Prediction: Venusian Phosphine is a Metabolic Product of Living Cells Already Detected As Unknown Absorbers

(Added later: since I wrote this, further research has provided evidence showing it is very unlikely that the unknown absorbers are biological. Not only was the phosphine paper a product of bad spectrometry that failed multiple attempts at replication, there are at least two papers - Jiang et al 2024, and Egan et al 2025 - that have provided good candidate abiotic explanations for what the absorbers could be.)

The last two years have provided us with the strongest evidence ever assembled of extraterrestrial life:

1. Prior theories about relic ecosystems surviving in the more Earth-like parts of Venus's atmosphere.
2. Detection of UV absorbers the size of bacteria in Venus's atmosphere, with no explanation as to their identity.
3. Prior, independent advancement of phosphine as a biosignature gas.
4. Detection of phosphine in the Venusian cloud decks with no explanation for its persistence.

Here I propose that Venus had an iron-sulfur ecosystem with a chlorophyll-equivalent that absorbs closer to the UV spectrum rather than visible light - essentially, "UV-synthetic" Venusian cyanobacteria. The oceans boiled away and Venus became hotter and more acidic from volcanism and possibly, their own Great Sulfuration (or Sulfur Oxidation, equivalent to Earth's Great Oxygenation.) The only survivors were the UV-synthetic Venusian archaebacteria that now live in the upper atmosphere. Today these have a life cycle like that described by Seager et al (2020), powered by UV and producing phosphine - Unknown Absorber Phosphine Producers (UAPPs.) They are likely related at great time depths to life on Earth. Initial research question is to see if areas of unknown absorbers correlates with phosphine, which can be done from Earth. Probes that collect material in the upper atmosphere could fairly straightforwardly check for aspects of biochemistry using an onboard instrument, and a sample return mission could be extremely productive.


Phosphine Production in the Clouds of Venus

If you're reading this you likely know that phosphine (PH3) was detected in the atmosphere of Venus - Vox explainer here; original paper by Greaves et al here. The measured concentrations are at biology-consistent levels, at an elevation where the pressure and temperature are similar to Earth's. This is by far the strongest evidence of extraterrestrial life yet discovered, with evidence from multiple sources.

Phosphine has been advanced as a possible seed compound delivered to Earth on comets or asteroids early in its history. But the chemistry of its formation in space (or on gas giants) is not mysterious. It's in the Venusian atmosphere where so far we can't explain its presence without some process that continuously replenishes it. One criticism of speculation about possible Venusian biochemistry is that just because we don't know how to make phosphine under Venusian conditions, doesn't mean we're looking at alien biology. True; but among these criticisms have not been any suggestions so far about what it might be. (Either way, we're about to learn something.) It's suggestive that this data is not completely unexpected - it can be fitted to prior hypotheses. We've been speculating more and more concretely for decades about how life might survive in the atmosphere of Venus for decades (see Morowitz and Sagan 1967.) A fairly elaborated model of microbial life in the atmosphere of Venus was advanced recently by Seager et al, consistent with observations so far. This should also increase our confidence in the Venusian-cloud-life hypothesis, that even before phosphine was detected, Sousa-Silva et al suggested phosphine as a biosignature molecule, independent of finding it on Venus.


A Related Mystery? The Unknown Absorbers



In visible light and false-color UV absorption. It's unusual to have such contrast in absorption at different wavelengths. Image credit syfy.com

For decades we have known that there are partciles about 10^-6 meters (the size of bacteria) in the Venusian atmosphere at a similar altitude (at 47 to 64km) as the phosphine detection above (at 57km and above). The dark bands we can see with the naked eye in the Venusian atmosphere contain more of them, but as you can see above in the UV image, they are much higher contrast (more absorbant). As with the origin of Venusian phosphine, the identity of the absorbers remains controversial, and Venusian biology had been advanced previously as a candidate explanation (Limaye et al 2018). The phosophine paper points out that there is more phosphine at mid-latitudes than the equator or poles, which by naked-eye examination of images of Venus, seems also to be where the absorbers are. It seems a relatively straightforward study to correlate the two, but as the absorbers move on a scale from minutes to days, data would have to be collected simultaneously. The stronger the correlation (especially within the same latitude) the more our confidence in the UAPP hypothesis of Venus cloud life would be increased.


What About Bacterial Life in Earth's Cloud Decks?

