Is life everywhere or nearly nowhere?

 kw: book reviews, nonfiction, exobiology, astrobiology, seti, exoplanets, origins of life

The title of a recent book by Nathalie A. Cabrol is astonishing: The Secret Life of the Universe: An Astrobiologist's Search for the Origins and Frontiers of Life. Why astonishing? First, let us consider the limits of what is known.

• In our solar system, until recently, only three planets have been considered habitable at least part of the time since the solar system was formed about 4.6 billion years ago (hereafter Ga): Venus, Earth, and Mars. Both Venus and Mars are considered "almost certainly dead", but hints of continued habitability are discovered from time to time.
• Many "ice moons", such as three of the Galilean moons of Jupiter, Europa, Ganymede and Callisto; Enceladus, a moon of Saturn; and Oberon, a moon of Uranus—all appear to have large subsurface oceans of liquid water, or actually brine, which could sustain life.
• Beyond the solar system, thousands of exoplanets have now been detected. A few hundred of these are at an appropriate distance from their host stars to be habitable, at least at present, if not for the long term.
• Most of the exoplanets so far detected and confirmed are less than 5,000 light years from Earth. A handful (so far) are at distances ranging up to 33,000 light years.

Further interesting information is found in the List of Exoplanet Extremes. 

What do these facts imply? As much as we might like to speculate about life (almost certainly bacterial or some analog thereof) on various solar system bodies, the confirmed occurrence of life in the solar system is found only on Earth. N=1.

Outside the solar system, we have partially probed a volume of space totaling about 80 billion cubic light years (considering the thickness of the galactic disk to be 1,000 light years). That's not bad; it is 1% of the volume of the Milky Way galaxy. However our galaxy is one of at least 200 billion, and probably more than a trillion, galaxies in the visible universe. We don't know how much universe lies beyond our visible horizon. Again, in all that space, known life: N=1.

From a numerical standpoint, the data we have relate to between a quintillionth and a quadrillionth of the known universe. That makes the book's title an astonishingly extreme overstatement.

On the other hand: The author, the director of the Carl Sagan center at the SETI institute, presents the principles by which life is likely to have arisen, and the evidence from all around the universe that the right chemistry to kick-start life exist nearly everywhere. This makes the book's title almost banally obvious! Isn't that great?

Rather than survey all of the author's points, I'll focus on a few of interest, that may be little known. Firstly, note that word "Origins" in the book's subtitle. Life may have started on Earth more than once. It may have arisen, been snuffed out, and arisen again, perhaps several times. Earlier incidences of life may not have been totally snuffed out, and still exist alongside "us".

Firstly, consider that the "standard DNA coding table" doesn't apply everywhere. For example, there are variations in the encoding of certain DNA codons (3-base groups) to amino acids (or to Stop) that are found in mitochondria. Various classes of eukaryotic organisms have different mitochondria, as revealed by their coding tables. Other microscopic critters, not all of them bacteria, have alternate coding tables. So far, 30 alternative coding tables are known, with the "standard table" bringing the total to 31. See List of Genetic Codes for more details.

Let's step back and consider the situation. There are 64 possible DNA codons. All known life on Earth uses 20 amino acids (one bacterial genus may use a 21st amino acid; I can't find out much information about it). There are dozens, perhaps hundreds, more possible amino acids. The 64-to-20 conversion involves numerous duplicate codes, which makes for a robust system. Many single-codon variations (micromutations, which are common), make no change in the protein being produced. How many possible coding tables are there? I am good at many kinds of math, but not the details of "permutations and combinations". The best I can figure, the number is at least 48x10³³ (a 35-digit number), but it could actually be an 84-digit number. Either way, it is a lot!

Is it safe to assume that life elsewhere in the universe also uses DNA and RNA and ribosome decoding to produce proteins from some 20 amino acids? Not really. It is not even safe to assume faraway life requires water. Dr. Cabrol mentions "life as we don't know it" from time to time. She considers places like the Saturnian moon Titan, where water ice is a rock and the primary liquid is methane. What kind of life could arise there? Water (our solvent!) is polar, but methane is nonpolar; perhaps the abundance of ammonia, which is polar, could make methane plus ammonia an appropriate solvent for generating life-as-we-don't-know-it.

