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Thread: The Astronomy Thread

  1. #21
    Sir Adrian's Avatar the Imperishable
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    Default Re: The Astronomy Thread

    And the 6th mass extinction is happening right now.
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  2. #22

    Default Re: The Astronomy Thread

    Quote Originally Posted by Flinn View Post
    Oh my every time I get to this thread I'm overwhelmed by the possibilities it has it terms of discussion
    Seriously, this is going to be the shieet. Thank you Douchebag and Flinn! I pity the fool who stumbles upon this forum and this thread in the middle of writing their Master's thesis or PhD.

    Quote Originally Posted by Flinn View Post
    I think that as of today, apart for a very small group of people that (usually) have religious reasons to deny it, everybody agrees that there will be life somewhere else in the Universe, without fault. The Universe in itself is so immense (infinite according to someone) that it's really impossible to not to have "more life", for a mere matter of brute numbers (in terms of chances I mean). So, assuming most of people will agree with that statement, what we do possibly not agree on is how frequent life is, and at which level of development it is (from the most basic bacteria to the most advanced civilizations, maybe even forms of "superior" life which we can only speculate on or imagine in fiction).
    I will have to take strong issue with this claim and not just because of my individual point of view but because of how many in the relevant scientific community take it. The bottom line is that we have no way of estimating the likelihood of something that has only been observed to occur once. Not even by that brute force logic of the sheer number of places where it could possibly occur.

    That is an intuition and essentially a belief. I do share that intuition in the sense that if we discovered the universe to be full of life, I would not be surprised at all. I too would find the opposite less intuitive, but probabilities and intuition are two very different things in an extreme case such as this. The life on planet Earth could be the most freakish fluke of nature in the entire vast universe, and we cannot estimate the probability of that being the case.

    By the way, I go through those same thought patterns frequently. "But hey Sept, listen now, the space is infinite from a human perspective*, and exoplanets are almost literally everywhere and...". But no, I have to consciously pull myself out of that hole.

    Quote Originally Posted by Flinn View Post
    just few days ago they have confirmed the discovery of a new group of extremophile bacteria that survived at 5 km underground, with a temperature above 135 °C (they have been found by a Chinese scientific mission, in a well drilled for other scientific purposes; previous "record" was at around 3,6 km and not above 120 °C. As per the definition of what "habitable conditions" means, such a discovery resets them, in the sense that finding the proof of life in such a harsh environment, multiplies dramatically the possibilities of finding life in other planets/moons even in our own solar system:
    This is my own reasoning and not based on what I have read by the experts. I personally find it troubling that the existence of extremophile life on Earth and life in improbable places in general is applied without criticism to other worlds. Seeing the adaptability of life, it is easier to understand how life once begun in favorable conditions could evolve to find its way to unlikely conditions. It is a different matter, however, whether life could be born directly in very hostile circumstances.

    I find things like the subsurface oceans of Europa extremely fascinating, but I cannot share the optimism of many in actually finding life there. But of course, we do not know the likelihood and the process of inanimate substances becoming alive. We have just observed the results of it happening once. In any case, I am not arguing for not trying to find life in even the unlikely places. Somehow I feel that it is our duty to try and try relentlessly.

    *We can throw around some insane number estimates but we do not understand them really. As individuals outside the confines of scientific inquiry, we have no capacity of estimating how many grains of sand there is in a glass jar when asked, let alone understanding how many are on a given stretch of beach.
    Last edited by Septentrionalis; February 23, 2021 at 01:01 PM. Reason: Typos galore
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  3. #23
    Jadli's Avatar The Fallen God
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    (Yaaay, I originally lost the post, so had to write most of the stuff again)

    Nice to see such a thread on TWC, studying astrophysics myself (4th year), so obviously interested in all this stuff (the topics discussed here is kinda why I started studying it)...

    I pretty much agree with everything Flinn said...

    Anyway, A very good point about space engine/drive and movement in space PoVG. This all comes from "basic" physics and has been kinda known from the beginning of space travel, so its really sad that most of mainstream sci-fi movies/shows have completely neglected it. Its not just about time durations, but simply the movement of the ships... they cant just suddenly "stop" or "change directions and so on, without killing everyone inside (due to the artifical acceleration created).

    The efficiency of our (propulsion) drives has been a core issue since day one, because as you all very likely know, the large majority of fuel (which is abot 75% mass of the rockets) is used just to leave Earth, so there is very little left for some actual movement in space, the ships are mostly just slightly "pushed" in the beginning, and then they mostly just continue with no thrust till they reach the destination, hence it takes a long time.

    The next step very likely is something based on fusion or fissions (hence a very little fuel and lot of energy), so the ships would be able to accelerate/deccelerate (which means just turning the ships an accelerate in opposite direction of course) during the flight, hence things would get faster. That would definitely allow/speed up our inevitable colonization/exploration of Solar System (at least for mining purposes). It would also solve many other issues, because long term survivability in zero G is an issue ...

    Based on the current knowledge physics (which is pretty complete in regards to how space travel works) even this wouldnt be enough to reach other stellar systems, and hence the exoplanets... Because as PoVG pointed out, it would still take a long time, as you cant go as fast as you want with manned missions. Sending an unmanned mission might be possible, as you might be ble to accelerate as much as you want. But of course, even the most efficient fuel is not endlessly efficient, and the faster you go, the more quickly you burn it... so the question is how much fuel would it have to carry to get there in a reasonable time even with the most efficient drives anyway (talking decades minimally, plus dont forget the information delay itself would be years).

    So we cant get there "personally" for sure, though we are already able to extract impossible information about exoplanets from observations due to our crazy machines... and we are working on even crazier missions (both earth and space), so we will be able to know much more in the foreseeable future

    Though that shouldnt bother us too much right now, as we have more than things to explore in our Solar System, we have barely set foot in it, so our focus should be mainly here I think. There are more than enough interesting objects in it. It seems our Solar System is not somewhat unique, so what we learn here can be easily extrapolated to the exoplanets. We already know many organisms that can live in crazy conditions... I think we will find some "fossils" on Mars perhaps, but much more interesting may turn out to be the moons of gas giants, especially Saturn and Jupiter of course, such as the ones with seas under their ice crusts, or Titan with ith methan cycle (similar to water cycle on Earth). If we find something even in such hardly habitable worlds, that would easily prove that some form of life is very common in space (at least bacteria and so on).

    I definitely agree with Flinn's opinion about probability of life.... Even if the probability of life was infinitely small, there are so many stars with (exo)planets in habitable zones out there (billions of billions) that the their number is pretty much infinite, hence, looking at it from the opposite angle, its pretty much impossible that some form of life wouldnt form. Also, there are so many complex molecules flying around in space, they pretty much just need to "fall" to a good planet. Of course, the question is what kind of life would be formed.. in 99,99% it would be just some bacteria and so on, so not someone you could talk to...