Earth's clouds do indeed contain lots of bacteria, and not just incidentally - some of them clearly evolved to take advantage of the precipitation cycle and indeed to deliberately cause ice to enucleate around it, like Pseudomonas syringae (this is actually economically relevant as the water ice-enucleation proteins produced by this species is used in the water fed into snow guns at ski resorts.) Bacteria have been found all the way up to 28 miles above the surface, where the pressure and temperature are both much lower and considerably less hospitable even to Earth's own life than the cloud decks on Venus. While we can't say there is an actual bacterial ecosystem in Earth's clouds (one which persists without interacting with the surface), we haven't really looked for one either; most of our interest in these organisms thusfar comes from studying plant pathogens that spread through weather events. It's worth pointing out that there is phosphine in Earth's upper atmosphere as well, with no clear mechanism for how it forms there. It should be noted that there is less in Earth's upper atmosphere by about 3 orders of magnitude; the levels in Venus's atmosphere are more similar to that found immediately around actively metabolizing bacteria on Earth's surface.


Toward an Evolutionary History of Venus

Why would life exist on the most hellish world in the solar system? The answer is that for at least 75% of its lifespan, Venus was a much more Earth-like planet with cooler temperatures and oceans.

There are two possible, not mutually exclusive stories that explain how this planet came to be the Venus we know today.

The first is that Venus was a little too close to the Sun, which caused its oceans to evaporate, plate tectonics to cease, and subsequent cataclysmic volcanism. As the oceans evaporated, the water vapor trapped the heat and accelerated the process. The deuterium/hydrogen ratio on Venus is about 150 times higher than Earth, where comets have at most a 3 times higher ratio than Earth, suggesting a very gradual loss to space of hydrogen from water and preferential retention of the heavier nucleus. Water lubricates plate tectonics, per Solomatov 2001. Climate modeling suggests that Venus may have had a habitable climate with liquid water at the surface until 715 MA ago (Way et al 2016.) The subsequenct evaporation of the oceans resulted in a planet where plate tectonics ground to a halt, and with no crustal mechanism to dissipate heat, and finally between 700 and 500 MA ago, Venus erupted in planet-wide massive flows that resurfaced the planet, utterly dwarfing any similar events on Earth (like the Siberian Traps.) This released the massive amounts of sulfur that we see today. This is the received wisdom and could entirely explain the modern state of Venus, and may alone be enough to explain all the sulfur.

There is another version of the story which reverses the causality - eruption causing evaporation, advanced by Way and Del Genio in 2019. It's worth noting that Venus has a thicker crust than Earth, owing to its lack of a large moon; therefore we should expect that the flows, when they do finally cause the crust to fail, are much stronger than in the parallel situation on an evaporated Earth.

The second possibility is obviously more speculative, a parallel to the Great Oxygenation in the history of life on Earth. In Earth's history, anaerobic cyanobacteria produced so much oxygen that they effectively poisoned themselves, but also set the stage for aerobic life. This could have been a great coincidence - there may just have happened to be genes close enough in design space to assemble oxyidation defenses and an aerobic metabolic pathway, and without such a coincidence, that may have been the end of life on Earth, or it may have settled into a simple bloom-and-bust oscillation as our bacterial mats may have for hundreds of millions of years evidenced by banded iron formations found in ancient rocks where they persist at the surface. (See discussion of endogenous extinctions here, which this section partly recapitulates.)

While an interesting idea, by Occam's razor we should spend no further time considering a possible Great Sulfuration, as we can explain the death of the Venusian surface ecosystem entirely based on abiotic meteorological and geological processes as above. It's also the case that the presence of increased CO2 relative to Earth can be easily explained by abiotic processes as well. Using ingenious reasoning about the necessary atmospheric pressure for flying dinosaurs' wings to function as well as the known rates of deposition of CO2 as carbon in continents and the ocean, we can arrive a figure of the equivalent of 85-100 bars' worth of CO2 trapped in the Earth's crust, similar to what is currently in the Venusian atmosphere. Presumably the atmospheric pressure of Venus was lower during its oceanic period owing to the same process, and rose subsequent to the evaporation, but I am not aware of any modeling retrodicting from oceanic evaporation 500-700 MA ago to the current pressure and mass of CO2 on Venus.

All this is to say that life on Venus may have gone a different way, but started quite similarly. We're now fairly confident the first metabolism on Earth was sea vent iron sulfur organisms, using sulfur in what is now oxygen's chemical role. The Great Oxygenation may have only happened when it did, a full 1.5 billion years after the first life and at least 800 million years after photosynthesis appeared, because an asteroid delivered molybdenum, allowing nitrogen fixation and more efficient anaerobic metabolism. Whatever the reason, had this happened prior to photosynthesis, we may have ended up with an Earth poisoned with sulfur or at least with a massive amount of oxidized sulfur.