I am reminded of the Lensman series of space opera novels by E.E. "Doc" Smith from 1948 to 1954. It concerns intergalactic warfare between water/oxygen-based life and methane/chlorine-based life. I am also reminded of what the character Ian Malcolm said in Jurassic Park, "Life will find a way." I am further reminded of Vital Dust by Christian deDuve, who calls life "inevitable" and "a cosmic imperative." There could be a lot of different kinds of life in the universe, and it's unlikely that we could eat any of it, nor that it could eat us!

Dr. Cabrol points out that planets seem to outnumber stars. Perhaps many stars have no planets, but many more stars have at least one planet, and usually more than one. What proportion of these are rocky (not gaseous like Jupiter, which may have no solid surface) and in the habitable zone of their host stars? Is it a percent or so? Exoplanet data so far indicates between two and three percent. A further constraint is that, as a Main Sequence star heats up during its existence, the shift of the habitable zone shouldn't move beyond the planet in less than 5 billion years or so. This is just based on the fact that life on Earth required about 4.5 billion years to produce us. We are still left with several billion possible planets in our galaxy alone that have the potential to produce life that can become "civilized" and sufficiently technological to send signals via radio or laser or something that we could possibly detect if we are close enough. "Close enough" keeps getting farther away as our own technology improves.

Let's consider that 5 billion year figure. Our Sun is a star of type G2, a little larger than average. Something like 75%-80% of all stars are smaller and lighter. The lighter a star is, the longer it burns hydrogen on the Main Sequence. During that period, it gradually gets hotter and brighter as helium accumulates in the core. I am interested in the larger half of the K series of stars. Their mass is between 0.75 and 0.9 solar masses, and they burn hydrogen for between 17 and 35 billion years, compared to the Sun's expected hydrogen burning life of about 10 billion years. Stars lighter than 0.75 solar mass have even longer "lifetimes," but they are more likely to produce large flares, which can damage or extinguish life from the surfaces of any planets in their habitable zones. So I favor focusing efforts such as SETI (Search for ExtraTerrestrial Intelligence) on stars in the range K5 to G2. Even a G3 star probably would have begun to burn us off its surface by now, as our Sun is expected to do starting about a billion years from now.

The author also considers the Drake Equation, which is a thought experiment that helps us consider the likelihood or prevalence of life in our galaxy (or the universe). It consists of a bunch of factors that are multiplied together to produce N, a possible quantity of detectable civilizations "out there". An important factor is, "How long does civilization Z emit a signal that we could detect, if we are close enough and have sufficient technological sensitivity?" Consider Earth. The first radio transmission that reached beyond "local" was in December 1901. Just about 124 years ago. 

At present, there are a few dozen "clear channel" AM radio stations that emit 50,000 watt signals 24/7, a larger number of FM radio stations of similar or even greater power, and many TV stations, mostly below 10,000 watts. However, more and more of our TV watching is moving to cable (including fiber optics), and digital signals are more efficient, so stations that do broadcast are using lower power. I have an in-attic antenna that presently receives more than 60 digital TV stations, so I don't use (expensive!) cable. Radio is beginning to go digital also. I predict that Earth will be largely "radio silent" before the 200th anniversary of Marconi's transatlantic radio transmission.

If an exo-civilization is typically detectable for only 100-200 years, even without extincting themselves, that cuts a big hole in all our speculations using the Drake equation. I'll have to think more about this…

The last chapter deals at length with our own danger of extincting ourselves. The author considers pollution, particularly CO₂ buildup plus methane buildup, an existential threat; she states clearly that our window of opportunity for ensuring long-term survival is small, a matter of decades at most. I agree in part, but my expectation is not so dire. I won't encroach on her thesis, though.

I will close this part with a hearty recommendation of the book. It is full of great ideas and great information, and very well written. A pleasure!

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If you aren't interested in errata, you can stop here. I ran across a few items, equally the fault of the author and the copy editor, that need to be corrected.

