Life from Elsewhere
The idea that life on Earth came from somewhere else has intrigued me since I first ran into it in Fred Hoyle’s work back in the 1980s. I already knew of Hoyle because, if memory serves, his novel The Black Cloud (William Heinemann Ltd, 1957) was the first science fiction novel I ever read. Someone brought it to my grade school and we passed the copy around to the point where by the time I got it, the paperback was battered though intact. Its cover remains a fine memory. I remember being ingenious about appearing to be reading an arithmetic text in class while actually reading the Hoyle novel.
In the book, the approach of a cloud of dust and gas in the Solar System occasions alarm, with projections of the end of photosynthesis as the Sun’s light is blocked. Even more alarming are the unexpected movements of the cloud once it arrives, which suggest that it is no inanimate object but a kind of organism.
I’ve been meaning to re-read The Black Cloud for years and this post energizes me to do just that, though this time around the old paperback will have to give way to a Kindle, as I had to pass the original back to its owner for continued circulation, after which it disappeared.
But back to panspermia. As the novel shows, Hoyle was interested not just in the nature of consciousness but likewise the matrix in which it can be embedded. By the 1980s, working with a former doctoral student named Chandra Wickramasinghe (Cardiff University), he was suggesting that dense molecular clouds could contain biochemistry, possibly concentrated in the volatiles of comets in their trillions. The notion that the inside of a comet could have become the source for life on Earth led the duo to propose that space-borne clouds might even evolve bacteria, which they explored in a 1979 book called Diseases from Space, an idea that was widely dismissed.
But leaving bacteria born in space aside, the idea that life can move between planets continues to intrigue scientists. We have, after all, objects on Earth that have fallen from the sky and turn out to have been the result of impacts on Mars. So if we can move past the question of life’s origin and focus instead on life’s propagation, panspermia takes on new life. Abiogenesis may be operational on the early Earth, but perhaps incoming materials from comets or other planets had their own unique role to play. Life in this case is not an either/or proposition but a combination of factors.
Be aware of a special issue of Astrobiology (citation below) which delves into these matters, with ten essays by the likes of Paul Davies, Fred Adams, Charles Lineweaver, as well as Avi Loeb and Ben Zuckerman, who from their own perspectives tackle the question of ‘Oumuamua as a technological object rather than a comet. The latter discussion reminds us that the discovery of interstellar comets moving through our Solar System widens the panspermia debate. Now we’re talking about the potential transfer of materials not just between planets but between stellar systems.
If panspermia does operate, meaning that life can survive space journeys lasting perhaps millions of years, then we might begin to speak of a common molecular basis for the living things we would expect to find widely in the universe. Paul Davies and Peter Worden point this out in their introduction to the special collection, noting that this view contrasts enormously with the more common view that life emerges on its own wherever suitable conditions can be found. In both cases, the implication is for a cosmos filled with life, but only panspermia argues for its natural spread between worlds.
The key word there is ‘natural.’ If panspermia does not occur via natural processes, what about the possibility of ‘directed panspermia,’ in which a civilization makes the decision to use technology to spread life as a matter of policy? It startled me in reading through these essays to realize that Francis Crick and the British chemist Leslie Orgel had proposed as far back as 1973 in a paper in Icarus that we investigate present-day organisms to see whether we can find “any vestigial traces” of extraterrestrial origins. Their paper offers this startling finish:
Are the senders or their descendants still alive? Has their star inexorably warmed up and frizzled them, or were they able to colonise a different Solar System with a short-range spaceship? Have they perhaps destroyed themselves, either by too much aggression or too little? The difficulties of placing any form of life on another planetary system are so great that we are unlikely to be their sole descendants. Presumably they would have made many attempts to infect the galaxy. If the range of their rockets were small this might suggest that we have cousins on planets which are not too distant. Perhaps the galaxy is lifeless except for a local village, of which we are one member.
I like that word ‘frizzled.’ It even gets past the spell-check!
We’ve looked at proposals for directed panspermia before in these pages, as for example in Robert Buckalew’s Engineered Exogenesis: Nature’s Model for Interstellar Colonization and my entry Directed Panspermia: Seeding the Galaxy, which focuses on Michael Mautner and Greg Matloff’s ideas on spreading life in the cosmos. Next time I want to dig into an essay from the new Astrobiology collection by Christopher McKay, Paul Davies and Simon Worden on the question of how we might use interstellar comets of the sort we now believe to be common to spread life in the galaxy.
A key question: Why would we want to do this? Or more precisely, how would we go about deciding whether spreading life into the cosmos is an ethical thing to do?
The paper we’ll look at next time is McKay, Davies & Worden, “Directed Panspermia Using Interstellar Comets,” Astrobiology Vol. 22 No. 12 (6 December 2022), 1443-1451. Full text. This is a paper in the Astrobiology special collection Interstellar Objects in Our Solar System (December 2022). The Crick and Orgel paper is “Directed Panspermia,” Icarus Vol. 19 (1973), 341-346.
