Life's futureOn earth, life has come a long way. Eons ago it emerged from its cradle under a then young sun. Will it find its destiny on the same planet, scorched to death by a hugely expanded old sun? Maybe not, if we succeed to offer life alternative pathways on far away worlds, which is the central idea of the Genesis project.Evolutionary bottlenecksCells are not cells, the difference between life's two main types, prokaryotes and eukaryotes, could not be more pronounced. Prokaryotes like bacteria have no nucleus, no internal organelles and do not reproduce sexually or coalesce into differentiated multicellular organisms. All in contrast to eukaryotes, which are in addition much bigger, typically ten thousand times in volume.With eukaryotic cells being so large, it is likely that the presence of oxygen in the atmosphere was a precondition for their emergence. Overall, earth took more than 1.5 billion years to develop eukaryotic cells, which indicates that the development of organisms of this level of complexity constitutes a major evolutionary bottleneck. Regarding the other habitable planets of our galaxy, it is hence often assumed that exobiological life, if present, would be mostly in evolutionary stages comparable to earth's prokaryotic phase and devoid of lifeforms comparable to terrestrial eukaryotes. Exploding complexityIn order to discern life with the naked eye, it has to be a multicellular organism, like a plant or an animal, or a macroscopic colony akin to microbial mats. For most of its history, three billion years and more, little could have been seen of the life flourishing on our home planet. This changed however with the advent of the Cambrian explosion, an intriguing period of only a few dozen of million years that reshaped earth's face once and forever.Animals with legs and eyes would lift their heads out of churning oceans and conquer barren continents together with the newly evolved plants. Afterwards, evolution did equally not stop to surprise. Dinosaurs, birds and mammals emerged jointly with trees, flowers and grasses. Eukaryotic cells celebrate a festival of complexity wherever one turns the head on today's earth. Distant worldsMaybe we always suspected it, but by now humanity knows for sure: exoplanets and alien solar systems come in sheer endless varieties. With regard to the host star mass, the radius, the mineral composition, the water content, the atmosphere of the planet and the distance to the host star. There is no one-size-fits-all planetary system blueprint. The conditions for life to prosper on potentially habitable exoplanets vary likewise.Some planets may stay temperate and tectonically active for several billion years, like earth, others for only a substantially reduced period. Planets with clement conditions could also remain utterly lifeless, f.i. when the primordial atmosphere is oxygen-rich, as for M-dwarf planets.This condition is likely to prevent life to emerge in first place, which implies conversely that complex life would have a chance to evolve on hitherto barren exoplanets if brought there by a Genesis craft. A mix of unicellular pro- and eukaryotes synthesized by an on-board gen laboratory would be enough to lay the foundations for a pre-cambrian biosphere. Interstellar payload deliveryInterstellar trips come with several preconditions. First of all one needs to be modest and settle for a spacecraft that weighs between a few tons and a few grams, if aiming for cruising speeds that range from 1000km/s, which corresponds to c/300, to close to the speed of light. Next a powerful laser, say of about 100GW, needs to be directed onto the perfectly reflecting shield of the spaceprobe. The reflected photons will then transmit enough momentum to propel the craft.Difficult as it is to accelerate an interstellar craft, it is even more demanding to decelerate on arrival. It is however possible to transfer the momentum of the craft to the tenuous interstellar plasma using a magnetic sail. To do the job, install a superconducting loop with a radius of about 50km, inject a current of the order of hundred thousand Ampere and wait a few thousand years. Given enough time, interstellar spacecrafts are capable to deliver payloads to a distant world. Jumpstarting evolutionA payload of eukaryotes could fast forward the evolution of a target exoplanet by several billion years. The cells could be synthesized either freshly on arrival or brought from earth as hibernating germs. Natural selection will take over once the initial biosphere is in place. Importantly, Genesis is about enabling life, not about destroying. The craft would consequently abort whenever complex life is detected from orbit.Planetary seeding ethicsRegardless whether you are vegetarian, vegan or not, nearly no one gets moral headaches when eradicating a few million bacteria while brushing teeth. Our mouth is not considered a protected habitat. But what about prokaryotic life on an