Two Obvious Problems for the "UAPP Cells" Hypothesis for Life on Venus

There are two major hurdles to overcome in any argument that there is life in the cloudtops of Venus. The first is the question of how life operates without water, or with very little water; this would actually be a more stunning find than merely life which can tolerate high acidity! The second is the failure thusfar to detect any organics in the atmosphere. Without water and organic molecules, it's very hard to see how this won't end up being an interesting abiotic route to phosphine production along with some crystal we weren't anticipating at that altitude. That said, organic compounds on Venus may not be as unlikely as one might think - there was a Venusian equivalent of the Miller-Urey experiment performed, where under conditions of the Venusian atmosphere, organic compounds including amino acids were produced.

Furthermore, there remain arguments for an abiotic explanation for the unknown absorbers, specifically ferric chloride (Petrova 2018). Interestingly, this is partly advanced to explain another mystery which is the presence of rainbows ("Venus glory"), first observed in 2014 in the Venusian atmosphere.


Implications for Evolution in General and the Future of Life of Earth

It is more likely than not that life on Venus will be distantly related to life on Earth. A massive amount of material has been transferred between bodies in the solar system, with actual numbers calculated here; at that same link you will see reference to the survival of uncontrolled re-entry during the Columbia crash by not just bacteria, but animals (C. elegans worms, found alive on the ground weeks after the crash.) This is actually the more boring possibility, because we would learn much more about the basic principles of evolution and the possibilities of biochemistry beyond Earth's provincial commitments, if we really had a novel origin. Either way, if there is life on Venus, the likelihood of life on Mars, Europa, Enceladus and even Titan jumps dramatically, even if it's "just" a long-lost relative. I expect that ultimately the impact of finding life on Venus will be some neat new biochemistry (the old extremophiles will seem quaint) and a bit more information about how evolution can proceed.

It is unclear how we should feel about Venusian cloud UV-cyanobacteria in terms of the Great Filter, which suggests that the more life we find in the universe and the closer in terms of evolutionary stage to humans, the more concerned we should be - because the more likely our own extinction is before we can colonize planets beyond our own. If further exploration of Venus yields trilobites or vertebrates and these cells are all that are left, we should worry much more. In contrast, if Venus never got past vast floating bacterial mats (either in its clouds or ancient oceans). that's a bit more comfortable for us.


REFERENCES

Bains W, Petkowski J, Sousa-Silva C, Seager S. Trivalent phosphorus and phosphines as components of biochemistry in anoxic environments. Astrobiology 19, 7 (July 2019): p. 885-902 doi 10.1089/AST.2018.1958

Glindemann D, Edward M, Kuschk P. Phosphine gas in the upper troposphere. Atmospheric Environment Volume 37, Issue 18, June 2003, Pages 2429-2433

Greaves JS, Richards AMS, Bains W, Rimmer PB, Sagawa H, Clements DL, Seager S, Petkowski JJ, Sousa-Silva C, Ranjan S, Drabek-Maunder E, Fraser HJ, Cartwright A, Mueller-Wodarg I, Zhan Z, Friberg P, Coulson I, Lee E, Hoge J. Phosphine gas in the cloud decks of Venus. Published: 14 September 2020. Nature Astronomy (2020)

Levenspiel O, Fitzgerald TJ, Pettit D. Was the Atmospheric Pressure Different at the Time of Dinosaurs? Chemical Innovation, December 2000 Vol 30, No.12, 50 – 55

Limaye SS, Mogul R, Smith DJ, Ansari AH, Słowik GP, Vaishampayan P. Venus' Spectral Signatures and the Potential for Life in the Clouds. Astrobiology. 2018 Sep 1; 18(9): 1181–1198. Published online 2018 Sep 12. doi: 10.1089/ast.2017.1783

Morowitz H & Sagan C. Life in the Clouds of Venus? Nature volume 215, pages1259–1260(1967). 16 September 1967.

Otroshchenko V.A., Surkov Y.A. (1974) The Possibility of Organic Molecule Formation in the Venus Atmosphere. In: Oró J., Miller S.L., Ponnamperuma C., Young R.S. (eds) Cosmochemical Evolution and the Origins of Life. Springer, Dordrecht. https://doi.org/10.1007/978-94-010-2239-2_40

Petrova EV. Glory on Venus and selection among the unknown UV absorbers. Icarus Volume 306, 15 May 2018, Pages 163-170

Seager S, Petkowski JJ, Gao P, Bains W, Bryan NC, Ranjan S, Greaves J. The Venusian Lower Atmosphere Haze as a Depot for Desiccated Microbial Life: A Proposed Life Cycle for Persistence of the Venusian Aerial Biosphere. Astrobiology. Published Online:13 Aug 2020. https://doi.org/10.1089/ast.2020.2244

Sousa-Silva C, Seager S, Ranjan S, Petkowski JJ, Zhan Z, Hu R, Bains W. Phosphine as a Biosignature Gas in Exoplanet Atmospheres. AstrobiologyVol. 20, No. 2. Published Online:31 Jan 2020 https://doi.org/10.1089/ast.2018.1954

