a tantalizing article in The Conversation, Robert Nichol (University of Surrey) offers a look at where new physics might just be emerging in conjunction with the study of dark energy. Nichol is an astronomer and cosmologist deeply experienced in the kind of huge astronomical surveys that help us study mind-boggling questions like how much of the universe is made up of matter, dark matter or dark energy. We’ve assumed we had a pretty good idea of their proportions but a few issues do arise.
One of them seems particularly intriguing. Nichol’s article asks whether dark energy, regarded as a constant, may not actually vary over time. That’s quite a thought. The consensus over a universe made up of normal matter (5 percent), dark matter (25 percent) and dark energy (70 percent) came together early in our century, with dark energy taking the role of the cosmological constant Einstein once considered. Although he came to reject the idea, Einstein would doubtless take great interest in the work of observational cosmologists like Nichol, who keep refining the numbers to reduce errors.
Addendum: I hate typos, and thankfully a reader pointed out that in the penultimate sentence above, I had accidentally typed “with dark matter taking the role of the cosmological constant,” when of course it should be dark energy. Now corrected. Not enough caffeine in play this morning, evidently.
Image: The University of Surrey’s Nichol. Credit: University of Portsmouth.
At the heart of the investigation is the Dark Energy Survey, an international effort involving some 400 scientists in seven countries. The survey’s latest numbers, Nichol reports, are that 31.5 percent of the universe is either dark or normal matter, with an error on the measurement of a scant 3 percent. The question of how almost 70 percent of the universe could be in the form of something we can’t see, and something that is indeed not associated in any way with matter, is what Nichol calls “the biggest challenge to physics, even after 20 years of intense study.”
Remember that we first learned of the acceleration of the universe by studying Type Ia supernova (SNeIa) explosions. These occur in binary systems when a white dwarf star begins drawing off material from its companion, usually a red giant. Reaching the Chandrasekhar limit (approximately 1.4 times the mass of the Sun), the white dwarf releases vast amounts of energy, forming a ‘standard candle’ for cosmologists because the luminosity of these events is completely predictable. In other words, supernovae like these have an intrinsic brightness that can be compared to what is observed, making their distance measurable. Plug in the observed redshift and astronomers can use supernovae to make measurements on the rate of the universe’s expansion.
Image: The Hubble Ultra Deep Field, a view of nearly 10,000 galaxies, a reminder of the stunning scope of cosmological studies. The snapshot includes galaxies of various ages, sizes, shapes, and colours. The smallest, reddest galaxies, about 100, may be among the most distant known, existing when the universe was just 800 million years old. The nearest galaxies – the larger, brighter, well-defined spirals and ellipticals – thrived about 1 billion years ago, when the cosmos was 13 billion years old. This image required 800 exposures taken over the course of 400 Hubble orbits around Earth. The total amount of exposure time was 11.3 days, taken between Sept. 24, 2003 and Jan. 16, 2004. Credit: NASA, ESA, and S. Beckwith (STScI) and the HUDF Team.
The Dark Energy Survey has now reported results on such supernovae over a decade of study which included thousands of such events. The paper makes for fascinating reading. Titled “The Dark Energy Survey: Cosmology Results With ∼1500 New High-redshift Type Ia Supernovae Using The Full 5-year Dataset” (citation below), it significantly adds to the number of observed supernovae. There is just a hint here of flexibility in the direction of a variable dark energy. Let me quote the paper:
The standard Flat-ΛCDM cosmological model is a good fit to our data. When fitting DES-SN5YR alone and allowing for a time-varying dark energy we do see a slight preference for a dark energy equation of state that becomes greater (closer to zero) with time (wa < 0) but this is only at the ∼ 2σ level, and Bayesian Evidence ratios do not strongly prefer the Flat-w0waCDM cosmology.
Untangling: The standard Flat-ΛCDM model is the current description of cosmological structure and evolution, using cold dark matter (CDM) and a cosmological constant (Λ). “Flat’ means that the total energy density of the universe equals the critical density (i.e., a flat universe that continues to expand but at ever slower rates). Again, the cosmological constant is what we associate with dark energy and use to explain the accelerating expansion of the universe. And as the paper makes clear, the DES data fit the existing model, but it’s interesting that a dark energy that varies with time is not ruled out, even if the evidence for this is only enough to hint at the possibility.
Now it gets more intriguing. Nichols points out that a second probe looking at Baryon Acoustic Oscillations (BAO), which are “relics of predictable sound waves in the plasma…of the early universe, before the CMB [cosmic microwave background],” likewise hints at the possibility of dark energy that varies with time. This work is being done with the Dark Energy Spectroscopic Instrument (DESI), which has taken position as the successor to the Sloan Digital Sky Survey (SDSS), which had focused on measuring galactic redshifts.
The DESI results are indeed provocative, especially when seen in light of the supernovae results. From the paper on that work (citation below):
…combining any two of the DESI BAO, CMB or SN data sets shows some level of departure from the ΛCDM model. Relaxing the assumption of a spatially flat geometry through varying ΩK [the curvature density parameter] marginally increases the uncertainties but does not change the overall picture. It remains important to thoroughly examine unaccounted-for sources of systematic uncertainties or inconsistencies between the different datasets that might be contributing to these results. Nevertheless, these findings provide a tantalizing suggestion of deviations from the standard cosmological model that motivate continued study and highlight the potential of DESI and other Stage-IV surveys to pin down the nature of dark energy. (italics mine)
As Nichol puts it in his article:
In particular, when DESI analyses the combination of its BAO results with the final DES SNeIa data, the significance of a time-varying dark energy increases to 3.9 sigma (a measure of how unusual a set of data is if a hypothesis is true) – only 0.6% chance of being a statistical fluke.
Most of us would take such odds, but scientists have been hurt before by systematic errors within their data that can mimic such statistical certainty. Particle physicists therefore demand a discovery standard of 5 sigma for any claims of new physics – or less than a one in a million chance of being wrong!
As scientists will say: “Extraordinary claims require extraordinary evidence.”
Indeed. If we do learn that dark energy varies over time, that would mean that there is less of it now than in the past. We would also need to reconsider our notions about the ultimate fate of the universe depending on this new variable. What a time for physics, when the European Southern Observatory is getting ready to start another massive redshift survey and the European Space Agency’s Euclid mission, launched in 2023, is engaged in its own compilation of redshift data. And then there’s the Vera Rubin Observatory in Chile, which will one day soon be adding its own results to the mix. And then there is the quantum question. Adds Nichol:
According to quantum mechanics, empty space isn’t really empty, with particles popping in and out of existence creating something we call “vacuum energy”. Ironically, predictions of this vacuum energy do not agree with our cosmological observations by many orders of magnitude.
