Mars Clay Findings Are GOOD: The Great Filter Could Be Behind Us

NASA has announced that Curiosity and Perseverance have found the strongest-yet evidence of life on Mars: vivianite and greigite. On Earth these minerals are found in sediments associated with microbial life.

Great Filter-Doomers will find this alarming. If life evolves easily (and quickly - in thermodynamics that's the same thing) then it should be everywhere. And yet, where is everyone? The galaxy appears to be dead. There must be a Great Filter between the appearance of life, and technological civilization leaving its solar system of origin.


It's worth pointing out that until about 700 MA ago, Earth was a boring microbial planet. There was basic multicellular life but until the Ediacaran, nothing that you could actually see with the naked eye, or that had complex organization. In fact for over a billion years it was stuck in a simple oscillation of build up oxygen, die back, build up oxygen, die back, encoded in the banded iron formations (in different redox mixes) visible in extremely old rocks like the ones above in Australia. An alien visitor would have sampled the boring microbial soup and moved on. Visiting a hundred million years later, it would have observed exactly the same situation. Life on Earth was very much like a "blinker" in Conway's Game of Life, with little sign it would ever break out of it. Based on our N of 1, thermodynamically, the appearance of life is likely (it was almost immediately after the Earth cooled!) - and similarly, the appearance of multicellular life is UNlikely.


For that reason, if there is a filter, there's a big question is whether the Filter is behind humanity, or in front of it. The discovery of microbial life on Mars, especially extinct microbial life, would be good news, in the same way that discovering an extinct civilization would be bad news. A thought experiment may help illustrate.

Imagine you send out a fleet of near lightspeed von Neumann probes. As they cover the galaxy, the reports come back to Earth: thousand then millions of planets with oceans of bacteria and/or blue-green algae, some living, some extinct, embedded in clay like the ones on Mars. But absolutely nothing multicellular, anywhere, besides our freakish Earth. Everywhere, simple one-dimensional ecosystems, some "blinking" forever like Earth almost did, but no dusty ruined cities, or eerily silent half-built Dyson spheres, or even alien cockroaches. Nothing beyond a Kardashev 0.001![1] Time to uncorck the champagne! The Great Filter is behind us! We're the first!

Now imagine the opposite case: ghost planet after ghost planet, civilizations that blossomed and then burnt out. Some of them had even sent out their own probes and learned their fate. We would be looking at our own future.

If we assume this Mars finding really is extinct microbes, we now have N=2 for the denominator of how frequently life evolves, and N=1 - where it never got past the microbe stage - a 50% rate of the Great Filter being behind us.[2] Assuming the principal of mediocrity, 50% of the aliens we're not seeing are microbes embedded in clay. 50% is hardly a guarantee of our eternal future among the stars but it moves the needle in the optimistic direction. You might think it would be boring to explore the Solar System and find only microbes on Mars, Venus, under the ice of Europa and Enceladus - but such discoveries should make you happy for humanity's future, especially if they're extinct.


FOOTNOTES

[1] Recently there have been efforts to establish a continuous Kardashev scale (rather than having only discrete classifiers for civilizations which surpassed certain benchmarks, "1" being the power output of a star); one paper assigns 2023 Earth a 0.7276 (Zhang et al 2023.) For very low Kardashev numbers, we could relate the SQ (sentience quotient) for intelligence to the Kardashev scale. Calculating a simple upper bound for the Kardashev number of "algal Earth" - assume a number of cells per meter of seawater equal to that during an algal bloom, times the surface area of Earth's ocean, times the energy budget of an algal cell, divided by the power of the Sun:

5.1x10^14 m^3 x 0.7 x 10^11 algal cells/m^3 x 10^-11 Watts/algal cell
divided by 3.84x10^26 Watts = 10^-12 Kardashev

-70 is the lower bound for SQ, to single-celled organisms, so we can say that -70 SQ converts to 10^-12 Kardashev. Humans have an SQ about +13. However human civilization cooperates to control more energy than a single human, so +13 does not correspond to 0.7276, but whatever the SQ of the human race as a whole, does. You can't get the Kardashev of a single human just by dividing 0.7276 by 8 billion because of the non-zero-sum effects of civilized cooperation.


[2] As written before, Venus had oceans until about a billion years ago. I would have liked to include it here as another microbial blinker planet that ran out of time before its own Ediacaran, with the evidence of both phosphine and microbe-sized UV absorbers in its upper atmospheres, as the remnant of its ecosystem. This would give us a denominator of 3, and even more confidence that the Great Filter is behind us. However, the famous phosphine paper failed multiple attempts at replication and two papers (Jiang et al 2024 and Egan et al 2025) have advanced good candidate abiotic explanations for what the absorbers could be.

Why Are UAPs Associated With Naval Aviation?

We're more likely to find artifacts from technology-using aliens - self-reproducing (von Neumann) probes - rather than the aliens themselves, or even to recognize and understand their signals against background, if any. Indeed, humans may be just at the technological threshold of building such probes right now, but we're far from any serious discussion of manned interstellar travel, and in fact it may never be biologically feasible. Such objects are likely to be found associated with lower gravity objects, ie the asteroid belt, where they can obtain materials and build more of themselves. The further they are from home, the less likely they are to adhere to some "mission", and the more likely they are to have mutated and been selected merely for fecundity (reproductive ability.) Therefore it's not obvious that they would be particularly interested in finding other examples of intelligence. They could very well be much more interested in finding other von Neumann probes, and humans might therefore not be the most interesting thing in the solar system to them. If this is the situation that obtains, this resolves a contradiction: other technology-using species have indeed appeared before us, but there's little evidence of them here.

If the von Neumann probes are built from metal, and one planet over the last few centuries suddenly has large metal objects moving around its surface (ships) and smaller metal objects moving much faster through the atmosphere - then THOSE might be interesting. You might expect the probes to be especially interested in locations with lots of ship and air traffic, and especially the ones with the fastest air-objects, especially if the fast air-objects come and go from the large metal objects on the surface. It's been observed separately by other writers that, from the standpoint of an off-world but in-solar-system alien observer of Earth's behavior in terms of natural processes, the appearance of metal objects in the atmosphere and then suddenly in orbit is the most interesting phenomenon that has appeared here for many millions of years at least.