    Quote Originally Posted by Flinn View Post
    So I'm pretty confident basic forms of life could be found almost everywhere there are the basic conditions for it: water in liquid form and basic chemical elements that are used to assemble amino acids.
    I honestly have no clue, though, of how rare "intelligent" life could be, for various reasons: first, it is obvious, by looking at our own system, where we have millions of bodies, that a combinations of elements like the ones you have on the Earth are pretty rare (giving for assumed that only rocky planets similar to our can give birth to intelligent life, for obvious reasons); second, it is not clear yet which kind of stars are better suited for hosting Earth-like planets: as of today, it seems that both yellow dwarfs (such as the Sun, approx 1/13 of all the stars) and orange dwarfs (approx 1/8) have the best chances, due to the fact that they seem to be more stable that red dwarfs (red dwarfs show to have frequent powerful solar flares that can possibly destroy any atmosphere and/or form of evolved life in their systems, and they represent approx 3/4 of all the stars!!!) or bigger stars (from white dwarfs up to blue giants, here I'm referring only to main-sequence stars of course), due to the fact that those stars have a shorter life, which might not allow enough time to develop superior forms of life; third, the very definition of "intelligence" is pretty subjective and can make the difference at that regards: for instance, most animals do have a form of intelligence, therefore if we look at this as our starting point, it needed roughly 250 millions year for the life to evolve from bacteria to intelligent life on Earth.. but if we believe that intelligence is the ability to shape the word around you, then we have to wait for hominids, sometimes like another 250 millions years; more points could be listed, but I'm sure you got my point by now.
    Yea. Imho, I like Drake's equation a lot, even tho its just a guess, not math. But its a very good guess that includes almost all/most things one needs to think about, when thinking about extrasolar life. One definitely needs to to think about time scales.... near us, there could have been many intelligent civilizations before us, or will have been before us, but its possible we are just not gonna live "in the same time" as them... If you look at Earth history, like 99,9% of its history there was no "intelligent civilization" able to space travel/communicate, and Earth is about 4 billions of years old, so yeah...

    Well, its actually somewhat clear which stars are better suited... exoplanets are a very new field in astrophysics, so most basic principles and so on is being researched or formulated right now (this year, we had an exoplanet class for the first time.... Therefore I also have lot of new interesting info I suppoe )

    Stars on main sequence of spectral types F,G (Sun),K are definitely kinda the only ones suitable (see spectral classification). So "slightly" heavier or lighter stars compared to Sun, which is the majority of stars. So you are prety much right with your assumptions (though Im not sure what do you mean by dwarfs). So basically heavier stars have too short lives for proper planets to even form (thats a pretty lengthy process itself indeed), and the lighter ones are too active (and if you realize that their luminosity is much weaker, it means that exoplanets must be much closer to their stars to be in a habitable zone, therefore the flares, eruptions are even more destructive).

    Other thing that is essential for stars to have planets in first place is definitely the abundance of heavier elements, as without them you of course wouldnt have any terrestrial planets (and moons similiar to the Jovian Moons), just gas giants. Pretty much all younger stars, such as our Sun, have them, but of course some systems might not (as that again may depend on many things). Plus, the elements are of course also needed for more complex molecules, hence the life.

    Based on current (theoretical) statistics, in average most (exo)planets are slightly larger than Earth and have orbital periods between 10-400 day, so thats good. (and pretty much every star that lives long enough is very likely to have planets of course)

    About the creation of life/habitability, a liquid water is essential, its basically a catalyst of life creation, because it allows all the various molecules to do a bunch of interesting life, and life may eventually come of it. There are not many other chemical compounds that can do the same, but it seems that methan and ammonia can serve a similar purpose (but less efficiently), so that opens more doors for life... possibly that means life is possible on Titan, despite the crazy low temperatures, we will have to see.

    Well, as you say Flinn, there is insane amount of information, topics and angles that we could discuss (after all, I have been studying it for years, so yea). Though I suppose lets throw in an interesting fresh thing or two from my recent exoplanet course to spark up some discussion.

    Regarding the question, whether our Solar System is unique or just a regular one(therefore, also asking whether life is a regular thing), I find this graph below extremely interesting...




    It shows all known exoplanets (so a few thousands) and our planets together, comparing the planet radius (in earth radius units, so 1 equals the radius of Earth) vs the distance of a planet from its star (in astronomical units, 1 equals a distance of Earth from Sun). So it shows that almost all exoplanets are much closer to their stars (hence mostly not in habitable zones as well of course), apart of other huge implications...

    So, curious what you guys think about it? It apparently seems to deny that our Solar System is a regular system (as based on the graph, our Solar System is completely different than the other ones, and parameters of our planets are not very usual as well, compared to the "mainstream")...


    BTW, to anyone interested in realistic space exploration/astronomy, I would definitely recommend the tv show The Expanse. Except the story, characters, meaning and all the stuff being extremely well done on its own (after all, its (one of) the best tv show(s), period, you are missing out, if you havent seen it yet), the future in it is portrayed so well, one is willing to accept that this is how thing are probably going to look in 200-300 years. Its science is very correct (compared to other sci-fi), the showrunner has a physics PhD after all, all the things we talked about in regards to moving in space are in it (the accel/decel,its effects on human body,..) and so much more other scientifically accurate stuff in it. Itd hard to watch most other sci-fi afterwards, because you see all the physics nonsense in it
    Last edited by Jadli; February 24, 2021 at 01:19 AM.

  4. #24
    Muizer's Avatar member 3519
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    Nice. My personal academic background is in earth science, but I've been reading up a lot on developments in the interdisciplinary field of Astrobiology. For me it's an amazing new angle on my field of study.

    So, what can life on earth tell us about the probability of life elsewhere? Apart from the obvious danger of exptrapolating from a single case, it comes down to two lines of reasoning

    The first one concerns the timeline of life on earth. For instance, one would think that the 'creation of life' would be 'hard' (i.e. an event of extremely low odds of completing). Yet, looking at earth's timeline, we see life emerge 'shortly' (less than half a billion years) after conditions allowed it to survive. So, unless we take into account the possible seeding of life from outside earth (panspermia theory) earth was either very 'lucky' or the odds of abiogenesis happening aren't as low as one might think. Interestingly, from there on it took nearly a billion years for the origin of photosynthesis, 2 billion years for the emergence of eukariotes and 2.8 billion years for multicellular life! (The numbers tend to shift from publication to publication and as research advances, usually pushing dates back, but you get the gist. It seems 'creating life' is 'easy', but getting from that to complex life is 'hard'. From this originates the hypothesis that in the universe single celled life might be common, but complex life very rare.