Probing the Galaxy: Self-Reproduction and Its Consequences
In a long and discursive paper on self-replicating probes as a way of exploring star systems, Alex Ellery (Carleton University, Ottawa) digs, among many other things, into the question of what we might detect from Earth of extraterrestrial technologies here in the Solar System. The idea here is familiar enough. If at some point in our past, a technological civilization had placed a probe, self-replicating or not, near enough to observe Earth, we should at some point be able to detect it. Ellery believes such probes would be commonplace because we humans are developing self-replication technology even today. Thus a lack of probes would indicate that there are no extraterrestrial civilizations to build them.
There are interesting insights in this paper that I want to explore, some of them going a bit far afield from Ellery’s stated intent, but worth considering for all that. SETA, the Search for Extraterrestrial Artifacts, is a young endeavor but a provocative one. Here self-replication attracts the author because probing a stellar system is a far different proposition than colonizing it. In other words, exploration per se — the quest for information — is a driver for exhaustive seeding of probes not limited by issues of sustainability or sociological constraints. Self-replication, he believes, is the key to exponential exploration of the galaxy at minimum cost and greatest likelihood of detection by those being studied.
Image: The galaxy Messier 101 (M101, also known as NGC 5457 and nicknamed the ‘Pinwheel Galaxy’) lies in the northern circumpolar constellation, Ursa Major (The Great Bear), at a distance of about 21 million light-years from Earth. This is one of the largest and most detailed photos of a spiral galaxy that has been released from Hubble. How long would it take a single civilization to fill a galaxy like this with self-replicating probes? Image credit: NASA/STScI.
Growing the Idea of Self-Reproduction
Going through the background to ideas of self-replication in space, Ellery cites the pioneering work of Robert Freitas, and here I want to pause. It intrigues me that Freitas, the man who first studied the halo orbits around the Earth-Moon L4 and L5 points looking for artifacts, is also responsible for one of the earliest studies of machine self-replication in the form of the NASA/ASEE study in 1980. The latter had no direct interstellar intent but rather developed the concept of a self-replicating factory on the lunar surface using resources mined by robots. Freitas would go on to explore a robot factory coupled to a Daedalus-class starship called REPRO, though one taken to the next level and capable of deceleration at the target star, where the factory would grow itself to its full capabilities upon landing.
I should mention that following REPRO, Freitas would turn his attention to nanotechnology, a world where payload constraints are eased and self-reproduction occurs at the molecular level. But let’s stick with REPRO a moment longer, even though I’m departing from Ellery in doing so. For in Freitas’ original concept, half the REPRO payload would be devoted to self-reproduction, with a specialized payload exploiting the resources of a gas giant moon to produce a new REPRO probe every 500 years.
As you can see, the REPRO probe would have taken Project Daedalus’ onboard autonomy to an entirely new level. Freitas’ studies foresaw thirteen distinct robot species, among them chemists, miners, metallurgists, fabricators, assemblers, wardens and verifiers. Each would have a role to play in the creation of the new probe. The chemist robots, for example, were to process ore and extract the heavy elements needed to build the factory on the moon of the gas giant planet. Aerostat robots would float like hot-air balloons in the gas giant’s atmosphere, where they would collect the needed propellants for the next generation REPRO probe. Fabricators would turn raw materials (produced by the metallurgists) into working parts, from threaded bolts to semiconductor chips, while assemblers created the modules that would build the initial factory. Crawler robots would specialize in surface hauling, while wardens, as with Project Daedalus, remained responsible for maintenance and repair of ship systems.
I spend so much time on this because of my fascination with the history of interstellar ideas. In any case, I don’t know of any earlier studies that explored self-reproduction in the interstellar context and in terms of mission hardware than Freitas’ 1980 paper “A Self-Reproducing Interstellar Probe” in JBIS, which is conveniently available online. This was a step forward in interstellar studies, and I want to highlight it with this quotation from its text:
A major alternative to both the Daedalus flyby and “Bracewell probe” orbiter is the concept of the self -reproducing starprobe. Replicating spacefaring machines recently have received a cursory examination by Calder [4] and Boyce [5], but the basic feasibility of this approach has never been seriously considered despite its tremendous potential. In theory, each self -reproducing device dispatched by the launching society would become an independent agent, slowly scouting the Galaxy for evidence of life, intelligence and civilization. While such machines might be costlier to design and construct, given sufficient time a relatively few replicating starprobes could search the entire Milky Way.
The present paper addresses the plausibility of self-reproducing starprobes and the basic parameters of feasibility. A subsequent paper [10] compares reproductive and nonreproductive probe search strategies for missions of interstellar and galactic exploration.