So we’re likely to be learning a great deal more in short order, for the Dark Energy Survey continues to compile its own data, and combining these with the above sources should give us a pretty good handle on the question of a variable dark energy. It’s intriguing to think that we may pin down why current dark energy studies are at variance with quantum mechanics. This is new physics of the kind that should make for Nobel Prizes down the road whatever the outcome of the combined data studies. Cosmology is in Nichol’s view likely entering a ‘new era of cosmological discovery.’
The Nichol article is “Dark energy: could the mysterious force seen as constant actually vary over cosmic time?” in The Conversation 10 October 2024 (full text). The DES paper is DES Collaboration, “The Dark Energy Survey: Cosmology Results With ~1500 New High-redshift Type Ia Supernovae Using The Full 5-year Dataset,” Astrophysical Journal Letters Vol. 973, No. 1 (1 October 2024) L14 (full text). The paper on the BAO measurements is DESI Collaboration et al., “DESI 2024 VI: Cosmological Constraints from the Measurements of Baryon Acoustic Oscillations” (abstract) and available in full text as a preprint.
Planetary Defense: Good News from the Taurids
Evidently discovered by French astronomer Pierre Méchain in 1786, Comet Encke was the first periodic comet to be found after Halley’s Comet. It was named after Johann Franz Encke, who first calculated its orbit. It comes into play this morning because it is considered the source of at least part of the Taurid meteor shower, which is the subject of new work out of the University of Maryland that has implications for our thinking about asteroid and comet mitigation.
Image: This is an image of short-period comet Encke obtained by Jim Scotti on 1994 January 5 while using the 0.91-meter Spacewatch Telescope on Kitt Peak. The image is 9.18 arcminutes square with north on the right and east at top. The integration time is 150 seconds. Credit: NASA.
The Taurids show up in October and November as Earth encounters this stream of debris in an area of its orbit thought to conceal possibly dangerous asteroids. The American Astronomical Society’s Division of Planetary Sciences annual meeting was the occasion for the announcement of the work earlier this week, as noted by Quanzhi Ye at UMD, who summarized the finding:
“We took advantage of a rare opportunity when this swarm of asteroids passed closer to Earth, allowing us to more efficiently search for objects that could pose a threat to our planet. Our findings suggest that the risk of being hit by a large asteroid in the Taurid swarm is much lower than we believed, which is great news for planetary defense.”
The UMD team, working with colleagues at the University of Western Ontario and the University of Washington, Seattle and Poolesville High School in Maryland, used data from the Zwicky Transient Facility telescope, a widefield astronomical survey at Palomar Observatory in California. The idea was to search for objects at least a kilometer in diameter left behind by a much larger source.
The result is heartening, as Ye explains:
“Judging from our findings, the parent object that originally created the swarm was probably closer to 10 kilometers in diameter rather than a massive 100-kilometer object. While we still need to be vigilant about asteroid impacts, we can probably sleep better knowing these results.”
Image: An image of the Taurid meteor shower taken in 2015 by Czech amateur Martin Popek, who produced this striking composite recording fireballs occurring roughly once an hour from the direction of Taurus. Credit: Martin Popek.
Sky surveys like those conducted at the Zwicky Transient Facility track potentially dangerous near-Earth objects, and the ZTF will be used to conduct follow-up studies on the Taurids in coming years. The unusually dusty Comet Encke is relatively large for a short-period comet, with a nucleus of 4.8 kilometers, and it is believed to have experienced significant and likely ongoing periods of fragmentation.
Each new result charting potential danger zones for our world is useful as we work out the likelihood of possible future impacts. While that hunt continues, so too does the effort to learn more about changing the orbit of a potential impactor, as witness the Double Asteroid Redirection Test (DART), a NASA mission that impacted the asteroid moon Dimorphos in 2022 and clearly disrupted the object. The European Space Agency’s Hera mission, launched on October 7, will assess the DART results when it arrives in two years (see A spaceship punched an asteroid — we’re about to learn what came next in the latest issue of Nature for more on this).
The original orbit of Dimorphos was oblate but became much more stretched out (prolate) after the collision with DART. The impact shortened the period of the asteroid’s orbit around its primary by 33 minutes. So we’re learning about at least one way to nudge an asteroid orbit, with other techniques still on the table for future study. Asteroid mitigation will drive near-Earth space technologies forward and move deeper into the system as we add to our catalog of potential impactors, one of which may eventually pose a threat significant enough to prompt action.
Advancing Space Technology and Preparing for Contact with Extraterrestrial Intelligence through Multilateralism
Is it possible that we can account for the Fermi paradox by looking to our own behavior as a species? Some science fiction of the 1950s pointed in that direction, as witness The Day the Earth Stood Still (1951). Dr Kelvin F Long addresses the question in terms of the ‘zoo hypothesis’ in the essay below, asking what our culture could do to make itself less threatening to any outsider. Long is an aerospace engineer, astrophysicist and author. He leads the Interstellar Research Centre, a division of Stellar Engines, which conducts research on the science and technology associated with deep space exploration. He is a Chartered Member of the Institute of Physics and a Fellow of the British Interplanetary Society. He tells me he wrote this article as a means of fundamental protest at the current conflicts engulfing humanity and as a plea to any observing ETI not to judge our species by the immorality of those who hold power over the potential of humankind. Also available on his site are two other documents pertaining to this topic: The Second Sun and Open Letter to the Permanent Members of the UN Security Council.
by Kelvin F. Long
As humanity reaches further out into the Cosmos through our long-range astronomical instruments and also robotic probes, our presence is sure to be noticed by any hypothetical extraterrestrial intelligence (ETI) that may also exist. Yet the development of our technology is not without complications given the potential dual use. Since it involves large powers and energies, this especially includes that any space propulsion machine can also be turned into a weapon. If ETI does exist then they will surely be mindful of how we use this technology and attempt to gauge whether we will bring peace and prosperity to any life in the Universe, or modes of destruction. Given this scenario, it is reasonable to consider that any civilisation that reaches a certain level will reach a point where they will be either permitted to continue in their advance outwards, or potentially face stagnation by clandestine means. It is argued that since within decades we are likely nearing this point of paradigm shift in space technology, the monitoring of our civilisation should be expected currently. In the near future we should prepare for the eventuality that we will either be greeted by intelligence from another world or forced to be restricted within a permanent zoo that constrains us to the Solar System. Preparing for this, such as through reforms of institutions like the United Nations, should be a key component of our nation state relationships through a moral and legitimate multilateral approach to problem solving, but also our exploration roadmaps.
