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Planetary 'autopsies' indicate worlds like Earth common in the cosmos
- kornork 7y agoMy physics isn't great, but why does it matter that these are white dwarfs? The article says "researchers studied six white dwarfs whose _strong gravitational pull_ had sucked in shredded remnants of planets" and "if they stray near its _immense gravitation field_, they “will be shredded into dust, and that dust will begin to fall onto the star and sink out of sight.” Isn't it the case that the gravitation field will be as strong as it was before the star died, or even weaker from blowing off its outer layers?
- mokus 7y agoI think it may be that while the field is more or less the same overall, the star no longer occupies as much of it so planets can get closer in where the gradient is steeper (and the tides can then rip the planet apart, giving us the chance to see its contents)
- _Microft 7y agoWhite dwarfs are interesting because they make up almost all of the current or future outcomes of most stars in the milkyway. -> https://en.wikipedia.org/wiki/White_dwarf https://en.wikipedia.org/wiki/White_dwarf The Roche-limit (the radius at which a satellite would be ripped apart) for the Sun-Earth system is at ~ 550000km. That's inside the current size of the Sun. So if the sun shrank a lot (white dwarfs are basically small, 'dead' stars which shrank to that size after the nuclear fusion stopped which had counteracted the attraction of the star's mass), Earth could actually be in such a low orbit and therefore fall apart due to the Sun remnant's attraction. -> https://en.wikipedia.org/wiki/Roche_limit https://en.wikipedia.org/wiki/Roche_limit
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- prewett 7y agoWhy would a decrease in the sun's radius cause a change in Earth's orbit? From those to articles it sounds like the mass of the sun will remain about the same, so the orbit should remain about the same. And less mass will cause the orbit to migrate outwards.
- the8472 7y agoShrinking of the star simply makes it possible to come within the roche limit without being inside the star. The inspiral would happen due to separate processes e.g. friction as the star sheds its envelope or due to interactions between multiple planets.
- bigwavedave 7y agoWhen the Sun enters the red giant phase, will the radius have expanded enough to consume the earth? I'm trying to remember if that was something my physics professor said years ago or if I heard it from someone less reliable and am merely attributing it to him...
- _Microft 7y agoWikipedia says the sun is expected to expand out to roughly the orbit of Venus (consuming it and Mercury) and turning Earth into a blob of molten rock.
- surfsvammel 7y agoEven if there are Earth like planets everywhere, we don’t know the probability that life appears spontaneously. Right? How does this change our outlook if one assumes The Great Filter hypothesis? Does this lower or increase that such a filter would be behind us or before us?
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- rantwasp 7y agotechnically it's not spontaneous. There are some thoughts out there that organic compounds can emerge from non-organic ones and, given enough time, "life" will emerge. One of my favorite books on this is "Regenesis: How Synthetic Biology Will Reinvent Nature and Ourselves" by George Church. I have also seen arguments for this in "The Blind Watchmaker" by Dawkins that was published in 1986.
- anon1m0us 7y agoWe do know the probability life appears is non-zero though, because it has happened. I don't know why all 9 steps to colonization can't be considered improbable, and therefore the filter be behind us and in front of us. We don't even know all the steps between "Step 8: Where we are" and "Step 9: Colonization." Maybe a moon is required for it. Maybe materials not found on this earth are required for it. I think we as a species have decided that colonizing Mars is possible. It might not be probable, but we can do it. We know how, we just haven't yet. Humans just might be the first intelligent life. If the Milky Way was already colonized, some civilization made the first leap to another planet. It's manifest destiny. We have to colonize the universe. It's our moral duty as an intelligent species to maintain awareness of the universe.
- ropiwqefjnpoa 7y agoThe science here and although it's different, makes me think of the "I’m Convinced We Found Evidence of Life on Mars" article posted here a few days ago. If they are able to draw these conclusions with such limited data, I doubt they've missed anything obvious on the surface of Mars.
- m3kw9 7y agoThe probability of no other intelligent life other than ours is near zero. The reason most question it is because we are relatively unintelligent, given we can’t even exit our solar system, and also see anything clearly in the next closest system.
- ravenstine 7y agoNo, they question it because there's no evidence that there's intelligent life elsewhere. Not only do we only have one known example of sapience in the universe, but only one example of sapience on a planet with over a million species of animals. As much as I admire crows, dolphins, and greater apes for their intelligence, they don't even come close to the intellectual capability of humans. The fact that there are habitable planets out there gives us hope that we will find extraterrestrial life, perhaps intelligent, but to assert that there must be life out there is speculation. To say that those who question whether there's extraterrestrial intelligence is pure arrogance.