    The second concerns an inventory of aspects of earth that are thought to be essential, or at least very beneficial for complex life. To name a few:
    - The earth lies within the circumstellar habitable zone, allowing the presence of liquid water at its surface.
    - The sun is bright enough that the CHZ is far enough away that earth did not end up tidally locked.
    - It lies within the galactic habitable zone, necessary for the presence of heavier elements and the absence of frequent destructive events and high radiation levels.
    - It has sufficient mass and magnetic field to retain its atmosphere (unlike Mars)
    - It has a large satellite stabilizing the tilt of its axis, stabilizing climates (again, unlike Mars).
    - It has Plate tectonics, which has been suggested as the mechanism that counters the increasing brightness of its star (around 30% since its origin?) and keeping surface temparatures stable.


    And I am sure there's more (e.g. Jupiter is thought by some to be a factor limiting the likelihood of catastrophic impacts and stabilizing planetary orbits in the solar system). I think astronomers may eventually narrow down what the probabilities are for earthlike planets in the habitable zones. But the formation of our moon may well have been a freak incident and I don't think the circumstances leading to the existence (and therefore the odds of it occurring) of of plate tectonics are fully understood.

    It is an interesting puzzle, but atm it looks like single celled life may be common and complex life vanishingly rare.

    Out of all this, what fascinates me is the early emergence of life. Reasoning form one case is dangerous, and it's certainly possible that life emerged as a chance event from a primordial soup, that there are countless near replicas of earth out there where this just didn't happen. On the other hand, it does not precluded the possibility that this universe is 'rigged' to produce life. That there are abiotic templates or precursors that form as surely and predictably as ice crystals in freezing water.
    Last edited by Muizer; February 24, 2021 at 02:55 AM.
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  5. #25
    Flinn's Avatar Dude of Steel
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    Default Re: The Astronomy Thread

    Fantastic posts all of you

    @ Sept

    That is an intuition and essentially a belief. I do share that intuition in the sense that if we discovered the universe to be full of life, I would not be surprised at all. I too would find the opposite less intuitive, but probabilities and intuition are two very different things in an extreme case such as this. The life on planet Earth could be the most freakish fluke of nature in the entire vast universe, and we cannot estimate the probability of that being the case.
    You have a point here, actually; as a matter of fact I called myself a "believer" and until I'm proved wrong, something that would take centuries probably, I can still be one Let's agree on the fact that it's likely to be proved in the future that universe is full of life, but also that as of today it's just still a speculation.

    @ Jadli

    wow, amazing post, thanks for sharing all those info. Since you asked:

    though Im not sure what do you mean by dwarfs)
    I'm referring to one of the definitions used to classify stars, see the example here, for instance the Sun is classified as a G-Type man sequence star, or a yellow dwarf.

    @ Muizer

    It is an interesting puzzle, but atm it looks like single celled life may be common and complex life vanishingly rare.
    pretty much my position as well
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  6. #26
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    Default Re: The Astronomy Thread

    Iridium in undersea crater confirms asteroid wiped out the dinosaurs

    I'm sure most of you know about the theory that Dinosaurs's extinction has been caused by an asteroid; for those who don't, they can read more here.
    However, this recent discovery seems to confirm beyond doubt that the mass extinction of the Cretaceous–Paleogene (aka K-Pg or K-T) has been caused by the impact of an 11 km C class asteroid, that landed on the surface at the Chicxulub crater with a power of approx 2 millions of megatons (by comparison, the actual estimated power of the assembled US-Russia nuclear arsenal is only around 100.000 Megatons!). The main proof to that is represented by the so called K-Pg or K-T boundary a thin line of Iridium sediments which marks the end of the Cretaceous Period, the last period of the Mesozoic Era, and marks the beginning of the Paleogene Period, the first period of the Cenozoic Era. While an event connected to a massive injection of Iridium in the atmosphere was undoubtedly connected with the extinction of dinosaurs (crystal clear evidence, there are no dinosaurs fossils above the K-T boundary), it was still controversial from where this Iridium came from: as said the mainstream theory, now confirmed, says that it came from an asteroid, since

    Iridium is rare in the Earth’s crust because it is a siderphile, which means that it dissolves in iron and therefore tends to sink into the Earth’s core. Iridium is much more abundant in asteroids, leading Alvarez and colleagues to conclude that the vaporization of an asteroid released large amounts of iridium into the atmosphere, which then fell to the ground as dust
    The opposing theory said that the Iridium was brought to the surface by an unusually long and intense period of active volcanism (over a million of years). The asteroid impact theory, on the other side, says that the extinction period lasted for much less (in the order of a few thousands years), which already seemed to be confirmed by geological observations; furthermore, the impact with a solid C type asteroid of that size would have most probably penetrated into Earth's mantle, thus releasing great amounts of sulfuric dioxide which further contributed to speed up the extinction process. Another supposedly connected event is related to the Deccan Traps: it is highly possible that the Chicxulub impact exacerbated or induced the Deccan volcanism, since the events occur at antipodes and have happened in the same period (65 millions years ago, approx); however, the Deccan eruptions lasted for 30.000 years, perfectly in line with the expected extinction window.

    And as the author of this discovery himself says:

    “We are now at the level of coincidence that geologically doesn’t happen without causation,” says Gulick. “It puts to bed any doubts that the iridium anomaly [in the geologic layer] is not related to the Chicxulub crater.”
    On a related personal note, when I was a lad my father brought me to the Gola del Bottaccione (close to Gubbio, in center Italy, around 30 km from where I grew up)


    This is the very place where Alvarez found the first evidences of the K-T iridium boundary. I remember it made a great effect on the young Flinn, knowing that I was witnessing and touching with my hands the evidence of an event that took place millions and millions of years ago.

    Now...I've always been fascinated, and scared, by the concrete possibility of an astronomical impact on Earth, as a matter of fact it's one of the most probable apocalyptic scenarios, maybe even the most probable one! (at the least of those non-related to humankind actions). It's undoubted that the acknowledgement of the existence of astronomical impact is actually very recent: it was Eugene Shoemaker that demonstrated them beyond doubt in 1963, less than 60 years ago! In all due honesty, I'm expecting to see more events similar to the Chelyabinsk meteor during my life, even though most of those events go unnoticed, due to the fact that they happen in areas far from any civilized settlement.

    According to statistics and observation of the Moon craters, it seems that events similar to that of Chicxulub might happen every 10 million years or so (in this case it is referring to asteroids or comets of 5 km and above); 1 to 5 km every 1 to 10 millions years, with near to 1 km bodies hitting Earth every 500.000 years (in this category the most dangerous one is the 1950 DA asteroid, which in case of impact could cause a planetary disaster, since the expected power is calculated at millions of ordinary modern nuclear bombs). However, even smaller objects, most of which have a yearly incidence, could cause a localized apocalyptic scenario, since many of them have a power similar or above to that of the first nuclear bomb (15 to 30 kilotons) and could destroy any major city in the world.