Keywords: Extraterrestrial Contact, United Nations
Introduction
Life on planet Earth has taken many millions of years to evolve to the complex life-forms that characterise Homo sapiens with all its intelligence and associated technological tools. Yet, for centuries, astronomers have speculated [1] that it may be possible that intelligent life exists elsewhere, and this search has informed some of the motivations for our national space programs [2]. Life may have evolved from the same primordial soup and simply been transmitted from one world to another, such as during planetary collisions during the early stages of the Solar System formation, or it may have separate points of evolution that are independent from each other. A discovery of life representative of a separate biogenesis from Earth [3] would be one of the most profound moments in the history of the scientific endeavour.
This search has become more poignant in recent years since the discovery of thousands of exoplanets around other stars thanks to amazing astronomical observatories like the Hubble Space Telescope, the Kepler Space Telescope and the James Webb Space Telescope. These observatories and others that succeed them are sure to change our perspectives on models of planets, stars and life in the Universe as their sensitivity and resolution improves with each decade of technological development. In our search for planets around other stars we have discovered Hot Jupiter’s, Super Earth’s, tidally locked planets and they range in compositions from mostly iron to mostly water [4]. It seems only a matter of time where instruments like this will be able to directly image exoplanets around other stars and fully characterise their atmospheric composition and possible evidence of technological industrialisation.
In a recent article published in Nature Astronomy, Crawford and Schulze-Makuch [5] has argued that it is likely that the apparent absence of Extraterrestrial Intelligence (ETI) in our solar system might be explained by a form of zoo hypothesis [6] in action around the emerging human civilisation. They argue it is either that, or we are the only intelligence that exists in the galaxy, and possibly in the Universe. This would be unsatisfactory since it would imply a special observer position for planet Earth in contradiction to a Copernican principle of cosmology.
Fundamental to the arguments regarding life visiting our solar system is the Fermi paradox, which asserts that there is a contradiction between our theoretical expectations for intelligent life emerging in the Universe and our apparent lack of observations to confirm it has indeed done so. The calculation for such a prediction is based on the number of galaxies, stars, and planets, their measured ages and spectral types when compared to the solar system from which we originate. From a statistical basis, a calculation of probability suggests that we are not special but perhaps typical of an average system that might evolve.
Even if a zoo containment policy was not in action by ETI around our solar system, assuming they exist, they would be wise to at least monitor our activity. In the future it is possible that we will send a robotic probe towards the planets of another star. Since the average distance between stars is 5 light years, any flyby probe crossing this distance in less than a century, would have a velocity of order 0.05c or 15,000 km/s which would have significant kinetic energy associated with its motion.
The Trinity nuclear test in July 1945 had an associated yield of 25 kilotons TNT equivalent, or around 100 TJ. An object with this energy travelling at a speed of 0.05c would only have to have a mass of around ~1 kg. A much larger mass, let’s say of order 1 ton, for the same velocity would have an associated energy of 112,300 TJ or approximately 26,900 ktons TNT equivalent which is around 1,100 Trinity events. Therefore, any probes sent from our solar system towards a potential habitable exoplanet would be of grave concern to any observing ETI. If a probe is able to be decelerated into orbital velocity this may put at rest some concerns and reassure its scientific nature, but before any deceleration takes place the probe would first travel the majority of the distance at the determined cruise velocity and therefore still require careful scrutiny of its intention and trajectory.
Reversing roles, if we detected an emerging species from a nearby star system that also appeared to be technological, in terms of them maturing to an advanced space capability we might also wish to characterise the threat level. Borrowing ideas from how such threats are categorised by nation states we might determine as: Green: Low threat, intention appears to be benign; Amber: Moderate, intention appears benign but advise caution subject to more data; Red: High threat, actions by ETI indicate a threat to humanity is likely. Indeed, we were potentially treated to such an opportunity in 2017 with the arrival of the interstellar asteroid ‘Omuamua, the nature of which remains controversial today [7].
An analogy for ETI observing humanity’s technological developments is the allied monitoring of German nuclear experiments during World War II. Particularly after 1938 when Otto Hahn first discovered nuclear fission and the creation of the ‘Uranium club’ to investigate the military benefits of a nuclear chain reaction. This effort by Germany prompted the creation of the Manhattan project in the United States, to construct the world’s first atomic bomb. Clearly Germany was seen as a significant global threat at the time.
The problem with any such categories is that threats come in many forms and can be intentional or unintentional. In addition, it is difficult to assess the impact on the development of a society by simply exposing them to a simple piece of knowledge or a technology. This has been well recognised by our own society since at least the 1960s with the publication of the Brookings Institution report which stated: “Certain potential products or consequences of space activities imply such a degree of change in world conditions that it would be unprofitable within the purview of this report to propose research on them. Examples include a controlled thermonuclear fusion rocket power source and face to face meetings with extraterrestrials” [8].
Imagine for example, if we went back in time and communicated to Stone Age people that stars were other suns. That innocent piece of information may have profound implications on social-cultural development and give rise to new philosophies. Alternatively, imagine if we gave them an item as innocent as a single wood nail. What inspiration and technological spin-offs would that promote now that they had been exposed to the broader possibilities?
In his famous physics lecture serious the physicist Richard Feynman imagined that there was a cataclysm and all scientific knowledge was lost or destroyed and he asked what one sentence would you want to be passed onto the next generation so that they could build up science and civilisation again. He opinioned that it was the “atomic fact, that all things are made of atoms…In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied” [9].
Now imagine that if ETI was to come here in a spacecraft propelled by technology which, to quote Arthur C Clarke, appeared to be “indistinguishable from magic” [10] to our eyes, since it was based on principles of physics we were yet to discover. It’s possible they would share that technology with us, but even if they didn’t, we might attempt to steal it. Alternatively, even if they refuse to discuss it, now that we have seen it, it will promote research programs in our society that one day leads to its maturation. In other words, the mere seeing of a new phenomenon is enough to spark interest from a curious species that may lead to its eventual creation here. A few years ago, this idea was suggested as a physics postulate by this author where “No information can be contained in any system indefinitely” [11].
In the television series Star Trek they codified these sentiments into an effective Prime Directive [12]. For this reason, any ETI would be concerned about contaminating our species with knowledge or technology and this would be a prudent reason to keep at a distance. Yet also, if they decide we have hostile tendencies as a part of our nature, they would be mindful not to give us any advantage scientifically which could accelerate our development and so increase the potential threat to them.
