Scientific reasoning helps us understand the intricacies of our world. But every so often, a phenomenon leaves scientists without a solid explanation. Here are four mysteries that scientists have yet to solve.

Scientists believe that — somewhere in the far depths of the cosmos — a major planet exists with a mass 10 times that of Earth. In 2014, scientists discovered a cluster of objects orbiting the sun, found beyond Neptune (known as the Kuiper Belt). Astronomers theorize that a ninth planet might be tucked away in the Kuiper Belt, and would explain the strange elliptical orbits of some objects in the Kuiper Belt. But even with our best instruments, this hypothetical ninth planet is too dim to detect.

It remains a mystery until scientists can either prove or disprove its existence. So does it really exist? Unless we have more advanced technology that is sensitive enough to detect reflected light traveling through space, scientists can’t confirm. Until then, astronomers can only speculate its location.

Five thousand blackbirds falling from the sky, thousands of flamingos and penguins found dead, and millions of fish washing up on shore. It sounds like the preamble for an apocalypse movie. There are incidents of mass animal deaths that have been recorded all over the world – from the countryside in Arkansas (2011) all the way to the Chilean coast (2009). Conspiracy theorists believe its the result of UFOs, government testing or that the world is coming to an end. Scientists theorize that it maybe the effects of global warming — salinity levels in the ocean are fluctuating — or disease among the specific group of animals. It’s possible that there isn’t one correct answer, but even scientists can’t pinpoint the reason why these animals are dying worldwide.

What if you woke up one day with an exceptional ability you didn’t have before? There are only a few cases of people who were not born with “prodigious” capabilities, but after surviving a physical trauma these abilities came forth. It's happened a few times before. A woman could suddenly recall her memories with precision and detail. A man who lacked musical ability for majority of his life became a piano virtuoso. A man with no prior academic accomplishments — and spent his adult life working as a furniture salesman — became a mathematical marvel and fractal artist.

This condition is called acquired savant syndrome, and is still not understood. What scientists do know is that savant skills is also evident in people in the autism spectrum, and it’s acquired when a survivor of a traumatic incident has damage to the central nervous system. What they don’t know is if the effects are permanent, whether we all have untapped abilities, and how to produce these abilities without physical harm.

Ghost stories exist across many cultures. Though there isn’t hard evidence that ghosts exist, there are enough people who claim to have seen a loved one that’s passed away, felt a presence, or been possessed. Ghost hunters use high-tech scientific equipment, including electromagnetic field detectors, Geiger counters or infrared cameras, to prove the existence of paranormal activity. Some scientists posit that ghosts don’t exist and are merely a result from toxic hallucinations (carbon monoxide poisoning, toxic mold), eerie sounds that heighten the senses, or sleep paralysis. Others believe those claims to be presumptuous because it’s possible we have yet to develop the proper equipment to identify supernatural signs of life.