25 October 2022 and on…

CS and I are reading Alien Oceans: The Search for Life in the Depths of Space, by Kevin Peter Hand. These are my chapter by chapter notes. We are now through chapter 7, and are enjoying it. It does not assume much science background, and thus spends a lot of time explaining things that we are familiar with (e.g. why water’s hydrogen bonds cause water ice to be lower density than liquid water). But it does a very good job of it, and those with background can skim; this would be a great book for a child or teen interested in science.

Front and Back Matter

The Prologue describes a descent to a seamount somewhere on the mid-Atlantic ridge. It does a reasonable job of laying out some basics re the nature of life in the deep ocean: (1) Ecosystems are driven by chemical and heat energy; (2) only sound serves as an effective long distance communication (or sensing) mechanism; (3) some creatures use bioluminescence. And, of course, it notes parallels between the physical environment of the deep ocean and environments that might exist elsewhere in the solar system. The writing is OK, with one or two poetic moments; I find it marred by what seems to me a bit of over-dramatization of possible trouble during the descent… it seems apparent they were never in danger.

The plummeting submersible created a shock wave of bioluminescence radiating away from us. Creatures large and small, from jellyfish to microbes, flashed.

Alien Oceans, Kevin Peter Hand, p 8

There are 8 pages of endnotes, mostly references but occasional elaborations on the text. So there is science here, but clearly the book is not an exhaustive treatment. The Index, not surprisingly, indicates a focus on various moons in the solar system, and the basic chemical and molecular constituents of water-based life.

C1: Ocean Worlds on Earth and Beyond

Six moons of the outer solar system likely harbor liquid water: GECTET (Gannymede; Europa, Callisto [Jupiter]; Titan, Europa [Saturn]; Triton [Neptune]). It is possible that Pluto, and the moons of Uranus (Ariel and Miranda) may have oceans, albeit some with a mix of water, ammonia and other substances. Mars and Venus may also, likely have had oceans in their pasts.

He argues that — as far as understanding whether life as we know it can evolve de novo, we need to look at the outer solar system. The discovery of fossils, or even of actual microbial life on Mars, would not due it: Mars and Earth have exchanged matter in the form of meteorites (270 Martian meteors have been found on Earth), including during the 3.6–4.4 billion years while life has existed on Earth*. Such cross ‘contamination’ is much less likely with the moons of the outer planets: simulations of the spreading of ejecta from earth show only about 1 in a million meters making it to either Europa or Titan, and those are too small to penetrate the icy surface and make contact with the oceans; the intense radiation on the surface of the moons would presumably sterilize any lifeforms along for the ride.

The chapter ends with a brief reprise of the exploration of Earth’s ocean abysses, the high point being the 1977 2Km descent of the Alvin into the Galapagos Rift and the discovery of ecosystems around hydrothermal vents. This irrefutably demonstrates the existence of chemosynthetically-based life that can survive at high pressures, which in turn suggests that life could evolve and exist in liquid oceans far from the sun.

* I was interested in just how far evidence goes for microbial on Earth. Wikipedia says:

The earliest known life forms on Earth are putative fossilized microorganisms found in hydrothermal vent precipitates, considered to be about 3.42 billion years old. The earliest time for the origin of life on Earth is at least 3.77 billion years ago, possibly as early as 4.41 billion years ago—not long after the oceans formed 4.5 billion years ago, and after the formation of the Earth 4.54 billion years ago. The earliest direct evidence of life on Earth is from microfossils of microorganisms permineralized in 3.465-billion-year-old Australian Apex chert rocks.

Wikipedia, https://en.m.wikipedia.org/wiki/Earliest_known_life_forms

C2: The New Goldilocks

Wednesday, 9 November 2022

For decades scientists have used the concept of the ‘Goldilocks zone’ to discuss the possibility of life in the solar system. This is the idea that life requires a certain temperature range (that allows liquid water), and solar energy to drive it, thus confining life to planets that are in particular range of distances from their stars. However, this thinking has ignored the fact that energy need not come from the sun, but can be provided by radioactive decay and/or heat from the core; nor has it considered the possibility of chemosynthetically-based life that can exist in water under immense pressure. So we need to revisit our thinking about ‘the zone.’

Water. An overly long explanation of the importance of water’s unusual property: that it becomes less dense when it solidifies due to its propensity for forming hydrogen bonds, and that the resulting ice will therefore rise to the top of a body of water and form an insulating cover over it, slowing the rate at which the entire body of water freezes.