Hart, Tipler and the Spread of Intelligence
These days, as Freitas went on to explore, massive redundancy, miniaturization and self-assembly at the molecular level have moved into tighter focus as we contemplate missions to the stars, and the enormous Daedalus-style craft (54,000 tons initial mass, including 50,000 tonnes of fuel and 500 tonnes of scientific payload) and its successors, while historically important, also resonate a bit with Captain Nemo’s Nautilus, as spectacular creations of the imagination that defied no laws of physics, but remain in tension with the realities of payload and propulsion. These days we explore miniaturization, with Breakthrough Starshot’s tiny payloads as one example.
But back to Ellery. From a philosophical standpoint, self-reproduction, he rightly points out, had also been considered by Michael Hart and Frank Tipler, each noting that if self-replication were possible, a civilization could fill the galaxy in a relatively short (compared to the age of the galaxy) timeframe. Ultimately self-reproducing probes exploit local materials upon arrival and make copies of themselves, a wave of exploration that would ensure every habitable planet had an attendant probe. Thus the Hart/Tipler contention that the lack of evidence for such a probe is an indication that extraterrestrial intelligence does not exist, an idea that still has currency.
Would any exploring civilization turn to self-replication? The author sees many reasons to do so:
There are numerous reasons to send out self-replicating probes – reconnaissance prior to interstellar migration, first-mover advantage, insurance against planetary disaster, etc – but only one not to – indifference to information growth (which must apply to all extant ETI without exception). Self-replicating probes require minimal capital investment and represent the most economical means to explore space, interstellar space included. In a real sense, self-replicating machines cannot become obsolete – new design developments can be broadcast and uploaded to upgrade them when necessary. Once the self-replicating probe is established in a star system, the probe may be exploited in various ways. The universal construction capability ensures that the self-replicating probe can construct any other device.
Probes that can fill the galaxy extract maximum information and can not only monitor but communicate with local species. Should a civilization choose to implement panspermia in systems devoid of life, the capability is implicit here, including “the prospect of exploiting microorganism DNA as a self-replicating message.” Such probes could also, in the event of colonization at a later period, establish needed infrastructure for the new arrivals, with the possibility of terraforming.
Thus probes like these become a route from Kardashev II to III. In fact, as Ellery sees it, if a Kardashev Type I civilization is capable of self-reproduction technology – and remember, Ellery believes we are on the cusp of it now – then the entire Type I phase may be relatively short on the way to Kardashev Types II and III, perhaps as little as a few thousand years. It’s an interesting thought given our current status somewhere around Kardashev 0.72, beset by problems of our own making and wondering whether we will survive long enough to establish a Type I civilization.
Image: NASA’s James Webb Space Telescope has produced the deepest and sharpest infrared image of the distant universe to date. Known as Webb’s First Deep Field, this image of galaxy cluster SMACS 0723 is overflowing with detail. Thousands of galaxies – including the faintest objects ever observed in the infrared – have appeared in Webb’s view for the first time. This slice of the vast universe covers a patch of sky approximately the size of a grain of sand held at arm’s length by someone on the ground. If self-reproducing probes are possible, are all galaxies likely to be explored by other civilizations? Credit: NASA, ESA, CSA, and STScI.
Early Days for SETA
The question of diffusion through the galaxy here gets a workover from a theory called TRIZ (Teorija Reshenija Izobretatel’skih Zadach), which Ellery uses to analyze the implications of self-reproduction, finding that the entire galaxy could be colonized within 24 probe generations. This produces a population of 424 billion probes. He’s assuming a short replication time at each stop – a few years at most – and thus finds that the spread of such probes is dominated by the transit time across the galactic plane, a million year process to complete assuming travel at a tenth of lightspeed.
Given this short timespan compared with the age of the Galaxy, our Galaxy should be swarming with self-replicating probes yet there is no evidence of them in our solar system. Indeed, it only requires a civilization to exist long enough to send out such probes as they would thenceforth continue to propagate through the Galaxy even if the sending civilization were no more. And of course, it requires only one ETI to do this.
Part of Ellery’s intent is to show how humans might create a self-replicating probe, going through the essential features of such and arguing that self-replication is near- rather than long-term, based on the idea of the universal constructor, a machine that builds any or all other machines including itself. Here we find intellectual origins in the work of Alan Turing and John von Neumann. Ellery digs into 3D printing and ongoing experiments in self-assembly as well as in-situ resource utilization of asteroid material, and along the way he illustrates probe propulsion concepts.
At this stage of the game in SETA, there is no evidence of self-replication or extraterrestrial probes of any kind, the author argues:
There is no observational evidence of large structures in our solar system, nor signs of large-scale mining and processing, nor signs of residue of such processes. Our current terrestrial self-replication scheme with its industrial ecology is imposed by the requirements for closure of the self-replication loop that (i) minimizes waste (sustainability) to minimize energy consumption; (ii) minimizes materials and components manufacture to minimize mining; (iii) minimizes manufacturing and assembly processes to minimize machinery. Nevertheless, we would expect extensive clay residues. We conclude therefore that the most tenable hypothesis is that ETI do not exist.