Tidal Locking is mentioned just a few times. It is not clearly explained, and I found this on page 97: "Callisto is tidally locked to Jupiter, orbiting around it in the same amount of time it takes Jupiter to rotate." Not so. Callisto takes 17 days to revolve about Jupiter, while Jupiter takes 10 hours to rotate on its axis. Callisto's rotation period is 17 days, so it always presents the same hemisphere to Jupiter. This is the same in principle as our Moon, which both rotates and revolves in 27.5 days (sidereal periods), so we always see the same hemisphere. In the quoted sentence, the second instance of "Jupiter" should be "Callisto". A second instance where the numbers are correct is on page 141: Pluto and its moon Charon are mutually tidal locked, always facing each other the same way, both rotating and revolving in 153 days.

An egregious typo, minor misspelling of a homonym on page 142: "pour" rather than "pore". To study a document is to pore over it, not "pour."

Information Mastery, a la Carl Sagan, is a proposed scale of technological advancement. It is mentioned on page 215, where it is stated that Level A represents 106 "unique bits of information" and Level Z represents 1,031 bits. This is a formatting error, compounded by the insertion of the comma. The two numbers ought to be 10⁶, or one million, and 10³¹, or ten million trillion trillion (a 32-digit number). I suspect a dumb copy-paste removed the exponent formatting. Anyway, the concept is fascinating.

Let us consider where we are as a civilization on Sagan's scale. The venerable Encyclopedia Britannica contains about half a million topics in 40 million words. I suspect that Sagan would consider a "unique bit of information" to represent about a paragraph. These half million topics then are each stated in an average of 80 words, which comes to a smallish paragraph. Worldwide, there are several printed encyclopedias, but they overlap. Thousands, nay, millions of articles and books and journals are published yearly. Then there's Wikipedia, which has (today) 62 million pages, and about 1/8 of that is in 6.9 million formal articles. All told, that puts us in the realm of a Level C or Level D civilization.

There are a couple other typos, but they have less import. I'll leave it at that.

Cabbie Philosophy

 kw: book reviews, nonfiction, astrobiology, cab drivers, philosophy, speculation

The idea for the book gelled when Dr. Charles S. Cockell was asked by a taxi driver in London, "Are there alien taxi drivers? People like me elsewhere in the universe?" The conversation, held during a taxi ride between King's Cross railway station and 10 Downing Street, Westminster, is recorded and enlarged upon in the first chapter of Taxi From Another Planet: Conversations with Drivers about Life in the Universe.

The book's 18 chapters deal with similarly searching questions the author discussed with various taxi drivers over a period of a few years (he rides a lot of taxis). I'll touch on a few of my favorites.

Ch. 4: "Should We Solve Problems on Earth before Exploring Space"? This is a common question, and the discussion ranged over several topics, such as the utility of weather forecasting aided by satellite data, resource discovery and conservation, and the numerous products that had to be developed just to get people into orbit and keep them alive and useful (think fountain pens and more secure ways of sealing diapers).

My father was once asked after a speech about the Apollo program and the Moon landings, "The astronauts left millions of dollars worth of machinery on the Moon. Of what use is that?" Dad replied, "Do you know where those millions of dollars are? Right here on Earth! Every dollar spent on the space program eventually wound up in someone's pocket: from technicians to miners to metal workers to computer programmers. Those dollars circulated in the economy, as space industry workers bought houses and groceries, paid workers to mow lawns or remodel kitchens, and bought fuel for their cars."

The author's discussion, on a taxi ride between Paddington station and Heathrow airport, eventually settled on defense from asteroids. The author mentioned the 10km asteroid that drove most dinosaurs extinct 66 million years ago; those not wiped out became birds. It would be scientifically accurate for a chicken-burger joint to label their wares "Dinosaur Burgers". He went on to tell of Barringer Crater in Arizona, where a smaller meteorite blasted out a mile-wide crater a lot more recently, about 50,000 years ago. He called it "a tiny rock"; for the record its size was about 150 feet (45 m) and it weighed something like 200,000 tons. Its velocity upon impact was about 20 km/s, or 70,000 km/hr (12-13 mi/s or 45,000 mph). NASA and other space agencies are spending significant amounts of money on telescopes, both on land and in orbit, to locate all the asteroids big enough to wipe out cities or states or continents. The DART (Double Asteroid Redirection Test) project was to learning how hard it is to deflect a small asteroid. Just for the record, those "significant funds" are a small fraction of the various "stimulus" packages perpetrated by the US government in reaction to the pandemic. That's where the cabbie's question should be aimed!