Way MJ, Del Genio AD, Kiang NY, Sohl LE, Grinspoon DH, Aleinov I, Kelley M, Clune T. Was Venus the First Habitable World of our Solar System? Geophysical Research Letters. First published: 11 August 2016 https://doi.org/10.1002/2016GL069790

All Attempts to Broadcast Our Presence to Nearby Stars Should Be Forbidden

Here you can find a list of when there might be a response to known prior contact attempts within a century, assuming immediate light-speed response, and whether there are known terrestrial planets around the stars. This is incredibly dangerous and reveals the presence of intelligence on Earth to anything that might be listening, and should be immediately stopped (see Stephen Hawking's take on this here.) Granted, astronomers' definition of habitable - "terrestrial planet orbiting in liquid water temperature zone" - leaves a lot to be desired.

Until now. Measurements of terrestrial planets can now show if there is an atmosphere and it contains hydrogen, oxygen, and N2, making at least some water quite likely (Konatham et al 2020.)

We can update the list of stars where we've already broadcast contact attempts, with these new stricter criteria. There are two planets with atmospheres and likely water that we have deliberately broadcast to: Teegarden's Star, a red dwarf (with two planets with likely water), with a response possible by 2036; and GJ273b (Luyten's Star), with a super Earth with likely water, responding at earliest 2043.

Two facts to modify our enthusiasm:

• Both are red dwarfs, which have a habit of flaring. However, Luyten's Star is quiet by these standards.
• Also, aliens looking at our solar system using the same definition would keep both Mars and Venus on this stricter habitable list. Both do have atmospheres and some water.

Proxima Centauri is the closest star but in this more-strict list of habitable planets, but we haven't deliberately targeted it. It's worth pointing out that even if there were a twin Earth there, we still wouldn't be able to hear them (the C-index - a rule of thumb, assuming that strength of a civilization's emissions and ability to detect increase in concert.)

(Encouraging to amateurs: Teegarden's Star was discovered by a group of non-professional astronomers poring over data online, without access to telescopes.)

Konatham S, Martin-Torres J, Zorzano M. Atmospheric composition of exoplanets based on the thermal escape of gases and implications for habitability. Published:09 September 2020https://doi.org/10.1098/rspa.2020.0148

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.

CNS Damage in Mice Experiencing Mars-Voyage-Like Radiation for Six Months

This is not good news. We should expect that humans undergoing a Mars trip, with selectively vulnerable hippocampi and dependent on complex behaviors for survival, will fare even worse per unit time, and worse still over the closer to twenty-four months for the out and back that such a trip would take. Regardless of air, water and food requirements, this is yet another barrier to even colonizing the rest of our own solar system, much less getting to another star, and another reason why we might never see interstellar civilizations composed of planetary-surface-evolved organisms rather than machines. Paper here, summary here.

An Existential Risk Comparable to the Singularity

Imagine that due to some breakthrough in computer science, we can determine (with certainty) that for a certain architecture, there are some designs that will "work"; that is, when activated, become a successful recursively self-improving general AI. Now assume that 13 such designs have already been tried. A tiny fraction to be sure; and yet in no case has there been any discussion before the research team turned each of them on, no input from other researchers, no public comment, and certainly no attention from policy makers of any sort.

The catch is that this architecture is highly iterative, and it has to run for a long time before you find out if it's going to "wake up" - consequently the researchers load the software and hardware into satellites, because the earliest any of them would "wake up" would be 2036. (For our purposes, assume once launched, these satellites are out of reach - like Elon Musk's car.)

I assume the AI safety community would have something to say about this; about people unilaterally turning on instances of this architecture, and placing it out of reach. Unlikely though it is, any one of those could wake up and we could find the Solar System transformed overnight, and not necessarily to humanity's benefit.

Why such an esoteric thought experiment? It's not really a thought experiment. There have already been 13 active attempts so far (that we know about) to signal nearby star systems. Given the constraint of the speed of light, the earliest we could hear back (or meet someone/something) from any of them would be 2036. Much like the satellite-launched AIs, once you send the message, you can't delete it from their inbox. The 1-in-29 million comes from the original Drake equation estimate of 3,500 civilizations in the galaxy, and one hundred billion star systems. Note that this thought experiment assumes every species is confined to one solar system, but if they have interstellar travel (and follow the signal back to the source) then that 1-in-29 million probability would be much higher.

AIs are at least designed by humans, with possible ethical constraints. Aliens able to visit our solar system would not in any way have our interests at heart. If you're in the rationalist community and you're concerned about a technological singularity, you should be very concerned about existential-risk-level-dangerous wildcat attempts to reveal our presence to other solar systems. This is called METI (Messaging Extraterrestrial Intelligence) instead of SETI, and you can read more about stopping it here.