The answer to that contention is, of course, that we haven’t searched for local probes in any coordinated way, and that now that we are becoming capable of minute analysis of, for instance, the lunar surface (through Lunar Reconnaissance Orbiter imagery, for one), we can become more systematic in the investigation, taking in Earth co-orbitals, as Jim Benford has suggested, or looking for signs of lurkers in the asteroid belt. Ellery notes that the latter might demand searching for signs of resource exploitation there as opposed to finding an individual probe amidst the plethora of candidate objects.
But Ellery is adamant that efforts to find such lurkers should continue, citing the need to continue what has been up to now a meager and sporadic effort to conduct SETA. I’m going to recommend this paper to those Centauri Dreams readers who want to get up to speed on the scholarship on self-reproduction and its consequences. Indeed, the ideas jammed into its pages come at bewildering pace, but the scholarship is thorough and the references handy to have in one place. Whether self-reproducing probes are indeed imminent is a matter for debate but their implications demand our attention.
The paper is Ellery, “Self-replicating probes are imminent – implications for SETI,” International Journal of Astrobiology 8 July 2022 (full text). A companion paper published at the same time is “Curbing the fruitfulness of self-replicating machines,” International Journal of Astrobiology 8 July 2022 (full text).
The Great Venusian Bug Hunt
Our recent focus on life detection on nearby worlds concludes with a follow-up to Alex Tolley’s June essay on Venus Life Finder. What would the sequence of missions look like that resulted in an unambiguous detection of life in the clouds of Venus? To answer that question, Alex takes the missions in reverse order, starting with a final, successful detection, and working back to show what the precursor mission to each step would have needed to accomplish to justify continuing the effort. If the privately funded VLF succeeds, it will be in the unusual position of making an astrobiological breakthrough before the large space organizations could achieve it, but there are a lot of steps along the way that we have to get right.
by Alex Tolley
In my previous essay, Venus Life Finder: Scooping Big Science, I introduced the near-term, privately financed plan to send a series of dedicated life-finding probes to Venus’ clouds. The first was a tiny atmosphere entry vehicle with a dedicated instrument, the Autofluorescing Nephelometer (AFN). The follow-up probes would culminate in a sample return to Earth, all this before the big NASA and ESA probes had even reached Venus at the end of this decade to investigate planetary conditions.
When the discussion turns to missions on or around planets or moons that may be home to life, the focus is on whether these probes could be loaded with life-finding instruments to front-load life detection science. The VLF missions are perhaps the first, to make detecting life the primary science goal since the Viking Mars missions in the mid-1970s, with the possible exception of ESA’s Beagle 2 (Beagle 2 lander’s objectives included landing site geology, mineralogy, geochemistry, atmosphere, meteorology, climate; and search for biosignatures [8]).
The approach I am going to use here is to start with what an Earth laboratory might do to investigate samples with suspected novel life. I will then reverse the thinking for each mission stage until the decision to launch a Venusian atmosphere entry AFN becomes the obvious, logical choice.
So let us start with the what science and technology would likely employ on Earth, assuming that we have samples from the VLF missions previously undertaken that indicate that the conditions for life are not prohibitive, and earlier analyses that suggest that the collected particles are not just inanimate but appear to be, or contain life. As we do not know if this life is truly from a de novo abiogenesis or common to terrestrial life and thus perhaps from Earth, there are a number of basic tests that would be employed to determine if the VLF samples contain life.
The key analyses would include:
1) Are there complex organic molecules with structural regularities rather than randomness? For example, terrestrial cell membranes are composed of lipid chains with a certain length of the carbon chain (phospho- and glycolipids peak at 16- and 18-length chains). Are there high abundances of certain molecules that might form the basis of an information storage molecule, e.g. the 4 bases used in DNA – adenine, thymine, guanine, cytosine, or an abundance subset of the many possible amino acids?
2) Are the cell-like particles compartmentalized? Are there cell membranes? Do the cells contain other compartments that manage key biological functions [5]?
3) Do the molecules show homochirality, as we see on Earth? If not, and the molecules are racemic as we see with amino acids in meteorites, then this indicates a non-biological formation. Terrestrial proteins are based on levorotatory amino acids (L-amino acids), whilst sugars are dextrorotatory (D-sugars).
4) Do the samples generate or consume gases that are associated with life? This can be deceptive as we learned with the ambiguous Viking experiment to detect gas emissions from cultured Martian regolith. Lab experiments can resolve such issues.
5) Do the samples have different Isotope ratios than the planetary material? On Earth, biology tends to alter the ratios of carbon and oxygen isotopes that are used as proxies in analyses of samples for paleo life. For example, photosynthesis reduces the C13/C12 ratio and therefore can be used to infer whether carbon compounds are biogenic.
