Ever wondered what's below Earth, considering space surrounds us in every direction? It's a question that sparks the imagination, and today, we're diving deep to find out! This exploration comes from the 'Curious Kids' series, designed to answer burning questions from young minds (and the young at heart!). If you have a question, send it to CuriousKidsUS@theconversation.com!
Let's start with the basics. If you've ever seen a model of our solar system, you'll notice something fascinating: all the planets, including our own Earth, generally orbit the Sun in the same flat plane, moving in the same direction.
So, what lies above and below this plane? And why aren't the planets scattered about, each on its own tilted path?
To unravel this, we'll tap into the expertise of planetary scientists who map our cosmic neighborhood.
Which Way is 'Down,' Anyway?
Gravity plays a huge role in how we perceive 'up' and 'down.' We feel pulled towards the ground, but this direction changes depending on where you stand.
Imagine pointing 'down' from North America. If you could draw a line straight through the Earth from your fingertip, it would point 'up' for someone on a boat in the southern Indian Ocean!
In the grand scheme, 'down' could be defined as being below the solar system's plane, known as the ecliptic. By convention, we see planets orbiting counterclockwise above the plane, and clockwise below it.
More Flavors of 'Down'
But is there anything special about the direction 'down' relative to the ecliptic? To answer, we need to zoom out. Our solar system is just one part of the Milky Way galaxy, which contains about 100 billion stars.
These stars, along with their planets, orbit the center of the Milky Way. Just as planets orbit their stars, these stars orbit the galactic center, but on a much longer timescale. And like the planets, the stars in the Milky Way tend to orbit within a plane, called the galactic plane.
Here's where it gets interesting: the galactic plane isn't aligned with our solar system's ecliptic. The angle between them is roughly 60 degrees!
Zooming out even further, the Milky Way is part of the Local Group of galaxies. These galaxies also tend to align within a plane, known as the supergalactic plane. This plane is almost perpendicular to the galactic plane, with an angle of about 84.5 degrees between them.
So, how do these celestial bodies end up traveling in these flattened paths?
It all goes back to how they were formed.
The Solar Nebula's Collapse
The story begins with a vast cloud of gas and dust called the solar nebula, which eventually formed the Sun and planets. Every particle had a tiny amount of mass, and these particles were drawn to each other through gravity.
Initially, the particles moved slowly. But over time, gravity caused the cloud to collapse and shrink. There was also a slight rotation, possibly due to a passing star. As the cloud shrank, this rotation sped up, like a figure skater pulling in their arms.
As the cloud continued shrinking, particles got closer, leading to more interactions, both through gravity and collisions. These interactions caused particles in tilted orbits to reorient themselves. For instance, a particle moving down through the plane might collide with one moving up, canceling out their vertical motion and aligning their orbits.
Eventually, the cloud flattened into a disc. Particles in similar orbits began to clump together, forming the Sun and planets we know today.
On a larger scale, similar interactions likely confined the stars in the Milky Way to the galactic plane and the galaxies in the Local Group to the supergalactic plane.
The Big Picture
So, what's 'below' Earth? Ultimately, there's nothing special about that direction. It's just the direction where not much in our solar system orbits.
If you journey far enough in that direction, you'd find other stars with their own planetary systems, orbiting in different orientations. And even further, you might encounter other galaxies with their own planes of rotation.
This brings up a fascinating point: the concept of 'down' is relative. If you asked a hundred people on your street, they'd all point the same way. But imagine asking that question to people across the Earth, or to intelligent life on other planets or in other galaxies. They'd all point in different directions!
Do you find this mind-bending? Do you think our understanding of 'down' would be different if we lived in a different galaxy? Share your thoughts in the comments!
Curious kids, if you have a question for an expert, ask an adult to send it to CuriousKidsUS@theconversation.com. Include your name, age, and city. And adults, feel free to submit your own questions – curiosity has no age limit!