If Threonine and Aspartate are Detected on Europa, They Must Have Been Recently Generated

Important paper for detecting biosignatures elsewhere in the solar system. Truong et al measure the decomposition rate of amino acids in conditions mimicking the under-ice oceans of Europa or Enceladus. Using that data, they infer whether any amino acids detected there are leftovers from early abiotic chemistry, or must have resulted from a more recent process. In particular threonine and aspartate are unstable over time and if detected at concentrations greater than 1 nM, they must have been generated recently. Click through to the paper below.

Truong N, Monroe AA, Glein CR, Anbar AD, Lunine JI. Decomposition of Amino Acids in Water with Application to In-Situ Measurements of Enceladus, Europa and Other Hydrothermally Active Icy Ocean Worlds. arXiv:1904.04407 [astro-ph.EP]

Deoxyribose From Abiotic Space Conditions

Another biomolecule, the pentose sugar that serves as the backbone of DNA, quickly produced in un-directed synthesis under conditions that obtain on ice in space. Given the speed with which the first life formed on Earth (0.1 GA after the planet cooled to a solid form) as well as increasing evidence like this about how easy it is to make nucleic acid building blocks under prebiotic conditions, it's also very likely that life forms everywhere with water and carbon - even in ice. (See here for most recent panspermia/evolution post.)

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.)

No Radio Signals from Oumuamua

To help rule out Oumuamua as an interstellar probe, it was investigated and found to have no detectable transmissions within 1-10 GHz down to powers of at least 300 milliwatts. Yes, this could be like an uncontacted tribe on Earth in 2018 saying that the drone that surfaced in their bay wasn't sent by people because it didn't give off smoke signals - but you have to start with clear assumptions of SOME kind and test them. That such a ship-like object is passing through the solar system is exciting, but since we found it very soon after we were first capable of finding it suggests that such objects pass through our solar system all the time.

Modeling Gamma Ray Bursts as Causes of Mass Extinctions

One of the explanations for the apparent rarity of life in the universe is the frightening gamma ray burst - perhaps life is astonishingly rare, and Earth has just been lucky to be in a narrow slice of space that for the last five billion years. But (almost?) everywhere else the planetary Petri dishes have undergone regular GRB autoclaving, or at least they got autoclaved before complex nervous systems develop. Putting numbers to this based on the observed distribution of GRBs, a recent paper modeled frequency and distribution of GRBs to estimate the chance over time of a GRB happening close enough to Earth to be life-damaging. Among their conclusions:

1) There's a 50% chance that a life-damaging GRB took place in the last 500 million years. Permian-Triassic extinction anyone?

2) The probability of a system being exposed to life-damaging GRBs goes up as you move toward the center of the galaxy. Many of our SETI efforts focused on our own galaxy have focused coreward, on the reasoning that there are more stars in that direction, therefore more chance of finding life. The reflex to this paper's model is to worry that we're looking in the wrong direction - but if you assume galaxy-colonizers, looking coreward may still be the best strategy - the GRB survivors on the galactic rim would be able to colonize inward.

Paper here.

Asteroids and Comets Exist On A Spectrum

At least some asteroids have an internal reservoir of ice (along with organics); that's the thought for objects like 24 Themis, which retains a high albedo despite being inside the frost line. We also have evidence that centaurs (the outer-system asteroids) are really just relatively close-in comets. Recently a team showed that there are dead comets residing in the asteroid belt among possible dormant ones.

Increasingly it's clear that comets and asteroids are really the same type of objects - mineral objects coated and/or filled with water and sundry organics - with their visual behavior and surface characteristics determined mostly by their position in the solar system. If they've been out at the edge of the system for most of their life and make a sudden close pass to the Sun, they'll lose a lot of water, quite spectacularly. Others (like Vesta) have been stably far enough inside the frost line for long enough that they're dry. For those of us who think the organics we'll find on and inside these objects will be the most interesting thing about them, the limited information we have so far is very frustrating. Consequently I'm more than eager for Dawn to arrive at the much more primitive, wetter Ceres in February 2015.

It's worth emphasizing that we can't be too humble about our level of knowledge about our own solar system. Fuzzy images of Ceres were only compiled by 2007, showing some interesting surface features (craters and a bright spot). That is to say, if aliens had landed on Ceres and made a giant sign with letters 100 miles high insulting us - on the biggest asteroid in our solar system mind you - we would only have finally have noticed it six years ago. I'm not worried that the bright spot will turn out to be a dirty picture drawn on the surface, but it's worth keeping our state of knowledge in mind before we start saying we have no evidence of [fill in the blank] in our solar system.

How Close Are We to Becoming a Kardashev II Civilization?