    An even less predictable treat comes from comets: asteroid are for the most located within the main asteroid belt, between Mars and Jupiter, and even those that have moved towards the internal solar system (such as the 1950 DA mentioned above) originates from there, and thus have a relatively regular orbit that will take them thousands or millions of years before they could actually hit another body (mainly rocky planets). Ecliptic comets originates from the Kuiper belt and the scattered disk and, just like the asteroids, they lie on the ecliptic plane. Isotropic comets, on the other hand, originates from the yet-to-be confirmed Oort Cloud: this means that their orbits are much more elliptic and unpredictable, since they can appear from every direction of the sky, tend to acquire a very high speed when entering the inner solar system and might leave very little time, if at all, to be discovered before they will actually have the chance to impact on the Earth.

    If you want to know more about the NEO (near earth object), the risk of impact and the possible defenses, check the Asteroid impact avoidance page.
    Last edited by Flinn; February 25, 2021 at 09:59 AM.
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  7. #27
    Morticia Iunia Bruti's Avatar Protector Domesticus
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    Default Re: The Astronomy Thread

    There is a third one, that the impact was a comet.

    https://www.nature.com/articles/s41598-021-82320-2
    Last edited by Morticia Iunia Bruti; February 25, 2021 at 02:53 PM.
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  8. #28

    Default Re: The Astronomy Thread

    Quote Originally Posted by Flinn View Post
    I remember it made a great effect on the young Flinn, knowing that I was witnessing and touching with my hands the evidence of an event that took place millions and millions of years ago.
    Great post overall. This is beside the theme of astronomy, but I get that same feeling when witnessing something really old. Like a dinosaur skeleton in a natural history museum (which I tend to seek out whenever visiting a new place) or a really old man-made object in a cultural history museum. I cannot describe it very well, but I get this mind-blowing feeling of time travel when I think that "this was a living and moving being longer ago than I can understand" or "someone made this with their own hands when human societies were completely different". Needless to say, I love museums. A lot.

    Quote Originally Posted by Flinn View Post
    Now...I've always been fascinated, and scared, by the concrete possibility of an astronomical impact on Earth, as a matter of fact it's one of the most probable apocalyptic scenarios, maybe even the most probable one!

    ...

    Isotropic comets, on the other hand, originates from the yet-to-be confirmed Oort Cloud: this means that their orbits are much more elliptic and unpredictable, since they can appear from every direction of the sky, tend to acquire a very high speed when entering the inner solar system and might leave very little time, if at all, to be discovered before they will actually have the chance to impact on the Earth.
    The same. Recently I have been moved to some degree by some experts saying that while we try to observe and keep track of known asteroids and comets native to our solar system and their trajectories, we have very little chance of detecting an actual interstellar object coming towards us. A rock with no albedo to speak of coming straight towards us from outside the solar system would be like a black point of a needle against the black sky. We could have a civilization-ending impact that we would observe only for the brief moment when it hit us. And soon nobody would be observing anything.

    I believe that 'Oumuamua was the first observed interstellar object, and we only caught the first glimpse of it when it was already on its way out of the solar system. I have been following the discussion on that which seems now to center on Harvard's Avi Loeb being more or less convinced that it is a solar sail produced by an alien civilization and everyone else convinced that it must be natural in origin, although we do not know what natural process could have produced it or made it accelerate on its way out.

    I do not have the competence to formulate a personal opinion on the matter, but I would like to ask the experts that if an alien solar sail *did* enter our space, could we tell it apart from 'Oumuamua by any means? As I have stated above, I am a skeptic of interstellar travel and I find it odd that a civilization would have any reason to send a probe or anything like that our way that would take hundreds of thousands of years to get back home. Then again, it could be emitting a signal at the speed of light (like our probes do) and could also be a derelict piece of equipment that has not served a purpose to the sender in a long time. Like our probes will eventually be. Do you guys have any opinion, intuition, or expertise on that?
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  9. #29

    Default Re: The Astronomy Thread

    Quote Originally Posted by Morticia Iunia Bruti View Post
    There is a third one, that the impact was a comet.

    https://www.nature.com/articles/s41598-021-82
    Thank you for the link, Mort, but it seems broken to me.
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  10. #30
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    Default Re: The Astronomy Thread

    Should work now.
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  11. #31
    Flinn's Avatar Dude of Steel
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    Default Re: The Astronomy Thread

    Quote Originally Posted by Morticia Iunia Bruti View Post
    There is a third one, that the impact was a comet.

    https://www.nature.com/articles/s41598-021-82320-2
    Ah yes good point, in fact for long they said it was a comet rather than an asteroid due to the superior speed (and consequent power at the impact) of the former over the latter. As far as I know this was supposed to justify the little chances that an asteroid above 5 km could have hit the Earth (as they are rare) while a similarly sized comet (there are supposedly billions in the Oort cloud of that size), due to the superior speed, should have the same impacting power of a 10/12 km wide asteroid... but this was connected with past understanding of how effective a cometary impact could be: as a matter of fact, due to their iced nature, comets tend to never reach the ground, but to explode in mid air, this because the extremely high heat caused by the attrition of the atmosphere will vaporize the iced gases and create an explosion before the cometary body could reach the ground, but, there are many buts actually

    - it really depends on the size of the body, potentially and iced body of many kilometres, even if exploded in mid atmosphere, could still send many debris to hit the ground
    - the distinction between an asteroid and a comet is purely theoretical, at the least in terms of composition: not all the iced bodies are comets, many are asteroids.. so we can only distinguish them because of their belonging to a specific group of bodies and their orbits (to be straight: asteroids come from the Main belt, comets from the Kuiper belt, scattered disc and Oort cloud)
    - it also depends on which elements compose the body; it is believed that comets are for the most carbonaceous chondritic bodies with an iced shell of water (mainly) or other gases/molecules (nitrogen, carbon dioxide, etc), but this is not an absolute truth, as far as we know
    - asteroids are of 3 main families, but depending on their size they can also have important parts of iced water or gases, which of course would change how they react when entering the atmosphere
    - some asteroids are nothing but "depleted" comets, iced bodies who have orbited for so long in the inner solar system that they have had their iced shell evaporated over billions of years of exposure to Sun radiation

    So I can safely say that we still not know much enough about those bodies to be able to exclude one hypothesis or the other, not a case that some of the most recent missions are aimed at asteroids, not only to look for the presence of possible organic molecules, but in general to better study and understand those bodies. As of today the only probable way to distinguish between the two groups is orbits, and that's actually where the article you linked to is focusing, Morticia