The fact that it's US Navy aviators who have reported many of the UAP sightings is obviously relevant. Given that the reported observations are made by multiple modalities (naked eye, radar, thermal) and official US agency reports describe as likely mostly physical objects, it's unlikely these are glitches: that is to say, either they're real, or they're made up, possible as sort of intelligence or misinformation operation that we civilians are caught in. But if it's real, two questions are important to the hypothesis.

First: is there really a higher rate of UAP sightings around US Navy aviation areas (as there seems to be so far, with sightings concentrated around San Diego and Virginia Beach) or is this just bias because there are more instruments and observers there? Such is the frequency of these events according to the reports that a relatively low-budget operation with some weather balloons over a low-traffic area could move the needle on whether naval air stations are "enriched" for these objects. (If it does not make any such observations, it would suggest either it's a misinformation campaign, or they're real but concentrated around naval air stations.) Related: do JFK or LAX have similar sightings? Or Heathrow? Narita?

Second: is it really an American (or mostly American) problem? Is the pattern repeated around the world at other countries' naval air stations? China or Russia might not be interested in sharing this kind of information, but NATO allies might be. That said, if an unfriendly country discloses it is seeing the same thing, and it has no explanation, then it's much more likely that these objects are real, and at least are not human-created phenomena.

Unexpected Ejection of Material from Asteroid Bennu

Of obvious interest to any panspermia hypotheses, especially those which favor replicators (Von Neumann probes or otherwise) using organics on low-gravity bodies as building blocks. Paper here. Abstract:

In early 2019, the OSIRIS‐REx spacecraft discovered small particles being ejected from the surface of the near‐Earth asteroid Bennu.sww Although they were seen to be ejected at slow speeds, on the order of tens of cm/s, a number of particles were surprisingly seen to orbit for multiple revolutions and days, which requires a dynamical mechanism to quickly and substantially modify the orbit to prevent re‐impact upon their first periapse passage. This paper demonstrates that, based on simulations constrained by the conditions of the observed events, the combined effects of gravity, solar radiation pressure, and thermal radiation pressure from Bennu can produce many sustained orbits for ejected particles. Furthermore, the simulated populations exhibit two interesting phenomena that could play an important role in the geophysical evolution of bodies such as Bennu. First, small particles (less than 1 cm radius) are preferentially removed from the system, which could lead to a deficit of such particles on the surface. Second, re‐impacting particles preferentially land near or on the equatorial bulge of Bennu. Over time, this can lead to crater in‐filling and growth of the equatorial radius without requiring landslides.

McMahon JW, Scheeres DJ, Chesley SR, French A, Brack D, Farnocchia D, Takahashi Y, Rozitis B, Tricarico P, Mazarico E, Bierhaus B, Emery JP, Hergenrother CW, Lauretta DS. JGR Planets. Dynamical Evolution of Simulated Particles Ejected From Asteroid Bennu. First published: 18 May 2020 https://doi.org/10.1029/2019JE006229

New Approaches on What the Fermi Paradox Means for the Future of Humanity

I was lucky to attend a video lecture by James Miller, economist at Smith College, facilitated by Joshua Fox. Thanks for having this event! I contacted James to let him know I would be posting this and to let him proofread my recapitulation of his argument so as to avoid mis-paraphrasing him; my thanks to him for taking the time to correct me on several points. Of course any errors are mine.

Much of this is familiar terrain for those of us who spend our time considering X-risk and the Fermi paradox. Miller's thesis is that we are at a critically important point in human history, a window where we think that in the near future we can start colonizing the galaxy (the year 2614 at earliest, by this calculation) but at the same time where we are smart enough to destroy ourselves. Since it is not obvious that the galaxy has already been colonized by other civilizations, there may be a Great Filter stopping this from happening. Miller uses the analogy of a person about to climb a mountain, believing that everyone else who has attempted it has died in the process.

Several challenges were discussed by attendees. (If you attended the lecture and want to claim credit for your question, please comment below, thanks.)

1. It's too early to say there are no civilizations; it may not be so easy to detect them or rule them out. We're still discovering metazoans in Manhattan so it seems a little early to rule out von Neumann probes on low gravity bodies in the solar system. We've barely begun to catalog the fauna of our own ocean floors. We could not detect a twin Earth emitting the same radio energy (the C-index), even if it was orbiting Alpha Centauri. Miller points out that even if there were only a few civilizations in the Milky Way preceding us, "the galaxy is older than it is big", and these earlier civilizations could have colonized it already.
   
   
2. He made the point that the things which prove advantageous in the midst of evolving on a single planet might have no such advantages in terms of galactic colonization. Very true; I would argue that we are much more likely to find alien artifacts, than the aliens themselves, as all of us meat-creatures might be stuck on our planets while our machines colonize the galaxy. To that end, (my point) it's entirely plausible that the Solar System could be littered with space probes and we haven't found any yet, or did, and just didn't know what we were looking at.
   
   
3. I would therefore extend Miller's analogy like this. Only in the process of climbing the mountain, does our climber develop wilderness skills and begin to see things that resemble his own boot tracks, etc. and finally as he approaches the summit realizes that lots of people have climbed it, come down the other side, and their descendants have built large villages which due to his previous ignorance he has not been able to locate. (Or, maybe just some of their livestock, trained birds-of-prey, etc. have made it.)
   
   
4. Active attempts to bring ourselves to the attention of aliens have occurred (METI) and been roundly criticized. Miller notes that the risk of extinction from aliens over the next few centuries is lower than eg bio-terrorism or an intelligence singularity. True; but we still may be making life more difficult for our descendants. Related to this, he proposes an ingenious experiment that for a month we should shout our heads off electromagnetically, and see if there is any strange activity. While I agree it's unlikely we'll get invaded next week, I still think the risk:benefit does not work out and there are just too many unknowns, and we may be screwing our distant descendants. Miller suggested that enforcing a moratorium on METI-like activities is probably impossible.
   
