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Mass Extinction and the Structure of the Milky Way (2013)
- DrScump 10y agoAbstract: "We use the most up to date Milky Way model and solar orbit data in order to test the hypothesis that the Sun's galactic spiral arm crossings cause mass extinction events on Earth. To do this, we created a new model of the Milky Way's spiral arms by combining a large quantity of data from several surveys. We then combined this model with a recently derived solution for the solar orbit to determine the timing of the Sun's historical passages through the Galaxy's spiral arms. Our new model was designed with a symmetrical appearance, with the major alteration being the addition of a spur at the far side of the Galaxy. A correlation was found between the times at which the Sun crosses the spiral arms and six known mass extinction events. Furthermore, we identify five additional historical mass extinction events that might be explained by the motion of the Sun around our Galaxy. These five additional significant drops in marine genera that we find include significant reductions in diversity at 415, 322, 300, 145 and 33 Myr ago. Our simulations indicate that the Sun has spent ~60% of its time passing through our Galaxy's various spiral arms. Also, we briefly discuss and combine previous work on the Galactic Habitable Zone with the new Milky Way model." TL;DR: our Sun's bumpy orbit through the spiral arms of out galaxy means periodic increases of comets and other bodies being jarred loose and later hitting Earth, resulting in mass extinctions. The full paper is a free download from this page.
- PhasmaFelis 10y ago...Huh. I always assumed that most stars kept approximately the same position relative to the rest of the galaxy. (Barring "up/down" oscillation if the orbital plane isn't perfectly aligned with the galaxy's.) There must be some kind of overall structure to maintain distinct spiral arms, right? Does the Solar System actually make a complete circuit of the bulk of the Milky Way? Is that unusual?
- rtkwe 10y agoThe Spiral arms aren't really cohesive bunches of stars but just bunches of relatively new stars that burn brighter than the older stars outside the spiral arms. http://www.space.com/24642-spiral-galaxies-milky-way-shape-explained.html http://www.space.com/24642-spiral-galaxies-milky-way-shape-e...
- Keysh 10y agoNo, in many spiral galaxies the spiral arms are present in older stars as well; that's why they're considered density waves in the stars. The contrast is stronger for younger stars, but it's there in old stars, too.
- gizmo686 10y ago>I always assumed that most stars kept approximately the same position relative to the rest of the galaxy. That was the original assumption. However, basic [0] orbital mechanics says that objects with smaller orbits orbit faster. If this were applied to the galaxies spiral arms, then as they continue to orbit, the inside ones would orbit faster than the outside ones, and the galaxy would become increasingly spirally. By this point, the galaxy would be so tightly wound that we would not even be able to see the spiral any more. A more modern hypothesis is that the arms are more like waves of high density. Individual stars move through the the arm. Since this high density region exerts gravity, stars that are moving out of it are slowed down, and stars that are moving into it are sped up. The end result is that orbiting stars tend to spend a little bit more time in the arm region then they would under a pure orbit. In doing so, they contribute to the mass of the arm, causing other stars to also spend more time in the arm then they otherwise would. The end result is a stable wave as all the individual stars move into and out of it throughout their orbits. https://en.wikipedia.org/wiki/Density_wave_theory https://en.wikipedia.org/wiki/Density_wave_theory [0] As in, just applying Newtonian gravity.
- mirimir 10y agoRight, density waves. But as rtkwe and the Wikipedia article note, there's also increased star formation in the higher-density arms. So more stuff hitting Earth also seems plausible.
- LoSboccacc 10y agoa visualization of the current model orbital path http://m.imgur.com/Eup0Yoa http://m.imgur.com/Eup0Yoa
- PhantomGremlin 10y agoIt's hard to be sure. But observing both the Wiki animation and this GIF, it appears that stars don't orbit at a constant radius from the galactic center. Rather, they appear to move significantly closer and further. Does that seem right? If so, that's much different than planets orbiting our solar system. To a first approximation our orbits appear circular. Yes I know there's a certain eccentricity but for most planets it's not much. I don't like the idea of our solar system getting too close to the galactic center. It gives me a vague sense of dread, like "bad things can happen there".
