21 Mysteries about Space No One Can Explain

The truth is out there, but no one’s found it yet.

Scientists and astronomers spend all day, every day, poring over data in search of answers to the universe's myriad questions, but they'll be the first to admit that outer space is really, really hard—if not entirely impossible, at least for our mortal minds—to figure out.

So given that even experts don't exactly know what's going on in the great beyond, it's only natural that us earth-faring folk would have some burning questions. Herein, you'll find the most mind-numbingly confounding. So strap in, and get ready for cognitive blastoff in three….two… one! And if you're actually interested in heading to infinity and beyond, prepare by learning the 27 Insane Things Astronauts Have to Do.

Just how big is the universe?

planets in space in the future

For those who slept through astronomy, here's a refresher: Our sun, a star, is surrounded by nine-ish (more on that later) planets. These star-planet clusters are called solar systems. Clusters of solar systems are called galaxies. The Milky Way—that's the galaxy we're in—is widely believed to have about 200 billion solar systems. Researchers have pegged the observable universe—that's what we can tangibly see—at about 150 billion galaxies. Honestly, though, it could go on, and on, and on, and on, and, well, you get the point.

In fact, a team of researchers at Oxford recently deployed a model that suggests the universe is at least 250 times larger than that. To put that the resulting figure in context, that's more zeroes than we can get away with typing without crashing your web browser. And that's just galaxies. Thinking about how that number applies to solar systems, let alone planets, is enough to melt anyone's brain. And for more brain-melting science, read up on the 20 Types of Artificial Intelligence You Use Every Single Day And Don't Know It.

So, um, where is everybody?


Yes, those staggering numbers indicate that we should've stumbled across alien life by now. Even if you take the most hesitant, even-keeled estimates—which come courtesy of recent Proceedings of the National Academy of Sciences research—about 1 percent of all planets in the universe are at the very least capable of fostering sustainable biological life. The folks at Wait But Why put it this way: For every single grain of sand on every single beach on Earth, there are 100 of these planets; in the Milky Way alone, there should be 100,000 intelligent civilizations. So, again, where is everybody?

Enter: The Fermi Paradox. Coined by physicist Enrico Fermi in the 1950s, the Fermi Paradox stages a valiant effort at answering this perplexing conundrum. To date, no one's been able to  solve it, but the astrological community largely splits off into two categories: that we're the only intelligent life in existence, or that there's an extremely good reason for why we've yet to discover our celestial cohabitants. For instance, maybe we're in a zoo-like situation, and extraterrestrial life observes us like we would a caged panda. Or perhaps we're just in a "rural" part of the galaxy and have yet to be discovered, sort of like how 15-century explorers had no clue ancient American tribes existed before setting out across the Atlantic. Crazy, right?

Where is Planet 9?

space prediction

Pluto is technically not a planet. But that doesn't mean our solar system is limited to eight planets. Scientists believe that there may be a ninth, undiscovered planet on the fringes of our corner of space. If you pay attention to orbital trajectories of out-there celestial bodies, like Uranus and Neptune, you'll notice peculiarities.

The reason is likely that there's a massive gravitational body out there—like a planet—pulling things out of whack. According to Konstantin Batygin, assistant professor of planetary science at the California Institute of Technology, the reason we may not have found "Planet 9" yet is "because it is staggeringly dim…With the best telescopes around, we could just barely detect it, we think." And for more brain-twisting science stories, This Is What Life Could Look Like 200 Years from Now.

What are black holes?

Black Hole Things You Believed That Aren't True

Black holes—galaxy-like formations where gravity levels are so powerful everything, including light, gets sucked into—remain deeply mysterious. Researchers estimate there may be as many as 100 million black holes just in in the Milky Way alone. But we don't know how they're formed, what they do, and, crucially, what happens if matter passes through one.

Which came first: The black hole or the galaxy?

black hole

Among the things that baffle scientists about black holes is when they were formed in the first place. Research from astronomers examining radio-frequency pictures that provide data about early galaxies suggests the black holes may have gotten an early start. "The significant implication is that the black holes formed first and then somehow they formed a stellar galaxy around them," said Chris Carilli, of the National Radio Astronomy Observatory in Socorro, New Mexico, one of the report's researchers.

What is dark matter?

dark matter

We don't really know what this stuff is, but scientists estimate that dark matter may make up about 25 percent of the total universe—a substance that works something like a spider's web, holding the planets, stars, and galaxies together. There's plenty of evidence that it exists, but it's a mystery what exactly it is. Maybe it's a compound of an undiscovered particle? Maybe it's a previously unknown property of gravity? No one's sure.

How hot is dark matter?

dark matter

One of the biggest questions about dark matter remains around its temperature—whether it's hot or not. Theories range from it being hot, warm, or cold, with one of the most widely accepted theories—the Lambda Cold Dark Matter model—maintaining that it is, like its nomenclature suggests, cold and dark. But the jury is still very much out.

What is dark energy?


In the 1990s, when a group of astrophysicists found that the universe's expansion was speeding up due to some sort of substance counteracting gravity, they dubbed this substance "dark energy." Believed to make up almost 70 percent or more of the known universe, theories differ on what exactly it is—a changing energy field known as "quintessence"? A property of space overlooked by Albert Einstein? It's a whole lot of something. We're just not sure what.

Where's our second sun?

Earth Orbiting Around the Sun Things You Believed That Aren't True common misconceptions

Purportedly, 80 percent of star systems are binary systems. They have two suns. Ours is not—at least not any more. Astronomers have suggested that, once upon a time, we may have had a second sun, which has been dubbed Nemesis. More recent research, looking at a cluster of young stars in the Milky Way, finds some support for this; apparently, almost all sun-like stars are born in pairs. But unless and until we spot a star whose composition is identical to our own, Nemesis will forever remain a mystery. And for tips on staying safe from the sole sun we still have, check out the 20 Ways the Sun Harms Your Health.