   
5. He argues that technological singularities of the paperclip maximizer variety are unlikely to be a major contributor to the Great Filter, because we would be able to see the boundary of it as it expanded (unless it was doing so at light speed.) My concern with this is that, while an AGI might be much smarter than its creators, it is still not omniscient, and the impact of its actions could in principle still outstrip its ability to predict that impact. This is the story behind the rise of human intelligence and the sixth great extinction that we're living through, but has happened in pulses of endogenous extinctions throughout Earth's history (the rise of superpredators every fifty million years or so, the Oxygen Catastrophe). The lesson of evolution here on Earth is that the smarter things are, the faster their behavioral plasticity "catches up with them" in exactly these sorts of disasters, so to suppose that alien paperclip maximizers are immune to this problem is to argue that a qualitative change in ecological dynamics has occurred.
   
   
6. There were two (possibly unappreciated) related questions asked: one about civilization perhaps being bad for sustaining civilization (witness declining birth rates in the developed world) and another that intelligences might prefer virtual reality - involution - to expanding into space. Miller points out the passive version of the "baseball bat" problem: you can live in heaven, but if a bad guy comes and bashes your server with a club and you as you sleep in your VR pod, that's the end of it. (Related: dynamic complex systems like minds, in principle, tend to drift toward delusion and suffer inherent cyclic crises.) It's a thesis for someone in psychology or a related field to note whether there is causation or just correlation between the increasingly encompassing virtual reality-like entertainments available in the developing world, and declining birth rates.
   
   
7. One questioner asked about the distinction between intelligence and civilization - humans have had a "civilization" only since agriculture. This was a really original line of thought. Therefore, there could be many alien intelligences, but few or no civilizations. One solution for humans avoiding the Great Filter would be to abandon civilization and go back to hunting-gathering - not directly suggested, but this is the only implication of such an argument I could think of. The extreme number of assumptions built in to discussion of alien civilizations should always be pointed out - civilization is something that collections of human nervous systems do, and it is not clear it is a necessary consequence of intelligence. (As a physician I ask: do we assume the aliens will have similar EKG waveforms and liver enzymes as us? No, because that's ridiculous. So we do we assume that the even more complex activity of another organ, that we don't even share with other animals on this planet, is automatically going to be meaningfully similar?)

There's also a psychological point to be made about "big picture" arguments (the singularity, the Fermi paradox, the simulation argument, etc.) They have a tendency to converge on either prophetic religion-like conclusions (e.g. the singularity as the rapture for nerds) or Lovecraft (the estivation hypothesis, which was mentioned in a question and made me think about this.) When we talk about these things, there are many many unknowns. In such discussions, I think there is a tendency for the resulting arguments to resemble the internal contours of the human mind, more than any future events in the actual external world; hence their regression to religion-like conclusions. This does not mean such an argument must be incorrect, but it should make us suspicious when a big-picture argument hews too close to our "ontological test pattern. "

Consider in contrast cosmologists' models of the distant future of the universe, which concern physical objects which we can now observe and characterize, using rigorous mathematical rules. These models often seem boring, meaningless, difficult to understand, and unsatisfying. This is exactly how we should expect most models will seem of things outside our own and our ancestors' experiences, or beyond the scale of time and space to which we are accustomed and which we are built to perceive; the further outside their experience, the moreso. This occurred to me when we were discussing the estivation hypothesis, though overall Miller's arguments do not set off many alarm bells for this quick-and-very-dirty heuristic.

Origin of Life in RNA Computing: Independent Suggestion of Organic von Neumann Probes

Previously I had advanced the idea that, if intelligence has arisen elsewhere in the galaxy, it is likely to have colonized the galaxy in some form, and therefore we are more likely to find their artifacts here in our solar system than hear or understand their EM signals.  Specifically I argue that von Neumann probes are more likely to be entities of organic chemistry we find on low gravity bodies, that as natural selection is universal law that such entities - even if dispatched to gather information - would eventually be selected for fecundity; that is, they would inevitably become cancerous.  If the water that seeded the early Earth contained such entities, whether or not they were intact, the tumor detritis of these cancerous von Neumann probes would provide the template for life on ancient Earth.  

We have not nearly approached the amount of solar system exploration, or elaborated an abstract theory of how to recognize life or its artifacts, to be able to say we have absence of evidence.  Indeed we find nucleobases on asteroids, though so far we have no evidence so far that they originated from processes beyond the natural ones we are aware of.  

In a new paper, Hessameddin Akhlaghpour makes the observation that while the RNA information processing behavior of life on Earth is not Turing complete, with some additional (not implausible) molecular machinery, it would be.  He then argues that life originated with such a molecular machine and we have not yet found it.  (H/T Marginal Revolution)

Akhlaghpour H.  A Theory of Natural Universal Computation Through RNA.  arXiv:2008.08814

Timeline of Manned Interstellar Travel, Based on Simple Economics: No Humans on Alpha Centauri Planets Until 2613

It has been estimated that a manned Mars mission would cost $100 billion. Compare this to the most recent unmanned lander, Insight, at $830 million; putting people on Mars then comes with a cost multiplier of 120.

The Initiative for Interstellar Studies estimates that an unmanned interstellar mission would cost at least "in the trillions"; Centauri Dreams cites Odenwald at $174 trillion. Assuming the same scaling, the lower and upper bounds on that then suggest that a manned mission would cost from $240 trillion to $21 quadrillion.

If on the other hand we take the projected cost of a manned mission to Mars, and assume it scales linearly with distance, a manned Mission to Alpha Centauri would cost $55 quadrillion.

