Science is one way we make sense of the world around us. Some might even say it’s the most rational way to figure out how things work in an otherwise inscrutable universe. But even science doesn’t have all the answers all the time. While researchers dedicate themselves to coming up with explanations, the rest of us get the chance to conjecture wildly and come up with our own likely false, yet largely fun hypotheses. Here are phenomena that have science stumped at the moment.

1 Immediately after the Kuiper belt beyond Neptune, there’s a sudden unexpected drop in the density of icy rocks. Scientists think it might be a mystery 9th planet that caused the density of rocks in this region to fall so suddenly, but they haven’t been able to find it.

The Kuiper Belt is a disc of icy rocks beyond the eight planets in our solar system. According to theoretical models, the density of the icy rocks beyond 50 astronomical units should increase. But the opposite is true. The Kuiper Belt ends suddenly, so the region beyond it is known as the Kuiper Cliff. Scientists have yet to come up with a reason for why the region containing these icy rocks ends so suddenly. One explanation that has been proposed is that a 9th planet approximately the size of the Earth existed in the region scattering the icy rocks we expect to find there with its gravitational force. However, astronomers have yet to find anything that resembles this hypothetical 9th planet.(source)

2 The Brule river in Minnesota splits into two waterfalls as a result of an outcrop of rhyolite rocks. One waterfall feeds Lake Superior. Geologists aren’t sure where the water in the other waterfall ends up.

It’s called “Devil’s Kettle Falls,” and some might say the Devil’s at work here, but geologists continue to employ science in their search for the other half of the waterfall. The reason we can’t just observe where the water goes is that it descends into a large cavernous depth called the “Devil’s Kettle.” The obvious guess is that the water joins Lake Superior at some point. However, scientists haven’t been able to prove it. They’ve tried pouring dye and throwing logs into Devil’s Kettle, but no signs of these things have later been seen in Lake Superior. Scientists plan on using a dye trace method to follow the water trail during low-volume periods to figure out what’s really going on. An alternate theory suggests that the water siphons off into an ancient subterranean lava tube.(source)

3 During thunderstorms, spheres of light with a lifetime of under five seconds have been observed floating around. Ball lightning, as it’s called, has been denied by some scientists, but the frequency of sightings and other evidence forces them to come up with an explanation for the phenomenon.

Ball lightning is an electrical phenomenon that is recorded as far back as Argentinian mythology. Eyewitness accounts of ball lightning run the gamut from bizarre to eerie. Some describe it as ephemeral balls of lightning that move up and down or sideways while hovering. Others claim the spheres move like they have some sort of intelligence guiding their movement since they’ve been seen entering houses through doors and traversing hallways. These recollections could easily be faulty or embellished, but scientists haven’t reached a consensus on what causes the most fundamental behaviors of ball lightning, such as its short lifespan and the odor that often accompanies it. The explanations that have been put forward include the hypotheses that ball lightning is burning vaporized silicon and that it’s microwave radiation interacting with ionized air.(source)

4 A massive object called “The Great Attractor” is pulling the Milky Way towards itself with as much gravitational force as a million billion Suns. Scientists have no explanation for the immense gravitational pull which is able to attract objects at 14 million miles per hour.

The Great Attractor is a massive heavenly object located in the Laniakea Supercluster. There aren’t a lot of bodies in its vicinity on which the Great Attractor doesn’t have an effect. Our very own Milky Way galaxy isn’t immune to its effects. The galaxy is moving towards this mysterious object in space as if it were under the effect of a million billion suns. Because of the position of the Milky Way galaxy’s disk, scientists haven’t been able to clearly observe the Great Attractor. What they are sure of is that it isn’t a black hole because even the most massive kind wouldn’t have this effect on a galaxy. What we do know is that the Milky Way is definitely hurtling towards the Great Attractor at 14 million miles per hour, so we’re destined to meet it at some point in our future even if we don’t know a whole lot about it.(source)

5 What is the size of the largest sofa you can get around a tight corner of unit width? Even mathematicians remain puzzled by the question.