- jamestnz 10y agoThe spiral arms are not fixed masses. If they were, they would quickly wind themselves up tighter and tighter, as the inner areas are orbiting faster than the outer parts. Within a short time the spiral arms would be dispersed. Instead, you can think of the spiral arms as being like the highest-density part of a traffic jam. In a traffic jam, cars are slowing down and bunching onto the back of the queue, while other cars are finally trickling off the front of the queue and speeding back up. In this way the traffic jam itself stays in a stable position, while individual cars constantly move through it. In other words, it isn't the same stars that make up the spiral arms over time. As stars orbit the galactic center, they move in and out of the spiral arms.
- colechristensen 10y agoPut a different way, a galaxy's spiral arms are like waves.
- anentropic 10y agoMind == blown
- cema 10y agoA good explanation. I think one detail may be corrected: a traffic jam typically goes backwards, with respect to the direction of the cars forming the jam, at a speed much slower than the speed of the traffic. Perhaps a similar behavior is observed with the galactic arms?
- DrScump 10y agoThe author explains it pretty well in the Batchelor interview: https://audioboom.com/posts/4827661-mass-extinction-and-the-structure-of-the-milky-way-joint-horner?t=0 https://audioboom.com/posts/4827661-mass-extinction-and-the-...
- flukus 10y ago> TL;DR: our Sun's bumpy orbit through the spiral arms of out galaxy means periodic increases of comets and other bodies being jarred loose and later hitting Earth, resulting in mass extinctions. Isn't only one of the mass extinctions (the dinosaur ending one) somewhat tightly linked to a comet impact? It seems as though it's finding a pattern that does no fit the data.
- metaobject 10y agoI believe a few of the mass extinctions are thought to have been caused by gamma ray bursts (GRBs) that were close enough to earth to either affect the atmosphere or the orgamisms on the surface.
- mcv 10y agoAre the causes of other mass extinctions known? I can imagine comet impacts can be hard to trace over billions of years. Especially when it's not just a single big one, but a period of increased impacts. Also, I believe the dinosaur extinction was not just a comet impact, but a combination of an impact and a period of increased volcanic activity. Could the volcanic activity be triggered by comets? I think the jury is still out, but it's an interesting field of study across many different fields (astronomy, biology, geology and probably more), and it has obvious implications for humanity's future on Earth, in space, and the chances of finding other life out there.
- flukus 10y ago> Could the volcanic activity be triggered by comets? That's an interesting question. My completely unqualified opinion would be no, an comet couldn't trigger the massive and ongoing volcanic activity that a mass extinction requires. I'd like to hear from someone more informed though.
- cifvts 10y agoCould a big enough comet impact cause the Earth behave like a liquid and therefore a wave destabilize the crust and increase volcanic events?
- steinystein 10y agoFull text: https://arxiv.org/pdf/1309.4838.pdf https://arxiv.org/pdf/1309.4838.pdf With what reasoning or evidence do they propose their new model of the galaxy? Is it: - extinction events, therefore new model or - astronomical data, therefor new model, and look how nicely it correlates with known extinction events
- T-A 10y agoA bit of both. They say that with the model depicted in Fig 1, based on Spitzer/GLIMPSE surveys [1], nine of eleven extinction events which they identify (the six "canonical" ones plus five other significant drops in marine biodiversity, Section 2.2) occurred while the solar system was passing through a spiral arm (Section 3). They then point out that it's easy enough to modify the model to fit all eleven events: we can't see what's on the other side of the galaxy, so we can hypothesize a "spur" there, similar to the Orion spur on our side, with some support for that idea coming from the symmetry of other galaxies. But even without such modifications, nine out of eleven is not bad. Spiral arms need not necessarily explain every single one of them. [1] http://inspirehep.net/record/817646?ln=en http://inspirehep.net/record/817646?ln=en
- steinystein 10y agoGreat summary. Thank you.