Note that the goals do not initially include using optical microscopes, or DNA sequencers. Terrestrial life is increasingly surveyed analyzing samples for DNA sequences. DNA reading instruments will only work if the same nucleobases are used by Venusian life. If they are, then there is the issue of whether they come from a common origin to terrestrial life. For bacteria-sized particles, electron microscopes are more appropriate.
The types of instruments used include mass spectrometers, liquid and gas chromatographs, optical spectrometers of various wavelengths, nanotomographs (nano-sized CT scans), atomic force microscopes, etc. These instruments tend to be rather large and heavy, although specially designed ones are being flown on the big missions, such as the Mars Perseverance rover. Table 1 below details these biosignature analyses to be done on the returned samples.
Table 1 (click to enlarge). Laboratory biosignature analyses for the returned samples, the instruments, and the specific outputs.
For the goal of detecting biosignature gases and their changes, table 2 shows the prior information collected from probes and telescopes that might indicate extant life on Venus.
Table 2 (click to enlarge). Prior data of potential biosignature gases in the Venusian atmosphere.
Given that these are the types of experiments on samples returned to Earth, how do we collect those samples for return? Unlike Mars, life on Venus is expected to be in the clouds, in a temperate habitable zone (HZ) layer. The problem is not dissimilar to collecting samples in the deep ocean. A container must be exposed to the environment and then closed and sealed. Apart from pressure, the ocean is a benign environment.
Imagine the difficulties of collecting a sample near the bottom of a deep, highly acidic lake. How would that be done given that it is not possible to take a boat out and lower an acidic resistant sample bottle? The VLF team has not decided how best to do this, but the sampling is designed to take place from a balloon floating in the atmosphere for the sample return mission.
Possible sampling methods include:
- Use of aerogels
- Filters
- Electrostatic sticky tape
- Funnels, jars, and bottles
- Fog Harp droplet collector
- Gas sampling bags
In order to preserve the sample from contamination and to ensure planetary protection from the returned samples, containment must be carefully designed to cover contingencies that might expose the sample to Earth’s biosphere.
Note that this Venus Return mission is no longer a small project. The total payload to reach LEO, that includes the transit vehicle, balloon and instrument gondola, plus Venus ascent vehicle, and transit vehicle to Earth, is 38,000 kg, far more massive than the Mars Perseverance Mission, double the launch capability of the Atlas V and Ariane V launchers, and requiring the Falcon Heavy. The number of components indicates a very complex and difficult mission, probably requiring the capabilities of a national space organization. This is definitely no longer a small, privately funded, mission.
But let’s backtrack again. The samples were deemed worth the cost of returning to Earth because prior missions have supported the case that life may be present in the atmosphere. What experiments would best be done to make that assessment, given a prior mission that indicated this ambitious, complex, and expensive effort was worth attempting?
The science goals for this intermediate Habitability Mission are:
1) Measure the physical conditions in the cloud layer to ensure they are not outside of a possible extremophile range. The most important metric is perhaps temperature, as no terrestrial thermophile can survive above 122 °C, nor metabolize in solids. A lower bound might be that water freezes at 0 °C, although salt water will lower that freezing point, so halophiles could live in salty water at below 0 °C. Is there water vapor in the clouds that indicates that the particles are not pure sulfuric acid? Allied with that, are the particles less acidic than pure H2SO4? Are there non-volatile elements, such as phosphorus and metals, that are used by terrestrial biology to harvest and transfer energy for metabolism?
2) Can the organic materials previously detected be identified to indicate biologic rather than abiologic chemistry? Are there any hints at compound regularity that will inform the sample return mission? Can we detect gas changes that indicate metabolism is happening, and are the gases in disequilibrium? Of particular interest may be the detection of phosphine (PH3) emissions, an unambiguous terrestrial biosignature, detected in the Venusian clouds by terrestrial ground-based telescopes in 2020.
3) Are the non-spherical particles detected in a prior mission solid or liquid, and are they homogeneous in composition (non-biologic) or not (possible life).
To be able to do these experiments, the mission will use balloons that can float in the Venusian clouds. They may need to be able to adjust their altitude to find the best layers (but this adds complexity, risk, and cost) and travel spatially, especially if there is a desire to sample the patchy cloud layers that are strongly UV absorbing and have been likened to algal blooms on Earth.
A balloon mission is quite complex and carries a number of instruments, so that cost and complexity is now substantial. A simpler, low-cost, prior mission is needed that will capture key data. What is the simplest, lowest mass mission possible that will inform the team that this balloon mission should definitely go ahead if the results are positive? What science goals and instrument[s] could best provide the data to inform this decision?
This earlier mission is designed around two sources of information that it can leverage. First, there are the many Venus entry probe missions from the early 1960s to the mid 1980s. The most intriguing information includes the observation that there were particles in the clouds that were not spherical as would be expected by physics, and this non-spherical nature might indicate cellular life, such as bacilli (rod-shaped bacteria).
