There are days when astronomers wake up inspired. When this happens, my friend, it is good to prepare – hence the good thing, to turn our world view upside down.
Recently, Jessie Christiansen, a NASA exoplanet specialist, had one of these days. She was at a stargazing event at Caltech, the California Institute of Technology, when she had a huge balcony.
Christiansen, while chatting away, commented to his colleagues that in the ancient times when dinosaurs walked the earth, our Solar System was on the other side of the Milky Way.
The effect was immediate: the participants were completely gaping. And it fell to her that most people had never thought of the geological and astronomical timescales at the same time. And the simple conclusion that "the dinosaurs had lived on the other side of the galaxy" was so incredible that it seemed invented – only it was true.
The researcher decided to go deeper. “I had the idea that mapping the evolution of dinosaurs along the rotation of the galaxy.” Christiansen took about four hours to create in PowerPoint (heard, Deltan?) An amazing animation of “galactic archeology,” which she published. (and viralized) on Twitter.
I have always been interested in galactic archeology, but I don't think this is what they meant.
Did you know that dinosaurs lived on the other side of the Galaxy? pic.twitter.com/ngGCAu0fYU
– Dr. Jessie Christiansen (@aussiastronomer) August 28, 2019
The video was brilliant because it shows how astronomy and paleontology combine. Both work with a similar timeline that deals with far-flung periods.
In addition, the animation highlights a fact that, while obvious, passes by many people: that just as the earth revolves around the sun, the sun revolves around the center of the galaxy. Thus, the entire Solar System (the Earth included) spends all the time traveling the Milky Way, and it takes about 250 million years to complete a lap.
And guess what? The age of the dinosaurs occurred just as the sun was on the opposite side of the galaxy from its present position.
Remember that dinosaurs took a long time to become dominant species. They arose long before, in a period called the Triassic. And then we have another coincidence: the Triassic phase was just the last time the sun was in its current position.
It took, therefore, exactly a galactic half-turn between the rise of the first dinosaurs and their total dominance on the planet, the famous Age of Dinosaurs – something that happened in the Jurassic period, and especially in the Cretaceous.
It was in the latter, which occurred between 145 million and 66 million years ago, that the most iconic species such as Tyrannosaurus Rex, Velociraptor and Triceratops emerged. These species therefore walked the earth when it was in a region diametrically opposite from the one we float today.
It is worth noting, however, that the sun's movement around the center of the Milky Way is not perfectly circular. The thing is a little more complicated and chaotic. Planetary systems move in different orbits and at different speeds. The farther the edges, the slower the star, and beyond that the galaxy itself is moving across the universe toward our neighboring Andromeda. This makes the movement of the sun more like a spiral than a circle.
The Sun, then, does not return to exactly the same point – but roughly speaking it can be. Because our star's orbit always keeps a similar distance from the center of the Milky Way despite following this spiral pattern.
That's why our Solar System doesn't just cross the Milky Way's core – thankfully. Because it is a very turbulent region, with many stars and high levels of radiation, life on the planet would probably not be able to stand, whether dinosaurs or mammals.
But the unanswered question, and the one Christiansen uses to end his animation, is: how will Earth be on its next galactic birthday? History proves that in 250 million years, absolutely everything will be different.