The
latest research on the sunlight received on most detected planets in the "habitable zone" (where liquid water can exist) indicates that life may really be exceedingly rare in the Universe.
Quote:"Photosynthesis, the life-giving process that allows plants and some microorganisms to convert light into organic matter, producing oxygen as a by-product, requires the right amount of sunlight. Not all stars can provide that.
The researchers calculated how much photosynthetically active radiation (PAR) — radiation in the wavelength range between 400 to 700 nanometers that photosynthetic organisms can use — the planets receive from their stars. They found that the planets orbit frequently around stars that are too cool to provide enough PAR. For example, a star about half the temperature of the sun would provide enough PAR to power some photosynthesis but not enough to create such a rich biosphere as Earth has.
In fact, only one of the planets in the studied sample, Kepler-442b, a super Earth orbiting a star some 1,200 light years away in the constellation Lyra, came close to receiving enough PAR to sustain a large biosphere, the scientists said in a statement.
Even though the study was done only on a very small sample of planets, astronomers know enough about the nature of stars in the Milky Way to assume that the right conditions for photosynthesis-driven life might be rare. Most of the stars in the galaxy are the so-called red dwarfs, dim stars about a third of the sun's temperature, too cool to generate any photosynthetic activity on the planets in their vicinity.
"Since red dwarfs are by far the most common type of star in our galaxy, this result indicates that Earth-like conditions on other planets may be much less common than we might hope," Professor Giovanni Covone, lead author of the study, said in the statement."
Of course this research result could be questioned on the grounds that "life as we know it" may not be the only form of life, or that photosynthesis may have just as likely evolved to utilize a different part of the light spectrum, if the predominant energy was in a different wavelength region. I don't think such arguments have much weight, however. For instance, if a radically different sort of photosynthesis in a different spectral region was possible electrochemically, it would presumably have evolved in such environments on the Earth. But it hasn't - no such new and different type of photosynthesis has ever been found.
This may then be one reason for the Fermi Paradox; this paradox is the observation that (aside from the problematical UFOs) there are no aliens here or anywhere else at least as observed by astronomers and SETI researchers, despite the fact that if they existed they would have presumably spread across the Galaxy and abundant evidence would have been found for them on Earth and in the Solar System.
This latest research of course assumes that if the conditions are appropriate life will inevitably evolve abiogenically (by chance and the laws of physics and chemistry). In reality origin of life research is no closer today to finding some such mechanism than it was 40 years ago. Some OOL researchers have suggested from their studies that life must be an exceedingly rare and lucky throw of the dice, a matter of 1 in quintillions at least. Accordingly, the unlikelihood of the origin of life is another reason life may be extremely rare in the Universe.
The conclusion seems to be that there are now two very strong reasons to provisionally believe that we are alone at least in this galaxy.
I think there's a major flaw in the assumptions. I know when the first exoplanets were identified, they were huge, massive Jupiter-sized objects, thus not comparable with Earth. The current article begins with a reference to "
potentially habitable Earth-like exoplanets". But we need to examine that phrase and find out what they mean. It turns out, these are not really Earth-like at all. Having moved beyond the earlier problem of only identifying extremely massive objects, the next sticking point is to only identify planets orbiting stars which are
not Sun-like.
The term
earth-like is clearly being misused, which then leads to a whole train of diversionary thought.
Still, one thing we should bear in mind is that on Earth, life is extremely resilient, living organisms being found occupying many niche environments which could readily be assumed utterly uninhabitable.
