Interstellar Earth

There have been many books and movies illustrating the idea that the Earth is part of an ecosystem of asteroids and comets, moons and planets that all spin around our sun.

What hasn’t been explored as much is the effect of an ecosystem on a much larger scale—the effect exerted on the Earth by objects in our interstellar and even intergalactic neighborhood.

How’s that possible? 

Sitting and reading this, you might think you’re not moving--but you are.

Let’s start with the Earth rotating around its axis like a spinning top. Our planet is eight thousand miles in diameter, or about twenty-four thousand miles around its equator, and one rotation each twenty-four hours means you’re moving at a thousand miles per hour as you speed around the Earth’s axis.

And we’re not stopping there.

The Earth itself is orbiting the sun at a speed of about 67,000 mph. The sun is rotating around the Milky Way’s galactic core at about 518,000 mph, the Milky Way moving around the center of gravity of our Local Group of galaxies at 90,000 mph and the Local Group is moving relative to our Super Cluster at a speed of about 1.35 million mph.

So how fast are you moving while sitting still?

As best as we can estimate, you’re moving at about 540 miles per second. If you went back in time by a year, you would need to travel more than twice the distance to Pluto to get back to the same physical spot in space you are now.

Over time, spaceship Earth travels a lot of distance.

And all that “space” out there isn’t empty, but kinda cloudy. As in, giant molecular cloudy. There are upwards of 8000 giant molecular clouds in our galaxy, ranging from twenty to two-hundred light years across, and as the Earth and sun orbit the Milky Way, we tend to run into “cloudy” galactic weather every few hundred millions years.

The effect can be dramatic, depending on the density and composition of the cloud, leading to kinematic heating and seeding of our atmosphere to form clouds, probably leading to “snowball Earth” scenarios where ice extends all the way to the equator--which scientists now think has happened at least once or twice. The timeline might seem impossibly huge, but in the time that complex life has existed on Earth, about a half billion years, we have completed two complete orbits around Sagittarius A (the supermassive black hole at the center).

In fact, many of the events we’d attributed previously to chance, like the asteroid impact that wiped out the dinosaurs, might not be random at all, but the direct result of the interstellar interactions the Earth has with passing stars or giant molecular clouds. In school, we’re taught that the closest star, apart from the Sun, is Proxima Centuri, at just over four light years away. It may seem like the interstellar neighborhood is static. 

But it’s not.

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In February of 2015, researchers were amazed to realize that just 70,000 years ago, near enough in time that our direct ancestors would looked up in the sky and seen it, Scholz’s star, a red dwarf, passed about a half light year from us. 

This led to a flurry of data crunching, leading scientists to discover that, for instance, four million years ago, a giant star, more than twice the mass of the sun, passed less than a third of a light year from us, and in just over a million years from now, another star will pass at just over a hundredth (yes, a hundredth) of a light year from our sun, grazing the solar system itself and affecting the orbits of the planets.

Scientists are now speculating that Sedna, the 10th planetoid of the Sun, the one after Pluto, isn’t even an original planet of our Sun. It was captured from a passing star over a billion years ago, when our solar system collided with an alien star’s planetary system. Hundreds of objects in the Kuiper Belt, the collection of planetoids past Uranus, are believed to have been captured from passing stars. 

And, of course, we had our the first interstellar visitor, ‘Oumuamua, which transited the solar system in 2017, followed close on its heels by the second, 2I/Borisov, in 2019. Which leads to the realization that we’re literally floating amongst interstellar debris, some of which is settling onto the Earth as we flash through space.

So we are continually mixing together with others stars and interstellar objects, and not on a time scale of billions of years, but on a regular basis every few million years—some scientists now even think that alien stars transit our solar system’s Oort cloud as often as every few hundred thousand years.

The gravitation effects of passing stars change the orbits of the planets over the course of millions of years. A change in Earth’s orbit might have triggered one of the biggest global warming events in its history. A massive ice age, started 35 million years ago, might have also been caused by another shift in Earth’s orbit, and that this same event disturbed the asteroid belt enough to precipitate several large asteroid impacts, one of which formed the Chesapeake Bay. 

And we haven’t even talked about the 95% of “stuff” floating around us, dark matter, that we can’t see or detect, other than knowing it’s there from its gravitational signature. With upgraded sensors and increased power in the Large Hadron Collider (LHC) in 2015, the world’s most powerful particle accelerator, many scientists had hoped to see evidence of dark matter.

But they’ve found nothing so far. 

Despite all of our technology and hundreds of years of peering into the cosmos, we still have no idea what makes up the vast majority of our universe. 

It was Stephen Hawking who first proposed that the missing dark matter may be in the form of invisible “primordial” black holes that were formed when our universe itself was created in the Big Bang.

Primordial black holes might have formed when the Big Bang created a super-dense soup of particles, with densities high enough to spontaneously form black holes. Recent research results using the Kepler satellite have restricted the size range of possible “black hole dark matter” candidates, but it is still a viable theory.