Ch 10: "Will We Understand the Aliens?" In Glasgow, a discussion ensued about whether we and aliens would be able to communicate. Consider this: Without the Rosetta Stone, it might still be impossible to decipher early Egyptian hieroglyphics. There are a few dozen scripts that are still unknown, and until about 20 years ago Mayan was one of them, until my brother's mentor, Linda Schiele, cracked the code. It helped that there are living Mayans, who still speak the language. Even though the written script fell completely out of use about a thousand years ago, the linguistic characteristics of spoken Mayan led Dr Schiele and her collaborators toward the right path. Also, what of dolphins and other vocal whales? Only recently has it been learned that sperm whales seem to have names. It's a start. But alien-human linguistics will be really hard. Dr. Cockell thinks that, because the scientific method has to be the same everywhere, and the basic scientific laws are universal, that scientific and technical terms will be the first terms we and aliens will be able to share, and much can then be derived from that.

Ch 17: "What is the Meaning of Life?" There is no person anywhere who has never asked this question. In the author's estimation, the answer, if there is one, depends on how rare or how abundant life is, particularly life with sufficient consciousness to ask the question. I'd put it in reverse: Live has meaning of we live a meaningful life. If there is no life, there is no need for anything to "mean" anything. We are defined primarily by the quality of our relationships. You or I may be a wonderful person; this will remain unknown unless we are wonderful to or for someone. Or if a person is evil, that is only manifested when he or she is evil towards others (even if the "others" are frogs being stomped "for fun" or flies getting their wings pulled off).

This delightful book is full of meaningful insights about "life, the universe, and everything", with no trace of the whimsy of  Douglas Adams. The author has the privilege of thinking about these things for his day job as an astrobiologist and an adviser to NASA. His humility and grace, relating to taxi drivers from sundry backgrounds, come through and confer wisdom to us, his readers.

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Coda: While persuading various generative art programs to produce the image above, generated by the Stable Diffusion engine in Playground, I kept a couple of others that I particularly liked, that were "almost there". The first was drawn by Dall-E3, the second by Playground 2.5.

Climate change or climate forcing?

kw: book reviews, nonfiction, astronomy, astrobiology, exoplanets, climatology, climate change, global warming

Do we need to save the planet? It doesn't need it. Do we need to save the biosphere? We don't yet have the power to end it. Do we need to save civilization? Probably. This last is the question taken up by Adam Frank in Light of the Stars: Alien Worlds and the Fate of the Earth. He takes a new approach, you could say a Galactic approach, even a Universal approach, to setting parameters around the future of human civilization.

Dr. Frank uses a quieter tone than the noisy polemicists in the toils of public debate. He is nonetheless speaking as a prophet, warning us all of the consequences of the greatest of human endeavors, "the project of civilization." I found it notable that he never mentions the IPCC Reports. This is not to say that he doesn't give them any credence, but he is preaching to the unconverted: I learned long ago, in Christian evangelism, it does no good to quote Bible verses to someone who doesn't believe the Bible. Similarly, the content and methods behind the IPCC's work are challenged at every point by "climate deniers", so it is no use appealing to those reports.

In this book the author begins with Carl Sagan's metaphor of Western civilization as a teenager, grown up in body but not in judgement. Here in the US at least, we give 15- or 16-year-olds licenses, and the keys, to drive automobiles, knowing full well that their minds won't mature, and they will have very poor impulse control, for at least ten more years. So, at the very least, we in the First World are like a teenager with the keys to the energy sources of Planet Earth, and we have shown an utterly insatiable appetite for more and more energy use. This chart is instructive:

This shows energy use per person (credit: Our Finite World). The technology to mine and use coal jump-started the nascent Industrial Revolution in about 1850. Petroleum and Natural Gas triggered a further jump beginning right after World War I, which was stalled by the Depression, and then re-invigorated by World War II. The "flat spot" from about 1970-2000 is the effect of the Arab Oil Embargo. I suspect the development of Fracking to rejuvenate oil production in non-Arab nations is responsible for the jump after 2000.