Extremophiles and Extreme Environments
Quote:Over the last decades, scientists have been intrigued by the fascinating organisms that inhabit extreme environments. Such organisms, known as extremophiles, thrive in habitats which for other terrestrial life-forms are intolerably hostile or even lethal. They thrive in extreme hot niches, ice, and salt solutions, as well as acid and alkaline conditions; some may grow in toxic waste, organic solvents, heavy metals, or in several other habitats that were previously considered inhospitable for life. Extremophiles have been found depths of 6.7 km inside the Earth’s crust, more than 10 km deep inside the ocean—at pressures of up to 110 MPa; from extreme acid (pH 0) to extreme basic conditions (pH 12.8); and from hydrothermal vents at 122 °C to frozen sea water, at -20 °C. For every extreme environmental condition investigated, a variety of organisms have shown that they not only can tolerate these conditions, but that they also often require those conditions for survival.
Quote:The mechanisms by which different organisms adapt to extreme environments provide a unique perspective on the fundamental characteristics of biological processes, such as the biochemical limits to macromolecular stability and the genetic instructions for constructing macromolecules that stabilize in one or more extreme conditions. These organisms present a wide and versatile metabolic diversity coupled with extraordinary physiological capacities to colonize extreme environments. In addition to the familiar metabolic pathway of photosynthesis, extremophiles possess metabolisms based upon methane, sulfur, and even iron.
Note, I am not entirely familiar with the Pa unit of pressure. A quick conversion, the stated 110 MPa is equivalent to about 1000 times normal atmospheric pressure.
(2021-06-29, 05:55 AM)Typoz Wrote: [ -> ]I think there's a major flaw in the assumptions. I know when the first exoplanets were identified, they were huge, massive Jupiter-sized objects, thus not comparable with Earth. The current article begins with a reference to "potentially habitable Earth-like exoplanets". But we need to examine that phrase and find out what they mean. It turns out, these are not really Earth-like at all. Having moved beyond the earlier problem of only identifying extremely massive objects, the next sticking point is to only identify planets orbiting stars which are not Sun-like.
The term earth-like is clearly being misused, which then leads to a whole train of diversionary thought.
Still, one thing we should bear in mind is that on Earth, life is extremely resilient, living organisms being found occupying many niche environments which could readily be assumed utterly uninhabitable.
Extremophiles and Extreme Environments
Note, I am not entirely familiar with the Pa unit of pressure. A quick conversion, the stated 110 MPa is equivalent to about 1000 times normal atmospheric pressure.
I don't think there is any reason why the astronometric observations detecting planets so far would have been selective of non-Sunlike stars, that is, mostly finding planets orbiting non-sunlike stars due to observation technique biases. The predominant detection method works when by chance the alien planet's orbital plane just happens to intersect our line of sight to the particular star in the Milky Way (which can be assumed to be a random distribution).
This is the partial occultation method, which depends on detecting the minute drop of radiance of the star as the planet moves across the face of its parent star. It doesn't depend on being able to directly optically detect the alien planet, or even to detect the minute motions of the star in response to the gravitation of the planet. The beginning and the end of this transit process will follow a typical radiance profile indicating the passage of a spherical body in front of the star. Furthermore, the great majority of stars have been found to be red dwarfs, as explained in the article. This isn't an observational artifact due to the detection technique, but a real estimate of the actual population spread.
Nothing in this method would seem to bias against sunlike stars. The tendency of the occultation method and the parallax and other optical methods to detect giant massive planets more than Earthlike size planetary bodies wouldn't seem to bias the estimate of the prevalence of unsuitable irradiance on the Earth-sized planets that are detected.
Your argument based on the existence of "extremophile" micro-organisms on Earth might be more persuasive, especially the ones that have found chemical energy sources other than sunlight and photosynthesis to maintain their metabolisms. Could an entire ecosystem be built up based on sulfur metabolism (for instance) rather than photosynthesis? I don't think we know enough to answer that question. Keep in mind that there would still be the baseline requirement for liquid water, and the unsuitability of any elements other than carbon to form the multitude of different long-chain molecules required for life of any kind - e.g. molecules equivalent to DNA, RNA and great numbers of different specialized proteins. Silicon is the closest, but it is probably still insufficient.
Why isn't "we've been looking for less than 100 years" ever floated as a reasonable answer to the Fermi paradox?