Heat Energy via Tidal Forces. One source of energy are tidal forces. With respect to moons, these are a function of (1) the difference gravitational forces across the moon (a function of its diameter), (2) the change in gravity as the moon orbits the planet (i.e. the eccentricity of its orbit), (3) the mass of the planet, and (4) and the period of the orbit. Or, in more intuitive terms, how strongly and frequently the moon gets ‘squeezed.’ For Earth, there is almost no tidally-generated heat, because the moon’s orbit is circular, and the masses of moon and earth are, compared to most of the solar system, relatively small.

In contrast, the mass of Jupiter, and the eccentricity of many of its moons orbits, make tidal heating a very significant influence. Io, Jupiter’s innermost moon, receives almost as much energy from tidal forces and Venus receives from the sun: it has a molten core and is the most volcanically active planet in the solar system. At the other extreme, Callisto is the farthest out of Jupiter’s large moons, and as a consequence, while it undergoes some tidal heating, it is not much, and its ocean is confined under a very thick and old crust of ice. In between Io and Callisto are Europa and Ganymede: Europa generates 10’s to 100’s of milliwatts per square meter, enough to maintain an ocean approximately 60 Km in depth, with a relatively thin ice crust of a few to thirty Km. [The thinness of the crust seems to matter because its surface chemistry may allow insights into the chemistry (and biology?) of the underlying ocean.] It should also be noted that Jupiter’s three innermost moons, Io, Ganymede and Europa, are tidally locked into eccentric orbits, so the tidal heating is stable.

Geochemistry of Life. Elements generally agreed to be essential for life are CHON-PSS (Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorous, Sulfur, and, in traces, Selenium). In addition to these, Earthly life uses smatterings of 47 other elements. Of these, while the Earth has plenty of heavier elements, the lighter elements CHON-PS, are present in greater abundance in the outer solar system as a consequence of how solar systems typically form. One issue to consider is that larger moons may have icy bottoms (because the pressure is sufficient to form a different phase of ice that is denser than liquid water) that isolate the water from the crust; smaller moons, like Enceladus and Miranda may have rocky floors, allowing water to mix with the rocky, chemically rich seafloors.

The chapter also talks a little about Carbon and Nitrogen availability; it seems to take the line that if the planet is far out enough for elements in their naturally occurring compounds to freeze, they are likely available on the moon (that doesn’t make sense to me since earth is hot enough that most of those substances except H2O would sublimate).

Here is the original version of a figure they reproduce showing which elements are important for life as we know it:

From: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC348800/figure/f1/

C3: The Rainbow Connection

Wednesday, 9 November 2022

This chapter is about spectroscopy. It describes how it was discovered, how it works generally, and how it has advanced our knowledge of the compositions of the gas giant moons.

• 1814: spectra (Fraunhofer).
  Fraunhofer’s process for making flint and crown glass, and his desire to understand the properties of the glass he was producing. Creation of first spectrometer (circa 1814), and his observation the the type of light source used (oil lamp, sun) determined, in part, the characteristics of the spectrum observed (e.g., Sodium line).
• 1860’s: Elements=>characteristic spectra; sun contains them (Bunsen, Krichoff).
  Bunsen and Kirchhoff make the connection between elements and characteristic spectra, including discovering absorption lines (dark areas where the element has absorbed particular frequencies). They also make the connection that the sun’s spectra indicates that it contains the same elements that are found on earth.
• 1800: Infrared light (Herschel).
  John Herschel discovers infrared light by noting that a thermometer positioned just below the visible spectrum cast by a prism showed elevated temperature.
• Water allows most wavelengths of visible light to pass through it, but it is very good at absorbing infrared light, and thus infrared spectroscopy can detect it.
• 1950’s – 1970 Water on Europa, and elsewhere (Moroz; Kuiper).
  In the late 1950’s Vassili Moroz began collecting data on various bodies in the solar system, and by the mid-1960’s he had detected water on Europa; in the 70’s this was confirmed by Kuiper, who with more sensitive instruments also detected water on Gannymede and Callisto.
• 1979: Shell of water ice on Europa; volcanism on Io (Voyager I and II).
  Voyager I and II spacecraft showed that Io had volcanism, and that Europa was covered by a relative smooth (if cracked) shell of water ice.
• 1995-2003: Sulfate chemistry on Europa suggests liquid ocean under ice.
  Gallileo spacecraft does flyby’s of Jovian system sending back huge quantities of images and other data. In particular, it used the NIMS (Near Infrared Mapping Spectrometer) to corroborate the existence of water ice and reveal further details about the chemistry which involved sulphates. The two leading candidates were sufuric acid and magnesium sulfate. Magnesium sulfate is found in earth’s oceans and hot springs, and its presence would imply the upwelling of water from an under-crust ocean. More recent spectroscopy seems to lean towards the salt interpretation, and also indicates the possible presence of sodium chloride.