Where did the moon come from?

tom kerss captures supermoon 2018

A popular theory is that it resulted from a huge collision of a "protoplanet" hitting the Earth around 4.5 billion years ago, and knocking off a chunk of debris. But other theories—like the relatively rote one of it being an asteroid stuck in our gravitational pull—persist. In any event, no one knows.

What Made Mercury?

planet mercury

Of all the planets in our solar system, Mercury may be the most mysterious. It's so close to the Sun that terrestrial telescopes can have trouble looking at it, and what we've been able to gather about it has left scientists scratching their heads.

A huge metallic core represents about half the planet's volume (Earth's is just 10%, by comparison). Some theorize it used to be a planet similar in characteristics to Earth and Venus, but had collision strip it of its crust or that the Sun boiled its crust. Either way, when it comes to this planet, there are a lot of questions without answers.

Who's the Arecibo Message going to reach?


The most powerful broadcast ever sent into space was beamed into the sky in 1974—aimed at the globular star cluster M13. The message (which consists of a graphic showing a human, our solar system, and strain of DNA, among other things) is not expected to reach its destination for about 25,000 years. But who knows: someone else might've picked it up in the meantime.

What causes quantum entanglement?

Quantum Entanglement

This is when two particles mirror one another or interact in some way, even though they are separated by huge distances, even at totally different corners of the universe. Einstein called it "spooky action at a distance" and for such entanglement to be happening would seem to require some kind of signals traveling between the particles—at a rate faster than the speed of light. This would be a pretty tough trick to pull off, but scientists have yet to find a fully satisfying explanation for the phenomenon.

What's antimatter?


It's like regular matter, but the opposite. Specifically, an antimatter particle has the same mass as a particle of matter, but with the opposite electric charge, so it destroys normal matter the moment it connects. While it's believed to have been created alongside matter following the Big Bang—and still remains in the universe today—scientists don't know exactly why. They just know we should stay far, far away from it.

What's "space roar" sound like?

Space Roar

It turns out that in space, you can hear something scream, or at least "roar." Researchers have detected a cacophony of radio signals that can make it hard to make out other signals being sent through space (though it would be impossible to hear with the human ear). Dale Fixsen, a University of Maryland research scientist, told Mental Floss that there are several theories for what causes this, from the possibility that the roar is coming "from the earliest stars" to "radio galaxies," but these are, after all, just theories.

How do stars explode?


When stars run out of fuel, they go out with a bang, exploding in massive blast known as a supernova. But while research and technology such as NASA's Nuclear Spectroscopic Telescope Array have illuminated much about the process, it still remains something of a mystery.

"Stars are spherical balls of gas, and so you might think that when they end their lives and explode, that explosion would look like a uniform ball expanding out with great power," said Fiona Harrison, the principal investigator of NuSTAR at Caltech, upon announcing the findings in 2014. "Our new results show how the explosion's heart, or engine, is distorted, possibly because the inner regions literally slosh around before detonating."

Are cosmic rays getting worse?

cosmic ray

High-energy particles from deep space known as "cosmic rays" have been striking the earth and may be getting worse, according to findings from NASA's Advanced Composition Explorer spacecraft. "In 2009, cosmic ray intensities have increased 19 percent beyond anything we've seen in the past 50 years," said Richard Mewaldt of Caltech. "The increase is significant, and it could mean we need to rethink how much radiation shielding astronauts take with them on deep-space missions." But what they don't know is exactly what's causing this uptick or exactly what dangers it might pose.

Is there a multiverse?


Any fan of Doctor Strange can appreciate that, as small as we may feel in this universe, it may be only one of potentially trillions of other universes. But while there are a number of legitimate reasons—like Chaos Theory, or the Butterfly Effect, or so-called "Daughter Universes"—to line up behind this ideation, there is, at the moment, no way to conclusively prove it one way or another.

Are they "daughter" universes?


A version of the multiverse theory, this idea grows from quantum mechanics, which describes the world in terms of probabilities and suggests that all possible outcomes do occur, each a "daughter universe" sprouting from the original—but we only live in the universe where one of those outcomes occurred. "And in each universe, there's a copy of you witnessing one or the other outcome, thinking—incorrectly—that your reality is the only reality," writes Columbia University physicist Brian Greene. But who really knows? No one.

…Or are they parallel universes?

Planet Earth Scientific Discoveries

Princeton University's Paul Steinhardt and Neil Turok, of the Perimeter Institute for Theoretical Physics in Ontario, Canada, suggested this concept, in which more dimensions exist than three of space and one of time. Greene puts it this way: "Our universe is one of potentially numerous 'slabs' floating in a higher-dimensional space, much like a slice of bread within a grander cosmic loaf."

Will it End With a Big Crunch?

asteroid hitting earth in the future

The Big Bang still remains shrouded in mystery, but that's doubly true of the Big Crunch—the end-of-everything theory that says the universe's ongoing expansion will eventually taper off and give way to gravity. In other words, all the mass in the universe (and potential multiverses) will be drawn together into an ever smaller space until it all exists in one unimaginably dense and hot point—and then gets wiped out.

Sounds unpleasant, sure, but hey! It probably won't happen for a few quadrillion years! And for more amazing facts that sound like something out of a science-fiction novel, don't miss these 20 Long-Predicted Technologies That Are Never Going to Happen.

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Alex Daniel
A journalist based in Brooklyn, New York. Read more
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