(2021-07-04, 02:06 PM)Will Wrote: [ -> ]Why isn't "we've been looking for less than 100 years" ever floated as a reasonable answer to the Fermi paradox?
My view is that with most of the factors involved we simply don't know enough to judge the probability that there actually are aliens attempting to communicate by radio means within a distance allowing us to detect them. Too many unknown factors.
But there are two factors that we do have at least some information on - these are the probability of life arising abiogenically (very nearly zero), and now the probable unsuitability of most otherwise Earthlike planets to have parent stars that are in the required spectral range and intensity at the planetary distance to support photosynthesis. It seems to me, these two factors probably effectively rule out the Star Trek Sci-Fi sort of assumption of multiple ETI races inhabiting and communicating and traveling over the galaxy.
This is confirmed by the empirical evidential fact that there have not been any unambiguous visits and contacts leaving identifiable unmistakable physical traces of high technology from somewhere else, at least on the Earth and so far in our visits to the other planets of our Solar system
But overall there is still too much uncertainty to hold any fixed firm opinion on the matter, if for no other reason than the uncertainty lent by the apparent presence of ETs visiting us since at least the late 1940s. I. e., in the form of the infamous UFO phenomenon, where a significant fraction or class of the cases are definitely of physical vehicles emitting and reflecting electromagnetic energy, quite apparently somebody else's hardware.
I know - clear as mud. But that's life.
I'm not sure that "the probability of life arising abiogenically (very nearly zero)" sheds any light on the matter. We could take many lines of thought on that, from miraculous intervention to panspermia, or consciousness pervading the universe ... I've not even begun because there are many more ways to look at this. But the mere fact that we are here indicates - unless we somehow take the pre-Copernican view that all of reality revolves around Earth - which I think is unjustifiable and somewhat hubristic, then inevitably this is just one tiny dot in the universe among many, many others.
(2021-07-05, 08:25 AM)Typoz Wrote: [ -> ]I'm not sure that "the probability of life arising abiogenically (very nearly zero)" sheds any light on the matter. We could take many lines of thought on that, from miraculous intervention to panspermia, or consciousness pervading the universe ... I've not even begun because there are many more ways to look at this. But the mere fact that we are here indicates - unless we somehow take the pre-Copernican view that all of reality revolves around Earth - which I think is unjustifiable and somewhat hubristic, then inevitably this is just one tiny dot in the universe among many, many others.
I think you greatly underestimate the true improbability of the existence of human civilization (even) in the inconceivably huge immensity of the Galaxy and the ensemble of billions of other galaxies. It is actually a matter of fine tuning on steroids.
The more thoroughly researchers investigate the history of our planet, the more astonishing and improbable the story of our unlikely existence becomes. The number and complexity of the varyingly unlikely astronomical, geological, chemical, and biological features recognized as essential to human existence have expanded explosively within the past decade. And an at least partial understanding of what was required to make possible the rise of a large human population and advanced civilization has greatly raised the number of fine tuning factors that are known to be necessarily responsible for our existence.
From Hugh Ross:
Quote:"More than 100 different features of the universe and the laws of physics must be exquisitely fine-tuned to make advanced life possible. More than 800 different features of our galaxy and planetary system must be fine-tuned for advanced life to possibly exist. The fine-tuning evidences rise exponentially as one proceeds from what is needed for microbes, to what is needed for plants and animals, to what is needed for humans to exist, and then for what was needed for human civilization to arise..."
Of course, to be accurate, this literally astronomical improbability is in the context of the philosophical naturalism or absolute materialism of the SETI researchers themselves. A wider view encompassing the possibility of the existence of higher spiritual realms able at will to introduce life into and manipulate the physical world could possibly overturn these fine tuning calculations. But at least most of the empirical evidence so far (admittedly early in humanity's search for other life and civilizations) is for our being alone, in accordance with the fine tuning estimates. Of course, that could change overnight.