It seems like a simple enough problem to grasp which isn’t the case with a lot of the big questions in mathematics today. The original question was posed by  Leo Moser in 1966 using rather drab mathematical terminology: “what is the shape of the largest area in the plane that can be moved around a right-angled corner in a two-dimensional hallway of width 1?” Assume that the shape in question is a sofa, and all of a sudden math unexpectedly has real-world consequences. Many have been able to come up with large shapes that would fit the requirements, but nobody who could conclusively prove that they had come up with the largest one. The largest shape that currently fits the bill is called “Gerver’s Sofa,” and it looks something like two lemons connected to each other.(source)

6 In July 1976, the Viking landers detected carbon 14-bearing gas in the soil on Mars which is evidence of organic life. However, other instruments built to detect organic molecules found nothing. The source of the carbon-14 detected by the landers remains a mystery.

Data collected from more recent expeditions shows that Mars had a wet surface sometime in its past, so it’s likely that it was hospitable to life at some point. When the Viking landers detected methane containing carbon-14 in Martian soil, NASA scientists were elated because it was a sure sign of life on the planet. But the festivities were short-lived because another instrument with sensors to detect organic molecules did not discover any positive signs itself. Some have been quick to call the landers’ findings a false positive, but the evidence suggests otherwise. A USC researcher found that the emissions contain data pointing towards a circadian rhythm, which is a strong sign of life. However, scientists are still not sure what caused the contradictory pieces of information collected on Mars in 1976.(source)

7 Moving bicycles are stable even if there’s nobody riding them. There are various hypotheses on why this happens, but no widely accepted theory.

Bicycles in motion are a mystery until you figure out how to ride them. From there on in, you never forget how to steer one. But what is a mystery is how bicycles manage to remain stable when in motion even if there’s nobody riding them. What propels the bicycle, in this case, is a push. After you provide that initial momentum, bicycles are able to correct for any wobbling and self-stabilize to steer themselves smoothly. They eventually slow down and fall, of course, but for the duration that the energy from the initial push is available, bicycles seem to be able to keep themselves stable. Scientists have competing theories on why this happens, and invisible hands holding bicycles up isn’t one of them.(source)

8 The water in three crater lakes at Mount Kelimutu in Indonesia has changed color a few times. Geologists aren’t sure how or why.

What makes the observation all the more fascinating is that they are all located on the crest of the same volcanic formation. Yet, the water in each of the three lakes can be three different colors at any given time. Not just that, those colors seem to change very quickly for no apparent reason. Kelimutu is an active volcano, so geologists seem to think that the minerals in the rocks have something to do with the capricious, color-changing behavior. These chemical reactions turn the water into every hue from brown to green to black. However, none of the researchers have been able to come up with an acceptable explanation of what causes this. Locals believe that the spirits of the dead congregate at one of the three lakes depending on their age.(source)

9 NASA has released a paper on how the revolutionary EM Drive works, but scientists still can’t explain how it defies Newton’s Third Law of Motion.

Unlike traditional engines, the electromagnetic drive or, EM Drive, relies on microwaves rather than propellants. That makes it a fuelless propulsion method, meaning that there is no fuel ejected from the engine in order create propulsion. The issue with the EM Drive is more theoretical than it is practical. NASA itself has released a peer-reviewed paper on its functioning, but scientists have been left baffled by how it seems to defy Newton’s Third Law of Motion: “Every action has an equal and opposite reaction”. In the case of the EM Drive, there’s the action of the rocket taking off, but no opposite reaction. The existence of such a mode of transport has led scientists to question the very foundations of modern science.(source)

10 Scientists can’t seem to agree on how to classify an ancient animal called the “Tully monster.” The creature appears to possess various features that could make it either a vertebrate or an invertebrate.

The Tully monster belongs to a genus called Tullimonstrum and is believed to have inhabited parts of present-day USA about 300 million years ago. Hundreds of fossils of the animal have been discovered. Despite the large numbers of samples available to scientists for study, they have been unable to classify the Tully monster as either vertebrate or invertebrate. The reason for this is that the Tully monster’s body was a juxtaposition of features observed in both vertebrates and invertebrates. The animal had fins, eyestalks, and a jaw at the end of a stick-like appendage. Different teams of researchers have come to different conclusions based on their study of the fossils. The man after whom the animal is named, Francis Tully, called his inability to classify the curious creature a “serious and embarrassing matter.” (source)