Shape however, is insufficient, as life must be able to interact with the environment to feed, grow, and reproduce. On Earth, these functions require a range of organic molecules – proteins, DNA, RNA, lipids and sugars. This implies that organic compounds must be present in these non-spherical particles; otherwise the shape may be due to physical processes, including agglomeration and/or merging of spherical particles.
The VLF team is also testing some of the assumptions and technology in the lab, confirming for example that autofluorescing of carbon materials works in concentrated sulfuric acid. Their lab experiments show that linear carbon molecules like formaldehyde and methanol in concentrated H2SO4 result in both UV absorption and fluorescence over time, implying that the structures are altered, as is found in industrial processes. From the report:
If there is organic carbon in the Venus atmosphere, it will react with concentrated sulfuric acid in the cloud droplets, resulting in colored, strongly UV absorbing, and fluorescent products that can be detected (…). We have exposed several samples containing various organic molecules (e.g., formaldehyde) to 120 °C, 90% sulfuric acid for different lengths of time. As a result of the exposure to concentrated sulfuric acid all of the tested organic compounds produced visible coloration, increased absorbance (mainly in the UV range of the spectrum), and resulted in fluorescence (…)
It should also be noted that Misra has shown that remote autofluorescing can detect carbon compounds and distinguish between organic material (leaves, microbes on rocks, and fossils) and fluorescing minerals [6,7].
Table 3 (click to enlarge). The science goals for the balloon mission, showing that the AFN is the best single instrument to both detect and confirm the non-spherical particles found in the prior Venus probes, and the presence of organic compounds in the particles. It can also determine whether the particles are liquid or solid, and estimate the pH of the particles.
Of the possible choices of instruments, the Autofluorescing Nephelometer (AFN) best meets the requirements of being able to measure both particle shape and the presence of organic compounds. This can be seen in table 3 above for the science goals of the balloon mission. The instrument is described in the prior post and in more detail in the VLF Report [1]. Ideally, both conditions should be met with positive results, although even both together are suggestive but not unambiguous.
Organic compounds can form in concentrated H2SO4, and cocci are essentially spherical bacteria. Nevertheless, a positive result for one or both justifies the funding of the follow up mission. Conversely, a negative result for both, especially the absence of detectable organic compounds would put a nail in the coffin of the idea that there is life in the Venusian clouds (a classic falsification experiment) – at least for that 4-5 minute data acquisition mission as the probe falls through the HZ layers of clouds where these non-spherical particles have previously been detected.
It could certainly be argued that life is patchy, and just like failing to catch a fish does not mean there are no fish to be caught, it is possible that the probe fell though a [near] lifeless patch and that other attempts should be made, for example the balloon mission that will take measurements over a wider range of space and time.
The first VLF probe mission begs the question of why we should even consider Venus as an abode for life. The prior missions have shown that the surface is a very hot, dry, and acidic environment which is inimical to life as we know it. The only suggestions for the presence of life are the aforementioned patchy UV absorbing regions implying organic compounds in the clouds, and the presence of the biosignature gas PH3.
For life to be on Venus, either the conditions must once have been clement to allow abiogenesis, or life must have been seeded by panspermia to allow it ultimately to evolve to survive in the cloud refugia when the oceans were lost during the runaway greenhouse era. Is there any evidence that Venus was once our sister world with conditions like Earth, but warmer, before the runaway greenhouse conditions transformed the planet?
The scholarly literature is divided, from the optimistic view of Grinspoon [2] and others that Venus had an early ocean that lasted for long enough (e.g. 1 Gy), to support life [3], to the pessimistic view of Turbet [4] that modeling suggests Venus never had an ocean (and that Earth was only able to condense one during the faint young sun period.
It is to try to answer these questions that the science goals of NASA’s and ESA’s DAVINCI+, VERITAS, and EnVision probes are designed to meet.
The VLF team, however, have supported their plan with the optimistic view that early Venus was clement and that life could have taken hold, and therefore a series of dedicated, life-finding missions will best answer the question of whether there is life on Venus, rather than establishing that a paleo climate on Venus was indeed present and lasted long enough to allow life to emerge, or long enough for it to have been transferred from Earth by the time we are sure life on Earth was present.
If the first VLF mission returns positive results, then it seems likely that the following missions, however designed and by whom executed, will push forward the science goals toward more life detection. Negative results could well derail subsequent life detection goals. The time frame will overlap with the Mars sample return mission that will collect the Perseverance rover samples for analyses back on Earth. It may well also overlap with the early results of biosignature detection on exoplanets. Whatever the outcome, the end of this decade will be an exciting time and will pose fundamental questions about our place in the galaxy.