So now we use four times as much energy per person as someone in 1820. That is a global average. Per-person use in the First World is in the 250-300 GJ/yr range, or 3-4 times the global average. So that is our "car". It has a lot of horsepower.

The question Sagan asked, based on figures from the 1960's, is, "Can the Earth provide the needs of human civilization, forever?" To abolish poverty worldwide, we'd need to roughly triple global resource use, particularly energy use. But we are seeing "cracks in the wall" already. Someone once said, to raise the entire population to the American level would require four more Earths.

What is Adam Frank's line of analysis? He continues with the Drake Equation, formulated in 1961,
that uses several factors to estimate the number of alien civilizations we might find using efforts such as SETI, the Search for Extra-Terrestrial Intelligence, which uses radio frequency reception, in hopes of overhearing the alien version of "I Love Lucy". He dissects this for us and then presents the uses of a method developed by Svante Arrhenius, 122 years ago, to determine how much the earth will warm based on how much extra carbon dioxide gets into the atmosphere. "Climate science" is not new stuff, folks!

The Arrhenius method doesn't just work on Earth. It was used to understand what happened to Venus, to raise its temperature to 600°F, and why Mars is a bit warmer than it would be without any atmosphere, though daytime highs in its "Tropics" range around -10°F. Mars and Venus both have an atmosphere containing 95% carbon dioxide. Venus has a very, very heavy atmosphere while the air on Mars is very thin, about 1% of Earth-normal. But our air contains, at present, 400 ppm CO₂, or 0.04%. Martian air with enough nitrogen added to have the density of Earthly air would still have 0.95% CO₂, nearly 24 times as much! So the temperature range on, for example, airless Phobos, compared to that on Mars, validates the Arrhenius analysis for a CO₂-induced greenhouse effect (yes, Phobos is colder).

After presenting the history of exoplanet discoveries—a few thousand are now known—the author turns the Drake Equation on its head, to determine the "Pessimism Line". That is his term for how pessimistic you need to be to say we are surely alone in the Universe: Knowing that the stars in all the galaxies range in age up to 10+ billion years, and that there are about 100 billion stars in each of 100 billion galaxies (or perhaps even more) in the visible Universe, how pessimistic do you have to be to strongly aver that our Human civilization is the first and (so far) only civilization to have arisen in the Universe?

In 1961 the only factor of 7 in the Drake Equation that was known was the rate of star formation in the Milky Way Galaxy, about one per year. All the other terms were speculative, and all possible values of, for example, the chance that a planet will be at a "just right" distance from its star (in the habitable zone), were strongly supported by various people. You could find someone who'd argue that the probability was close to zero; someone else who'd argue that any star that had planets probably had at least one in the habitable zone. Now, with a few thousand known exoplanets, we know that nearly every star has multiple planets, and about 40% of those have at least one planet in the habitable zone. So the unknown terms are:

• Can life form easily, or not?
• Once formed, can life develop "intelligent" species easily, or is it very hard?
• Is the likelihood that an intelligent species will form a global civilization large, or small? and 
• Once formed, how long will such a civilization continue?

By turning all this around backwards, the combination of these "biological" and "sociological" terms needed to make it very unlikely that more than one civilization has ever been formed, was found to be 10^-22. That is one in ten billion trillion. This is a quantitative estimate of how hostile the Universe must be to civilization, for us to be alone in all space and time (to date). Effectively, this analysis presents you with a pile of sand, a trillion tons of it, containing ten billion trillion grains, and asks, "Knowing that at least one sand grain represents a civilization in the Universe, how likely is it that no other grain of sand represents a planet with a civilization? Not one single one?"

For most of us, the thought that civilization arose only once in ten billion trillion attempts is rather ludicrous. Even Peter Ward with his Rare Earth analysis, is probably not that pessimistic!