It's worth pointing out here that world GDP is $80 trillion. Let's assume an annual economic growth rate over time of 2%. Let's also assume that starting tomorrow we put ALL of GDP toward such a mission - that is, every last human is working this mission and just barely otherwise just barely surviving as peasants eating crumbs.

Assuming an annual economic growth rate over time of 2%, then at earliest, we can launch a manned interstellar mission at the earliest by 2227; at latest, by 2501.

But forget about that. Because neither you, nor any other human on this planet will sign up tomorrow for their descendants being reduced to slavery for centuries for a space mission, which is what those numbers assume. So let's assume we continue to spend money on space exploration at the same rate that we in the US currently are - about 0.11% of GDP. This is already quite a generous assumption, given that most countries can't afford to dedicate such a fraction of wealth to endeavors that don't quickly return on investment. If you're more optimistic and want to set the relative rate of expenditure (over centuries) to the highest it has ever been (in a democracy - you said you were optimistic right?) that's 1966 USA, which is about twice what it is today, and only makes it happen 35 years earlier. (This is more dependent on economic growth than space program expenditure.) So let's stick with current NASA budget fraction, and assume that the future space program is ONLY working on this one mission.

By these assumptions, we can launch the mission at earliest by 2570; for the upper bound estimate, by 2845.

Our fastest spacecraft so far would take another 30,000 years after launch to get there. Let's be more optimistic and assume that the light sail technology we're talking about for unmanned probes also applies to manned craft, and can get the ship up to 10% of the speed of light. Therefore, taking into account travel time and speed-of-light delays, we wiill get the interstellar "Eagle has landed message" at an absolute cheapest earliest date of 2618.

Of course this is still unrealistic, because we're still assuming mission development starts in earnest tomorrow, assuming every government on Earth will let us use a NASA-sized fraction of their GDP for this, and that they will continue to cooperate for at least 550 years building the mission. Think of this in reverse: it's as if in 1470, the middle of the War of the Roses, and the Russians and Poles and Lithuanians still throwing off the Mongol yolk, everyone started spending money and cooperating on a project and continued to cooperate on it until this year.

I think it is unlikely, barring unforeseeable scientific revolutions, that human beings will leave the Solar System this millennium. I think it is likely that there will be civilization or species-threatening or destroying events in this millennium. This discussion of colonizing other planets to mitigate existential risks has a scatter plot listing a probability of event happening within 200 years/risk of civilizational collapse for nuclear war, coronal mass event, rogue AI, and nuclear war as 90%/20%, 70%/90%, and 95%/70%.

Using those same numbers, in the time period until launch there's a greater than a 96.6% chance of a rogue AI, and a greater than 99% chance of coronal mass event or nuclear war.

But fully automated probes could get out more quickly, particularly if we design self-reproducing von Neumann probes. We should start terraforming Mars now, as practice for remotely terraforming planets with von Neumann probes for when we eventually get there. We have time to terraform them, because if physical human bodies ever do get there, it will be in the distant future. But we do not have that much time to get the launch the hardware, which suggests we should at least colonize the Moon as insurance. Cryonics and hibernation technology at this point is still basically science fiction. These numbers are depressing given our previous dreams, but we calibrated on going from powered flight to standing on the moon in 2/3 of a century.

Profits From Asteroid Mining

After the very cool news showing pretty solid evidence that an asteroid breakup and bolide shower was likely responsible for the mid-Ordovician ice age (Schmitz et al 2019), I read about one candidate parent body (or what's left of it) for the L-type chondrites, 433 Eros. This article states that 433 Eros contains "...20 billion tonnes of aluminum and similar amounts of metals that are rare on Earth, such as gold and platinum."

So I set out to calculate the mineral value, based on current prices. For aluminum, I see bauxite cheapest at $50/ton. For gold and platinum, I couldn’t find values per ton of ore so I looked up the current prices (US$1533 and $955/oz resp. as of this writing) then look up average richness of the ores (1 oz/ton and 0.1 oz per ton resp.). Assuming similar richness in asteroid ores to deposits on Earth, would be over thirty-three trillion dollars, which is about 41% of the annual GDP of Earth. And that’s assuming an average 2% growth rate. (The article I linked to calculated twenty trillion, which it may have been closer to in 2014.) Granted, obviously the value will drop when there is suddenly an influx of valuable metals, but I'm assuming you're smart enough to leak the ore slowly and somehow get it to the surface with causing any repeat Chicxulubs.


A question and an observation:

1) How to get down to the surface? Gliders? Can you make gliders out of the (maybe partly processed) material that are disassembled at the surface? There are a number of established concerns that have gathered investors for this enterprise, but that I found, none of them has described how they would get material to the Earth's surface.

2) Most proposals involve mining the asteroids where they are, rather than bringing them nearer to Earth. There's actually a Wikipedia article with a good roundup and list of the companies, but that also points out that Osiris Rex will bring back 60g at a cost of 1 billion dollars.

3) At 2900 cubic kilometers, even if 433 Eros were a perfect sphere (which it's not) it would be just under 9 km to the farthest point from the surface. The deepest operating mine on Earth is South Africa's Ashanti Mponeng at 3.84 km deep. But on Eros, there would not be the same increase in heat and all the attendant problems of real gravity - so the proper comparison is to distance to the pit face. El Teniente in Chile is digging out a single (underground) road that is 17 km, and there are overall in that one mine 3,000 km of tunnels. Compare to Earth, which may have mineral deposits more than 4km below the crust, but we may never got to them - and past the crust, the inside of the planet is a waste because the mantle is molten and mixed. Of course the lay conception of asteroids as solid rocks is usually not correct, as most of them we've interacted with have been rubble piles barely held together by gravity.

4) I selfishly want asteroids to be mined in my lifetime because I believe that's where we'll find evidence of alien life - in the form of small mutant von Neumann probes made from organic chemicals.

