4 ms·

OK, I'll bite. What do the facts say would happen when a brown dwarf passes through the inner solar system? Is the ejection of planets implausible?

garmaine 6y ago
The facts say that such an event has an extremely low probability of happening, as our solar system is still intact after 4.5 billion years and solar systems remain around nearly all stars we look at, so the probability of this happening is so low as to not worry about it.
- wcoenen 6y ago
  I actually agree that the probability of such an event is very low on the scale of a human lifetime or even the lifetime of our species, and I'd never worry about it. I had interpreted your "why would it be scary" question as "what kind of bad things would happen if a brown dwarf did get close?", but I guess it was instead a rethorical question implying something about low probability. Hence the confusion. That said, there is a problematic selection bias in your statement about our solar system. Only stable systems can produce observers, so of course we find ourselves in a stable system. For now ;-)
  - garmaine 6y ago
    Yes, I meant "why are you scared?" It's a huge problem I've encountered where a very large percentage of the population get freaked out about things like black holes, rogue planets, gamma ray bursts, the sun eventually going nova, etc. As someone whose background is astrophysics and planetary science, I find it totally bizarre. Like, we just found out the universe is a way, way bigger place--full of planets between the stars. Maybe humans will visit these worlds someday as we planet-hop between the stars. What civilization could we make near these cold, but resource-rich worlds? What if they had tidally-heated moons with liquid oceans... what sort of life would evolve without the energy of a star? But no, people's first reaction is "OMG is this going to kill me?!" I've even had someone get angry at me for bringing up the topic (that the sun will go nova billions of years from now) and making them depressed. I just don't get it. > That said, there is a problematic selection bias in your statement about our solar system. Only stable systems can produce observers, so of course we find ourselves in a stable system. For now ;-) That's why I mentioned other exosolar systems. So far as we can see, basically every stellar object that we look at has stable planetary system. We mostly find planets by periodic transit events, which requires the plane of formation to be aligned with us. You can calculate the statistical chance that this is the case, and sure enough when we look we find roughly that percentage of stable planetary systems. If there were rogue planets or primordial black holes out there likely to encounter us, then those other systems would be just as vulnerable and we would expect to see fewer percentage of visible stable planetary systems than predicted. That is not the case. We would also expect consistent groups of long-period comets from the interactions of these passing objects with the Kuiper belt and Oort cloud, but there is no consistent grouping. We would expect a history of random heavy bombardment periods in the crater history of the moon, mars, mercury, and other datable planetary bodies in the solar system. Instead we see just one period, the late heavy bombardment which coincides with the synchronization of the orbits of Jupiter and Saturn in the late stages of solar system formation. Etc. etc. When I first saw the headline I thought "wait a minute, that cannot be right." And sure enough, it's not. There aren't 100's of rogue planets in our particular stellar neighborhood, but rather scattered around the nearby region.
- AtlasBarfed 6y ago
  That could be survivor bias, but you're probably right.

garmaine 6y ago

The facts say that such an event has an extremely low probability of happening, as our solar system is still intact after 4.5 billion years and solar systems remain around nearly all stars we look at, so the probability of this happening is so low as to not worry about it.

wcoenen 6y ago
I actually agree that the probability of such an event is very low on the scale of a human lifetime or even the lifetime of our species, and I'd never worry about it. I had interpreted your "why would it be scary" question as "what kind of bad things would happen if a brown dwarf did get close?", but I guess it was instead a rethorical question implying something about low probability. Hence the confusion. That said, there is a problematic selection bias in your statement about our solar system. Only stable systems can produce observers, so of course we find ourselves in a stable system. For now ;-)
- garmaine 6y ago
  Yes, I meant "why are you scared?" It's a huge problem I've encountered where a very large percentage of the population get freaked out about things like black holes, rogue planets, gamma ray bursts, the sun eventually going nova, etc. As someone whose background is astrophysics and planetary science, I find it totally bizarre. Like, we just found out the universe is a way, way bigger place--full of planets between the stars. Maybe humans will visit these worlds someday as we planet-hop between the stars. What civilization could we make near these cold, but resource-rich worlds? What if they had tidally-heated moons with liquid oceans... what sort of life would evolve without the energy of a star? But no, people's first reaction is "OMG is this going to kill me?!" I've even had someone get angry at me for bringing up the topic (that the sun will go nova billions of years from now) and making them depressed. I just don't get it. > That said, there is a problematic selection bias in your statement about our solar system. Only stable systems can produce observers, so of course we find ourselves in a stable system. For now ;-) That's why I mentioned other exosolar systems. So far as we can see, basically every stellar object that we look at has stable planetary system. We mostly find planets by periodic transit events, which requires the plane of formation to be aligned with us. You can calculate the statistical chance that this is the case, and sure enough when we look we find roughly that percentage of stable planetary systems. If there were rogue planets or primordial black holes out there likely to encounter us, then those other systems would be just as vulnerable and we would expect to see fewer percentage of visible stable planetary systems than predicted. That is not the case. We would also expect consistent groups of long-period comets from the interactions of these passing objects with the Kuiper belt and Oort cloud, but there is no consistent grouping. We would expect a history of random heavy bombardment periods in the crater history of the moon, mars, mercury, and other datable planetary bodies in the solar system. Instead we see just one period, the late heavy bombardment which coincides with the synchronization of the orbits of Jupiter and Saturn in the late stages of solar system formation. Etc. etc. When I first saw the headline I thought "wait a minute, that cannot be right." And sure enough, it's not. There aren't 100's of rogue planets in our particular stellar neighborhood, but rather scattered around the nearby region.
AtlasBarfed 6y ago
That could be survivor bias, but you're probably right.