C4: Babysitting a Spacecraft

Discussed Tuesday, 15 November 2022

Using Gallielo to conduct gravity measurements of Europa. First, to get Galileo to Jupiter, three gravity assists were used: one from Venus, and two from Earth. Once in orbit around Jupiter, Galileo can do flybys of Europa and other moons.

In the case of Europa, the gravity well is somewhat elongated, because Europa is tidally locked to Jupiter, and thus the planet itself is a bit elongated. Furthermore, the distribution of mass within Europa also effects the shape of its gravity well, and this in turn effects the speed of spacecraft as it flies by Europa. The speed can be measured by tracking the wavelength of the signal which is changes according to the speed of the spacecraft due to the doppler effect; to measure variations in Europa’s gravity, one needs to be able to measure speed down to a precision of milimeters per second. These measurements allow the calculation of Europa’s Moment of Inertia

The moment of inertia refers to the amount of forced needed to alter the rotational speed (spin) of a particular object, and it can be characterized as the sum of moments of inertia of each layer of the object. An object with a dense outer layer will have a greater moment of inertia than an object of the same overall density, but where most of the mass is in the inner layer. An object with a dense outer layer will have a moment of inertia of about .66 MR**2; an object of uniform density will have a moment of .4 MR**2. Europa has a moment of .34 M*R**2. To get a moment this low, the only straightforward way to get it is to have a three-layer model where there is a middle layer that is not very dense, such as would be the case with a layer of ice or water 80 – 170 Km thick.

C5: How I Learned to Love Airport Security

Discussed Tuesday, 15 November 2022

This chapter is about detecting magnetic fields from a distance. It is useful to distinguish between two types of magnetic fields: intrinsic fields [not sure if that is the right term], and induced fields; the latter are magnetic fields that are caused by external magnetic fields that induce a current in a material, which turn produces a magnetic field. The bottom line is that Europa has an induced magnetic field due to the influence of Jupiter — and we can tell this because its strength and polarity shifts over time depending on how it is interacting with Jupiter; furthermore, the strength of the induced field tells us that it is likely due to the presence of salt water (which conducts much better than pure water or ice).

C6: Lady with a Veil [Enceladus]

==> Wednesday, 23 November 2022

Enceladus is one of Saturn’s 50+ moons. It is only 504 Km (~300 miles) in diameter, and orbits Saturn every 33 hours. Given its size, one would not expect much of it beyond an airless, cratered surface of water ice. But while it’s northern hemisphere is pock-marked with craters, it’s southern hemisphere is mostly smooth, indicating that it has been resurfaced recently. Furthermore, a veil of water vapor and particles emanates from its south pole.

This is what we knew in 1981 following observations made by the Voyager mission. In 2005 Cassini arrived in the Saturn system, and, among many other activities, collected data on Enceladus. Cassini was able to detect a forest of plumes coming off the south pole, and on a subsequent fly-by was able to fly through the plumes and use the craft’s two mass spectrometers to identify their constituents: the primary ones were water, CO2, methane, and small organics (e.g., ethane, propane, and so on). A second instrument was able to analyze the constituents of ice grains in the plumes and found salts — NaCl, MgSO4 and KCl — which was important because it indicated that Enceladus was not a captured comet, and suggested that there was interaction between water and rock (since that is how salts are typically produced). The instrument also found evidence for SiO2, which is also found in oceans, and indicates significant heat, i.e. geothermal activity. A final fly-by measured the amount of hydrogen present, and found more than would be expected due to the breakdown of water or organic compounds; the best explanation is that hydrogen is being released from hydrothermal vents.

The combination of salts, silica, methane and hydrogen found in the plumes of Enceladus all piece together giving shape to a chemically rich ocean with a hydrothermally active seafloor.

