« Prev Next »
January 13, 2014
|
By:
Bruce Braun
Did We Need The Moon?
Looking out at the night sky, if we are so lucky, we see above us a familiar luminous orb. Our moon. Its beauty is enduring and its necessity to us remains tantamount. The moon has been vital to the development of life as we know it on Earth. When evaluating the possibilities of extraterrestrial life, we're often confronted with the fact that we simply don't possess sufficient data. Thus, when thinking of it, it is helpful to look at our own evolutionary history and our geologic records to see how complex life was possible on Earth. In the grand puzzle the moon is a significant jigsaw piece.
Let us go back four and a half billion years into the Earth's past, long predating dinosaurs and the most meager forms of organic matter; we see oceans of boiling magma and the bubbling of liquid rock. The air is composed primarily of hydrogen and helium, the two most common elements in the universe. Geologic debris hurl down from above, relentlessly bombarding the surface. One day (you must forgive the author for forgetting the specific date), a wandering protoplanet, collides with Earth. Then, the solar system was young and rife with collisions from small bodies, bumping into each other and accumulating mass, like snowballs, occasionally forming protoplanets (or fully fledged, proper planets). The protoplanet that struck Earth, Theia, was roughly the size of Mars. If our planet had ever borne an apocalyptic day, that was it. Fittingly enough, Theia borrows its name from the Ancient Greek Titaness Theia, who gave birth to Selene, the moon goddess.
When Theia impacted primordial Earth, hot material from both Earth and Theia was ejected into orbit. This material which was made of chunks of the mantle belonging to the Earth and Theia, coalesced into our moon. The Earth and the moon are made of the same stuff. To the eye, this spectacular series of cosmic events would be awe-inspiring; the moon appeared twenty times larger, before it eventually receding into its familiar appearance in the sky today.
The ramifications would have been pervasive if Theia had never come near Earth. Winter, spring, summer and autumn would be no more. Our seasons and climatic stability come from the stabilization the moon's gravitational pull exerts on our tilt.
To understand axial tilt, or obliquity, imagine your right hand with the fingers curled in the direction of the planet's rotation and with the thumb pointing towards its north pole.
Obliquity determines the amount of sunlight a planet receives at its equatorial and Polar Regions. A tilt too far off the mark of twenty-three degrees, and our climate might prove inhospitable for the development of higher life. One extreme possibility leads to the oceans freezing, leaving Earth stranded in a permanent ice age. A tilt of ninety degrees would result in the Polar Regions becoming akin to hot deserts. With an destablized tilt, large scale rapid climate change would be a common theme in Earth's history, potentially increasing the rapidity of large-scale extinction events and hindering life's development. It is not difficult to imagine that only the most extreme and hardiest of organisms would flourish in this moonless meteorological turbidity.
In the early days, the relative proximity of the moon provoked greater oceanological and geologic effects than exists today. Owing to the relatively greater proximity, the lunar tides possibly reached hundreds of meters in height. Waves were critical in the development of life. According to Peter Ward, paleontologist and coauthor of the book "Earth: Why Complex Life is Uncommon in the Universe'', intertidal pools are one of the best places life could have formed. The swishing water brought a wide variety of substances that may have been difficult otherwise. The moon, in other words, was a key ingredient in the prebiotic cooking recipe that formed our biology.
It seems our friend Luna rotates our sphere harmoniously, but in young times our relationship was more intense. It is possible that those same tidal forces exerted effects beyond the waters, heating up the planet and triggering geologic convection. The infancy of plate tectonics, the great continental plates churning and wonderfully reshaping our planet into new moulds over the ages, may have been birthed from the sky. It is a rather romantic notion, that our various streams of naturalistic observations appear to converge into a singular cosmic coincidence.
To investigate the complex interplay between plate tectonics and life, let us consider that our planet is the only one with shifting continents in the solar system. Without plate tectonics, there is no recycling of carbon. After carbon is used in the atmosphere, it progresses into the soil, where it is digested by microbial organisms until it is spurred out again by volcanic mechanisms. It nourishes our planet over time, and is involved with the maintenance of our magnetic field. The magnetic field as acts as a shield, warding off solar wind and dangerous cosmic rays that would be damaging to our DNA. Our atmosphere would slowly erode. It is suspected that the lack of plate tectonics contributed to Venus's current condition as a scalding locale, the victim of a runaway greenhouse effect.