In general, it would be prudent to speculate when might ETI be most concerned about a human presence in space and therefore warrant actions to mitigate our excess and reach? Since our progress in space is primarily driven by our technological capacity, our advance with science and engineering machines would be of primary importance and at some point, we would reach a peak of maximum interest and therefore a decision point upon which to take actions over our continued activities in space. This is arguably becoming more important since our technological level is rapidly approaching the point where interstellar missions may become possible in future generations since the science case for making the journey is compelling [13].
Indeed, this author has previously estimated that if there are any ETI civilizations within 200 light years distance then first contact may potentially occur any time in the next 100 – 200 years [14]. This is on the basis that technology advances at a certain pace of generations with increasing levels of performance, to eventually maturate to the required level to achieve a given mission over a set distance at a minimum cruise speed. For example, a mission to the nearest star Proxima Centauri at 4.3 light years in 100 years trip time would require a cruise speed of 0.05c, which is a factor ~150 times what we could do in space today with our most advanced propulsion technology, which suggests at least two orders of magnitude improvement required in our current technological state of art before the interstellar mission becomes feasible.
Detecting Emissions
The evidence to support or refute any solutions to the Fermi Paradox by long-range observations depend on our ability to detect emissions from deep space that might demonstrate technology use, such as through deliberate communication transmissions or on accidental release of power and propulsion signatures that might indicate an ETI presence. The detection of emission signatures from space as potential evidence for ETI has been discussed extensively by the astronomer Carl Sagan [15].
Historically all efforts towards the Search for Extraterrestrial Intelligence (SETI) have been focussed on the detection of transmitted radio communications. One of the factors that has influenced this program is the previously believed position that messaging through radio waves (or lasers) is cheaper when compared to sending reconnaissance probes [16], but this is no longer necessarily the case thanks to innovative programs like the Breakthrough Initiatives Project Starshot [17].
In recent years however the perspective on messaging is changing and there is an increased emphasis of technosignatures [18]. This is especially important since the power spectrum emissions of any propulsion technology would likely be several orders of magnitude higher than any transmitted communication signals through radio waves [19].
Since astronomers rely on the detection of natural astrophysical emissions to inform their physical models, it follows that any artificial emissions would also be detected by those same astronomers, so that they could be analysed for either their natural or artificial nature. Therefore, to contain human civilization, to include our awareness of an ETI presence in the galaxy, any artificial emissions coming towards our solar system would have to be filtered by them before arriving at our detectors.
Any filtering would also have to span an enormous range. Diffuse hard x-ray emission from the gas giant Jupiter has been measured at 3.3×1015 erg/s [20]. A recently discovered supergiant x-ray transient XTE J1739-302 was measured with a luminosity or radiated power of 1036 erg/s [21]. A typical supernova at its maximum brightness might have a luminosity exceeding 1043 erg/s, which is a billion times that of the Sun in our own solar system. A Black Hole binary reached a peak gravitational wave luminosity of 3.6×1056 erg/s [22].
The power spectrum from an advanced propulsion fusion engine might be characterised by around 1022 erg/s which would correspond to around 1015 W propulsion jet power, appropriate for a vehicle motion in the range 0.1-0.15c [23]. There are in fact a range of ideas for space propulsion that have been proposed in the literature, from sails to beamers [24], fusion [25] to antimatter [26], relativistic ramjets [27] to space-drives [28], Unruh radiation drives [29] and other methods [30, 31]. To make significant progress, research is required on all of the physics and engineering concepts derived by human imagination and then appropriate links to physics effects in order to estimate the range of emission properties. This includes going beyond known physics and even into the speculative fields of space-time drives or warp drive [32] and wormholes [33], using the tools of General Relativity theory.
How do we distinguish in our models between the discovery of a new astrophysical object and the spectrum from an artificial source such as a power and propulsion technology indicative of industrialisation by ETI? Our interpretation of any data depends strongly on the accuracy of our scientific models to describe physical phenomena in astrophysics but also the physics and engineering of advanced spacecraft machines and how they operate [34].
If a zoo containment policy of our solar system and humanity were in place by ETI, then this raises the question of how this would be practically policed, and a basic analysis of the requirements suggest that it would in fact appear to be rather impractical. Indeed, if we imagine a containment zone around our solar system that was a hollow sphere of radius 100 Astronomical Units, this will have a shell volume of ~2.81×1029 m3.
If we then assumed that any artificial megastructure that made up this filtering material was only 100 m in thickness and assumed a light but smart microporous and transparent optically thin material, perhaps similar to silica aerogel, with an average density of 20 kg/m3, which can survive in space environments whilst maintaining its strength. This then would require a perimeter shell mass of around ~5.62×1030 kg which is approximately ~3 times the mass of our own sun. It would also be noticed gravitationally since it would influence the planetary orbits, and it would need an ability to self-adjust its position to prevent drift.
The use of any material density beyond the one assumed here, such as for metals, would significantly increase the megastructure mass of such a perimeter. If such a material was acting as an emissions filter, the internal matrix of the substance would have to be designed in some way to block out artificial signatures but permit the transmissibility of natural signatures from astrophysical sources to not alert us to the strategy in operation.
In addition, since the presence of our civilization is continually increasing through our robotic probes, the diameter of the wall must be enlarged periodically or altered in some way which may require in-situ management. But then if it is allowed to expand what would be the limit of the containment policy? The barrier would also have to be dynamically operable to allow the passage of long-period comets on eccentric orbits or interstellar objects like ‘Oumuamua [35] and 2I/Borisov [36] to get through and enter our solar system. Instead, perhaps their arrival itself represents evidence that falsifies a containment barrier?
The shell would also have to have a temperature less than the 2.72 K cosmic background microwave radiation, and probably close to 0 K, to prevent its detection through thermal imagers, and so that it did not absorb any energy from its surroundings due to its high transparency. Since it surrounds a star, there is a risk of it trapping the energy from that star in a manner similar to a Dyson sphere, and so any energy passing through it from the star could not undergo attenuation and must be fully transmissible. We might refer to this as a Kelvin shell due to its thermodynamic constraints. It would be manifest of a perfect crystalline material with minimal amorphous material inclusions.
Currently, the Voyager probes launched in 1977 are at a distance of 136 AU for Voyager 2 and 165 AU for Voyager 1 respectively. Since they have apparently been allowed to pass well beyond the 100 AU distance of our solar heliosphere and are also still transmitting science data to the Deep Space Network, this implies that if any such containment wall were in place, it would have to be much further out, and perhaps well into the Oort Cloud. This would then allow for another century or so of human expansion into space as our probes become more sophisticated technologically.
