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The Midnight Planétarium watch was a collaboration between Van Cleef & Arpels and Christiaan van der Klaauw. The watch is made of 396 separate parts and features the six closest planets orbiting the sun in real time (Uranus and Neptune were left out because you probably won’t live long enough to see either one complete a full orbit).
Alien Post #7: The Formation of the Solar System & the Search For Habitable Worlds Elsewhere
Around 4.6 billion years ago, there was a giant nebula. Think of it as a cloud made of things like hydrogen and helium (mostly). It eventually got so large that it’s own gravity started pulling the cloud closer together, increasing its density and heat. This kept happening until it got so dense and so hot that nuclear fusion started and it became a star (our Sun).
The nebula, before becoming a star, (and just like everything in the universe) was spinning. To conserve this energy, as the nebula shrank and grew hotter it also flattened out forming a disk shape and the spinning got faster.
Some of the dust amidst this disk collided, eventually some of them clumping together. Just the simple fact that some of these clumps of dust had clumped together gave them larger gravitational pull than their surrounding dust particles - this is enough to drag all the other dust in it’s orbit to it. These dust clumps gathered enough mass over time to become tiny planets. As they grew, their gravity pulled more matter into the forming planets. After a chaotic time where the growing planets collided with objects and threw other developing planets out of their orbit and into others, planets cleared their own orbits (Pluto’s not a planet because it’s orbit isn’t cleared). Eventually the eight we know today were left standing, rulers of their given orbits.
The young Sun’s solar wind blew any nebular gasses far out into the solar system, leaving it too hot for lighter material to stay on the inner part of the solar system like helium hydrogen and water. This is why the far off planets are all gas giants. The forming planets farther out were able to hold onto the gasses that couldn’t form as close to the sun as Mars and closer.
Why this is important in the search for habitable exoplanets:
When we study extrasolar systems, what little we know seems to suggest that they formed in a similar way to our solar system. This gives us a lot to work with in the search for Earthlike planets out there.
Kepler’s third law is, right now, our best tool. It goes like this:
P^2/a^3 or, the period of a planets orbit (how fast it orbits its star) is proportional to the cube of it’s average distance from the star.
If you know how fast it orbits it’s star, you know the average distance of the planet from the star too.
How do we know the speed of orbit? This is actually deceptively simple. When we look at a star through a telescope, we have a steady level of brightness that only drops in intensity when something passes in front of the star: like an orbiting planet. If you see the stars brightness dip every 365 days, you’ll know it’s exactly as far from it’s star as the Earth is from our Sun.
Why is this important?
Going back to how our solar system formed, we know gas giants form farther from there sun than the distance of Mars, so a gassy planet can’t orbit it’s star every 365 days.
What about water then?
Water is a lighter material and wouldn’t be able to form with a planet as close to it’s star as Earth is. How do we then have so much damn water on Earth? Well a couple hundred million years into the formation of the solar system, perhaps during the chaotic period I mentioned earlier, there was a heavy bombardment of the planets. It is thought that many comets struck Earth during that period (which lasted 500,000,000 years). On average it would’ve taken either 2.5 comets every year or one comet every 2.5 years for Earth to have received all the water it has today (comets have frozen water on them). This is why we have liquid water on Earth.
In order for an Earthlike planet in another part of the galaxy (or another galaxy altogether) to have all the necessary things for life as we know it, it would need to have a picture matching the formation of our solar system quite well. Keep searching!