Before we set out to explore the cosmos, we’d first have to know everything there is about our own neighborhood. And yet, other than the general position of things and a few specific details here and there, we know surprisingly little about what’s going on in our own solar system – especially in its most distant, darkest corners.
10. The Moons of Mars
In the past few years, various missions to Mars have given us a fairly good idea of what the planet is like. Its moons, however, are a different story altogether. Phobos and Deimos are 17 and 9 miles in diameter, respectively, and are perhaps the weirdest moons in the Solar System. Their size and composition make them look more like asteroids than moons, though that’s really all we know about them.
We have no idea where either of them came from, though some scientists do believe that they’re disintegrated parts of a bigger moon that used to exist a few million years ago. Others maintain that based on their composition, Phobos and Deimos are closer to a class of asteroids found in the asteroid belt, suggesting that their origins lie outside the solar system.
Venus is quite similar to Earth in some ways – like its size and mass – though in most other ways, it may as well be a different class of planet altogether. Its surface is perhaps one of the most hostile places for life in the Solar System, with temperatures reaching up to 900 degrees Fahrenheit. That’s hotter than Mercury, thanks to a severe greenhouse effect caused by its thick, choking atmosphere.
It’s also one of the most mysterious planets in the Solar System, despite its close proximity to Earth. We don’t know why it spins in a counterclockwise direction – unlike any other planet except Neptune – or why the winds in its atmosphere blow at speeds of up to 220 miles per hour, or even what its surface really looks like.
The most important mystery of Venus, though, is whether it harbors any kind of life. While its surface is definitely too extreme for any kind of life, Venus’s atmosphere could have the right, Earth-like conditions for rudimentary life forms. In fact, photographs of the planet taken back in 1927 do reveal dark, irregular patches in its atmosphere that absorb about the same amount of ultraviolet light as some bacteria and algae species on Earth.
8. The Oort Cloud
The Oort cloud is a shell made up of icy objects at the very edge of our solar system – a region so far away from us that we have no equipment to even observe it. The Sun is too far for its light to reach here, and our only chance at photographing it – Voyager 2 – would take another 300 years to reach it. That begs the question: how do we know it even exists?
It all goes back to a Dutch astronomer in the 1950s – Jan Hendrik Oort – who was trying to understand long-period comets. While most comets return within a few hundred years, long-period comets take thousands of years to complete an orbit, and seem to come from arbitrary directions in the sky instead of the predictable orbits of short period comets.
His answer was the Oort cloud, which is now a widely accepted explanation for long-period comets. It’s a vast boundary of the Solar System made up of icy bodies of all shapes and sizes, though that’s really all we know about it. We don’t know how the Oort cloud was formed, how thick it is or what its bodies are made of, even if it’s easily the largest structure in the Solar System we know of.
7. The Kuiper Belt
Where long-period comets could be explained by the Oort cloud, short-period comets likely come from another major grouping of icy bodies in the Solar System: the Kuiper belt. Named after one of the most influential planetary scientists of all time – Gerard Kuiper – the Kuiper belt is perhaps the largest structure in the Solar System after the Oort cloud.
It’s also one of the most mysterious, as all Kuiper Belt Objects, or KBOs, lie in a distant region of the system, making its exploration impossible. Many of them are made up of materials right from the earliest days of the formation of the Solar System – some even have moons of their own!
The most enduring mystery of the Kuiper belt, however, is the range of colors we see whenever we photograph those objects. Till now, we’ve photographed about 1,000 KBOs, and all of them seem to emit a range of colors – from blues to whites to reds, even if they should ideally be a single pixel of color due to the distance. It could be a natural result of volcanoes, cosmic rays or a variety of other possible reasons, though it could also be signs of rudimentary forms of life, as organic matter tends to glow red in observations taken from afar.
6. Saturn’s Hexagon Storm
Saturn has been a subject of interest for astronomers for millenia, mostly due to its fancy, unique rings – even if all of the outer planets also have rings of their own. Far more fascinating and mysterious, though, is its surface. Unlike Earth, Saturn is a gaseous planet made up almost entirely of hydrogen, along with some helium and trace amounts of other gasses like methane and ammonia.
To say that Saturn’s surface is active would be an understatement, as it’s home to many diverse weather events that we’ve never been able to fully explain. By far the weirdest, though, is a hexagon-shaped storm located at its north pole. First discovered by the Voyager spacecraft in the early 1980s, it’s about as wide as two Earths, though that’s really all we know about it. We don’t know how it was formed – as we’ve never observed a non-circular, polygon-shaped storm anywhere else in the Solar System – or even how long it’s been active for.