The above physics and engineering requirements illustrate why zoo containment via a physical shell would be problematic and at first glance it could be argued that the lack of finding such a structure may be seen as a partial falsification of the zoo hypothesis. Clearly this would be a project for an advanced technological civilization that goes way beyond the current state of art for human technological maturity and likely implies a high Kardashev level [37] to construct such a large megastructure if indeed it were ever possible.
Alternatively, there is no containment wall and instead it is an artificial boundary that is in some way policed by ETI probes to monitor what we send out there. But then this does not solve the problem of how to prevent us from detecting the presence of ETI in deep space through our astronomical observatories; unless their cloaking and propulsion technology is so advanced that it is beyond our present comprehension. For example, they could have an ability to dampen electromagnetic and gravitational waves as they move across the Cosmos and head towards us; although it is difficult to imagine how this would be completely impermeable. Overall, this implies a contradiction in our understanding and logic for how we are framing the Fermi Paradox within a zoo hypothesis.
It is possible that ETI exists in abundance, but they have made a joint decision not to engage with humanity or to release evidence of their existence and so this results in a null contact. They continue to remain in a stealth mode and do not share any information with us and only keep us under continued observation for their own security. But the technology used in their engines would have to be based on principles so advanced of our science that emissions such as due to electromagnetic waves would not occur.
In effect such an advanced society would be operating a strategy similar to the Planetarium Hypothesis [38] suggested by the science fiction writer Stephen Baxter where external reality is engineered and all we see a form of illusion. Intelligent extraterrestrial life may be in abundance but all signs of it are hidden from our gaze.
On the assumption that some form of containment policy did exist, from our perspective this might manifest itself in the continued failure of our technology programs which aim to achieve far reaching science goals. The sabotage of our technological advancement was explored in the novel The Three-Body Problem written by Liu Cixin [39]. We may get to a point of constructing an interstellar probe for example, but they will never go beyond a certain speed making journey times too long, or they will simply fail in their mission in deep space away from our ability to observe any sabotage of our vehicles.
After many attempts at trying to cross the interstellar void, and presumably at large economic cost, pressure would build on political systems to cease the attempt in the interest of other priorities. In addition, this would also lead to a belief among humanity that interstellar flight is simply not possible since the challenge is too great. A full stagnation of our technology programs past a certain containment zone in space would have been achieved and we may be none the wiser.
We can make preparations to test the existence of a containment zone by equipping our space probes with the appropriate technology and instrumentation sensors to pick up any deep space objects or interference in our probes. Just recently the Voyager 1 mission experienced a major computer malfunction [40], which after months of effort was fixed by designers at the Jet Propulsion Laboratory by uploading corrective programming. The error was put down to a faulty chip and was likely due to the increased cosmic ray flux as the probe goes further out into the interstellar medium and away from the protection of the solar heliosphere magnetic field. Yet, if there were interference in the probe, how would we know the difference or if indeed it has happened already? [41]. These sorts of issues need to be discussed by mission planners in parallel with planning for post-Voyager missions which have been proposed [42, 43, 44].
Breaking out of the Zoo
The U.S President Ronald Reagan recognised the potential impact of an ETI presence in a speech to the United Nations General Assembly in September 1987 in which he said “I occasionally think how quickly our differences worldwide would vanish if we were facing an alien threat from outside this world” [45]. In his speech he was emphasising how much unites the different groups of humanity rather than what makes us different. An imagined alien threat may have been somewhat over dramatized, but the point is still well made, that our disunion is not just a threat to them, but also to ourselves in creating a just and harmonious society. Indeed, this might be precisely what ETI is waiting for, before any meaningful level of inter-species dialogue can take place between two distinct and original interstellar species.
There is a simpler way to break out of any hypothetical zoo and it is one for which all nations of the world should take notice. If it was the case that there are many intelligent technological civilizations out there, but they choose to contain us, perhaps we should instead seek a path of humility and realise that it is highly improbable that we have more wisdom that the collective minds of many vast civilizations that may have existed for millions of years. Perhaps then this should be a prompt for us to look in the mirror at who we are as a species and who we want to become. To conduct ourselves in a manner that would not invite such a containment policy.
Recently, Western nation’s commemorated eighty years since the Normandy invasion of Europe during World War II and the many brave lives lost in the attempt to secure Europe from the grip of Nazi Germany. A mere two decades prior to this was World War I; the supposed war to end all wars. Looking at the world today in 2024, have we changed that much? For all our technological progress and the great truths uncovered by scientific discovery, isn’t our nature fundamentally the same as it always was? A diverse humanity in conflict with each other. This may simply be a result of our evolution through natural selection and undoing millions of years of our nature may not be a trivial undertaking.
We attempted some progress towards a more peaceful union in the construction of the United Nations in 1945 following World War II, and before that the League of Nations following World War I. At the United Nations, this is where all countries can at least sit at a table together and talk through differences without resorting to conflict. But is this institution working? How many conflicts rage around the world today, where it remains impotent to intervene? The United Nations was a good idea, but it clearly needs fundamental reform.
In issue 48 of The Federalist Papers written by James Madison in 1788, he makes a thought-provoking suggestion: “Happy would it be if such a remedy…could be enjoyed by all free governments; if a project equally effectual could be established for the universal peace of mankind” [46]. Whilst adopting a Federalist system for the whole world may be a step too far at this time, perhaps we can at least strive to increase our democratic union.
There may be another way in which the United Nations can be reformed and could lay the foundations for a more peaceful union that is also democratic, whilst also recognising the sovereignty of individual nation states. That is to address Article 27 of the United Nations Charter where “Each member of the Security Council shall have one vote” [47], for a two-thirds majority, and yet only certain states are given the power of a veto. These are the permanent members who include the United States, United Kingdom, France, Russia and China, all of which also happen to be nuclear armed states.
Historically, when a conflict continues with the loss of much civilian life despite attempts at resolutions by members of the United Nations, one can find evidence of a veto by one of these permanent members. As of spring 2024 the veto has been used a total of 277 times. This is split into 128 (Russia), 85 (United States), 29 (United Kingdom), 19 (China) and 16 (France) [48, 49]. How many conflicts could have been avoided if the veto power was not there?
Removing the veto power of permanent members and allowing each nation to have one vote may be the only way to fully achieve a democratic union of all countries in the world, whilst also protecting individual nation state sovereignty and preventing the homogenisation of a diverse set of rich human cultures, where diversity should also be seen as a factor in generating maximum creativity for problem solving. However, given the very different population sizes of countries some mechanism would be needed to ensure proportional representation. This might be in a manner similar to the method used by the United States Congress where all states have equal representation in the Senate but a proportional representation in the House of Representatives.