– Kevin Peter Hand, Alien Oceans: The Search for Life in the Depths of Space, p 103

The next question is how big this subsurface ocean might be. Unlike the case with Europa, where Jupiter’s tilted magnetic field induces a magnetic field that enables estimates of the ocean’s size, Saturn’s magnetic field is not tilted and does not induce a field in Enceladus. Instead, they looked at the degree of wobble — libration – in Enceladus’ orbit which enables an inference that there is an ice shell ranging from 16-26 Km thick, with a liquid ocean below ranging from 26 – 31 Km deep.

The final question is how long Enceladus’ ocean has been around. It could not be more than 100 Ma, because Saturn’s rings are not stable enough to be older, and it could be younger. This question is of interest because we don’t know how long it takes for life to emerge: 100 Ma might be more than enough, or it might not….

C7: The Queen of Carbon [Titan]

==> Wednesday, 23 November 2022

Titan is Saturn’s largest moon. It’s year is about 30 earth years, and its day about 16 earth days. Its atmosphere is 95% N2, and 5% CH4, and is 1.5 times as thick as earth’s. It’s surface temperature is -290° F, and its pressure 1.5 bars. In some ways it would look quite earth like, but with a surface of water-ice, and weather consisting of a cycle of gaseous, liquid and solid methane that creates analogs of terrestrial weather and hydrologically shaped landforms. This could also create conditions for life, but it would be life that is very different from what we have on earth.

The fact that Titan has an atmosphere, and a substantial one at that, is a mystery. Methane is very fragile moecule, and will only last on the order of 10’s of millions of years. The leading hypotheses involving methane being released from Titan’s interior, either gradually or in geologic events. This hypothesis is also supported by the presence of Argon 40 in the atmosphere; Argon 40 is only produced by the breakdown of radioactive Potassium, which indicates geologic activity in the core of the planet that is releasing Argon to the surface.

There is evidence for a subsurface water ocean on Titan. It is not as clear as that for Europa, because Titan’s atmosphere precludes spectroscopic examination of the surface, but there is some limited evidence that is consistent with the surface being made of water ice. More telling is gravitational data collected by Cassini which shows the Titan changes shape as it orbits Saturn: It’s k₂ Love number, an indication of how much it deforms relative to the gravitational stress placed on it, suggests that there is a liquid ocean beneath a 100 Km ice shell; estimates of the depth of the ocean range from 70 – 100 km. A second piece of data that suggests a liquid ocean is 36 Hz Schumann resonance. On earth, this resonance is due to lightning and resonance between earth’s ionosphere and the conductive surface of the earth with its ocean, lakes and water vapor. On Titan, Saturn’s magnetic field could generate the signal, and resonance could occur between its ionosphere and… not its surface which is made of non-conductive ice and methane, but a subsurface salt-water ocean at a depth of 55-80 Km beneath the surface.

C8: Oceans Everywhere

Monday 28 November 2022

This chapter reviews the worlds – beyond Europa_(Jupiter), Enceladus_(Saturn), and Titan_(Saturn) – where oceans are likely to exist, and their astrobiological potential. He notes that we simply don’t know enough about the moons of Uranus, and so there may be other possibilities as well. But here are the other candidates:

• Ganymede_(Jupiter). The largest moon of Jupiter has its own intrinsic magnetic field, as well as an induced-time varying one. The first means that Ganymede must have a molten core; the second that it must have a salty subsurface ocean. The molten core is due to either radioactive decay in the core, tidal heating (it is in a forced eccentric orbit around Saturn), accretional heat (left over from its formation), or some combination. Regardless, two thirds of it has been re-surfaced, with bizarre (furrow systems) and familiar (bright lightly cratered terrain) signs of tectonic activity. Gravity data indicates the ice/water layer is about 800 Km thick, with a water later at about 170 Km; interestingly, the bottom of the ocean is thought to consist of Ice III (and perhaps V and VI as well). The denser-than-water forms of ice that coat the bottom inhibit the water-rock interactions that my infuse water with the chemistry needed to support life, but on the otherhand nothing precludes the possibility of vents or other tectonic features in the bottom ice that would permit interchange.
• Callisto_(Jupiter). Callisto is three times farther from Jupiter than Europa, and although it has an eccentric orbit it is too far out to benefit from much tidal heating. Nevertheless, it has an induced magnetic field that indicates a salty subsurface ocean that is 100-300Km deep. On the other hand, it’s surface is uniformly cratered and appears to be about the age of the solar system, indicating that there is no interaction between the ocean and the surface, and it is cold and pressured enough that the ocean’s bottom will consist of Ice III, etc.
• Triton_(Neptune). Triton’s surface is very fresh, with a texture resembling a cantalope, and it appears to be issuing black plumes that rise about 8 Km above the surface. The leading theory about the plumes is that they are due to a solid-state greenhouse effect where sunlight is passing through Nitrogen ices and then encountering dark organic material which causes the ice around it to sublime and eventually erupt from the surface. While there is no direct evidence of an ocean, Triton’s fresh surface (less than 10 Ma) is hard to explain by any other mechanism than resurfacing from a subsurface ocean. Assuming there is an ocean, it would have to be supported by radioactive decay, as Triton’s orbit is a nearly perfect circle (though early in its history when it was captured by Neptune there would have been considerable tidal heating.
• Pluto. Pluto is a world of ices — water, methane, CO₂ and Nitrogen, with water ice forming much of the ‘bedrock’ of the planet, while the other ices flow or erupt on top of it. The evidence for an ocean on Pluto is a vast icy planar region called Sputnik Plantia (within a larger region called Tombaugh Regio) that according to gravitational data is a basin. Sputnik plantia is aligned with Charon which is locked to Pluto, and this suggests that Sputnik plantia is the densest region of Pluto, which could be expalined by a large area of water ice. This is based on rather tenuous data, but it is the best explanation at this point.

C9: Becoming Inhabited

Monday 28 November 2022

Conditions for the origination of life are more extensive than for habitability: Conditions for habitability are water, access to the elements necessary for life, and access to energy to support life.
Conditions for the origin of life include conditions for habitability, but also require a catalytic surface to support reactions to produce complex molecules, as well as an unknown amount of time.

Time. Regarding the amount of time required for life to originate, our only data point is the earth. We know that the earth coalesced into a planet about 4.66 Ga, than the first oceans formed 4.0 – 3.8 Ga, and that the earliest known fossils are in the range of 3.4 to 4.0 Ga. This suggests that life arose quite quickly, on the order of a few hundred Ma. Furthermore, the age of the oldest fossils is a conservative estimate of when life begin, because, barring some astronomically unlikely coincidence, life would need to be common and widespread for us to have a reasonable chance of finding fossils of it. So perhaps life arose *very quickly*  — within 10’s of Ma.

Catalysis. Lifeforms use enzymes to catalyze the reactions that enable them to exist, grow and reproduce. Prior to life, there must be some mechanism to support reactions that transform the small molecules found in the abiotic environment into the complex molecules found in living organisms. Non-enzymatic catalysis generally involves metals, like platinum, with which simple molecules interact: that interaction weakens their bonds, and makes it more likely for them to combine with other molecules, forming more complex molecules. Concentration of substances, for example by evaporation, can also, in a sense, be a form of catalysis, in that it increases the probability of reaction.

Basic Attributes of Life: Compartmentalization; Metabolism; and Information Storage and Replication. Compartmentalization is seen in all life forms, and is needed to contain and protect the mechansims of life. One scientist has posited that early forms of compartmentalization might have been something like sea foam… Information storage and replication is necessary to support self-replication, perhaps the defining characteristic of life. For all life on earth this is done via DNA; quite a few scientists think that RNA served as a precursor vis a vis the information storage and replication functions (but what came prior to RNA is a mystery). Metabolism is simply the use of energy to power the reactions that support life. …I’m a little surprised that nothing is said about early mechanisms for capturing and storing energy, and how those arose.

Metabolism. Metabolism, for all organisms but plants, boils down to combining an oxidant (sulfide, CO2, O2, peroxide, nitrate, and iron and manganese oxide minerals) which will receive an electron with reductants (hydrogen, methane, hydrogen sulfide, various organics, and a host of different minerals) which will give up an electron. In a sense, the environment is full of chemical disequilibria that are waiting to be tapped, and microbes are very good at developing mechanisms to ‘close the circuit’ for different forms of disequilibria.

Environments in which life could have originated.  With energy and common basic chemicals like water, ammonia and methane it is pretty straightforward to create the building blocks of life: nucleic acids, sugars, amino acids. The two extant hypotheses are tide pools and hydrothermal vents.