    What we can be sure about the Chixhulub impact is: a body of at the least 10 km reached the ground and it had a high percentage of iridium, the rest is pure speculation IMO
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  12. #32
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    Default Re: The Astronomy Thread

    While i read sometimes popular scientific articles about astronomy, i'm honestly not intelligent (and interested) enough to understand the abstract theories behind it.^^

    Here is a new theory from the University Mainz about Dark Matter and its connection with a fifth dimension, which is probably the reason, why its so difficult to discover Dark Matter.

    https://link.springer.com/article/10...52-021-08851-0
    Last edited by Morticia Iunia Bruti; March 02, 2021 at 08:44 AM.
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  13. #33
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    Default Re: The Astronomy Thread

    yes, sadly I know from where you are coming from

    I'm not a physicist at all, and I had a humanistic formation, and if one lacks the proper knowledge of mathematics, it's nearly impossible to even approach certain theories. It took me years even to understand the basics of the "string theory", and as of today I'm still not good at explaining those basics to someone else. When trying to understand those "new" theories, everything boils down to few points IMO:

    - they are theories: for instance, the string theory is popular, but many of the most important physicists, especially those related to Hawking, do consider it to be excessively complex and a "nightmare".. as such they are subject to revision, reinterpretation and even cancellation.
    - mathematics is the art of the Cosmos, someone said: most of the physics rules have been detailed on paper long before they have been proved on the field; this is very much the case of most of Einstein's theories, but more in general this is widely valid for the Astronomy. Just like any other form of "art", either you have the talent or you don't, just that
    - our perception, and thus the ability to understand certain concepts, changes with the generations. My grandfather would have never understood the concept of atom or molecule, I distinctly remember being 6 when I was told what that was.. in other words, what today is prerogative to few, will one day become a common knowledge (hopefully!)

    Said the above, my point here is that one does not really need to fully get into the quantum mechanics to follow up with the implications of the rules and theories they define: example, you don't really need to know what a light quantum is (aka photon), but knowing that it's maximum speed in the "void" is approx 300.000 km/s, a simple concept, is an important info, as it defines the highest possible speed in the Universe, at the least according to our actual knowledge That's just a crude example, but it illustrates my point I think.
    I myself like to read scientific articles (astronomic ones in particular), and honestly whenever I got blocked with something I don't understand I simply move on.. I'll try to catch the general sense, and if I can't I look for other similar articles that might be easier to be understood.

    However, as I said above in one of the other posts of mine, fully understanding the rules of quantum physics will be essential to "master" the Universe.. I'm pretty sure that what we will discover will be far beyond any actual fiction, it has been always so and will always be so (ask Icarus ).
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  14. #34
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    Default Re: The Astronomy Thread

    Well, seems I kind of havent made the question implied by the graph that I posted clear enough... What I was trying to say by all that:

    Its extremely difficult to observe an exoplanet (we dont actually observe them to be clear, but only how they effect its star, except a few very rare cases... And the effects are.... extremely small) as they are so much smaller and their luminosity is pretty much zero compared to stars. And the system must be orientated in a certain way towards us, to be theoretically even able to observe it. So logically, the most easily detectable exoplanet is as large (large diameter) as possible, and is extremely close to its star (plus the orientation). Its almost impossible to detect Earth-like exoplanet in a distance of 1 au from its star... but if its much closer to its star, it becomes possible (but then its usually hardly in CHB).

    So, again, logically, the methods of detection that we use are able to detect mostly only such exoplanets. Hence, unsurprisingly, what are the most frequent types of exoplanets that we observed? Larger planets than Earth, or even gas giants (some are kinda close to being a brown dwarf, so it would be a kind of multi star system), the so called Hot Jupiters, and those objects are extremely close to their star. Large majority of them closer than even Mercury!

    Our observations creates a huge question then (keep in mind the graph has a logarithmical scale, so the distances of star-exoplanet are much shorter than Sun-Earth). Are we actually observing "regular" stellar systems, or are we observing possibly just some very uncommon peculiarities (galactic freaks I guess )? Those systems we observe are definitely special to some extent. When the first exoplanets were observed, there was lot of disbelief amongst the astrophycists, as large majority of candidates were the gas giants in near proximity to its star. That seemed to oppose the theory of planety creation, as gas giants can be formed only far from stars (the outter systems). In the end, they found out it must have happened due to migration of planets... hence that the gas giants formed far from its star, but then migrated closer (so it actually didnt break the theory). But based on the new theory, it s not very likely that this happens in a system (though its still a very new field), so that again supports the big question about peculiarity.

    So what all this likely means - there is a huge observational bias with exoplanets. Again, based on what we observed, it seems our solar system is not typical at all (not a single exo system is similar to ours, eventhough we have already detected an 8-exoplanet system), which in turn means we shouldnt assume that life as we know it is typical. So.... we actually know nothing of what regular stellar systems looks like? Its possible



    BTW, observational bias of other kinds is not something new in astronomy, there have always been lot of issues with it. Things always work a bit differently than what you observe. For example, it used to be very problematic to determine, how each type/class of stars is abundant (how many hot/huge stars, how many dwarfs, ....), still kinda is. Because the luminosity of an object doesnt increase linearly with stellar parameters (mainly surface temperature and radius), but at much higher dependances (and decrease of brightness vs distance is also not that simple). So at first, it looked like there are relatively many huge (so also hot) stars, but it turned out they are pretty much "just" extreme peculiarities. Because you observe many huge stars, even at large distances, while you dont see any "normal" stars at such distances. The other extreme is that in our relative proximity, we see a lot of red dwarfs (main sequence stars with much smaller mass and luminosity than Sun) and other smaller less luminous objects, while there are no huge stars at all. Again, make sense of it... But yes, by now, the estimates have been narrowed down pretty sufficiently (basically, huge stars are extremely rare, and types of stars like red dwarfs are extremely common)...



    Quote Originally Posted by Flinn View Post
    @ Jadli
    wow, amazing post, thanks for sharing all those info. Since you asked:

    I'm referring to one of the definitions used to classify stars, see the example here, for instance the Sun is classified as a G-Type man sequence star, or a yellow dwarf.
    Well, its just a classification, so everyone can call things however they want, so no big deal. Though I dont like calling Sun-like stars as dwarves... especially when there are so many much smaller objects

    Quote Originally Posted by Muizer View Post
    The second concerns an inventory of aspects of earth that are thought to be essential, or at least very beneficial for complex life. To name a few:
    - The earth lies within the circumstellar habitable zone, allowing the presence of liquid water at its surface.
    - The sun is bright enough that the CHZ is far enough away that earth did not end up tidally locked.
    - It lies within the galactic habitable zone, necessary for the presence of heavier elements and the absence of frequent destructive events and high radiation levels.
    - It has sufficient mass and magnetic field to retain its atmosphere (unlike Mars)
    - It has a large satellite stabilizing the tilt of its axis, stabilizing climates (again, unlike Mars).
    - It has Plate tectonics, which has been suggested as the mechanism that counters the increasing brightness of its star (around 30% since its origin?) and keeping surface temparatures stable.