Putting Numbers on Panspermia: Material From Earth Impacting Outer System Moons, and Escaping Solar System

In a simulation, Worth Sigurdsson and House (2013) (WSH) retrodict that Europa, Callisto, Titan, and Enceladus have received 1,900, 370, 510 and 340 metric tons of material from Earth, with 3.4 billion metric tons from Earth ejected from the solar system entirely. Enceladus may be less interesting if it really did only form in the cretaceous, but the others have all been there since the start of the solar system. WSH state explicitly that they didn't try to estimate the viability of life surviving the journey, but it cannot be repeated enough that we now have evidence that living things - metazoans, in fact - can survive uncontrolled re-entry with minimal protection, as some worms that were on board the Columbia were found alive on the ground weeks later. We're now able to start putting bounds at least on local panspermia (within our own solar system), though it would be interesting to estimate the chances for gravitational capture by surrounding stars. This is exciting not only to flesh out the realism of panspermia as traditionally considered, but also the idea of very small, molecule- or cell-sized organic von Neumann probes passively spreading between lower-gravity bodies.

A very basic calculation using water surface area and the time it took for life to appear on Earth, shows that all other things being equal, there is a 1-in-3 chance of indigenous life on Europa. An experiment in reproducing impact conditions and local conditions on these moons, along with adding most-likely-transferred Earth fauna, seems that it would be fairly easy to do - a sort of Miller-Urey experiment for local panspermia.

R.J. Worth, Steinn Sigurdsson, and Christopher H. House. Seeding Life on the Moons of the Outer Planets via Lithopanspermia. Astrobiology, Dec 2013.

Asteroid Bennu is Ejecting Dust; Also, "Alien Tech" on Bennu? (Hint: No)

One solution to the Fermi paradox is that there's evidence around us and we just haven't noticed it yet. An estimate of 20 MA for colonizing the whole Milky Way has been advanced, and if von Neumann probes (VNPs) are possible, then they should be around us. We have a tendency to think of VNPs as industrial-age metal objects like Apollo 11, but organic VNPs could diffuse between low-gravity bodies when interstellar comets or asteroids pass through solar systems. Therefore, when we start finding some interesting high molecular weight organic polymers with non-random monomer sequences in the sample-return specimens from asteroids like Bennu, we should seriously consider that this might be what we're looking at. It is therefore interesting that Bennu is ejecting material (see here and here), which would be required if the VNPs are cellular- or molecular-scale chemical replicators that spread passively.

Here ends the serious part.

Admittedly this is an extraordinary hypothesis, and it requires consistent extraordinary evidence to support it. However, noticing that asteroids have boulders on them isn't extraordinary.

Look! Boulders! And they're circled! Gosh, that MUST be alien tech!
One excitable UFO-hunting schmendrick insisted (after doing a complex analysis in Microsoft Paint, i.e. circling the boulders) that Bennu is "littered with alien tech". Then so is the construction site near my house! So is the desert! There are boulders all OVER the place - my gosh, we're surrounded by alien tech! Run! Apparently skulls have also been spotted. Space pirates? This is a particularly morbid form of pareidolia.

Could Modern Bacteria Seed Early Earth? Could Bacteria in Earth Ejecta Do the Same for Extrasolar Planets?

The C-index is this: how close would we have to be to an identical twin Earth to detect them with our SETI searches, given our current detection technology and our (their) emissions? Many argue that we would identify zero twin Earths this way because to detect them, they'd have to be within 3 LY or so - closer than the closest star.

But this post is asking a different question: if modern archaebacteria were seeded onto Hadean prebiotic Earth (say, an iron-sulfur species like the ones that our best guesses show were the last universal common ancestor of all life on Earth) - would they run rampant and colonize the whole world, or would they collapse, relying on some pre-existing network of metabolites produced by other cells? This is relevant to the question of passive colonization of simple organisms from Earth to nearby stars over arbitrary time scales. Archaebacteria in particular are a concern for NASA in terms of contaminating other planets.

This idea has been floated multiple times, including by astronomer and writer Fred Hoyle. Here is how the process of passive colonization could work. Asteroid impacts are sometimes powerful enough to eject surface material at greater than escape velocity. This is how we have over 100 fragments of Mars on Earth right now. If this happens, some bacteria may survive the initial shock, heat, then freezing and dehydration (some bacteria can survive these conditions; and in any event it doesn't have to be many.) Some of these meteorites will escape Earth orbit. If in vacuum and cold they're stable for arbitrarily long periods, they'll just accumulate in the solar system as septic Earth-meteorites over time. Some percentage of these fragments will interact with a solar system body (e.g. Jupiter) and be accelerated to solar escape velocity (like Oamuamua was in its native system.) Some percentage of those will enter another solar system (this is likely to happen once every 15 billion years, based on calculations inspired by Oamuamua.) Some percentage of these fragments will pass through a solar system with "primitive" planets with a liquid water-CO2 atmosphere like the early Earth. Some percentage of fragments will actually strike those planets, and some percentage of bacteria will make it to the surface intact.

Of course there are many unknowns and I only cited one number. We need to know the bacterial "burden" blasted out of orbit per unit time - none of those in our lifetimes, probably not even Tunguska; the percent chance of survival; the stability over time once frozen (being in solid phase is certainly not absolute protection against radiation). The frequency of planets is roughly known, but not the frequency of terrestrial CO2-water worlds, although reasonable bounds could be placed. As to surviving re-entry, this tends to raise the most eyebrows - but it's worth repeating that roundworms on the Columbia did in fact survive uncontrolled re-entry and were found alive on the ground weeks later. Inside a large iron-silicate rock they may be even better protected.

The most uncertain part of this list of attrition factors is the last one we've now come to, the chance of the bacteria fluorishing on the new planet (lack of metal ions for enzymes, or presence of cyanide, low volcanic activity if we're relying on the iron-sulfur archaebacteria; etc.) But we can start actually filling in the values for passive ("dumb") colonization - the equation to show how fast Fred Hoyle's "lifecloud" and Arrhenius's panspermia would actually occur. Note that this is a different concept from the organic von Neumann probes that could also unintentionally seed life as a side effect, although mechanics would be the same, and we would still be looking on watery low-gravity bodies for evidence of them, like comets and asteroids.

