What do you mean by ‘we have’ 4-5 billion years? A lot happens in that time. Theres a several percent chance of destructive orbital dynamical chaos in the inner solar system during that timeframe coming from the eccentricity of Mars or Mercury, the Earth will almost certainly pop into Venus mode from the increasing solar luminosity by 1.2 gigayears from now (if some parameters are overly harsh maybe as little as 300 megayears and DEFINITELY by 2 gigayears from now). And amusingly enough if we have a longer period of time before popping into the runaway greenhouse, there is a reasonable chance of a carbon crisis in which atmospheric carbon falls low enough that it becomes the limiting factor in biomass production due to the slowing geosphere and increasing burial of carbonate rock. And the average mammalian genus lasts what, ten, twenty million years?
This being said, I again point out that events like this have almost certainly happened many times over the history of the solar system. Even if events like this are rarer than every few tens of megayears due to the larger than average mass of this star, the sun was only 1% dimmer a hundred million years ago. Runaway greenhouses aren’t THAT easy to get going and I believe there is evidence from the KT impact that the atmosphere was only strongly disturbed for a short time, potentially single digit years. And there are large impacts not associated with mass extinctions, leading some paleontologists to suggest that they only are associated with mass extinctions when the biosphere was already strongly stressed by something chronic like a large flood basalt eruption. (I myself am partial to the idea that the KT event in particular represents an ongoing low-level flood basalt eruption that got kicked into high gear for a few thousad years by the more or less worldwide 9-pointer earthquake the impact would’ve generated, providing a double punch). The biosphere and complex life in general is not threatened by impacts.
4-5 gy is stellar lifetime that most astrophys guys throw out there when discussion of solar sys/Earth comes up.
I agree with the flood basalt/ volcanics postulation, i was never convinced they were extinction driver by themselves.
I thought the orbital danger was Venus, as it is still so close to us on perihelion that it has gravitational interaction.? Reminds me of the exoplanet system found with 5 planets inside the orbit of Mercury, we are a pretty unusual system...
I recall seeing a paper with orbital dynamical simulations in which they found a 2 percent chance that over the remaining lifetime of the sun, the orbital eccentricity of Mercury would increase such that it interacted with Venus, either hitting Venus or getting boosted onto an Earth-interacting trajectory which could lead to a collision or eject it from the solar system altogether, and which puts Venus on a much more closely Earth-interacting orbit. In one simulation out of the 2,500 they did, Mars’s eccentricity was perturbed until it became Earth-crossing.
Remember that there is a bit of a selection effect when it comes to looking at exoplanets—we see the compact large planet systems much more easily than systems like ours. The latest work I’ve seen has suggested that we are a less common class of star system but that stuff like ours might be something like 10% of star systems. Nobody REALLY has a handle on planet formation yet, and it looks like there may be several very different ways that planets and planet-forming material can migrate around the protoplanetary disc during the planetary accretion stage that people argue bitterly over in the literature.
What do you mean by ‘we have’ 4-5 billion years? A lot happens in that time. Theres a several percent chance of destructive orbital dynamical chaos in the inner solar system during that timeframe coming from the eccentricity of Mars or Mercury, the Earth will almost certainly pop into Venus mode from the increasing solar luminosity by 1.2 gigayears from now (if some parameters are overly harsh maybe as little as 300 megayears and DEFINITELY by 2 gigayears from now). And amusingly enough if we have a longer period of time before popping into the runaway greenhouse, there is a reasonable chance of a carbon crisis in which atmospheric carbon falls low enough that it becomes the limiting factor in biomass production due to the slowing geosphere and increasing burial of carbonate rock. And the average mammalian genus lasts what, ten, twenty million years?
This being said, I again point out that events like this have almost certainly happened many times over the history of the solar system. Even if events like this are rarer than every few tens of megayears due to the larger than average mass of this star, the sun was only 1% dimmer a hundred million years ago. Runaway greenhouses aren’t THAT easy to get going and I believe there is evidence from the KT impact that the atmosphere was only strongly disturbed for a short time, potentially single digit years. And there are large impacts not associated with mass extinctions, leading some paleontologists to suggest that they only are associated with mass extinctions when the biosphere was already strongly stressed by something chronic like a large flood basalt eruption. (I myself am partial to the idea that the KT event in particular represents an ongoing low-level flood basalt eruption that got kicked into high gear for a few thousad years by the more or less worldwide 9-pointer earthquake the impact would’ve generated, providing a double punch). The biosphere and complex life in general is not threatened by impacts.
4-5 gy is stellar lifetime that most astrophys guys throw out there when discussion of solar sys/Earth comes up.
I agree with the flood basalt/ volcanics postulation, i was never convinced they were extinction driver by themselves.
I thought the orbital danger was Venus, as it is still so close to us on perihelion that it has gravitational interaction.? Reminds me of the exoplanet system found with 5 planets inside the orbit of Mercury, we are a pretty unusual system...
I recall seeing a paper with orbital dynamical simulations in which they found a 2 percent chance that over the remaining lifetime of the sun, the orbital eccentricity of Mercury would increase such that it interacted with Venus, either hitting Venus or getting boosted onto an Earth-interacting trajectory which could lead to a collision or eject it from the solar system altogether, and which puts Venus on a much more closely Earth-interacting orbit. In one simulation out of the 2,500 they did, Mars’s eccentricity was perturbed until it became Earth-crossing.
Remember that there is a bit of a selection effect when it comes to looking at exoplanets—we see the compact large planet systems much more easily than systems like ours. The latest work I’ve seen has suggested that we are a less common class of star system but that stuff like ours might be something like 10% of star systems. Nobody REALLY has a handle on planet formation yet, and it looks like there may be several very different ways that planets and planet-forming material can migrate around the protoplanetary disc during the planetary accretion stage that people argue bitterly over in the literature.