Tide pools. In tide pools, concentration and dehydration can cause simple molecules to combine – amino acids can link together into peptides, and sugars and nucleic acides might have linked into precursors to RNA and DNA. Note as well that tide pools would have a wide variety of minerals that might act as catalysts, and that they would be bombarded by ultraviolet radiation, both of which could further creation of complex compounds. The ebb and flow of tides would also have supported a cycle of desiccation and then refreshment with new basic materials.

Hydrothermal vents. Vents have a rich and continual source of simple molecules – methane, hydrogen, ammonia, sulfide – and they are flowing through large porus, metal-rich chimneys that could catalyze synthesis of more complex molecules; furthermore, this is happening at very high temperatures, which can also further reactions. And, furthermore again, the porous nature of the chimneys provides compartments in which might serve as a scaffolding for the eventual self-replicating container components of life. Another positive aspects of hydrothermal vents is that they are protected from surface disruptions, which would have been common during the Hadean eon of the earth.

Discovery of Life Elsewhere. If we discover life elsewhere, it could provide insight on where life originated on earth. We were to find traces of life on Venus, that would favor the tidepool origin. Life on Mars could be explained in either way. Discovering traces of life on the moons of the outer solar system would favor the hydrothermal vent hypothesis.

C10: Origins in an Alien Ocean

For Tuesday, 6 December 2022

Lost City hydrothermal vents are not like black smokers: they are closer to hand-warmers than blow torches, emitting a warm (70 – 100° c) plume of gases and minerals produced by serpentinization, an exothermic reaction between deep mantel rock (mafic) intruding into the seafloor where it reacts with seawater. This type of hydrothermal vent is interesting because serpentinization could occur in many places — they do not require the tectonic activity and internal heating the drives black smokers. All they require is contact between mafic rocks like periodite and ocean water.

Lost City is a field of hydrothermal vent towers, made of glistening white carbonate rock. Some of the towers rise well over 100 feet above the sea-floor, giving the impression of ancient cathedrals dotting this beautiful landscape. The name is perfect for this site – it looks like a lost civilization, hiding away in the depths of our ocean.
From a distance, the carbonate has a texture that reminds me of wax candles with solidified drips along the side. The work of the Spanish architect Antoni Gaudi, and in particular his magnificent Sagrada Pamilia cathedral, is the closest thing I can think of that resembles the tall towers of Lost City. It is a truly magnificent environment.

Kevin Peter Hand, Alien Oceans, p 151

Two meter cnidarian…

Serpentinization produces molecular hydrogen, which, in combination with CO₂, can serve as food for methanogenic microbes. Methanogenic microbes are quite ancient, and their metabolism could represent the first metabolic system used by life. Serpentinization is also not too hot, so it will not ‘cook’ the more complex molecules that are formed. And the alkalinity of the water produced by serpentinizatoin is quite high, meaning that a proton gradient exists between the outside and inside of the vent structures, and proton gradients are one of the ways cell work.

Serpentinization could be common on many worlds. One place we have evidence for it is on Enceladus: the silca, metahne, CO₂ and hydrogen in the plumes are consistent with serpentization on the seafloor. “Given the low gravity on Encedladus, nearly one-hundredth of the Earth’s, I wonder if there might be vast carbonate chimneys, kilometers high, rising above the seafloor like geological skycrapers, reaching toward the ice shell.“

C11: Building an Ocean-World Biosphere

For Thursday, 15 December 2022

• There are many reductants (compounds with ‘spare’ electrons), but few oxidants (to receive the electrons).
• IF CO₂ is the only oxidant, then life may exist, but be very energetically limited. This was the case with the first ~2 Ga on earth, before cyanobacteria evolved to make use of sunlight. Photosynthesis bumps up the energy of electrons in Carbon Dioxide and Water so that the carbon can be synthesized into carbohydrates and other components of life, while releasing Oxygen.
• Initially Oxygen played a geophysical role, oxidizing iron in the oceans and continents. Eventually it built up in the atmosphere, creating a store of oxidants for all the reductants already present in the environment, so that more complex forms of life could evolve (circa 650 Ma) to complete the circuit.
• However, the photosynthetic bumping up of C and O electrons to catalyze the production of organic molecules does not work in the outer solar system due to lack of sunlight as an energy source. But there are alternative energy sources: radiation.
• The surface of Europa is bathed in radiation, due to Jupiter and its magnetic field, and also emissions of energetically charged particles from Io. These particles can interact with Europa’s ice and create H₂O₂, and then O₂ (both observed on Europa’s surface) and then O₃. If other elements like sulphur and carbon are present, they can be processed into carbonate, sulphate, and carbonic acid. All of these are oxidants.
• O₂ and O₃ have also been observed on the surface of Ganymede.
• The other thing that needs to happen is for the oxidants on the surface of the worlds to get into the ocean; this cannot be assumed when we are considering ice shells that are 10’s to 100’s of kilometers thick. Furthermore, this needs to happen regularly, so that life can be sustained.