Even if a direct removal of this power is not feasible, perhaps there are variations on this idea which might be adopted as an alternative. This might include for example that with the five permanent members, for any veto to be carried forward it must have a majority among those five members, which means three against and two for any resolutions proposed by members. That would at least represent some progress towards a more cohesive union and dilute the right of any one nation to act on its own and prevent the will of a majority.
Is it reasonable that a single member of an institution which has 193 members in total has the power to prevent a resolution by a majority of the other representative? Indeed, this is manifest of Empire building and gives permission for unilateral actions of one state against another; the likes of which has so defined the last century of conflicts.
Instead of removing the veto it could be argued that it should be expanded to include more members, but this was already tried in the original League of Nations, where at one point the League Council included 15 countries with veto power and where it was difficult for decisions to be made on any complex issues. If the veto power is removed entirely from all nations, this would create a much more democratic process and arguably create the conditions for increased problem solving as nation states are forced to negotiate a settlement.
Whilst the veto allows states to act in their own sovereign rights and best national interests, removing it would force more of a consideration for international best interests and taking a broader view of humanity as one people. Is it not time to consider that adherence to a charter of rules-based order is more important than a principle of unanimty? Indeed, this may also be a pathway towards a more democratic union along the lines of the principle of subsidiarity at a local nation state level, but enhanced co-operation at a global level among civilised nations seeking to address common problems on the planet.
For sure removing the veto would come with consequences, particularly to those permanent members. Yet it would prevent for example the attack on one country by another without a much broader coalition agreement.
Where is the moral leadership on planet Earth today? It is certainly not being provided by any of the existing permanent members. Where are the grown-ups demanding people put their weapons down and break bread? This also highlights the ineffectiveness of the world’s religions, powerless to intervene, and lacking in courage to protect those caught in the middle of global conflicts. If any moral code laid down to the people of Earth should prompt them into action, “Thou shalt not kill” is certainly one of them. Yet, no definitive and unambiguous call towards peace is made by the leaders of these religions.
It should not be assumed that the conduct of these nations is not being observed closely with long term consequences to how our species will be permitted to advance, or even stagnated towards extinction in the interest of a higher principle than any for which we are currently aware.
In general, in the modern integrated geopolitical world, it should be harder to take unilateral action by one state against another, and when action is required, it should involve a multilateral approach. This would prevent the excesses of one dominant party against another, but also the moderation caused by the other members would result in a more reasonable approach to problem solving that represents a consensus position. For sure, such a decision would take a significant amount of courage and trust by the permanent members, but perhaps that is the bridge that must be crossed if our world is to become unified.
It has been argued that removing the veto would lead to the withdrawal of the permanent member states since they can no longer defend their security interests [50]. This may be so, but nations cannot have it both ways, they either want to exist in isolation or construct a harmonious existence with other nations, consistent with a peaceful and prosperous future for planet Earth. Faced with the potential contact with ETI in the near future, we should ask ourselves what arrangement would facilitate a better contact scenario? One where ETI is expected to engage in dialogue with 193 separate entities, or one where it engages with a representative body for which all nations have influence?
Imagine if the roles were reversed, and ETI came to our planet, but they came in 193 different missions representing that many different societies among their civilisations. How confusing would we find that? What would it say about their own societies lack of cohesion to give us pause for concern in reaching any agreements?
This all points towards a requirement for radical reforms in the governance model and how its various missions are executed and monitored. After all, for those permanent members that would oppose a removal of the veto, this sort of conduct gives their argument legitimacy. The primary function of the United Nations should be to prevent conflict, broker peace settlements, protect the innocent and help to create the conditions for a more prosperous human condition on this planet Earth.
That said, it is acknowledged that in removing the veto this potentially creates the conditions for a different type of geopolitical environment, where countries now attempt to ‘buy’ others votes by the promising of large infrastructure investment projects that would benefit their society. A form of nation state barter if you like. It would all need careful consideration.
The author also acknowledges that his own understanding for how the United Nations operates may be somewhat naive, and in fact the veto may be acting as a form of linchpin on the entire geopolitical diplomacy effort. To remove it may lead to unstable conditions which are difficult to predict. Nobody is a true predictor of the possible futures that may unfold. Yet, it must also be acknowledged that the existing system is not working.
To emphasise some of the positive achievements of the United Nations, in 2005 a study by the RAND corporation [51] concluded that the United Nations provides the most suitable institutional framework for nation building missions, with an emphasis on a comparatively low-cost structure and success rate, and the one with the greatest degree of international legitimacy. It is also a champion of human dignity through the Universal Declaration of Human Rights, first adopted in 1948.
Currently there is a campaign for a United Nations Parliamentary Assembly as a global network of parliamentarians, non-governmental organizations, scholars and citizens that advocate for democratic representation and an influence over global policy [52]. To date 137 nations have so far endorsed the idea. Such a suggestion might go some way to addressing some of the existing problems, but it depends on whether it has any actual power to influence resolutions.
In terms of our activities in outer space Crawford [53] proposed that a World Space Agency is required, possibly acting under the auspices of a federal world government. If the International Space Station in Low Earth Orbit has achieved one thing it has been demonstrating that different nations around the world can co-operate together behind a shared scientific exploration endeavour. This serves as a beacon of hope for what may be possible when we work together, and especially as humanity begins a new age of space exploration in the settlement of the Moon and Mars.
It is likely that significant reforms to our multilateral institutions would be difficult to implement if there is no will do so. Yet, let us not pretend then that the United Nations represents any form of democracy in action. Although the Charter states the words “We the Peoples of the United Nations” [47] the reality is that it has presided over the DisUnited Nations and continued conflict in international affairs. Until we are prepared as a global community to make the changes required to our governing institutions that leads to a more just world, it may be that for any observing ETI we are considered a threat that is to be contained.
A Cosmic Perspective
This is a planet that is spinning through space suspended in a dance of gravity around the Sun, itself spiralling around the Milky Way galaxy, a mere speck of dust in a vast and infinite universe. As we look at our world, we should be reminded of the words of Carl Sagan who said “Our posturings, our imagined self-importance, the delusion that we have some privileged position in the Universe, are challenged by this point of pale light”. He continued “To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we’ve ever known” [54].