- fizixer 10y agoAs a non-astronomer, I hadn't thought of that but now that I read the abstract, it makes complete sense (assuming evidence supports the thesis) - Might be related to why moon's surface is so scarred and yet in many centuries of recorded (astronomical) history (since the invention of telescope) we haven't seen any major lunar impact events. - Also I was reading the other day how our solar system is going through a local "bubble" (region of unusually low interstellar density) but is heading towards a certain G-Cloud. Mind blowing stuff. I guess once we have fixed the planetary mess (climate change) and biological-aging, we'd have a serious type-I [2] problem to worry about (and we can't even handle/track the inner solar system objects yet, NEO, asteroids, etc). [1] https://en.wikipedia.org/wiki/Solar_System#Galactic_context https://en.wikipedia.org/wiki/Solar_System#Galactic_context [2] https://en.wikipedia.org/wiki/Kardashev_scale https://en.wikipedia.org/wiki/Kardashev_scale
- bamboozled 10y agoWhat needs to be fixed about biological aging exactly?
- fizixer 10y agoEhh ... it needs to be eliminated? [1] [1] https://en.wikipedia.org/wiki/Life_extension https://en.wikipedia.org/wiki/Life_extension
- mirimir 10y agoThe Great Common Task :) > Fedorov stated that the struggle against death can become the most natural cause uniting all people of Earth, regardless of their nationality, race, citizenship or wealth (he called this the Common Cause). https://en.wikipedia.org/wiki/Nikolai_Fyodorovich_Fyodorov https://en.wikipedia.org/wiki/Nikolai_Fyodorovich_Fyodorov
- bamboozled 10y agoOh right, that's going to make fixing climate change nearly impossible isn't it? It would make the population boom of the last century and associated wide-spread destruction of the natural environment look like a picnic. I guess if your able to upload your consciousness into a computer or some other some Transhuman fantasy like that it would probably be a much better outcome for the natural world and everyone left in the realm of mortals.
- Gargoyle 10y agoHmmm. If this hypothesis held up, you'd want to factor it into the Drake Equation. Number of systems that didn't cross some threshold of intensity or frequency of arm crossing events that could cause mass extinctions often enough to make intelligent life impossible to develop. Or something like that.
- d4nt 10y agoI suppose it's possible that just the right amount of mass extinction events are necessary for intelligent life to emerge. Too many and evolution doesn't build up any momentum, too little and there isn't enough change to make intelligence (i.e. adaptability) worth having. So the Drake equation would need to be looking for that Goldilocks zone of mass extinctions.
- flukus 10y agoIsn't the reverse just as likely, that many potential paths to intelligence were snuffed out by extinction events. The currently accepted theory is that it the evolutionary pressure of climate change was enough for us to evolve intelligence.
- baking 10y agoI think that humans as a species are more likely to survive a mass extinction event (even if 99% of the population is killed) through manipulation of their environment, stored food, eating rodents, insects and fish, and the cooperation of communities for having babies and raising children. Therefore, mass extinctions might serve as a winnowing out of dominant species that can't adapt to major changes. Of course the adaptability of humans has not yet been tested in that way (unless you count the recent ice age.) Also there is the whole "multi-planetary species" option.
- deleted 10y ago[deleted]
- ryan-allen 10y agoI wonder when we're due for another crossing?
- codeulike 10y agoSo how long till next arm?
- blauditore 10y agoI don't know where we stand now, but there are two arms and a galactic year is ~250 million terrestrial years, so I'd say a priori on average ~250/2/2 = ~60 million years from now.
- fastball 10y agoProbably better to take the average of the last known extinction events and extrapolate from there. Average time between events: 96 Myr. Time since last event: 33 Myr. Time to next event: 63 Myr. Wow, surprisingly close to your method. Pack up your bags boys, we're gonna get extincted in 60 million years.
- vorg 10y agoThere are two thick arms, and two thin ones in the picture, as well as a spur (the Orion Spur in which our Sun presently dwells). The article postulates the existence of a second spur on the far side of the galaxy where we can't see, based on the history of extinction events in the past 250 million years and the observed symmetry of many other spiral galaxies.
- mkempe 10y agoThere are two danger periods: passing through the galactic plane (duration 100k years every 35Myr) and passing through the galactic arms (duration 10Myr every 120Myr). The article only discusses passage through the arms. We're currently moving away from the galactic plane, which our solar system last crossed 3Myr ago. According to the article there are 11 extinction events spread across the last 500Myr, which corresponds to two orbits of our solar system around the galaxy but one traversal through the arms and spur (they're also orbiting, more slowly). Right now we're in the Orion Spur; the authors seem to attribute an extinction phase near the last exit from this spur; the spur is 1 kly across, so I estimate our solar system takes 3 Myr to transit the width of the spur. I think our next destination is the Perseus Arm, 6.5 kly away, so we should reach it in about 20 Myr.