- ericb 7y ago> only one example of sapience on a planet with over a million species of animals. We're not so sure on that score: https://siberiantimes.com/science/casestudy/features/f0100-stone-bracelet-is-oldest-ever-found-in-the-world/ https://siberiantimes.com/science/casestudy/features/f0100-s...
- bashallah 7y agoWe are the only one in the boxes we have made. That does not mean there are not other boxes.
- raducu 7y agoThe anthropic principle goes both ways. I've read this thought experiment somewhere -- imagine, you're locked in a cell and are given a set of lockpics, and you are told you have to pick the lock of the door and get out, or in 1 minute a neurotoxin is released that will kill you. You have no idea how to pick locks, but you try anyway and you manage to open the lock in 10 seconds. You are asked how tough do you think the lock was? You reply "it was really easy, I have no idea how to do it, yet I did it in 10 seconds, easy!". What you don't know is there were also another 1 trillion cells and you're the lone survivor -- the lock was incredibly hard to pick, with a 1 in a trillion chance of success, but to you, the survivor, without external information it seemed really easy, you were just incredibly lucky.
- andrewflnr 7y agoSo, to be clear, are they doing spectroscopy on the spectra of these white dwarfs? Do they have to be looking at it at the exact moment the planet gets shredded or do the chemicals they're looking for remain in the star's atmosphere?
- ssijak 7y agoJames Web telescope will be able to do that. I hope that it gets deployed without issues because it would be able to provide strong indicators of extra terestrial life
- acqq 7y agoFrom their paper (link in my other message): "(White dwarfs) WDs are the remnant cores left behind when a star ejects its hydrogen-rich outer layers after the red giant phase. These remnant cores are ~0.5 M (solar masses) and about the same radius as Earth, are no longer powered by fusion, and slowly cool over time. Because of their high densities, and thus strong gravitational fields, elements heavier than helium rapidly sink below their surfaces, becoming unobservable. Nonetheless, spectroscopic studies show that the atmospheres of up to half of WDs with effective temperatures <25,000 K are “polluted” by elements heavier than He (3–5). The source of these heavy elements is exogenous, coming from accretion of debris from rocky bodies that previously orbited the WDs (6–9). We exploit this pollution to measure the elemental constituents of extrasolar rocky bodies." So the answer is "the later."
- SubiculumCode 7y agoI am not an astronomer, but in terms of empirical evidence, for the longest time the only prior we had was our own solar system. Thus the natural best guess should have been that (at least for stars similar to our own) earth-like rocky planets near our size should be the most frequent occurrence.
- acqq 7y agoThe paper: https://science.sciencemag.org/content/366/6463/356 https://science.sciencemag.org/content/366/6463/356
- vfc1 7y agoA possible explanation of why we haven't found anything is because intelligent live once developed will quickly overload the ecosystem and start causing things like climate change and quickly make the planet inhabitable, this could all happen in less than 2 million years which is nothing on the cosmological scale. There was running water on Mars and it's within the goldilocks zone. Probably Venus too, both those planets had stable conditions for the emergence of life for billions of years. Once a species like humans starts spreading like a virus and taking over the ecosystem, it can easily go downhill very fast (cosmologically speaking).
- inamberclad 7y agoI think that at this point we're pretty confident that there have never been any advanced civilizations on Mars. We'd see their chemical and isotopic residues. Here's a good talk on filters: https://www.youtube.com/watch?v=k7fLNvpl0c8 https://www.youtube.com/watch?v=k7fLNvpl0c8
- vfc1 7y agoNot an expert here, but after a billion years, what would be the detectable residues of such civilization could realistically be detected? I mean everything made of organic material would be gone, and all constructions would have been turned to dust. Not saying that there was anything ever in Mars or Venus in terms of intelligent life, but non-intelligent life what traces would it leave?
- TheGallopedHigh 7y agoLikely radioactive substances that were once in large amounts with long half-lives
- vfc1 7y agoFor example, we are now moving away from nuclear due to the dangers associated, so we only have it for less than 100 hundred years. The half-life of uranium is 4.5 billion years. Let's say civilization of earth is wiped out and someone visits the planet a billion years from now. Could they tell that there was something here just by the levels of uranium, assuming that say we only used it for 200 years before moving fully to clean energy?
- sbmthakur 7y agoAssuming there are intelligent species living in nearby systems(with not such advanced tech), it's unlikely that they can notice us unless we can control the light intensity of our Sun. Because that's the only object they're probably looking at.