As discussed by Deardorff [55] the motivation for any type of containment may be for protecting any existing ETI civilizations from the aggressive tendencies of other emerging species. Any society that exhibits such characteristics will also become self-destructive and so it would be a sensible policy of ETI to not interfere in the development of emerging societies until they can at least demonstrate they can get over this phase of their development and achieve a state of peaceful cooperation with others. If they do become destructive then this would only serve to illustrate their unfitness to join a broader collective.
In the 1951 science fiction film The Day the Earth Stood Still, the alien visitor Klaatu gives a speech to the world. He refers to the creation of a galactic police force of robots that have absolute power over hostile life-forms, but where the conditions are created where civilizations can exist free from aggression and war, free to pursue more profitable enterprises. Klaatu states “It is no concern of ours how you run your own planet, but if you threaten to extend your violence this Earth of yours will be reduced to a burned out cinder” [56]. How would we change if we were really faced with such an ultimatum from outside?
Arthur C Clarke explores this in his 1953 novel Childhood’s End [57] when an alien race known as the Overlords descend to Earth and set about changing it. This includes the creation of a new World Federation using the United Nations to create a golden age of prosperity. Yet, for the humans in the story things do not end well as they eventually say goodbye to their children. When the aliens reveal themselves to humankind, they coincidently have the appearance of the devil, highlighting the illogical prejudice of our species.
In 2023 the United States Congress House Oversight Subcommittee held hearings [58] on the claims of pilots and former federal employees that unidentified anomalous phenomena (UAP) have been seen flying through our atmosphere today. It is interesting to note, following this saga on the social networks since, the suggestion of a spiritual component to the phenomena is being raised by some, with any potential ETI not being seen as our brothers and sisters among the stars, but rather as angels and demons.
Recently, the Vatican has released a document with new guidelines on the norms for discerning alleged supernatural phenomena [59]. Although the supernatural phenomena of interest to the Catholic Church is multi-varied as miracles, they also include the possible of ETI as divine apparitions.
It is these kinds of speculations which have a propensity to cause disharmony in human relationships and prevent our species from indeed achieving childhoods end. One must wonder what Carl Sagan would have thought about all this when he wrote his 1995 book The Demon-Haunted World [60] in an apparent reference to the irrationality of human thinking. Heaven and Hell do exist, and they exist simultaneously here on Earth today, manifest of our actions or inactions and “With our thoughts we create the world” [61].
In 1945 atomic bombs were dropped on the Japanese cities of Hiroshima and Nagasaki and with the hundreds of thousands of deaths that followed certainly hell on Earth existed for them. Today, in our world of global conflicts there exists over 13,000 nuclear warheads in stockpiles around the world which have a combined energy of around 4,000 Mtons TNT equivalent. Asteroids will hit the Earth with a velocity of between 18 – 30 km/s depending on their origin. Assuming such a spherical object was made entirely of Iron with a density of 7,890 kg/m3, with this total energy it would have a diameter of around ~200-300 m across – equivalent to several football sized fields and where the environmental consequences of such an impact would be devastating.
Depending on the impact angle, ground target density and material, the impact would make a crater perhaps as large as 10 km in diameter and generate global environmental effects that are too profound to consider. In the distant future a new intelligence species may evolve on Earth and they would find themselves studying the fossilized remains of Homo Sapiens the way that we study the dinosaurs that disappeared 66 million years ago.
Given the conflicts that still rage around our planet, it is nothing short of insanity that we risk escalation where a new extinction level event presents a real and present danger as an existential threat to our species. If the United Nations is to have a function, it surely must be to prevent such a scenario as this from ever happening, and if it does happen, we can surely point to the Permanent Members as complicit in humanity’s destruction.
The Permanent Members of the United Nations are a result of winning World War II and they have helped to create the modern world that we live in and the periods of stability that we do enjoy. Yet they are also creating the conditions for instability by their conduct in the world and the constant wars, imposed ideologies and atrocities as crimes against humanity. Instead, imagine a future where instead of fighting each other, they were working towards a peaceful co-existence on Earth and in space; as they have done in the exploration of Antarctica and with the International Space Station. Imagine a future where we were building colonies on the Moon, the first cities on Mars, exploring the outer planets and beyond. What new discoveries await us as a grand prize in those undiscovered lands of hope?
Although it cannot be proven, it is possible that the Cosmos has a fundamental qualification for becoming a part of it instead of just being constrained to one planetary biosphere. Those that engage in disunion, conflict and war are not welcome among the intelligent life forms so natural to the stars. For those that engage in peaceful co-operation with each other and construct a union among a civilised people who value creativity, imagination and compassion to each other, even infinity defines no boundary to what may be achieved.
Perhaps only when we step up and recognise the changes that are required within ourselves, will ETI be prepared to fully engage with us. A global multilateral institution like the United Nations is clearly a primary candidate for such change, and if is not, then it is at least complicit in the disharmony of our world. Until then, like animals in a zoo, the broader truths of the wider universe may forever be hidden from our gaze.
Summary
The possible discovery of ETI is one of the most exciting pursuits of the scientific endeavour which will also have profound implications for our social-culture and our understanding of the Cosmos. Yet, whilst we search with enthusiasm for them, we should not be so sure that they are also keen to meet us. This is due to our nature and the tendency to construct technologies which can be used for the purpose of destruction rather than creation. This would be of grave concern to any ETI that exists in our galaxy which values self-preservation and life.
On the assumption that they do exist, and they also have concerns about us, we have speculated on the possibility that a zoo containment policy may be in place around our solar system and surrounding nearby space. Although we have also suggested that a physical containment zoo would be impractical to implement.
To ensure that containment, it may be necessary for ETI to take direct actions to limit our technology growth or the reach of that technology into deep space. This could be through methods of sabotage or other clandestine operations hidden from our view that ultimately result in the moderation of our capability to go further and faster. As President Reagan once said “Perhaps we need some outside, universal threat to make us recognize this common bond” [45]. Yet, they may already be here, and we would be extremely wise to pause and take notice. Benford has suggested that perhaps we should be looking for ETI lurkers within our own solar system and this idea has merit [62].
Since humanity is now reaching a point where certainly missions that travel at speeds of 100 km/s are possible today, and much higher speeds of order 1,000s km/s appear possible towards the end of this century, it would be prudent for us to build protection mechanisms into our space probes to detect the presence of ETI or their attempts to interfere in our space probes. This might include booby-traps in our software programming, or technology sensors which can detect their presence. Whilst this possibility may seem fantastic, this would be the most sensible way to test if a zoo hypothesis containment policy were in action around our solar system.