    - And I am sure there's more (e.g. Jupiter is thought by some to be a factor limiting the likelihood of catastrophic impacts and stabilizing planetary orbits in the solar system).
    Yea, always plenty more... having a large gas giant in the outter system is very important for creation of life for sure, we kindy funnily need it to do two opposing things at different times.

    At early stages of Earth developement ( I mean when its already formed, not when its a just a hot fresh rock), it seems instrumental for life that lot of asteroids and comets were falling down the Earth's well. That has for sure brought the majority of water, and possibly also life (as I said, there are lof pretty complex molecules floating around the space). There is (almost) no water at the beginning, becase terrestrial planets form from the heavier alements, while the light elements are "moved" further from Sun... thats why you have terrestrial planets in the inner system and gas giants in the outter system (and ice gians, Uran and Neptun, in even farther outter system). That we have all the water can be probably largely contributed to Uranus and Neptun switching their places (yes, thats 100% confirmed), which destabilized orbits of almost everything in the outter system. (BTW, not sure if you guys know, but Uranus is kinda the funniest planet. Its axis of rotation is moreless tilted towards Sun, therefore the poles are "looking" at Sun, not its equator. Therefore also its moons are also orbiting very funnily. This was likely caused by the switching with Neptun)

    And then afterwards, we of course need the giants to be stabilized, so the life has all the crazy amount of time, to actually develop without any catastrophics intrference. That is now largely done by our friend Jupiter (and of course his other giants friends to some extent). It probably indeed stabilizes orbits of planets, but mainly it stabilizes all the dwarf planets and asteroids. It locks them in their position/orbits. You can read about Kirkwood Gap to see some part of it, my head kinda hurts when trying to imagine how exactly does all this orbital resonance works



    Quote Originally Posted by Muizer View Post
    I think astronomers may eventually narrow down what the probabilities are for earthlike planets in the habitable zones. But the formation of our moon may well have been a freak incident and I don't think the circumstances leading to the existence (and therefore the odds of it occurring) of of plate tectonics are fully understood.

    It is an interesting puzzle, but atm it looks like single celled life may be common and complex life vanishingly rare.
    Well, its been narrowed down a lot. There are billions of earth-like planets in the habitable zones. But of course, thats just one of the many ingredients necessry for the creation of life.

    Yea, the abundance of basic life vs complex life is kinda same as many other things. The "successful" examples of anything are always much more common than the failure and so on.

    Quote Originally Posted by Septentrionalis View Post
    I believe that 'Oumuamua was the first observed interstellar object, and we only caught the first glimpse of it when it was already on its way out of the solar system. I have been following the discussion on that which seems now to center on Harvard's Avi Loeb being more or less convinced that it is a solar sail produced by an alien civilization and everyone else convinced that it must be natural in origin, although we do not know what natural process could have produced it or made it accelerate on its way out.
    Well, I would just like to point out that interstellar may be kind of a broad term. Because our Sun is not old as the universe, neither it belongs to the first generation of stars that formed. Stars are created in huge cold clouds of matter (diameter in order of thousands or even ten thousands of light years) and many stars form from one cloud.... Thus, they are in a star cluster (they may stay together or kinda dissolve into a stellar association, though you can still find out where they come from). So basically in the beginning each star has been "trading" some of its resources with other stars, and there for sure sure still are some remmants of that on their way between stars, or just scattered around. Basically, Oort Cloud is likely filled with these kinds of objects, lot of them are surely interstellar.

    I would say Oumuamua is special because it is a "newcommer" . Once we get proper probes to Kuiper Belt/Oort Cloud, we will able to examine many such objects closely.

    Well, you cant rule out that it isnt of alien origin, it could be (even the humanity might be ) but likely it isnt. There are lot of objects of crazy velocities and trajectories that are of much a larger mass. There are even whole stars (hence also solar systems) that are kinda doing stuff like this on galactic scale.... Due to the gravitational forces and all that (as they sometimes also have a sense of humour) stars rarely can be pretty much shot out from their assocciations/cluster, and they are just flying somewhere away, might even leave a galaxy.

    Though, even if it wasnt an alien artifact, it could hypothetically carry very interesting materials/molecules or some basic biologials elemebts, so it would have been extremely interesting to look into it, one way or another (I suppose it would have been easier to study this object, then similar Oorts Clouds, as its way too far... so shame we werent able to look into its inside)

    Quote Originally Posted by Septentrionalis View Post
    I do not have the competence to formulate a personal opinion on the matter, but I would like to ask the experts that if an alien solar sail *did* enter our space, could we tell it apart from 'Oumuamua by any means? As I have stated above, I am a skeptic of interstellar travel and I find it odd that a civilization would have any reason to send a probe or anything like that our way that would take hundreds of thousands of years to get back home. Then again, it could be emitting a signal at the speed of light (like our probes do) and could also be a derelict piece of equipment that has not served a purpose to the sender in a long time. Like our probes will eventually be. Do you guys have any opinion, intuition, or expertise on that?
    Well, I mean, if they made a ship, we would of course eventually see its weird shape and so on. But using asteroids that you put on crazy trajectories and velocities (via various gravitational effects and forces) might be perhaps more effective than any engine. So I mean, using asteroids for some kind of travel might be a thing... The rocks are kinda the same all over the galaxy/universe, so you probably wouldnt see anything special about it. Though, I assume if it was an alien probe, there would be various weird signals and temperatures and all this kind of stuff.

