When I contemplate all the ways the universe can kill us, I feel that we are extremely lucky. At any moment a gamma-ray burst could set the world ablaze, but it is not likely to happen. We detect around 1 gamma-ray burst every day, but fortunately, the universe is vast, and most of these bursts are in other galaxies. Some have suspected that an event like this might be responsible for one of five mass extinctions in Earth's history, but there isn't good evidence for it.
We know that at least one mass extinction was caused by an asteroid, although a massive outbreak of volcanoes at the same time was equally responsible. In the event of a supervolcano eruption today, this would create a worldwide catastrophe.
In 1859 a Coronal Mass Ejection from the sun collided with the Earth's magnetosphere causing sparking and fires at telegraph stations. Such an event would be much more damaging today because we are much more wired than we were then.
It turns out that in early solar system development, gas giants tend to fall into lower orbits likely displacing the smaller planets. However, the gravitational tug of Saturn, Uranus, and Neptune kept Jupiter in place. It is also suspected that the Earth started at a different orbit than where it ended up, where it got pulled around by the gravity of the other planets and other objects. This is called planet migration. The other planets still affect the Earth's orbit, in something called the Malankovich Cycles, but fortunately, the solar system long ago settled into a stable configuration.
There are likely many more rogue planets traveling between the stars than there are planets orbiting the stars, making these like gravitational missiles. However, interstellar space is also vast.
About 4.5 billion years ago, a Mars-sized planet collided with the Earth, causing the ejection of enough material to form the Moon.
Supernovas can destroy life up to 50 light-years away.
It is suspected that there are many black holes between the stars in our galaxy that we don't know about.
It might be that the reason why we haven't detected alien life is that the universe is a very hostile place.
Just as a side note, in the "known space" series of science fiction novels, there were a dozen alien species living within a 60 light-year radius of Earth. On the galactic scale, this is minuscule, but might be plausible. I would expect to find maybe one because a sphere with a radius of 60 light-years is a pretty big volume.
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On Fri, Mar 25, 2022 at 12:51 AM Larry wrote:
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