Kardashev II civilizations have the power capabilities of an entire star. One way to do this would be to capture the star's energy with a Dyson sphere (below).


Futurists and science fiction types (myself included) often over-simplistically extrapolate current, very strange trends (in terms of the rest of history and nature), especially exponential ones. Despite that, people are looking for Dyson spheres for real as part of SETI. I think this program carries so many assumptions that it's doomed; but let's have some fun and say Dyson spheres are for galactic wusses that don't have the stones to just generate the power themselves. If we humans are eventually going to produce enough power to match our own star, how close are we? Is this something that should be discussed during the next election cycle?

Take a guess. Here are the numbers: the current energy output of humans is about 5x10^20 J per year (since this is energy over time, we're really talking about power). The Sun's output is 1.2x10^34 J per year. So how close are we? A factor of 24 trillion, that's how close.


Let's assume, even more stupidly, that our energy curve will continue to rise the way it has in the twentieth century (see above), despite the fact that the vast amount of that area under the energy-time curve (again, power) came from spending stored chemical potential energy in fossil fuels. The curve has gone up 1x10^14 J about every 15 years - arithmetically, not geometrically. At this rate of increase, the sun will have burned out long before we ever match it. (If you want to be a smartass, you could say that this means that we will eventually match the sun's power because the sun's output will drop drastically. But even then the constraint which determines this is the sun, not how fast our energy output grows.)

Another way of looking at it: if you wanted to match the sun's power by burning fossil fuels, then using the energy density of oil, you would have to burn an amount of oil equal to the mass of the Earth, 50 times per second.

What is this, XKCD?

You're saying, "Fossil fuels? Of course you idiot, you can't get to the Kardashev big leagues powering your civilization on combustion engines!" Fine, let's make an Earth out of antimatter, and gradually crash pieces of it into this Earth. You could put out as much as the sun for about a hundred million years, by shooting pieces of the anti-Earth at us at a rate of a million tons per second. (I guess you hold the Earth together with duct tape to keep it from flying apart during all these shenanigans.) Assuming you don't start with the part of the Earth where you're sitting it would probably look cool, but even so I bet you'll quickly be getting some neat-o cancers from all the high-energy photons this produces, and maybe even just diffuse axonal injury knocking you unconscious in minutes. Incidentally my suggestion is to start with Belgium.

Above: Belgium, at left.

There will still be people objecting, i.e. the Ray Kurzweils of the world, that problem-solving abilities (AI) will grow exponentially, and therefore the energy-producing capacity will follow. Fine. The question for them is what is going to power these other exponential trends, at much more mundane time horizons? (Like the singularity that's apparently scheduled for seven decades from now.) If the answer is "AIs will have god-like intelligence and they'll be able to do it and we can't understand", then why shouldn't we also believe doomsday prophets like Harold Camping who say their gods are coming, and make their claim with exactly the same amount of verifiability and comprehendibility? If you think Kurzweil makes sense, you should also read about the economist Julian Simon's commodities bets, because you should agree with him - although I find that singulatarians somehow find reasons to dislike over-optimistic economists, probably mostly just out of mood afiliation and status considerations.

Final answer: we are not going to become a Kardashev II civilization any time soon, and no one really knows how to get there or what this means, because the definition necessarily involves processes we don't understand. But I'm still fine with dropping large amounts of antimatter on Belgium.

ADDENDUM: This is from Wikipedia about the sun's power generation and for some reason I find this shocking.

The power production by fusion in the core varies with distance from the solar center. At the center of the Sun, theoretical models estimate it to be approximately 276.5 watts/m3,[54] a power production density that more nearly approximates reptile metabolism than a thermonuclear bomb.[b] Peak power production in the Sun has been compared to the volumetric heats generated in an active compost heap. The tremendous power output of the Sun is not due to its high power per volume, but instead due to its large size.

Putting it in socioeconomic terms, the sun is like China - the per capita income is actually not impressive but it's huge, so the multiplier is big.

A Moore's Law Argument for Panspermia

From Sharov and Gordon's paper Life Before Earth at arXiv. The implication is clear from the figure - that life has followed a logarithmic complexity trajectory, which is cooler to refer to in terms of Moore's law, but that at 4.5 GA ago (the formation of Earth from the stellar accretion disc) the complexity is not 0. Their figure crosses that line at a complexity of about 10^4.5, meaning a 30,000 bp genome. For reference, the smallest chemical replicators in nature are viroids (RNA that reproduces in plants), mostly around 2,000 bases, although hepatitis D is a virus essentially parasitic on other viruses with a similar genome size. The smallest replicators with independent metabolism are the Mycoplasma (a medically important genus discovered by Leonard Hayflick), generally under a million bp. Your genome is about 3 billion base pairs.