Oumuamua – named after the Hawaiian word for ‘scout’ – was the first interstellar object we’ve ever observed in real time, though other than that, we know almost nothing about it. First spotted by University of Hawaii’s Pan-STARRS1 telescope back in 2017, the flying body was nothing like any other piece of rock we’ve ever come across.
For one, Oumuamua was about ten times as long as it was wide, which is unusual for other bodies we’ve seen flying about in space. It was also red in color, possibly from all the radiation it would have been exposed to over the eons.
Its weirdest characteristic, however, was its speed – or more accurately its acceleration. Oumuamua was speeding up like it was propelled by an external force other than gravity, allowing it to enter and leave the Solar System instead of getting stuck orbiting the Sun. While comets have been observed to speed up near the sun due to its sheer gravity and heat, Oumuamua didn’t have a tail or any other feature of a comet, making that kind of natural acceleration impossible.
4. The Coronal Heating Problem
The Coronal Heating Problem is one of the oldest unsolved mysteries in astrophysics: why is the Sun’s corona, or its atmosphere, so much hotter than its surface? We know that all of the Sun’s heat and energy comes from the powerful nuclear fusion reactions going on in its core, though they manage to heat up the surface by barely 10,000 degrees Fahrenheit. That’s a lot, though nowhere near enough to be the energy powerhouse of the Solar System that is our Sun.
The heat is largely produced in its atmosphere, or the corona – the space where things start to get ionized into plasma due to the heat, as temperatures here can reach as high as two million degrees Fahrenheit. As you can guess, that shouldn’t happen; it’s like feeling warmer the farther away you get from a bonfire.
This transfer of heat from the Sun’s surface into its atmosphere has baffled scientists ever since it was first discovered in the 1940s. It’s not just one problem, either – we don’t know how that heat is transferred, how it’s sustained or even whether it’s a continuous event or multiple small explosions that look like a single event from afar.
When Voyager 2 flew past Uranus back in 1986, it reported nothing of note. It seemed to be a planet devoid of any character or special features – just one of the many icy bodies found in the distant reaches of the system, only much bigger.
As we’ve found out in the years since then, though, Uranus may be the most fascinating and mysterious planet in the Solar System. For starters, its spinning axis is almost-completely perpendicular to its axis around the Sun, which means that it’s revolving sideways. We’re not sure why that is, though some scientists think that it’s a result of its collision with a large body during the early years of the Solar System.
More curiously, Uranus’s atmosphere is unlike any other planet’s we’ve observed in the Solar System. In its lower, denser regions, temperatures can dip as low as -370 degrees Fahrenheit, which should ideally move up to about -100 Fahrenheit in the upper reaches. According to readings taken by the Voyager crafts in the 1980s, though, Uranus’s outermost atmosphere can get as hot as 1,300 degrees Fahrenheit.
This dramatic shift has perplexed astronomers and physicists ever since. Because of its distance, no part of Uranus should get even close to as hot as that, and it’s clear that it’s caused by something happening within its atmosphere. What that is, however, is anyone’s guess, as we’ve never observed such a weather phenomenon anywhere else in the Solar System.
2. Planet 9
The region beyond the orbit of Pluto until the boundary of the Oort cloud is sparsely-lit and mind-bogglingly vast, making it impossible for even our best equipment to scout it. That begs the question: are there other large bodies – possibly even planets – hiding in the darkness that we’ve just never seen?
If a study from 2016 published in The Astronomy Journal is to be believed, the answer is a definitive ‘yes’. Researchers studied various known Kuiper belt objects and found that six of them were going around the Sun in weird, abnormal orbits. The distortion was towards the same side in all six cases, too, which suggests that they’re being pulled by the same large object.
According to their calculations, this body is about ten times larger than Earth, even if we’ve never directly photographed or even observed it. Since then, we’ve found at least thirteen more Kuiper belt objects with similarly-distorted orbits.
1. The Moon
The moon is our nearest and most familiar neighbor in this vast, cold expanse called space, though till now, we have no clue about where it came from. Scientists just can’t agree on a single unified theory on the true origins of the moon, and it seems that every new study on the topic raises more questions than it answers.
The prevailing theory is known as the Giant Impact Hypothesis, which states that the moon was formed as a result of a collision between a young Earth and a Mars-sized planet called Theia. The debris from the collision came together over millions of years to give birth to the moon, which could explain its unusually large size.
If that were true, though, the moon would be completely made out of material from Theia. Samples brought from the various Apollo missions directly contradict that, however, as the moon has since been found to be almost identical in composition to Earth, especially its mantle. While it rules out the giant-impact theory, it does seem to suggest the moon and Earth formed in the same region of the Solar system, likely during its early, tumultuous years.