Initially I was tempted to make a stab at setting bounds on 50% chance of colonizing another star, but many of the probabilities would be just guesses. It's clear that this is quite a list of attrition factors, reducing the chance nearly to zero for any one cell or asteroid strike on Earth to seed a future alien ecosystem. But over geologic time there have been quite a few of these strikes, and assuming vacuum-frozen surviving bacteria are stable for a long time (a relative straight-forward thing to test), then the solar system has been slowly filling up with septic asteroids - some of which no doubt have been ejected. So for the near-term, this is unlikely to produce lots of passively seeded worlds, but over arbitrary time, the universe would be accumulating archaebacteria from every place that life evolved. If we think of the Sun as a second-generation main sequence star, then planets of third generation stars are more likely to have been seeded by second-generation ecosystems - and may have more metals available in the ashes of the second generation stars from which they're built.

Other quantitative predictions: a one-third chance of life on Europa.

Interstellar and Intergalactic Panspermia

Active colonization time estimates for the galaxy are invariably much shorter than the lifespan of the galaxy. Passive diffusion would take longer of course but empirically observed Oort cloud mixing intervals even this far from the core for the sun are on the order of 10^5 years. Lingam and Loeb (2018) calculate the delivery of amino acids between star systems but not timescales; still, they estimate an upper bound for the size of interstellar objects for our system (a 10 kilometer-radius asteroid) and Alpha Centauri (an Earth sized planet.) This is a second source pointing to the fact that we may be an interstellar backwater, uniquely un-exposed to evidence of replicators* relative to the stars around us.

Where intergalactic material transfer is concerned, of course given the distances involved we should expect the process to be slower, both in terms of at an absolute rate and moreso in terms of colonizing systems, since the ratio of number of incoming objects:number of systems to receive material will be quite low. That said, a) there are extragalactic stars in the Milky Way right now, and b) we're actually talking about an exponential rather than linear rate if there are replicators* of any sort being introduced. This excludes infrequent but massive events like intergalactic collisions, like those which the Milky Way has undergone repeatedly in the past.

*I deliberately use the term replicators as a catch-all to include "space-viroids" (most likely), von Neumann probes, "cancerous" (mutants selected for fecundity over original function) or otherwise, or deliberate colonizations by agents with some kind of intention (least likely.)

Ice Volcanoes on Ceres May Provide Replicators Means of Spreading

Extraterrestrial replicators (be they naturally-evolved, or von Neumann probes or the mutant descendants thereof) are at least as likely to be based on organic chemistry as on clanking iron-age technology, as is often imagined. Material returned from comet Wild-2 showed that it was actually an extraterrestrial comet, and had amino acids on it. Other investigations have shown the presence of nucleobases (the components of DNA and RNA.)

Even Arrhenius-style "panspermia" spread by passive diffusion on astronomical timescales is not implausible, as our Oort Cloud has mixed with close-passing stars' clouds on the order of once every 0.1 MA (and we should assume this happens to other stars as well.) However, for passively spreading replicators, higher-gravity bodies like planets or large moons are dead ends because they have no means of escaping the gravity well.



Water geysers on Enceladus, from space.com
This is why comets and wet carbonaceous asteroids are the best places to look, and why the Hayabusa-2 probe on Ryugu is so important. Same for the Dawn probe. Europa and even Enceladus may be a tough sell as passively escapable gravity wells, but now we see evidence of active water volcanoes on Ceres through its life span.

Interstellar Object Oamuamua is Releasing Vapor

A Nature paper by Micheli et al demonstrates that outgassing is one plausible explanation for the subtle changes being measured in Oamuamua's trajectory. It also happens to visually look like a comet, though with much more silicate than organic material on the surface. There's less and less distinction between asteroids and comets - that is, a "primitive" (wet, not-yet-burned-off) body like Ceres is more comet-like than a drier body like Vesta. More here on the (now established) phenomenon of interstellar mixing and what it means, more speculatively, for von Neumann probes and/or the panspermia hypothesis.

Note: I refuse to use the apostrophe for Oamuamua because it misses up alphabetical order, and also, is dumb. Sue me, Hawaiians.

Another Interstellar Asteroid - This One a Permanent Resident of the Solar System

Asteroid BZ interested astronomers right away, because it is retrograde, in a 1:-1 resonance with Jupiter - suggesting that it was captured from outside the solar system just as ours formed, and is therefore older than the rest of the solar system.

But more interesting than that, it took several unlikely events for it to be captured and continue in a stable resonance over time (see last paragraph in the Orbit section.) This very strongly suggests that there are interstellar objects passing through the solar system all the time. For such an object to be captured so quickly, so early in the history of the solar system means that there must be enough of them to get trapped by freak aligments. Another way of looking at it is that fast = likely.

This is consistent with a similar argument made about Oamuamua, an interstellar asteroid that is currently passing rapidly through the solar system. Within a year of the first telescope that could detect such an object being activated, it found such an object. Good luck? Or constant interstellar material passing through? (It didn't take long to find BZ either, once we started looking.) The relevant point is that while the vast distance between stars is often cited as a form of quarantine for macroscale beings like us, it is certainly not such a quarantine, even on brief geological time scales, between pools of organic molecules. More here about periodic close passes between stars and interstellar mixing here and here, and (most speculatively) that if von Neumann probes exist, they are likely to interact with comets and asteroids with organics, rather than planets.

Finding Extraterrestrial Organics is Old News; Let's Look for Evidence of Life

There's a new mass spec study[1] of crystals from two meteorites, one of which in turn has material originating from two separate parent bodies. The objects were about 4.5 billion years old, i.e. dating to the birth of the solar system, and showed evidence of organics resulting from aqeous reactions. Some findings of interest: "...signatures of low-mass C5 to C10 hydrocarbons at around 70 to 200 atomic mass units." Not much benzene, suggesting that any aromatic rings are locked up in larger structures. We're finding organics everywhere we look it seems, including Ceres, and that includes even amino acids and nucleobases. Given how quickly after the Earth formed we started seeing evidence of self-replicating molecules (at least the ancestors of cells, if not cells themselves), this means that life originated quickly on Earth, and therefore was a highly probable event.