The first question we should ask here is what we even mean when we say "genome size", and why we care (which the authors do somewhat address). There is a difference between absolute number of base pairs in each cell, non-repetitive DNA (information), and functional complexity. If you want to talk about plain old absolute number of base pairs by mass in the cell, then plants win that one hands down, because they sometimes have many many copies of each chromosome - 20 or more. Modern corn has 6. Fine then; you want to talk about non-repetitive DNA, i.e. the Kolmogorov complexity of genomes? If you want to make a compressed file of a genome, some organisms have long stretches of repeats that can be compressed by saying "[repeat] x a million"; I don't think that complexity is what we're talking about either. (For the record, humans have more non-coding repeat DNA than coding DNA. Coding is about 3% of our genome, and just the most common type of repeat, the Alu element, is 5%.) Even taking that into consideration, yes, vertebrates have bigger non-repeating genomes than most other organisms, but among the vertebrates, non-repeating genome size and behavioral complexity do not correlate. Unless you're willing to concede that fish are smarter than you, because they have bigger non-repeating genomes. (I'm not willing to concede that.)

I think what we're really talking about here is functional complexity - the phenotype that the DNA produces in extension - and the best approximation of this is the number of genes. The authors of this paper refer to functional non-redundant genome, and even then - are you ready? - by this measure, protozoans win. Yes, amoebas and giardia. The kicker is that Trichomonas, which causes an STD, holds the record for the most genes of any organism yet sequenced. (I debated including a picture of its effects but I decided against it. You're welcome.) So it's time to retire your vertebrate chauvinism, or at least find another justification for it, because you're not that complex. For more on this, see the C-value paradox.*


All hail Trichomonas, our genomic superior. This is the one that infects humans; another one in the same genus infected T. rex.

That said, functional non-redundant genome size may still not be a totally awful indicator of genome complexity over geological epochs, but there are still further issues worth pointing out: they assume a constant trend and argue for it based on several other provincial (terrestrial) examples of complexity. We can't really assume that an algorithmic approach to processor speed and scientific publication rates give us the correct start date, and therefore so does the origin of all life, especially when the chemical substrate must have been different early on (see the RNA World hypothesis). They also get a little greedy reducing things to big picture neat-o ideas; for example, the Singularity makes an appearance. I think it's worth pointing out that we're still working out the troublesome details of the origin of replicator chemistry under early-Earth conditions and there are some fairly good answers now, but if replicators predate the Earth that begs the question of under what conditions did they appear. I've made the argument repeatedly that replicators could spread on comets and asteroids but it's much less likely that they originated there. Too cold, too dry, boiling point of solvents too high under low pressure atmosphere.

Of course it's an interesting paper (link here) but that doesn't mean it's correct. If it is correct, it means the evolution of life elsewhere is even more certain than it was before, which makes the Great Filter all the more daunting.


*My own take on the the C-value puzzle is that it's actually not that puzzling, unless of course you assume behavioral complexity must mean genomic complexity. For one thing, those protozoans have very complex life cycles, and have managed to preserve a lot of the behavior of eukaryotes that their single-celled prokaryotic comrades never had; the vast majority of our own cells are coddled in a vast bureaucracy that protects them from the outside world, and even if they screw up and die or reproduce out of control, there are a trillion more of them and an immune system to kill them just in case. There is also very little pressure on multicellular eukaryotes not to let their genomes accumulate a lot of junk, much of which is likely to be non-coding repeat elements. The amount of extra energy it takes your cells to reproduce their Alu elements today is far, far less than the amount of energy it takes you to scratch your head, and you aren't starving because of that either.

The C-Index: How Far Away Could We Hear Earth?

The C-Index is a quick-and-dirty way to determine the likelihood of our detection of, and our detection by, other technology-using aliens. Current technology changes over time, and this drives both what we emit (how loud we are), and what we can detect (how well we can listen).

So how close would we have to be to a twin Earth before we could hear it, i.e. hear ourselves? If twin Earth were orbiting Alpha Centauri, could we hear it with our own technology? How about fifty years from now?



In a post at David Brin's blog, he rounds up arguments about our own relative silence by stating "even military radars and television signals appear to dissipate below interstellar noise levels within just a few light years. Certainly they are far less visible -- by many orders of magnitude -- than a directed beam from any of Earth's large, or even intermediate, radio telescopes." (Interestingly, none other than Seth Shostak of SETI is credited with this observation.)

So right now it looks like our C-Index is ~3 light years. If you're interested in this kind of thing you probably already know this isn't even as far as the next closest star, which is 4.3 light years away. They could be right there, chattering just as loud as us, and we still wouldn't know.

Below: the yellow dot is the portion of the Milky Way into which our radio waves have expanded (r=100 LY),  but our current C-index is only 3% of that radius, and therefore contains just 0.027% of that speck.