    It cant be emitting at the speed of light, but I suppose closer to speed of light (anyway we would prob notice). Such an object surely cant return to them , so I think this would make sense only if something was on it, that would stay here I suppose. BTW, Phoebe (Saturn's moon) is also an interesting object, its from Oort Cloud (so possibly even farther). (In The Expanse, there was actually something similar with Phoebe as with Oumuamua... It was sent from elsewhere, carrying lot of nasty things that were meant to arrive at Earth... but Saturn saved us by catching it)

    Quote Originally Posted by Flinn View Post
    Ah yes good point, in fact for long they said it was a comet rather than an asteroid due to the superior speed (and consequent power at the impact) of the former over the latter. As far as I know this was supposed to justify the little chances that an asteroid above 5 km could have hit the Earth (as they are rare) while a similarly sized comet (there are supposedly billions in the Oort cloud of that size), due to the superior speed, should have the same impacting power of a 10/12 km wide asteroid... but this was connected with past understanding of how effective a cometary impact could be: as a matter of fact, due to their iced nature, comets tend to never reach the ground, but to explode in mid air, this because the extremely high heat caused by the attrition of the atmosphere will vaporize the iced gases and create an explosion before the cometary body could reach the ground, but, there are many buts actually
    Yea, for asteroid to not burn in atmosphere it must have over cca 60-80 meter diameter (ofc depends on lot of other things as well, such as an angle). They are kinda small if you think about it, but do a huge damage due to their insane velocities... and hence they have insane kinetic energy when they crash

    Quote Originally Posted by Flinn View Post
    yes, sadly I know from where you are coming from

    I'm not a physicist at all, and I had a humanistic formation, and if one lacks the proper knowledge of mathematics, it's nearly impossible to even approach certain theories. It took me years even to understand the basics of the "string theory", and as of today I'm still not good at explaining those basics to someone else. When trying to understand those "new" theories, everything boils down to few points
    Yea, its kinda easier for a laic to understand stuff like string theory than as a scientist to be honest . Cause you are presented a seemingly finished summarized product written in a way that is easy to understand it. When you are actually looking at this kind of stuff as a scientist/physicts, hence you are looking at all the crazy equations, competing sub theories and so on, its kinda harder...


    PS

    I assume that the next big step in astronomy might be an observation of an exomoon (a moon of an exoplanet). Assuming the moon is large enough compared to the exoplanet, there is kinda nothing stopping the current methods from detecting it, except that its even harder... There are already several candidates... but confirming them will be hard
    Last edited by Jadli; March 03, 2021 at 12:39 PM.

  15. #35
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    Default Re: The Astronomy Thread

    Quote Originally Posted by Morticia Iunia Bruti View Post
    While i read sometimes popular scientific articles about astronomy, i'm honestly not intelligent (and interested) enough to understand the abstract theories behind it.^^

    Here is a new theory from the University Mainz about Dark Matter and its connection with a fifth dimension, which is probably the reason, why its so difficult to discover Dark Matter.

    https://link.springer.com/article/10...52-021-08851-0
    Quote Originally Posted by Flinn View Post
    yes, sadly I know from where you are coming from

    I'm not a physicist at all, and I had a humanistic formation, and if one lacks the proper knowledge of mathematics, it's nearly impossible to even approach certain theories. It took me years even to understand the basics of the "string theory", and as of today I'm still not good at explaining those basics to someone else. When trying to understand those "new" theories, everything boils down to few points IMO:

    - they are theories: for instance, the string theory is popular, but many of the most important physicists, especially those related to Hawking, do consider it to be excessively complex and a "nightmare".. as such they are subject to revision, reinterpretation and even cancellation.
    - mathematics is the art of the Cosmos, someone said: most of the physics rules have been detailed on paper long before they have been proved on the field; this is very much the case of most of Einstein's theories, but more in general this is widely valid for the Astronomy. Just like any other form of "art", either you have the talent or you don't, just that
    - our perception, and thus the ability to understand certain concepts, changes with the generations. My grandfather would have never understood the concept of atom or molecule, I distinctly remember being 6 when I was told what that was.. in other words, what today is prerogative to few, will one day become a common knowledge (hopefully!)

    Said the above, my point here is that one does not really need to fully get into the quantum mechanics to follow up with the implications of the rules and theories they define: example, you don't really need to know what a light quantum is (aka photon), but knowing that it's maximum speed in the "void" is approx 300.000 km/s, a simple concept, is an important info, as it defines the highest possible speed in the Universe, at the least according to our actual knowledge That's just a crude example, but it illustrates my point I think.
    I myself like to read scientific articles (astronomic ones in particular), and honestly whenever I got blocked with something I don't understand I simply move on.. I'll try to catch the general sense, and if I can't I look for other similar articles that might be easier to be understood.

    However, as I said above in one of the other posts of mine, fully understanding the rules of quantum physics will be essential to "master" the Universe.. I'm pretty sure that what we will discover will be far beyond any actual fiction, it has been always so and will always be so (ask Icarus ).
    To put this in perspective: I studied both differential geometry and relativity/cosmology for several years and that paper you linked, Morticia, is way beyond me. I even daresay that none of us is too stupid to understand it, it's just that scientific fields behave fractally: They become more and more specialised and if you are not familiar with the standard tools, notions and abbreviations of the sub-sub-sub-field at hand you have no hope of understanding their papers. Even seemingly familiar words can obtain completely different meanings in scientific language, like the word "bulk" in the linked article. Everyone knows the meaning of it in ordinary English but it almost certainly has a specific meaning in the way they use it.

    Quote Originally Posted by Jadli View Post
    Epic snip
    The point about the observational bias in exoplanets and the possible extra-ordinarity of the Solar System is interesting. On the one hand it is not hard to argue that given the complexity of life as we observe it on earth it is not unexpected that our planetary setup be quite out of the ordinary. On the other hand there is such a huge amount of matter and energy (and dark matter we are somehow failing to observe properly) in the universe, which is even expanding all the time, that it seems quite unlikely we are unique in our situation. I guess it is really a question we can never really answer satisfactorily due to our many observational biases and due to the fact that the probability of us existing has collapsed to 1, so we cannot properly calculate any reasonable expectation value of intelligent life existing. (Apart from the fact that other forms of "intelligent life" may well be entirely beyond what we can even conceptualise.) It really is a pity we already existed when we first observed ourselves (Best wishes from the weak anthropic principle!)
    Last edited by Iskar; March 04, 2021 at 05:20 PM.
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    Default Re: The Astronomy Thread

    Quote Originally Posted by Jadli View Post
    Well, I would just like to point out that interstellar may be kind of a broad term. [...] I would say Oumuamua is special because it is a "newcommer" . Once we get proper probes to Kuiper Belt/Oort Cloud, we will able to examine many such objects closely.
    I apologize if my meaning was not clear within its context, but Oumuamua was, I have been told, the first object that we have observed having come from outside our solar system.

    Quote Originally Posted by Jadli View Post
    Well, I mean, if they made a ship, we would of course eventually see its weird shape and so on. [...] Though, I assume if it was an alien probe, there would be various weird signals and temperatures and all this kind of stuff.
    Have you done any reading on Oumuamua or the debate concerning its origin? One of the main arguments for its artificial nature is its elongated shape that is unlike anything we have seen so far. Also, it was witnessed speeding up when moving away from the sun (where it should have been slowing down), and there was no gas emission that could explain such push. Further, its brightness was varying to a great degree (tenfold) on a steady interval. All that is what lead Avi Loeb to speculate that the object may be a very thin light sail.