C12: The Octopus and the Hammer

Tuesday, 20 December 2022

What if, for the past several million years of human evolution, instead of looking up at the night sky and seeing stars, we saw a solid shell ofice above us? What if we lived within a world like Europa, with a ceiling of ice in the sky? And what if we could not even see the ice because it’s dark and no sunlight penetrates; instead we could only feel and hear the ice as it creaked and cracked. And what if that ice ceiling were full of nutrients to feed and sustain life?

Within the ocean of an ice-covered moon, would there be an evolutionary pressure to develop into an intelligent, tool-using species? If enough oxygen was available, how might life evolve (or not) from microbe to multicellular life to intelligent, tool-using life? What selection pressures could lead to technology?

— Kevin Peter Hand, Alien Oceans, p 184-185

• Contingent versus Convergent evolutionary features. Contingent means that a feature is tied to the way things are: for instance, the size of a bird’s wings to the nature of the atmosphere and gravity; convergent means that the feature keeps reappearing in different contexts because it’s so useful: for instance: xxeyes; limbs; ability to move.
  • Senses: Hearing, smell, taste and touch seem obviously useful in a deep dark oceanic environment. Less common senses such as detecting electric and magnetic fields, and sonar, would also be useful in such an environment. Sight, less so, though we know of microbes that can use infrared photons for photosynthesis, and organisms that can detect infrared radiation.
  • Light in the deep ocean. Besides geothermally-produced radiation, it could also be possible for organisms to evolve bioluminescence for reasons such as metabolizing oxygen (where light is produced as a ‘waste’ product; , then exaptation could lead to it being used for other purposes (signaling) and would provide selective pressure for the evolution of sight. It might also be possible for ice shells — for example in the case of Europa — to be less than 500 meters thick, thus allowing some light to penetrate from the surface. (But with most prior estimates of the thickness of ice shells being in the 10’s to 100’s of kilometers in thickness, this seems tenuous.
  • Likely Habitable niches. The two most likely candidates for habitable niches are hydrothermal vents on the bottom of the ocean, and brine-cicles hanging from the ice roof at fractures or other places where nutrients from the surface might leak through. Note that while black smoker vents are relatively ephemeral– decades to centuries — serpentinizing vents are much older: White City is in the range of 30,000 years old. Also mentioned is that example of the Snake Pit hydrothermal vents in the Atlantic, where bowl-like structures on the sides of hydrothermal vents contain hundreds or thousands of baby shrimp.
  • Differences in 3D versus 2D Environments: The nature of the environment has some bearing on whether life might have evolved to use tools.
    Escape. One point is that escape is easier in the 3D world (where organisms can move in any direction through an atmosphere or ocean), and so there could be less pressure to use tools as a means of defense.
    Limited mobility => stability. Another point is that if your mobility is limited (as would be more the case in a 2D environment), there is a greater payoff in ‘settling,’ developing agriculture, and creating tools and buildings to support this. Furthermore, settling means that whatever is created is not constrained by the need for portability, and that it can be stored and over time tool building can develop into a craft.
  • If tools did develop in the oceans, to what uses might they be put? One use we can imagine is harassing the energy and material flows of hydrothermal vents. Similaly, mutatis mutandis, we can imagine harnessing the flow of resources from cracks or vents in the ice-roof.