exoplanet? There is no way to decide whether the prospect of complex life is worth more than an extant bacterial film. This is not a setting human ethics has been developed for.The possibility that most of the billions of potentially habitable planets harbor only primitive life, that is unicellular organisms well below the complexity level of earth's eukaryotes, may also be factored in. In this situation, the overall balance will not be altered if an extant bacterial-level biosphere is superseded by a Genesis craft with highly developed terrestrial eukaryotes. Ethical issues become irrelevant altogether for the case of habitable but sterile exoplanets, the setting that may be realized for M-dwarf planets. Not for human benefitThe time scales involved imply that the Genesis project cannot be justified by utility considerations. It may take ten thousand years for the craft to arrive and a few hundred million years for complex multicellular organisms to emerge as the result of natural selection. No individual and no organization has the lifespan to wait that long. This is a problem when sticking to the letter of human ethics protocols, which state that ethically acceptable is only what is beneficial for humans. Transcending the utilitarian perspective one may think of alternative motivations to carry out the Genesis project, such as aesthetics. Isn't life as such something to admire?Selected Media Resonance
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Original ArticlesTitle: Why planetary and exoplanetary protection differ: The case of long duration Genesis missions to habitable but sterile M-dwarf oxygen planetsAuthors: C. Gros Journal-ref.: Acta Astronautica 157 263 (2019). Time is arguably the key limiting factor for interstellar exploration. At high speeds, flyby missions to nearby stars by laser propelled wafersats taking 50-100 years would be feasible. Directed energy launch systems could accelerate on the other side also crafts weighing several tons to cruising speeds of the order of 1000\,km/s (c/300). At these speeds, superconducting magnetic sails would be able to decelerate the craft by transferring kinetic energy to the protons of the interstellar medium. A tantalizing perspective, which would allow interstellar probes to stop whenever time is not a limiting factor. Prime candidates are in this respect Genesis probes, that is missions aiming to offer terrestrial life new evolutionary pathways on potentially habitable but hitherto barren exoplanets.
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Universal scaling relation for magnetic sails: momentum braking in the limit of dilute interstellar media The recent progress in laser propulsion research has advanced substantially the prospects to realize interstellar spaceflight within a few decades. Here we examine passive deceleration via momentum braking from ionized interstellar media. The very large area to mass relations needed as a consequence of the low interstellar densities, of the order of 0.1 particles per cm3, or lower, are potentially realizable with magnetic sails generated by superconducting coils. Integrating the equations of motion for interstellar protons hitting a Biot Savart loop we evaluate the effective reflection area A(v) in terms of the velocity v of the craft. We find that the numerical data is fitted over two orders of magnitude by the scaling relation A(v) = 0.081ARlog3(I/(βIc)), where AR=πR2 is the bare sail area, I the current and β=v/c. The critical current Ic is 1.55 106 Ampere. The resulting universal deceleration profile can be evaluated analytically and mission parameters optimized for a minimal craft mass.
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Developing Ecospheres on Transiently Habitable Planets: The Genesis Project
It is often presumed, that life evolves relatively fast on planets with clement conditions, at least in its basic forms, and that extended periods of habitability are subsequently needed for the evolution of higher life forms. Many planets are however expected to be only transiently habitable. On a large set of otherwise suitable planets life will therefore just not have the time to develop on its own to a complexity level as it did arise on earth with the cambrian explosion. The equivalent of a cambrian explosion may however have the chance to unfold on transiently habitable planets if it would be possible to fast forward evolution by 3-4 billion years (with respect to terrestrial timescales). We argue here, that this is indeed possible when seeding the candidate planet with the microbial lifeforms, bacteria and unicellular eukaryotes alike, characterizing earth before the cambrian explosion. An interstellar mission of this kind, denoted the `Genesis project', could be carried out by a relatively low-cost robotic microcraft equipped with a on-board gene laboratory for the in situ synthesis of the microbes. |
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