    Quote Originally Posted by Jadli View Post
    It cant be emitting at the speed of light, but I suppose closer to speed of light (anyway we would prob notice).
    What do you mean? All of our communications with our own probes happen practically at the speed of light. If it's 4.2 light years to Alpha Centauri, 4.2 years is approximately how long it takes to send a transmission there.
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    Default Re: The Astronomy Thread

    Quote Originally Posted by PointOfViewGun View Post
    For manned missions, I think the limitation is not the speed but acceleration. The human body can not endure higher than Earth's gravity acceleration for a prolonged time. We can withstand 5gs commonly for a brief of time though pilots can go up to 9gs. For a journey to be manageable though you're pretty much limited to simulating Earth's gravity. At 9.8 m/s it would take about a year to reach the speed of light (ignoring the limitations with reaching the speed of light of course). At that point you traveled about 4 light years.

    Alpha Centauri is 4,367 light years away. Speeding up till the half way and then speeding down the other half with 9.8 m/s, it takes about 65 years to get to Proxima Centauri b.

    Without some kind of science fictionesque travel method it's quite hard to go anywhere meaningful.
    Taking a year to accelerate to the speed of light on a trip that would take at least 4 years anyways is not a problem, so an acceleration of 1g is perfectly adequate if you could maintain it.

    And you might be able to sustain higher g for long durations if the humans were in some kind of suspended animation, I don't think that has been analyzed. The ship could be automatically guided during the high g acceleration.

    But no matter how you reach the speed of light, it will take enormous amounts of energy and reaction mass to do so. Even an extended 1 G acceleration is beyond our current technology.

    The nuclear pulse propulsion designs like Project Daedalus might be able to reach up to a few percentage of the speed of light. The nuclear pulse propulsion and the nuclear salt-water rocket seem within our near tetm technical capability.

    So acceleration I don't see tas the problem, getting to speeds near that of light is.

  18. #38
    Jadli's Avatar The Fallen God
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    Default Re: The Astronomy Thread

    Quote Originally Posted by Iskar View Post
    The point about the observational bias in exoplanets and the possible extra-ordinarity of the Solar System is interesting. On the one hand it is not hard to argue that given the complexity of life as we observe it on earth it is not unexpected that our planetary setup be quite out of the ordinary. On the other hand there is such a huge amount of matter and energy (and dark matter we are somehow failing to observe properly) in the universe, which is even expanding all the time, that it seems quite unlikely we are unique in our situation. I guess it is really a question we can never really answer satisfactorily due to our many observational biases and due to the fact that the probability of us existing has collapsed to 1, so we cannot properly calculate any reasonable expectation value of intelligent life existing. (Apart from the fact that other forms of "intelligent life" may well be entirely beyond what we can even conceptualise.) It really is a pity we already existed when we first observed ourselves (Best wishes from the weak anthropic principle!)
    Indeed

    Yea, as I said, Im 99,99% positive that that we, and the life in general, is not special at all. Just kind of like to explore other angles, to point out that ppl who want to deny it, definitely have lot of hard data at their disposal.

    Anyway, the meme brings up an interesting paradox about life



    Quote Originally Posted by Septentrionalis View Post
    I apologize if my meaning was not clear within its context, but Oumuamua was, I have been told, the first object that we have observed having come from outside our solar system.

    Have you done any reading on Oumuamua or the debate concerning its origin? One of the main arguments for its artificial nature is its elongated shape that is unlike anything we have seen so far. Also, it was witnessed speeding up when moving away from the sun (where it should have been slowing down), and there was no gas emission that could explain such push. Further, its brightness was varying to a great degree (tenfold) on a steady interval. All that is what lead Avi Loeb to speculate that the object may be a very thin light sail.

    What do you mean? All of our communications with our own probes happen practically at the speed of light. If it's 4.2 light years to Alpha Centauri, 4.2 years is approximately how long it takes to send a transmission there.
    Well, What I tried to say may have sound kind of confusing, because in my posts I usually go from one stance on the matter to another, often opposing myself in the same post...

    Yea, I dont object what you say, just was offering some other ways to look at it. Its definitely one of the most exotic things we had the opportunity to see in our Solar System. Though, didnt know it was speeding up when leaving Sun, will check that out... perhaps graviational forces...

    About the speed of information, I was kind of being hyper precise ... yea, its definitely close to it, but I would expect that on distances in orders of light years even the minor discrepancy could create considerable delays. Unless of course the only information you require is to see the rock, which of course happens at the speed of light

    Quote Originally Posted by Common Soldier View Post
    Taking a year to accelerate to the speed of light on a trip that would take at least 4 years anyways is not a problem, so an acceleration of 1g is perfectly adequate if you could maintain it.

    And you might be able to sustain higher g for long durations if the humans were in some kind of suspended animation, I don't think that has been analyzed. The ship could be automatically guided during the high g acceleration.

    But no matter how you reach the speed of light, it will take enormous amounts of energy and reaction mass to do so. Even an extended 1 G acceleration is beyond our current technology.

    The nuclear pulse propulsion designs like Project Daedalus might be able to reach up to a few percentage of the speed of light. The nuclear pulse propulsion and the nuclear salt-water rocket seem within our near tetm technical capability.

    So acceleration I don't see tas the problem, getting to speeds near that of light is.
    Acceleration is how you get to the speed of light, hence that is the problem I would say, but yea, indeed. The issue is kind of a paradox. To accelerate, you need to move your own mass, your ship. To accelerate it you need fuel, but when you add the fuel, you also need more energy/fuel to move it. Hence even with the technology of future, it is still very questionable, not even talking of the mass limit and all the funky relativistic effects.

    Would likely be a one way trip though, at least for the pioneers... because if you think about it, reaching the speed of light is one thing, but getting back is whole another level of craziness. You would need some amount of fuel to reach the speed of the light, but if you wanted to get back, you would need 4 time more fuel. Because once you reach the speed of light, you will need to turn your ship and deccelerate to "stop accelerating", that will require the same amount of fuel. And then you need to speed up to the speed of light again, heading home, and then deccelerate again to park at Earth...

    Anyway, one more astro meme into the fray

    Last edited by Jadli; March 16, 2021 at 04:09 PM.

  19. #39
    Morticia Iunia Bruti's Avatar Protector Domesticus
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    Default Re: The Astronomy Thread

    A new theory about the possibility of breaking the Warp Barrier:

    https://iopscience.iop.org/article/1...61-6382/abe692
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  20. #40
    Flinn's Avatar Dude of Steel
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    Default Re: The Astronomy Thread

    Since it was mentioned here, I guess it makes sense to share these videos about Ingenuity's first flight

    From Perseverance


    onboard camera
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