Dr. Frank then goes further, asking, "What does it take for a civilization to be sustainable, very long-term?" Numerous isolated and semi-isolated civilizations on Earth have risen and fallen. It seems even Earth, so hospitable to life of many kinds, can he hostile to civilizations…or, at least, unforgiving of egregious errors. Further, civilizations that fell, did so quickly. The environmental disasters, caused by the Easter Islanders and the Mayans all doing what people do to have a thriving society, reduced populations to about one tenth of what had once been in just one or two generations. Even today, there are fewer Mayans than there were in 1200 AD. These are two examples of civilizations that fell not because of conquest by someone else, but at their own hand. Two cases of a teenager driving right off a cliff.

The book closes with an appeal to wake up and grow up. It would be well to heed it. To my understanding, no civilization yet produced on Earth has figured out the trick to sustaining itself without perpetual growth. In the US, a growing GDP is required for a "robust" economy. The US government recently announced a 4.1% annual growth rate (that really means 0.335% growth for that particular month). It is good in a way. But if it keeps up, we can project it into the future: In just 17 years, GDP would double, and it would keep doubling again every 17 years. By 2100 AD the US GDB would be 27 times what it is today. What chance is there of that happening? Hmmm??

Suppose we finally get the analysis right, and find out that, for human civilization on Earth to be sustainable for 100, or 1,000, or 10,000 years, we would have to reduce our population to at most two billion, and the general lifestyle and level of energy expenditure (both personal and corporate) would need to match that of Peru (about ¼ of what us Americans are used to)? Then what? I'll tell you what: whatever the actual level of lifestyle really is, in time the biosphere will enforce it.

We are not divorced from Earth. We cannot act as though we were not part of nature. Nature can get along without us. We cannot get along without nature. Civilization is an experiment. It may be one that eventually fails. The Pessimism Line only tells us how unlikely it is that we are on the only planet to develop civilizations. It doesn't tell us how long they last. That part of the Drake Equation is still entirely unknown.

I would put it this way: If there is any chance for a global civilization to develop and thrive, and properly care for all its members, without constant growth in both population and standard of living, we need to figure that out right away. Or we, too, will crash, just a bigger version of the Mayans or Easter Island.

Magnetic Martians

kw: astrobiology, musings

Fourteen years have passed since images like these were proclaimed as possible fossils from Mars. The controversy has quieted down, but not gone away. It took me a while to locate an image with a scale bar on it. The first objection to these was, if they are remnants of cells, they are much too small.

During the hot part of the public discussion, every article that mentioned these "worms" implied that they are composed of calcite. I was not paying enough attention at the time to look further into it. Recently, I happened to read a more detailed analysis that stated they are a mix of iron oxides, including magnetite. Now that got my attention. Then an even better article showed up: "Chains of magnetite crystals in the meteorite ALH84001: Evidence of biological origin" by E. Imre Friedmann, Jacek Wierzchos, Carmen Ascaso, and Michael Winklhofer; PNAS, January 2001. I don't know how I missed it at the time.

If the apparent lumpiness of these chains represents cells, they are roughly 150nm in diameter, which is small even for nanobacteria, and apparently too small for protein synthesis machinery to function (assuming Martian bacteria used proteins). But if each of these items was a chain of mineral grains in a single cell, the size problem vanishes.

Most of this image is taken up by a single bacterial cell. Within it is a chain of magnetite particles, which it uses to detect and orient with the Earth's magnetic field. Allowing for the differing scales of the two images, this chain is the same size as the chains of grains from Mars.

But, it is objected, Mars has no magnetic field. That doesn't mean it never had one. Its core is frozen now, but must have been molten at an earlier time, simply from the cosmology of planet formation. Early in Mars's history, it did have a magnetic field, it is likely to have had an atmosphere and liquid water; lots of physiographic features on its surface show this.

If life got a start on Mars as soon as it did on Earth, there may have been a period as long as a billion years for it to evolve and flourish, before the loss of water and atmosphere made everything extinct. In the late 1990s, the trend of the debate was decidedly anti-Martian life. Now, the pendulum is back the other way.

Aliens everywhere? Pack your microscope...

kw: book reviews, nonfiction, science, astrobiology, space science

Peter Ward and his colleague Don Brownlee made a host of constituencies mad when they published Rare Earth four years ago. Their conclusion is that, while life in the form of microbes may be rather common throughout the Universe, complex animal life, however constituted, the kind of life that makes cities and spaceships and radio signals, is probably exceedingly rare. Read Rare Earth for a thorough, and thorougly entertaining, study of the requirements of complex life.