Meanwhile, it would be a sensible policy to encourage the better angels of our nature and maintain the bonds of affection between nations that are so essential to a peace-loving society which promotes compassion and wisdom as the defining characteristics of what it means to be a human being in a vast and expanding Cosmos, where we may not be alone. As the great scientist Albert Einstein said “Our task must be to free ourselves from this prison by widening our circle of compassion to embrace all living creatures and the whole of nature in its beauty” [63].
Any change is likely to necessitate fundamental reforms to our existing multilateral institutions. It is also likely to require the emergence of a new and inspirational moral leadership class that is currently in abeyance. It could be argued that the lack of moral leadership creates the conditions for global conflict and disunion among an otherwise peaceful people. In relation to space, it should certainly be our task “to avoid the extension of present national rivalries into this new field” [64].
Ultimately, the nations of the world must decide “whether societies of men are really capable or not, of establishing good government from reflection and choice, or whether they are forever destined to depend, for their political constitutions, on accident and force” [65]. A change to the status quo at the United Nations may be the only hope for humanity as we look out upon the precipice of either our fate or our destiny. One of these futures is waiting for us.
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Third Time’s a Charm: A Planet at Barnard’s Star
If you follow the fortunes of the stars closest to us, you know that Barnard’s Star has always excited interest, both because of its proximity to our system (about six light years) but also because of the early work on the star performed by Peter Van de Kamp at Sproul Observatory (Swarthmore College). That work, which ran until the early 1970s, initially appeared to show a Jupiter-class planet at the star but the results were later explained as instrumentation errors in Van de Kamp’s equipment.
It was a cautionary tale, but credit the astronomer for working tirelessly using astrometry to attempt to validate a conclusion we now take for granted: There are planets around other stars. In 2018 we seemed to have a solid detection of a much different planet candidate via Guillem Anglada-Escudé (Queen Mary University, London) and Ignasi Ribas (Institute of Space Studies of Catalonia and the Institute of Space Sciences, CSIC in Spain), indicating a super-Earth of 3.3 Earth masses in an orbit near Barnard Star’s snowline (see A Super-Earth Orbiting Barnard’s Star for that coverage), but no confirmation followed.
Indeed, we may have been looking at stellar activity in this second detection rather than a planet, according to a new paper announcing the discovery of a planet below Earth mass at the star. On the 2018 work, the paper notes that “ESPRESSO data does not support the existence of the 233 d candidate planet.” See Paul Robertson’s A very stealthy alias: the impostor planet of Barnard’s star for a detailed look at the detection and the stellar activity explanation.
But this new announcement of a Barnard’s Star planet looks to be solid. Lead author Jonay González Hernández (Instituto de Astrofísica de Canarias) and team, working at the European Southern Observatory’s Very Large Telescope (VLT) made the find with the help of ESPRESSO (Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations), the successor to the highly successful HARPS spectrograph, capable of teasing out the wobble induced in the star by a planet.
We now have a low-mass planet, as confirmed by HARPS at the La Silla Observatory, HARPS-N (on La Palma, Canary Islands) and CARMENES at the Calar Alto Observatory, Spain. Twenty times closer to Barnard’s Star than Mercury is to the Sun, the planet orbits in 3.15 Earth days and has a surface temperature around 400 K. The planet is about half the mass of Venus, or three times the mass of Mars. Says Hernández:
“Barnard b is one of the lowest-mass exoplanets known and one of the few known with a mass less than that of Earth. But the planet is too close to the host star, closer than the habitable zone. Even if the star is about 2500 degrees cooler than our Sun, it is too hot there to maintain liquid water on the surface.”
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Image: This stunning panorama shows the Milky Way galaxy arching above the platform of ESO’s Very Large Telescope (VLT) on Cerro Paranal, Chile, where the work on the new Barnard’s Star discovery was performed. At 2635 metres above sea level, Paranal Observatory is one of the very best astronomical observing sites in the world and is the flagship facility for European ground-based astronomy. The extent of our galaxy’s cloudy and dusty structure can be seen in remarkable detail as a dim glowing band across the observation deck. Credit: ESO.
Indeed, Barnard’s Star b (which I see is being referred to simply as Barnard b) may not be the only planet here. The paper makes note of three other candidates currently under investigation using ESPRESSO. Here we have to be careful. The radial velocity data show several signals at periods less than 10 days: The paper reports periods of 3.15 d, 4.12 d, 2.34 d and 6.74 d, sorted by strength of the signals. The researchers cannot confirm these signals at this point, but are able to model a system that fits the data. Let me go a bit into the weeds here. From the paper:
[The modeled system] would correspond to a system of four sub-Earth mass planets with mp sin i = 0.32, 0.31, 0.22 and 0.17 M⊕. All candidate planetary orbits would be located inner to the habitable zone of the star, with orbital semi-major axes between 0.019 AU and 0.038 AU. Thus all the candidate planets would be irradiated more than the Earth with incident fluxes between 2.4 S ⊕ to 10.1 S ⊕, and their equilibrium temperatures, assuming albedo of 0.3, would be in between 440 K of the inner planet to the 310 K of the outer planet.
Let’s untangle this (this is how I learn things). The four potential planets that emerge from this model are described by mp sin i, which helps us determine a minimum mass (mp) for a planet. What is at stake here is the inclination angle (i) of the planet’s orbit as viewed from Earth, but because we cannot see such planets, we can go from an edge-on orbit (sin close to 1) to a face-on orbit, where sin i is small and the mass of the planet is much higher. So the numbers above refer to minimum masses that could be higher depending on how the system is tilted to our point of view. If these other worlds exist, they’re all too close to the star to fit the liquid water habitable zone. Indeed, the S value in the quote refers to solar flux, which in the case of the hypothetical planets would be 2.4 to 10.1 times the stellar radiation that Earth receives from the Sun.
In any case, the authors are careful to add that confirming an actual four-planet system at Barnard’s Star would take many more observations using ESPRESSO:
These observations would need to be done with sufficient cadence to sample these planet periods as well as with enough baseline to be able to properly model the activity of the star, in particular, those activity signals associated with the stellar rotation.
So the hunt continues, encouraged by the one newly confirmed planet, as we scour this and other nearby red dwarfs for evidence of small rocky worlds. We can look ahead to ANDES, the ArmazoNes high Dispersion Echelle Spectrograph, which will be used in conjunction with the European Southern Observatory’s Extremely Large Telescope, a 39-meter instrument that will be the largest visible and infrared light telescope in the world. Located at Cerro Armazones in Chile’s Atacama Desert, the telescope should see first light as soon as 2028.
The paper is Hernández et al., “A sub-Earth-mass planet orbiting Barnard’s star,” Astronomy & Astrophysics Volume 690 (October 2024). Full text.