It's also relevant that polyaromatic hydrocarbons (PAHs - for instance, tar, graphite, anthracene in coal, and fullerenes) have been found in nebulas, as well as in Titan's atmosphere. Not only are they thought to be quite common in the universe, but possibly crucial to the origin of life (see PAH World Hypothesis.) PAH's are predicted to make up a large portion of the carbon at the surface of carbon planets. While carbon planet systems (unlike our own silicate system) were theorized only recently, it turns out that the Hypatia Stone, a bizarre meteorite found in the Egyptian desert, is loaded with PAHs and originated from outside our solar system - possibly as impact debris from just such a planet.[2] (It's becoming increasingly clear that objects from outside the solar system enter it frequently. First Wild-2 (which had amino acids in it), then Oamuamua, and now Hypatia. We've found these things on the Earth's surface without looking that hard for them! Given these observations, we should expect that interstellar mixing on relatively short geologic time scales is the rule.

This suggests several things and begs several questions.

- If a pile of complex molecules were delivered to Earth - say, a bunch of RNA that survived intact inside an impactor - that pushes back the question of the origin of life, but it also suggests it's very likely elsewhere.

- Have we looked for polymerized RNA or amino acids? Mass spec can detect and distinguish small fragments.[3]

- You might ask, why RNA? Why assume any similarity to Earth biochemistry? This raises the larger question of, if there is active extraterrestrial biochemistry in asteroids, how could we detect it? This is the question asked about desert varnish (which has been speculated as evidence of a shadow biosphere of non-DNA based life operating here on Earth under our noses.) If we did find alien biochemistry, how would we know what we were looking at, against the background of organics that we already know is there? While we haven't seen anything that obviously screams "alien biochemistry", that's the point - HOW does something look if it screams "alien biochemistry"? Are there general principles of such systems? You can't just look for macromolecules - if those are composed of the some monomers, they won't necessarily carry information (e.g. aliens trying to figure out our biochemistry from sequencing the fatty acids in our membrane phospholipids will not learn very much.) So it has to be a macromolecule with a limited number of discrete subunits. So far our samples have been limited t one biosphere. If we ever get enough complex organics from a sample return mission to be able to afford to destroy some of it in aqueous chemistry experiences, that will be a boon to astrobiology.

- If there is such a thing as a simple space-borne organism - or even the remnants of aberrant von Neumann probes that have "gone to seed" after eons-long selection for fecundity over their exploration functions - it would make sense to be adapted to low gravity bodies that are cheapest to move back and forth between. If Earth's biosphere is just overgrown von Neumann probes, that might just be because we're a dead end at the bottom of a gravity well.

Previous post on alien evolution, First Interstellar Asteroid? It's Interstellar, But Not the First We've Seen


REFERENCES

[1] Queenie H. S. Chan, Michael E. Zolensky, Yoko Kebukawa, Marc Fries, Motoo Ito, Andrew Steele, Zia Rahman, Aiko Nakato, A. L. David Kilcoyne, Hiroki Suga, Yoshio Takahashi, Yasuo Takeichi and Kazuhiko Mase. Organic matter in extraterrestrial water-bearing salt crystals. Science Advances 10 Jan 2018: Vol. 4, no. 1, eaao3521. DOI: 10.1126/sciadv.aao3521

[2] Georgy A.Belyanin, Jan D.Kramers, Marco A.G.Andreoli, Francesco Greco, Arnold Gucsik, Tebogo V. Makhubela, Wojciec, J.Przybylowicz, Michael Wiedenbeck. Petrography of the carbonaceous, diamond-bearing stone “Hypatia” from southwest Egypt: A contribution to the debate on its origin. Geochimica et Cosmochimica Acta, Volume 223, 15 February 2018, Pages 462-492.

[3] Zhaojing Meng and Patrick A. Limbach. Mass Spectrometry of RNA: Linking the Genome to the Proteome. Brief Funct Genomic Proteomic. 2006 Mar; 5(1): 87–95.

Modern Technology and von Neumann Probes: And Again, the Fermi Paradox

Good discussion here of how modern technologies (3D printing) could be applied to building our own self-replicating space probes, which in turn inevitably leads to a Fermi paradox discussion. Replicating probes are the way to go because they cover more territory faster. Authors cited in the article place lower and upper bounds on time to colonize the galaxy with self-replicators from 3.75 to 300 million years. Either way, it's difficult to square an apparently empty galaxy with these numbers, or indeed with the feasibility of such an endeavor. In fact, Frank Tipler (who made the upper bound estimate here) went so far as to argue that this has to mean there are no other intelligent aliens.

This version of the Fermi paradox can be solved by any of these:

- Most likely: they're around, and we haven't looked enough, or don't recognize them, or they avoid us because they're more interested in their own replication than in contacting other intelligent species, for some strange reason. We should expect that any self-replicating probes we find will have undergone natural selection to be primarily good at making copies of themselves, and secondarily at performing whatever mission their initial long-ago designers created them for.

- We're over-optimistic, and self-replicating probes are not feasible.

- These time estimates are not conservative enough.

- We really are the only intelligent species, or at least life is extremely rare.

Water Vapor From Europa's South Pole

PART I: Europa has water vapor plumes at its south poles, consistent with tidal heating (Science paper here.) These are more easily understood but no less exciting than the water vapor plumes seen last year over the south pole of Saturn's moon Enceladus, which turned out to contain organics.