References
1. Seager S, et al Venus Life Finder Study (2021) Web accessed 02/18/2022 https://venuscloudlife.com/venus-life-finder-mission-study/
2. Grinspoon, David & Bullock, Mark. (2007). Searching for Evidence of Past Oceans on Venus, American Astronomical Society, DPS meeting #39, id.61.09; Bulletin of the American Astronomical Society, Vol. 39, p.540
3. Way, M. J.,et all (2016), Was Venus the first habitable world of our solar system?, Geophys. Res. Lett., 43, 8376-8383, doi:10.1002/2016GL069790.
4. Turbet, M., Bolmont, E., Chaverot, G. et al. Day-night cloud asymmetry prevents early oceans on Venus but not on Earth. Nature 598, 276-280 (2021). https://doi.org/10.1038/s41586-021-03873-w
5. Cornejo E, Abreu N, Komeili A. Compartmentalization and organelle formation in bacteria. Curr Opin Cell Biol. 2014 Feb;26:132-8. doi: 10.1016/j.ceb.2013.12.007. Epub 2014 Jan 16. PMID: 24440431; PMCID: PMC4318566.
6. Misra, A.K., Rowley, S.J., Zhou, J. et al. Biofinder detects biological remains in Green River fish fossils from Eocene epoch at video speed. Sci Rep 12, 10164 (2022). https://doi.org/10.1038/s41598-022-14410-8
7. Misra, A. et al (2021). Compact Color Biofinder (CoCoBi): Fast, Standoff, Sensitive Detection of Biomolecules and Polyaromatic Hydrocarbons for the Detection of Life. Applied Spectroscopy. 75. 000370282110339. DOI:10.1177/00037028211033911.
8. Beagle 2. https://en.wikipedia.org/wiki/Beagle_2 Accessed July 2, 2022
Starlight: Toward an Interstellar Biology
If you could send out a fleet of small lightsails, accelerated to perhaps 20 percent of the speed of light, you could put something of human manufacture into the Alpha Centauri triple star system within about 20 years. So goes, of course, the thinking of Breakthrough Starshot, which continues to investigate whether such a proposal is practicable. As the feasibility study continues, we’ll learn whether the scientists involved have been able to resolve some of the key issues, including especially data return and the need for power onboard to make it happen.
The concept of beam-driven sails for acceleration to interstellar speeds goes back to Robert Forward (see Jim Benford’s excellent A Photon Beam Propulsion Timeline in these pages) and has been examined for several decades by, among others, Geoffrey Landis, Gregory Matloff, Benford himself (working with brother Greg) in laboratory experiments at JPL, Leik Myrabo, and Chaouki Abdallah and team at the University of New Mexico. At the University of California, Santa Barbara, Philip Lubin has advocated DE-STAR (Directed Energy Solar Targeting of Asteroids and Exploration), a program for developing a system of modular phased laser arrays that could be used for asteroid mitigation and as propulsion for deep space missions.
Out of this grew Directed Energy Propulsion for Interstellar Exploration (DEEP-IN), which homes in on using tiny wafer probes for interstellar travel. Also known as Starlight, the program is now the subject of a paper in Acta Astronautica that takes interstellar mission concepts into the realm of biology. Working with Stephen Lantin and a team of researchers at the UCSB Experimental Cosmology Group, Lubin is examining how we can use small relativistic spacecraft to place seeds and microorganisms for experimentation outside the Solar System.
Image: Initial interstellar missions will require a complete reevaluation and redesign of the space systems of today. The objective of the Wafer Scale Spacecraft Development program (WSSD) at the University of California Santa Barbara (UCSB) is to design, develop, assemble and characterize the initial prototypes of these robotic platforms in an attempt to pave a path forward for future innovation and exploration. This program, which is just one venture of the UCSB Experimental Cosmology Group’s Electronic and Advanced Systems Laboratory (UCSB Deepspace EAS), focuses on leveraging continued advances in semiconductor and photonics technologies to recognize and efficiently address the many complexities associated with long duration autonomous interstellar mission. Credit: UCSB Experimental Cosmology Group.
Biology Beyond the Heliosphere
The goal of Starlight is not to seed the nearby universe — that’s an entirely different discussion! — but to conduct what the paper calls ‘biosentinel’ experiments, sending them not to another star but to empty interstellar space to help us characterize how simple biological systems deal with conditions there. This could be seen as a step toward eventual human travel to other stars, but the paper doesn’t dwell on that prospect, wisely I think, because what we learn from such experiments is vital information in its own right and may teach us a good deal about abiogenesis and the possibility of panspermia as a way of scattering life throughout the cosmos.
We may, in other words, be able to characterize biological systems to the point where we understand how to protect human life on a future interstellar mission, but the goal of Starlight is to begin the experimentation that will tell us what is possible for living systems under a wide variety of conditions in deep space. Such missions are, in effect, scouts. Putting them onto interstellar trajectories could open up pathways to larger, more biologically complex missions depending on what they find.