- DrScump 10y agoHere's an excellent interview of Jonti Horner by John Batchelor on this topic (free podcast): https://audioboom.com/posts/4827661-mass-extinction-and-the-structure-of-the-milky-way-joint-horner?t=0 https://audioboom.com/posts/4827661-mass-extinction-and-the-...
- Sukotto 10y agoNeat coincidence to see this on the front page today. On the train this morning I was re-reading David Brin's "The Deadly Thing at 2.4 Kiloparsecs". His 1984 article examining Earth's fairly regular mass extinctions and what might be causing them. As a new forward to the story, Brin mentions the OP-linked theory. Imho, the article still holds up well and you can read it here: http://davidbrin.blogspot.jp/2015/07/the-deadly-thing-at-24-kiloparsecs-are.html http://davidbrin.blogspot.jp/2015/07/the-deadly-thing-at-24-...
- Cozumel 10y agoThere's interesting parallels with the Hindu Yugas here. https://www.thoughtco.com/the-four-yugas-or-epochs-1770051 https://www.thoughtco.com/the-four-yugas-or-epochs-1770051
- averagewall 10y agoIt might be interesting if the people who invented the Yugas could have had any awareness of mass extinctions and the structure and behavior of the galaxy. Since they surely didn't, there's obviously no connection at all and it's not interesting - just made up myths.
- TheREALDonald 10y agoCozumel, I think you should get a pet. Then, whenever you feel like posting some esoteric rubbish, you just go pet your furry buddy instead. We win. Pet wins. Maybe you win.
- antonmks 10y ago"significant reductions in diversity at 415, 322, 300, 145 and 33 Myr ago" - it seems that periods between extinctions events are so large that you can easily fit there hundreds and even thousands of civilizations like ours. So not much to worry about, we will have plenty of opportunities to kill ourselves before a comet does us in.
- dghughes 10y agoI'm not a math wizard but going by that pattern it seems the periods are getting shorter. I tried to find a sequence https://www.wolframalpha.com/input/?i=415,+322,+300,+145,+33,+.. https://www.wolframalpha.com/input/?i=415,+322,+300,+145,+33....
- marcosdumay 10y agoMy bet is that is because of observation biases. We don't know a lot about distant past, and may have lost some events that we'd call great extinctions if they were recent.
- mrec 10y agoThe periods (intervals between events) there would be [93, 22, 155, 112] My. That doesn't look like they're getting shorter.
- swamp40 10y agoBut they are getting closer! :)
- edem 10y agoI'm a bit puzzled here. I thought the arms themselves were moving around the galactic core. What does the Sun pass then? Little hint?
- rusanu 10y agoApparently they're rather static: https://en.wikipedia.org/wiki/Density_wave_theory https://en.wikipedia.org/wiki/Density_wave_theory
- brutuscat 10y agoOriginally, astronomers had the idea that the arms of a spiral galaxy were material. However, if this were the case, then the arms would become more and more tightly wound, since the matter nearer to the center of the galaxy rotates faster than the matter at the edge of the galaxy. The arms would become indistinguishable from the rest of the galaxy after only a few orbits. This is called the winding problem. Lin and Shu proposed in 1964 that the arms were not material in nature, but instead made up of areas of greater density, similar to a traffic jam on a highway.[3] The cars move through the traffic jam: the density of cars increases in the middle of it. The traffic jam itself, however, does not move (or not a great deal, in comparison to the cars). In the galaxy, stars, gas, dust, and other components move through the density waves, are compressed, and then move out of them.
- nabla9 10y agoSpiral arms are density waves. They move at different velocity than stars that make up the arm. http://i.imgur.com/dtb8WrD.gifv http://i.imgur.com/dtb8WrD.gifv
- ptr_void 10y agoIs this supposed to be some sort of academic joke? Reminds me of http://tylervigen.com/old-version.html http://tylervigen.com/old-version.html Maybe this isn't, sometimes science do work in strange ways.