C13: The Periodic Table of Life

Tuesday, 20 December 2022

Requirements for Life

• Solvent: Water
  => Alternates: ammonia ; liquid hydrogen; formadehyde*
• Elemental Building Block: Carbon
  => Alternates: Silicon; less likely, germanium, tin, lead, and silicon-carbon
• Information Storage and Reading: DNA
  => Alternates: octal DNA; ???
• Structural and functional modular building blocks: carbon-centered nucleic acids, amino acids, fatty acids and sugars ( except Archaea use phytanes as their building blocks.**
  => Alternates: plastics; phosphonamides; sulfonamides
• Energy storage: phosphate
  => Alternates: citric acid; acids of arsenic
• Containers. “Exotic lifeforms on Titan might instead build membranes from structures called azotozomes. These are molecules, currently hypothetical, made from nitrogen-rich organic compounds, according to Paulette Clancy, a chemist at Cornell University who came up with the idea. They would, she thinks, be capable of operating in the ultra-low temperatures of a place like Titan.”
  “Or perhaps there could be life without any membranes at all. Lifelike chemical reactions have been shown to occur on the surfaces of certain minerals, including pyrites and various clays. These often contain networks of pores and cavities that could serve the compartmentalising function of lipid-based cells. Or biological reactions might be contained within drops of liquid floating in planetary atmospheres.”

In general, the constituents of life must be stable enough to stay together, but not so stable that they can’t be manipulated as the organism grows and reproduces

Formaldehyde. “Perhaps the most promising general-purpose alternative to water is formamide, a colourless organic liquid composed of carbon, hydrogen, oxygen and nitrogen (all elements common in the universe) that can dissolve many of the same chemicals as water—including proteins and dna. It can also stay liquid at up to 210°C, making possible a large range of chemical reactions on planets with more extreme surface temperatures than Earth’s. Formamide is such an intriguing alternative to water that some astrobiologists even argue that it might have been the main solvent used by the earliest forms of terrestrial life.” [https://www.economist.com/science-and-technology/2022/05/25/how-to-improve-the-search-for-aliens]

* Phytane: building block of archia organisms “Phytane is a non-polar organic compound that is a clear and colorless liquid at room temperature. It is a head-to-tail linked regular isoprenoid with chemical formula C20H42.”
[…] 
“Phytanyl groups are frequently found in archaeal membrane lipids of methanogenic and halophilic archaea (e.g., in archaeol). Phytene is the singly unsaturated version of phytane. Phytene is also found as the functional group phytyl in many organic molecules of biological importance such as chlorophyll, tocopherol(vitamin E), and phylloquinone (vitamin K1)“
— https://en.wikipedia.org/wiki/Phytane

https://www.economist.com/science-and-technology/2022/05/25/how-to-improve-the-search-for-aliens

Searching for signs of life [Economist]

See: https://www.economist.com/science-and-technology/2022/05/25/how-to-improve-the-search-for-aliens

• Gradients in an environment—zones of sharp change in, for example, heat or electrical voltage or chemicals. According to Dr Girguis, “all living organisms that we know of establish gradients of one kind or another to maintain themselves at a kind of disequilibrium from the environment.” Some of these gradients occur at cellular and microscopic scales, and can be incredibly sharp and therefore distinguishable from non-biological processes. Others are larger-scale. In marine sediments on Earth, for example, microbes work together to oxidise methane, a process tied to the chemical reduction of sulphate ions. “We see gradients in methane and sulphate concentration over centimetres, and they’re really pronounced,” says Dr Girguis. “This is a biological manifestation of their activity and yet this is detectable by simply making abiotic measurements.” [https://www.economist.com/science-and-technology/2022/05/25/how-to-improve-the-search-for-aliens]
• Complex Molecules. “Another tactic would be to study the complexity of the molecules at a particular location. Biological molecules are selected and shaped by evolution to do specific jobs within an organism, such as assembling or disassembling other molecules, or signalling between cells. That often requires unusually energetic chemical processes, which in turn need the help of catalysts. On Earth, these catalysts are protein molecules called enzymes which are, themselves, the product of evolution. Finding complex molecules of any sort might thus be considered a potential biosignature. ” [ibid.]
• The Lego Principle. “The idea here is that life is recognisable by its use and reuse of a selected set of molecules. Abiotic samples scooped up from an alien world would be expected to contain a wide array of organic molecules, some of them in fairly small amounts. A biological sample, by contrast, would contain large numbers of just a few distinctive molecules. Molecules that are chemically similar (left-handed and right-handed versions of an amino acid, for example) might have markedly different concentrations if they came from a biological sample, whereas they would probably be present in near-equal numbers in a non-biological one. Spotting patterns like these would be independent of the specific biochemistry involved.” [ibid.]