Intelligence Itself as the Great Filter

[I have an article on the Singularity coming up at the European science/fiction magazine Concatenation in a couple months. Please visit their website ahead of time!]

I referred to the Great Filter in an earlier post.  This is the idea that the great silence the Fermi paradox seeks to explain is not illusory:  we really are alone.  If that is the case, then since we know of one example of life and intelligence which did evolve, there must some event or set of events that dramatically decreases the odds of life evolving, becoming intelligent, and spreading from its home or at least signalling its presence.  By self-indication arguments, we can assume that many other species have achieved a level of intelligence similar to our own, but that something must have happened afterward to keep them from persisting or expanding.  This means it is also likely that the filter is still in front of us, i.e. that we will go extinct or at least be permanently confined to our solar system.  I'm increasingly unable to discount the idea that intelligence itself is probably, usually, an evolutionary dead end. 

The less interesting version of this idea is that given the way evolution works, intelligence is invariably layered on top of older systems like emotions and appetites, which were previously constrained by the limits of their behavior but once amplified by intelligence quickly destroy the surrounding ecosystem.  (Essentially, the Special Agent Smith argument, but stripped of misanthropic moralizing.)

The more interesting version is that once a self-aware entity understands that pleasure and survival are separable - i.e., that its survival signal is not the same as its actual survival - and has the means to manipulate the former intentionally (ie full simulation and/or goal manipulation, which are the ultimate ends of heroin, pornography, and ideology) then the end is close.  This is a much more pessimistic version of involution.  Singularities could be thought of as either of these - a form of ecologic degradation that doesn't result in interstellar colonization, or as an opportunity to dissolve into fantasy worlds.

Finally, it could just be that it's incredibly unlikely that any life which evolves from matter, at the bottom of a gravity well, with a life-cycle inextricable from such an environment (needing an atmosphere, solvent, a complex web of other replicators), simply cannot expect to expand across a universe where even inside the comparatively cluttered galaxies the possible new homes are separated by light years.  To a first approximation, the universe is made of vacuum with some dark matter.  It may be then that every star is surrounded by an insurmountable Wallace Line.

Where Are the Post-Singularity Replicators: A New One for Fermi and Bostrom

One of the underlying assumptions of singularity arguments is that not only will technology improve sufficiently to hit an inflection point beyond which tools improve themselves to the point of something usefully called intelligence and reproduction, but that this is basically inevitable, as long as we don't destroy ourselves before then. (Whether the singularity would destroy us is another question.) A final assumption is that sufficiently advanced post-singularity machines will be able to preserve or add to themselves, or replicate, by recruiting "dumb" matter far better than current Earth biology can, as we do when we eat and breathe.

If we make the additional assumption that any intelligence in the universe which uses tools and has behavior will incrementally improve those tools - then the same should happen for any other species.

Taking these assumptions as valid, we should assume that the universe we observe should already be heavily influenced by singularity events. But it is NOT obviously behaving in any way that dumb matter doesn't behave. I observed in a previous post that singularity arguments, taken to their conclusion, track Bostrom and Fermi: if these are such powerful principles in the evolution of the universe, shouldn't we already be experiencing the consequences?

Even more generally speaking (outside of singularity arguments) shouldn't we assume that, given enough time, most matter and energy will eventually be locked up into replicators, if living things and/or intelligence continues to expand? It's worth emphasizing that all of the arguments are some version of the self-indication argument, although the where-are-all-the-singularity argument is a hypothetical SIA, which I am using to argue against the probability of a singularity.

The most likely answer, based on what we know so far, is that there have been no singularities, which in turn means that it is less likely than we might otherwise have thought that we will have a singularity. While some version of panspermia seems more and more plausible, the seeding of young worlds with nucleobases and amino acids isn't exactly what people have in mind in these discussions. Indeed the absence of expanding "life clouds" argues not just against singularities as such but against the indefinite expansion and survival of life. But there are a number of possible counterarguments:

- Entropy wins; matter and energy also get locked up into black holes faster than life and/or intelligence can employ that matter for their own preservation.

- By the nature of physics, only a very small fraction of matter and energy can be pressed into service as a substrate for life and intelligence.

- Replicators are always unstable processes. This solves Fermi's paradox by making Drake's omega attrition factor much more influential to the outcome.

- Most of what we observe is indeed the result of such processes (galaxies, stars, our own solar system?) and we either don't have the pattern recognition skills to see it or are only observing a vanishingly small slice of possible data. (This one makes for the best science fiction ideas, and also is more analogous to Bostrom than Fermi.)

- Humans are the only species that uses tools and improves them.

- We're lucky and we're the first, or one of the first, and the expanding sphere of others' computronium hasn't hit us yet.

If I had to bet, I would bet against the last two.