I think the emphasis on biology here is heartening, for space research even in the near-term has been top-heavy in terms of propulsion engineering, obviously critical but sometimes neglectful of such critical matters as how to create closed loop life support. Even a destination as nearby as Mars forces us to ask whether humans can adapt long-term to sharply different gravity gradients, among a multitude of other questions. Thus the need for an orbital station dedicated to biology and physiology that would inform mission planning and spacecraft design.
But that kind of complex starts with humans and examines their response in nearby space. What Lubin and team are talking about is studying basic biological systems and their response to conditions outside the heliosphere, where we can begin experiments within the realm of interstellar biology. Any lifeforms we send to interstellar space will be exposed to conditions of zero-g but also hypergravity, as during the launch and propulsion phases of the flight. We would likewise be working with experiments that can be adjusted in terms of exposure to vacuum, radiation and a wide range of temperatures affecting a variety of sample microorganisms.
A Fleet of Interstellar Laboratories
How to experiment, and what to experiment on? Remember that we’re dealing with payloads of wafer size given our constraints on mass. The UCSB work has focused on the design of a microfluidics chamber that can provide suitable conditions for reviving and sustaining microorganisms on the order of 200 μm in length. The paper refers to performing ‘remote lab-on-a-chip experiments,’ using new materials, discussed within, that are enhanced for biocompatibility. I don’t want to go too deeply into the weeds on this, but here’s the gist:
[New thermoplastic elastomers] can be manufactured with diverse glass transition temperatures and either monolithically prepared with an imprinter or integrated with other candidates, such as glass. Polymerase chain reaction (PCR) on a chip is another area that will evolve naturally over the next decade and is one of many biological techniques that could be incorporated in designs. It is also possible that enzymes could be stabilized in osmolytes to perform onboard biochemical reactions. For the study of life in the interstellar environment, it is necessary to include experimental controls (in LEO and on the ground) and the use of diverse genotypes and species to characterize a wide response space…
The biological species best suited for this kind of investigation will have to have key characteristics, the first of which is a low metabolic rate in a chamber where, due to mass restrictions, nutrients will be limited. Also critical is cryptobiotic capability, meaning the ability to go into hibernation with the lowest possible metabolic rate. A tolerance for radiation is obviously helpful, making certain species clear candidates for these missions, especially tardigrades (so-called ‘water bears’), which are known for being ferociously robust under a wide range of conditions and are capable of reducing biological activity to undetectable levels.
We know that tardigrades can survive high radiation as well as high pressure environments; they have been demonstrated to be capable of enduring exposure to space in low Earth orbit. A second outstanding candidate is C. elegans, a multicellular animal small enough that a teaspoon can hold approximately 100 million juvenile worms. Also helpful is the fact that C. elegans has a rapid life cycle of about 14 days, and can, like tardigrades,be placed into suspended animation for later recovery. Other prospects among organisms and cell types are examined in these pages, and the authors call for near-term experiments on mammalian cells to delve into their response to space conditions.
Clearly, a high radiation environment, as found between the stars, offers the chance to study how life began by varying the degree of radiation shielding to which prebiotic chemicals are exposed:
The high radiation environment of interstellar space provides an interesting opportunity to study the biochemical origins of life in spacecraft with low radiation shielding versus those equipped with protective measures to limit the effect of galactic cosmic radiation (GCR) on the prebiotic chemicals, possibly shedding light on the flexibility in the conditions needed for life to arise.
Thus a spacecraft of this sort can also become an experiment in abiogenesis, the formation of nucleic acids and other biological molecules having heretofore been recreated only under laboratory conditions on Earth or in low-Earth orbit. Designing the equipment to make such experiments possible is part of the ongoing developmental work for Starlight.
An interstellar experimental biology probes the factors that make some organisms better adapted for space conditions, but it does hold implications for human expansion:
Selecting for species that are physiologically better fit for interstellar travel opens up new avenues for space research. In testing the metabolism, development, and replication of species, like C. elegans, we can see how biological systems are generally affected by space conditions. C. elegans and tardigrades are inherently more suited to space flight as opposed to humans due to factors like the extensive DNA protection mechanisms some tardigrades have for radiation exposure or the dauer larva state of arrested development C. elegans enter when faced with unfavorable growth conditions. However, as there is overlap between our species, like the human orthologs for 80% of C. elegans proteins, we can begin to make some predictions on the potential for human life in interstellar space.
Any time we ponder sending life forms into space, including simple bacteria that may have contaminated lander probes on other planets, we run into serious issues of planetary protection. I want to look at the paper’s discussion of those in the next post, along with a consideration of space-based biology in the context of concepts that could offer backup systems for Earth.
The paper is Lantin et al., “Interstellar space biology via Project Starlight,” Acta Astronautica Vol. 190 (January 2022), pp. 261-272 (abstract).
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