Enceladus	Europa

The reason this is so interesting is not just the possibility of life in these alien oceans, but the broader implications for the spread of chemical replicators on water-containing low-gravity bodies. Increasingly it seems that many asteroids are just dried-out comets that last their external volatiles, like we just watched in accelerated fashion with ISON. It's now well-established that both asteroids and comets contain amino acids and nucleobases (PNAS paper there), both from samples of fallen meteors as well as sample return missions like Stardust, which brought back material from comet Wild-2, which turned out to have an extra-solar origin (as well as carrying the amino acid glycine). If there are replicators - either natively evolved, or von Neumann probes, mutant or otherwise - it is likely they'll be composed of easily available building blocks in low gravity environments, and spread during Oort cloud exchange between adjacent solar systems.

Another implication is that the answer to the Fermi paradox may be that we're a little premature in saying there's no evidence of life. This is especially true since humans haven't even made 50 soft landings on other bodies in our own solar system. The Dawn mission to Ceres arrives in 2015 and the findings will be interesting no matter what.

As an aside, replicators that spread between stars would ideally avoid gravity wells like Earth, because we're dead-ends, at least without expending huge amounts of energy to get back out. That said, if you think simple life at the scale of a virus or prokaryote couldn't survive re-entry simply by sheltering in a crack on a rock, try again. The C. elegans worms carried aboard the Columbia were found alive in a Texas swamp 3 weeks after the shuttle broke up on re-entry. And they're multicellular.

(Of note for amateur astronomers: here's a Twitter feed for a quick check of the positions of Jupiter's moons relative to Earth. If it's cold and clear where you live, take advantage and get out there with a telescope!)


PART II: Movie Review, Europa Report

Fittingly enough I watched Europa report about two weeks before this news came out. It's on Netflix, and if you have Netflix, go watch it right now. (Trailer) It's a recently released independent and I'd count it among the better science fiction movies I've seen. A la 2001 and other hard science fiction works, there's not a lot of screwing around with normal filmy conventions; although maybe too much character development for my taste, because character development is not what this film is for. It's a technically accurate, very un-wild-eyed tale about the first manned landing on Europa, told mostly in raw video logs from the spacecraft with occasional after-the-fact narration from the mission chief on the ground. Beyond that I can't tell you too much without spoiling the movie, but you don't need me to. My only criticism, and it's not really a criticism, is that at times I felt like it was made as a trick to get more young people excited about the next phase of space exploration. If that's true, they still made an excellent movie. (Like I said, not a criticism.)

Proposal: One Way to Find von Neumann Probes

Find their relay stations. Still very much bound by our assumptions about how communications work (and that such probes would care to communicate with each other) but still translates to an actionable plan that can be approached reasonably with current technology.

List of Organic Compounds Found in Sutter's Mill Meteorite

A paper by Pizzarello et al using NMR and mass spec of material extracted from the meteorites has shown many new compounds. I'm always frustrated when papers look at chemistry of extraterrestrial samples and doesn't use basic organic techniques (like NMR) so I was very happy to read this one. Of note, the extraction method used by this team is a new one and more closely resembles conditions on early Earth. The excitement about this paper is that it brings us closer to supporting a panspermia model for the origin of life on Earth. It also supports the idea that meteors (and comets) might actually be harboring some kind of active chemistry - and if we're going to look for von Neumann probes or indeed any replicator chemistry, we should start with the low gravity bodies right here in our solar system. Some of the compounds they found are below:

Pizzarello S, Daviodski S, Hollanda G, Williams L. Processing of meteoritic organic materials as a possible analog of early molecular evolution in planetary environments. Published online before print September 9, 2013, doi: 10.1073/pnas.1309113110.

The Fermi Paradox Thickens: More on Colonization Times for Von Neumann Probes

In a previous post I discussed the possibilities of replicators being aided in their diffusion between star systems by close passes; I also pointed to an interesting paper by Forgan et al looking at projected travel times of interstellar probes, based on powered vs. gravity-assist travel. A new paper (on which Forgan is the senior author) looks again at this problem using a Monte Carlo simulation approach, and gets an interesting but as always frustrating answer.

First, the paper would be valuable if all it contained was the excellent review of prior work done on this NP-hard version of the traveling salesman problem. (You think planning your road trip taxes a server?) In particular, they point to a prior paper arguing that von Neumann probe expansions could be slowed or stopped by mutant probes where a predator-prey dynamic evolves in the population and the probes hunt themselves to extinction. I had previously written about self-replicating probes becoming cancerous (a statistically more likely outcome) and turning to expansion above any other mission they previously had; but this only makes the Fermi Paradox more vexing rather than solving it.

Their approach was to simulate the galaxy as having 1 star per cubic parsec (so no local "backwaters"), with self-replicating probes moving at approximately the speed of Voyager I, 1000 m/s. They then compared replicating and non-replicating probes; not surprisingly, self-replicators were much much faster, exploring 100% of a box of 100,000 stars in at most 30 million years. In the replicator condition, the number of probes is no longer the constraint, and contact can occur in (possibly massive) parallel rather than serially. Of note: the authors also include a requirement for communication of which stars have already been explored, although if we assume a robustly replicating probe, this is unnecessary. ("Robust" means that the time and ability to replicate enough probes to successfully reach the neighboring stars are small relative to travel time.)

The authors correctly note that this short time frame makes the Fermi Paradox more vexing. So the alternatives with respect to self-replicating probes are:

1. They're here and we haven't found or noticed them yet.

2. They're not here, because
2a. Replicating probes are not possible or not effective (they can't be made at all, or they mutate)
2b. intelligence capable and willing to build such probes appears more rarely than once every 30 million years in a volume of 100,000 stars (they choose not to, or they don't evolve in the first place, or they wipe themselves out before they create them)

2a seems unlikely because we already know that replicators can develop through natural selection. This leaves us with 1 and 2b. It is certain that we have only the barest knowledge of the rest of our solar system, and gravity wells are expensive to get out of. My prediction is that we'll find evidence of such probes on low gravity bodies (asteroids, comets, small moons) as we continue to explore, but that once we find something strange, it will take time for us to understand what we're looking at.

Hat tip to Ben Weaver.