Agree or disagree, you'll find they raise questions that need to be discussed even as we imagine a universe like that of Star Wars or Star Trek. My own conclusion is that this portion of the Galaxy has only recently begun to produce civilizations: Stars formed (in this region of the Galaxy) prior to our Sun have too few heavier materials with which to form rocky planets such as Earth, large enough to hold an ocean for five or ten billion years.

Also, stars formed only 1-2 billion years ago have larger amounts of rocky material, but even a larger proportion of heavy metals and radioactive materials; they are likely to form super-earths that hold too much water (no continents), and stay hotter longer. So there is a window of opportunity, which may be rather narrow, maybe not. I think we are on its leading edge.

OK, with that out of the way, I say, "Who better than Peter Ward to discuss the various kinds of life that may arise, both here and elsewhere?" Complex life of any kind may be rare...or not. But life analogous to bacteria and viruses is likely to be found nearly everywhere. In his new book, Life As We Do Not Know It, Dr. Ward warns that it may be hard to recognize as life.

His opening example is telling. When subsea hydrothermal vents were first found, there was a lot of thin, snotlike material floating around. It got in the way of observations of the big clams, crabs, and tube worms. The scientists often had to move around or wait for the water to clear so they could get nice looking photos. It was quite a while before anybody thought to capture some of the slime and look at it. It turned out to be bacterial life, in a profusion that probably outweighs the nice clams and worms. It happens to be their food, too!

It seems ludicrous. Any grazing or browsing animal weighs less than the biomass of forage needed to sustain its life. So what did they think the clams and tube worms were eating? But this is just the problem. We don't really know the limits of earthly life, in terms of temperature, pressure, or chemistry.

If you take a pinch of soil from your yard, and spread bits of it onto petri dishes containing the ten or so common nutrient mixes you can get from places like Cuisenaire or Cole-Parmer or Ward, you'll get dozens or hundreds of bacterial colonies, and if you're lucky, perhaps twenty or thirty different species. If instead, you shake that same soil sample with water, then screen for the portion smaller than two microns. Pulverize and use genetic probes, you'll find evidence that there were tens of thousands (or even millions) of different species present.

Here, this'll blow your mind: Ordinary ocean water, whether sampled shallow or deep, contains three or four parts per billion of viruses. Doesn't sound like much...it comes to 20 to 50 million virus particles per cc! Not only that, but almost every living thing on the planet contains a ppb or so of viruses, including you our me. I we had a kind of light that "saw" only viruses, the entire biosphere and all bodies of water would be outlined in a ghostly filigree of viruses, down to its last detail.

To jump to the chase, the author presents his reasons for considering viruses as living beings. Though they require living cells to reproduce, there are many species of animal parasites whose biochemistry is defective such that they cannot live outside their host.

Just to make you feel secure: the vast majority of animal species are parasites. Even though some, such as the follicle mites that live in the forehead hair follicles of at least 95% of us, are called "commensal" because they don't seem to do harm (How they might benefit us is totally unknown. Any benefit is strictly one-way, so I call them parasites).

What is life? We need enough of a definition that we'll recognize it...we just can't fall back on "I'll know it when I see it." My own formulation: "Life is a process that results when aperiodic crystals grow in an environment strongly out of equilibrium". Dr. Ward proposes, "Life metabolizes, life replicates, life evolves." Simple and functional, and more testable. It doesn't depend on a particular kind of genetic mechanism or "bio"chemistry.