Furthermore, recall that quite a large portion of mass was originally dislodged from Earth. If the planet retained those portions of the crust, then the ocean basins would be fuller. Water takes up the mass majority of the planetary surface now, but the aquatic proliferation would be even more penetrating if we retained our crust. Subtract a geologic mechanism for the rising of mountains, and we have a water world, with perhaps the occasional volcanic island cropping up here and there. It is not a positive prospect for the development of terrestrial life, to be sure.
There are multiple webs of argument that point to the necessity of the moon to the development of human life, and complex life that asks for long-term stability. The collision of a protoplanet, a large moon forming event in the inner planets, is thought to have a low probability of occurring in the first place. On the other hand, we simply don't possess sufficient data on the prevalence of moons elsewhere in the universe. Despite this sometimes frustrating astronomical ambiguity, there is one conclusion that may be reasonably drawn: An Earth without a moon is a world without witnesses.
For further reading:
1. Hoffman, M. ‘'The Moon And Plate Tectonics: Why We Are Alone''. SpaceDaily. (2001).
2. Pullen, L. "Plate Tectonics Could be Essential for Life''. Astrobio. (2009).
3. Ward, P. et al. Rare Earth: Why Complex Life is Uncommon in the Universe. 180-197. (2000).
4. Foing, B. "If We Had No Moon". Astrobio. (2007).
5. Dorminey, B. "‘Rare Earth' Revisited: Anomalous Large Moon Remains Key To Our Existence". Forbes. (2013).
Image credit:
Figure 1: (Via Fahad Sulehria)
Figure 2: (Via Wikipedia)
Figure 3: (Via NASA/JPL)
November 09, 2013
|
By:
Bruce Braun
The Curious Idea of Jovian Life
In the distant night horizon is a pale and beige orb hovering above us. If you had an amateur telescope, you could perceive reddish rings encircling it, and perhaps its scenery in your head, all the while whimsically reminiscing about the time your fifth grade teacher spoke of its intense heat, mass, and pressure. The mere notion of life existing in such an unwelcoming environment would be absurd-except, it was an formerly idea taken very seriously by scientists until additional evidence ruled out its likelihood.
So why write about it?
The history of Jovian biological speculation is a fascinating case study that demonstrates how science works. Dealing with the unknown, it illustrates creativity, curiosity, and ultimately, the restraining virtue of rationality; it is a perfect example of how developing astrobiological models are formed. Without further adieu, let us begin our fun foray into antiquated territory:
The connection between science fiction and science dynamic. As science leads, science fiction inspires. And this special bond can go both ways. The first roots of the idea of Jovian life went back to the experiments of Stanley Miller and Harold Urey in the 1950s. They sought to validate the earlier hypothesis that conditions on primitive Earth, so in far as those conditions may be replicated in a modern laboratory, could yield organic products from their inorganic precursors. The components involved in the experiment were methane, water, ammonia, and hydrogen, inlet with a continuous electrical stream (which was to replicate the intense lighting conditions of primordial Earth). In triumph, amino acids, the building blocks of protein and life, were found. Yet, we need not visit a chemistry laboratory for an example of this Frankensteinian quirk of chemistry and biology; the planet Jupiter itself may represent a planetary version of his experiment.
The jovian atmosphere contains hydrogen, methane, ammonia, and water, and is tempered by turbulent weather and lighting. The possibility of biota, at least in the upper-atmosphere, was hypothetically proposed by Carl Sagan and Edwin Salpeter three years after the Pioneer 10 flyby of Jupiter, in 1976. He compared the Jovian ecology to our terrestrial oceans. Ammonia-based life, was not terribly out of the question. Experiments done by Siegal and Giumarro showed that certain microorganisms could survive in ammonia-rich atmospheres. It would do the reader injustice not be informed of this marvelous video, narrated by Sagan himself, in which he describes life in a gas-planet. It is called ''Carl Sagan's Cosmos: Life on Jupiter", from his Cosmos. It may be found in a web search. In it, the ecology of floating, jellyfish-like ''floaters'', are described, and massive creatures of intelligence are pictured swimming along in the upper atmosphere, staying aloat by pumping helium out of its interior, conveniently leaving the lighter gases, such as hydrogen, within. In this way it may be reminiscent of a hot-air balloon. These floaters are imagined to be terrible in scope-many kilometers across. They would eat organic molecules found in the atmosphere, or create their own from air and sunlight, in the same way plants do. The reader is highly encouraged to view the visual.