- nthcolumn 10y agoNot so goldilocksie after all
- vanderZwan 10y agoWasn't this theory part of the inspiration of the story arc for the Mass Effect games?
- spenrose 10y agoMaybe update the title to say (2013)?
- jmeyers44 10y agoThis is eerily similar to the plot of The Three-Body Problem[1], specifically the cyclical development of intelligent life and its race to avoid mass extinction caused by intersecting one of three suns in its stellar system. [1]https://en.wikipedia.org/wiki/The_Three-Body_Problem https://en.wikipedia.org/wiki/The_Three-Body_Problem
- perseusprime11 10y agoI heard this is a great book but could not get into this book. I was listening to an audio book. Maybe I should try a physical book next time.
- jmeyers44 10y agoHighly recommend (I read the physical book). It picks up after the first 100 pages or so.
- exhilaration 10y agoThe audiobook worked for me but I do admit it's written in a very different style than most western sci-fi novels.
- perseusprime11 10y agoOne of the reasons why we need to find a way to get to Mars and other places where humans can thrive. If we were the only wonder in the world, imagine the travesty of getting wiped out.
- avz 10y agoHow would Mars help? Mars, like Earth, is on a tight (1.6 AU) gravitational leash of the Sun. When the Sun dives into one of the galactic arms, so do Mars and Earth. That said, interplanetary travel is probably something we need to get good at before we try the interstellar kind, so in a way, Mars settlement brings us a tiny bit closer to galactic safety.
- yourapostasy 10y agoIf I'm reading that paper correctly, then we need more than interstellar capability, we need near-intergalactic capabilities. We would have to be solidly past a Kardashev Type II and almost attaining a Type III classification, to either move our own solar system, or establish habitats in safer galactic zones outside the arms (like outside the galactic poles or positioned above the arms). Perhaps these transitions is the Fermi Paradox's Great Filter: might it be exceedingly difficult for a civilization to hit the Kardashev Type II-III level and implement the necessary avoidance/mitigation sufficiently fast enough?
- legolas2412 10y agoFrom Wikipedia entry on milky way, "These oscillations were until recently thought to coincide with mass lifeform extinction periods on Earth.[148] However, a reanalysis of the effects of the Sun's transit through the spiral structure based on CO data has failed to find a correlation.[149]". Those papers are from 2008 and 2009. Is this paper proposing something different?
- cheez 10y agoThis isn't new. I remember reading about this years ago. I suppose the new contribution is offering an actual model to do this.
- llccbb 10y agoInterested parties should also look at the work of Dr. Adrian Melott[0]. [0] https://scholar.google.com/citations?user=GWB114EAAAAJ&hl=en&oi=ao https://scholar.google.com/citations?user=GWB114EAAAAJ&hl=en...
- ucontrol 10y agoOh shut up. The number of people that keep living in denial and rationalization of their sub-optimal circumstance astounds me. Just face it and be honest. There is nothing noble in being a 50 year old for an infinity given the option to be youthful and mentally/physically fit instead. Vanity, superficiality, shallowness... All these buzzwords that criticize something that is perfectly natural to desire, in an effort to signal some higher moral ground. Come on.
- milquetoastaf 10y agoYea I am signalling the moral high ground because HN is full of fucking sociopaths who want to live forever so they can execute their dumb ass startup until the heat death of the universe or learn new languages - at the expense of completely fucking up the world and our place in it. It helps to take a look in the mirror sometime. Life extension technology is going to ruin humanity and the earth. Look up this comment in fifty years and tell me I'm wrong.
- dredmorbius 10y agoMake that 500 years, and you might get some takers to seal the deal ....
- milquetoastaf 10y agoFair point. I will extend my offer even up to a thousand years.
- dang 10y agoWhoa! we ban accounts for posting this uncivilly. Please (re)-read the site guidelines and don't do this again. https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newswelcome.html https://news.ycombinator.com/newswelcome.html We detached this subthread from https://news.ycombinator.com/item?id=14291715 https://news.ycombinator.com/item?id=14291715 and marked it off-topic.