What kinds of non-Earth life might we find, somewhere (even on Earth)? The author proposes Terroan to designate "life as we know it", so we can then distinguish as alien, "life as we do not know it." Terroan life is composed of cells with a lipid cell membrane, is based on Carbon, Hydrogen, Oxygen, and Nitrogen (CHON), employs water as the main solvent, and uses DNA to encode and RNA to translate genetic codes to proteins via the Universal Genetic Code (UGC). In order of increasing "alienness", we might list

• Certain bacteria that slightly violate the UGC. For example, some mycoplasmas use one of the "stop" codes (the U-G-A sequence) to encode for tryptophan.
• The parent organism of our Mitochondria; these organelles have their own, somewhat different, genetic code and reproduce independently.
• Organisms using one of the approximately 10⁷⁵ other UGCs that might be devised, though only about 10⁵⁰ of them keep redundant codes in groups. The mycoplasmas mentioned above could be included here also.
• Viruses, which are non-cellular.
• Organisms that use a solvent other than water, such as methane or a strong ammonia/water solution at very low temperatures, or hydrogen sulfate (sulfuric acid if excess water is present) at high temperatures.
• Organisms that use a polymer other than DNA to encode its genetics. (Note that silicate rocks consist of Si-O and Si-Al-O polymers. Feldspar life?)

I can think of one attribute that might make really alien life hard to recognize. Velocity. Let's look at plants. How do you tell the difference between a living and freshly-dead slice of Oak leaf? Oak trees are proverbially slow growing, though they grow leaves quickly enough each Spring. Within the cells of the leaf, though, under the microscope you can see cytoplasmic streaming going on. The insides of a cell seem to revolve complete every two or three seconds, in spite of the fact that it is encased in a porous cellulose box. Loose cells from the inside of your cheek also show streaming as long as Oxygen is present, though it is slower.

Both animals and plants of Terroan life exhibit at some scale, motions that can be observed directly by our 20-frames-per-second visual systems. That is anything from a speed just faster than the minute hand on a wall clock to velocities that blur like a spinning figure skater. But suppose we find objects in an environment whose kinematics disallow motions of such rapidity, or that are composed of much stiffer material?

A science fiction story I read was about an odd rock in an astronaut's collection, kept in a terrarium with other rock specimens from the apparently desert planet he'd visited. Every week or so, it seemed this rock had moved a little. Finally, after setting up a time-lapse camera, he was able to see that, over a few months, the odd rock moved away from the more lighted part of the terrarium, then moved to the glass side and began slowly (very slowly) grinding at it, seemingly in an attempt to escape. Perhaps it "lived" on a time scale that to it, seemed like running to a barrier and grinding through in the space of a few moments. I wonder what the astronaut seemed like from its viewpoint?

We know, kinematically, living creatures that live ten or a hundred times faster are implausible. But there is no limit to how slow one may go.

There is a point to the book. We need to expand the "tree of life" to include viruses and RNA life, at the very least, so as to include all Earth-originated and/or -developed life. We think RNA life is extinct, if it originated at all. But it may be created soon in the laboratory. Bacteria with added DNA codes have been created in the laboratory, so they are aliens. Mars probably once hosted living creatures, at least bacteria or something similar; and it may do so today, some distance below ground. Europa might have life, though the energetics are forbidding. Titan seems to have a "just right" mix of energetics and complex chemistry, that life of some kind is likely.

Thus, Dr. Ward proposes that we send people to Mars and to Titan, to look for it. Because of the differing probable history, and the known differences today, a Paleontologist needs to go to Mars and a Biochemist to Titan (better, more than one of each!). Mars is likely to have fossils, and a Paleontologist by definition is good at finding fossils. Titan doesn't seem to have anywhere on its surface that could contain fossils, but is likely to have a strong chemical signature of life processes in many places. Just what a Biochemist is prepared to determine.

You know, that's a pair of really good ideas. I hope we do it. The biggest hurdle? We have to get used to the idea that a Saturn/Titan mission is definitely one-way. Radiation there is less than near Jupiter, but still deadly over the span of a few months at most (Jupiter orbit is a DOA environment at any arrival speed less than 0.1c). Mars is probably one-way also. Can we afford to send heavy digging equipment to Mars, so astronauts can get dug in before they die of radiation poisoning? Just getting there, the DNA in 1/3 of the body cells gets damaged per year of exposure to the interplanetary environment. You gotta get a hole dug first (10m deep at least), then go there fast. Then, there is a chance to return. Send a backhoe to Mars first!

Though I was a bit put off by Rare Earth, I understand the reasoning. I find Life As We Do Not Know It much more optimistic.