However, the likelihood of this, shown by later experiments, was diminished. It seems that the forces of convection, powerful gusts in the Jovian atmosphere, would probably blow any promising molecules into the lower atmosphere. There, the rigid pressures and intense temperatures would do away with them. Jupiter is a far cry from the tranquil orb that it appears in the night sky. And, most importantly, there has yet to emerge any form of evidence of Jovian biology. Carl Sagan, a cautious skeptic himself, noted the hypothetical nature of this in his introduction that 1976 paper by restating that the plausibility of life in a gaseous giant does necessarily correlate to its likelihood.
Yet Isaac Asimov's words do have an appeal to the imagination:
"If there are seas on Jupiter, think of the fishing".
For further reading:
1. Heppenheimer, T. Colonies in Space. 2007.
2. Sagan, C, et al. Particles, environments, and possible ecologies in the Jovian atmosphere. Astrophysical Journal Supplement Series. 32, 737-755. 1976.
October 16, 2013
|
By:
Bruce Braun
Alien Asteroid Miners, And How We Can Detect Them
There are various ways scientists hope to detect intelligent life in space. From monitoring incoming radio signals, looking for visual signatures of a habitable world, to wearing tinfoil hats with antenna arrays, perhaps the most interesting way is to look for their mega-engineering projects. Mega-engineering is concerned with structures and projects on a tremendous scale. It's not unreasonable to think that our astronomical neighbors haven't already tried this; the demand for more resources and places to house a growing population makes astroengineering a common-sense goal. For example, Dyson Spheres are hypothetical structures they might make that we could detect. The former could take care of energy, but what about raw resources: minerals and precious metals? Look no further than your friendly neighborhood asteroid belt.
Asteroid mining makes sense. Even on Earth today, asteroid mining companies, backed by innovators and visionary billionaires, are developing plans and technologies to aid them in the upcoming space ''gold rush'' of the 21st century. Silicon, platinum, palladium, nickel, and water, which can be broken down into hydrogen and oxygen to make rocket fuel, are all examples of lucrative gems to be found, according to a Wired article. It's not hard to imagine why an advanced civilization would take advantage of these opportunities, as well as extensively develop the corresponding infrastructure required for such a large scale operation. The interesting thing about this is that mining in space produces evidence that we can detect.
Since our miners would be digging only for certain species of chemicals, the chemical content of the asteroid belt would not resemble what we'd expect if left untouched. Since asteroid belts and their parent star are formed from the same primordial interstellar dust, (described in a process called the nebular hypothesis), scientists can predict the chemical makeup of far-away asteroid belts by looking at the metal content of the parent star. With spectroscopy, which analyzes the light emitted off of astronomical objects (such as asteroid belts) and from their stars, we can ascertain all this information. Different chemical species will produce different spectral lines, so if we use spectroscopy and notice a debris field missing several chemical species that ought to be there, that is difficult to explain.
Another way scientists can browse for space mining projects is by considering the size many asteroids in the belt should be, and comparing that with what sizes they actually are. The large asteroids would likely be the victims of mining endeavors, increasing the relative number of smaller bodies compared to larger ones, and thus changing the size distribution of the belt. We can predict the approximate size distribution by accounting for the radiation pressure and balance of gravity. (If that's not a powerful example of the predictive power of scientific theory and mathematics, then I don't know what is). Of course, evidence of this occurrence alone isn't good proof of industrious miners; the same result could occur through the impacts of large bodies, but it does raise an eyebrow. Your hopes of finding extraterrestrial intelligence here would be encouraged if there were further evidence of thermal fluctuations in the belt. Industrial mining would create an unusual temperature distribution, as the mechanical process would heat up dust significantly and toss it out.
It's not the most reliable way to conduct SETI inquiries, but asteroid mining enterprises present a hypothetical way to detect, and narrow down astrobiological candidates. It is a little disappointing that a mining operation would have to be very large-scale to detect, and that our instruments of detection need further refinement for our goal. On the other hand, the more ideas we have that could be used to look for life in the universe, the better!
For further reading:
1. Forgan. D. et al. Extrasolar Asteroid Mining as Forensic Evidence for Extraterrestrial Intelligence. International Journal of Astrobiology. 10, 307-313 (2011)
2. Wall. M. ''New Asteroid Mining Company Aims to Manufacture Products in Space''. Wired. (2013).
3. Villard. R. "Asteroid Forensics May Point to Alien Space Miners". Discovery. (2011).
4. Morley. C. "Could We Observe Aliens Mining Asteroids?''. Astrobites. (2011).
Image credit: (Via NASA/JPL-Caltech)
Share
Close
