By David Ward
How will it all end? It is easy to take our perch on this little planet for granted. Space is a lethal place and our bubble of protection that we live in may be more precarious than we would like to admit.
Aside from the usual worries like climate change and nuclear war, what are some of the threats to our existence? About a million years from now a very unwelcome visitor will come calling, Gliese 710. This small star only half the size of the sun is probably not on your radar, but if you were to live far in the future it definitely would be. There is nothing remarkable about it, there are literally billions just like it in our galaxy.
Do you ever have that creepy feeling on the back of your neck like something is following you at night? Gliese 710 is doing just that, speeding towards us at 32,000 miles per hour. It is not going to hit the Earth. That would be a disaster for sure, but it is going to plow right through something called the Oort Cloud.
Way out beyond the orbit of Pluto a vast reservoir of comets, trillions of them, lazily orbit our sun barely affected by its gravity. Every now and then a comet falls out of this cloud like Comet NEOWISE last summer. It took thousands of years for it to get close enough for us to see it because the Oort Cloud is so far away. Think of the Oort Cloud as a giant hornet’s nest. One or two hornets flying around is not too dangerous, but you definitely do not want to poke a stick in that nest and stir it up. That is exactly what Gliese 10 will do.
Millions of comets will fall into the inner solar system slamming into all the planets including us. The reign of terror from outer space will last several million years. Just one hit by a comet 5 or 10 miles across, if it fell into an ocean, would send miles high tidal waves flooding across the continents. Most everything flammable on the Earth’s surface would burn, and dust lingering in the atmosphere for hundreds or thousands of years would block sunlight, throwing us into an ice age for millennia.
But wait — if anyone survives all that, there is more. We are being dragged around the galaxy by our sun. Like a pony gently bobbing up and down on a merry-go-round our sun climbs up through the galactic plane and then descends through it again. This regular cycle is tied to mass extinctions here on Earth. Why? Because when we are going through the more dense part of the galaxy, things get more crowded, and we have to watch out for incoming objects of mass destruction. About 30,000,000 years from now that is where we will be.
After that it is unlikely anyone will still be around, but the Earth, hardly recognizable, will still be going around the sun. What will its final demise be? Our sun is progressing towards the red giant phase of its life, swelling up like a bloated beach ball and getting hot! Do you want to see what one looks like? Find the reddish star Aldebaran to the upper right of Orion. That is our sun a few billion years from now.
Hundreds of millions of years from now global warming from hell will descend upon us, but this time it will not be our fault. In about a billion years the oceans will boil away leaving the Earth with a hot oppressive atmosphere of steam. It does not stop there. The sun in its expansion will engulf the planet Mercury, then Venus. The Earth too will probably be inhaled by our giant red sun and actually continue on its orbit inside the outer layers of our star. Pushing through the hot gases that make up the sun will slow the Earth down causing it to plunge inward in a death spiral.
That will be the end of our beautiful little planet, and maybe if we are lucky and resourceful enough, our descendants will be watching from a safe vantage point like one of the moons of Jupiter or Saturn. But what about the whole big thing we live in, the universe? It will last forever, right? Not so, say the people who think about such things. They have thought up several possibilities for the end of everything and given them scary names like the Big Crunch, the Big Rip, Vacuum Decay, and Heat Death. All of these are way, way off in the future except for one which could be just around the corner.
There is nothing we can do about any of this, so you might as well just go out and look at the stars. Orion is riding high in the sky in the early evening. The brightest star in the sky, Sirius, is to his lower left. The Pleiades star cluster is to the right of the Great Hunter. We are very lucky to witness such a sight.