We'll never be able to fully grasp the vastness and complexity of this solar system, let alone the Milky Way and the universe.
There are so many things that we don't understand outside of this drifting ball we live on.
As the universe expands, we're pushed farther away from all the answers we hope to discover.
One question that's been hypothesized for many years is the existence of another planet in our solar system.
So far, we have discovered nine planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto (which was reclassified as a planet in early 2018).
Now, some scientists are certain another planet exists, but believe it's "hidden."
"Every time we take a picture there is this possibility that Planet Nine exists in the shot," Dr. Surhud More, an associated professor at the Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo told Washington Post.
(If you're wondering why it's called Planet Nine, it could be because it was first discovered when Pluto was declassified as a planet.)
More explains that Planet Nine may lie just beyond Neptune, but, unfortunately, no telescope has been able to spot it.
Some even believe that this new planet is much bigger than Earth, and lies 1,000 times further away from the sun.
Despite being basically "invisible," Michael Brown, an astronomer at the California Institute of Technology, told the news outlet that he feels "eternally optimistic" that Planet Nine exists.
Why is there optimism? It all started back in 2014.
Scientists discovered several mini-ice worlds at the edge of our solar system that followed similar paths around the sun.
"If things are in the same orbit, then something's pushing them," said Scott Shepherd, an astronomer at the Carnegie Institution for Science in Washington who discovered the planetoid.
Having said that, there's a lot of ground for scientists to cover to pinpoint the location of the mysterious planet.
Since Planet Nine is believed to be so far away from us, it's hard to detect it. According to the Washington Post, "planets twice as far away look 16 times dimmer," meaning "Planet Nine would be 160,000 times dimmer than Neptune."
At this point, "there's really a brick wall," Kevin Luhman, an astronomer at Pennsylvania State University, said.
Also, light pollution from the Milky Way or the glare of a bright star may be hiding Planet Nine.
It's also possible that the planet's orbit is way beyond the point at which we can detect it, which means we would have to wait thousands of years for this mysterious ball to swing back.
There is hope.
Luhman suggests that looking for the heat glow the planet emits may be the key to verifying its discovery.
Until then, we'll have to wait ever so patiently.
[H/T: Washington Post]