Our place in space
The solar system is a bizarre place with its alien planets, mysterious moons and strange phenomena that are so out-of-this-world they elude explanation. Scientists have discovered ice-spewing volcanoes on Pluto, while Mars is home to a truly "grand" canyon the size of the United States. There may even be a giant, undiscovered planet lurking somewhere beyond Neptune. Read on to find out some of the strangest facts about planets, dwarf planets, comets and other incredible objects around the solar system.
Uranus appears to be a featureless blue ball upon first glance, but this gas giant of the outer solar system is pretty weird upon closer inspection. First, the planet rotates on its side for reasons scientists haven't quite figured out. The most likely explanation is that it underwent some sort of one or more titanic collisions in the ancient past. In any case, the tilt makes Uranus unique among the solar system planets.
Uranus also has tenuous rings, which were confirmed when the planet passed in front of a star (from Earth's perspective) in 1977; as the star's light winked on and off repeatedly, astronomers realized there was more than just a planet blocking its starlight. More recently, astronomers spotted storms in Uranus' atmosphere several years after its closest approach to the sun, when the atmosphere would have been heated the most.
Jupiter's moon Io has towering volcanic eruptions
For those of us used to Earth's relatively inactive moon, Io's chaotic landscape may come as a huge surprise. The Jovian moon has hundreds of volcanoes and is considered the most active moon in the solar system, sending plumes up to 250 miles into its atmosphere . Some spacecraft have caught the moon erupting; the Pluto-bound New Horizons craft caught a glimpse of Io bursting when it passed by in 2007.
Io's eruptions come from the immense gravity the moon is exposed to, being nestled in Jupiter's gravitational well. The moon's insides tense up and relax as it orbits closer to, and farther from, the planet, generating enough energy for volcanic activity. Scientists are still trying to figure out how heat spreads through Io's interior, though, making it difficult to predict where the volcanoes exist using scientific models alone.
Mars has the biggest volcano (that we know of)
While Mars seems quiet now, we know that in the past something caused gigantic volcanoes to form and erupt. This includes Olympus Mons, the biggest volcano ever discovered in the solar system. At 374 miles (602 km) across, the volcano is comparable to the size of Arizona. It's 16 miles (25 kilometers) high, or triple the height of Mount Everest, the tallest mountain on Earth.
Volcanoes on Mars can grow to such immense size because gravity is much weaker on the Red Planet than it is on Earth. But how those volcanoes came to be in the first place is not well known. There is a debate as to whether Mars has a global plate tectonic system and whether it is active.
Mars also has the longest valley
If you thought the Grand Canyon was big, that's nothing compared to Valles Marineris. At 2,500 miles (4,000 km) long, this immense system of Martian canyons is more than 10 times as long as the Grand Canyon on Earth. Valles Marineris escaped the notice of early Mars spacecraft (which flew over other parts of the planet) and was finally spotted by the global mapping mission Mariner 9 in 1971. And what a sight it was to miss - Valles Marineris is about as long as the United States!
The lack of active plate tectonics on Mars makes it tough to figure out how the canyon formed. Some scientists even think that a chain of volcanoes on the other side of the planet, known as the Tharsis Ridge, somehow bent the crust from the opposite side of Mars, thus creating Valles Marineris. More close-up study is needed to learn more, but you can't send a rover over there easily.
Venus has super-powerful winds
Venus is a hellish planet with a high-temperature, high-pressure environment on its surface. Ten of the Soviet Union's heavily shielded Venera spacecraft lasted only a few minutes on its surface when they landed there in the 1970s.
But even above its surface, the planet has a bizarre environment. Scientists have found that its upper winds flow 50 times faster than the planet's rotation. The European Venus Express spacecraft (which orbited the planet between 2006 and 2014) tracked the winds over long periods and detected periodic variations. It also found that the hurricane-force winds appeared to be getting stronger over time.
There is water ice everywhere
Water ice was once considered a rare substance in space, but now we know we just weren't looking for it in the right places. In fact, water ice exists all over the solar system. Ice is a common component of comets and asteroids, for example. But we know that not all ice is the same. Close-up examination of Comet 67P/Churyumov–Gerasimenko by the European Space Agency's Rosetta spacecraft, for example, revealed a different kind of water ice than what is found on Earth.
That said, we've spotted water ice all over the solar system. It's in permanently shadowed craters on Mercury and the moon, although we don't know if there's enough to support colonies in those places. Mars also has ice at its poles, in frost and likely below the surface dust. Even smaller bodies in the solar system have ice - Jupiter's moon Europa, Saturn's moon Enceladus, and the dwarf planet Ceres, among others
Spacecraft have visited every planet
We've been exploring space for more than 60 years, and have been lucky enough to get close-up pictures of dozens of celestial objects. Most notably, we've sent spacecraft to all of the planets in our solar system (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune as well as two dwarf planets:Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune as well as two dwarf planets: Pluto and Ceres.
There could be life in the solar system, somewhere
So far, scientists have found no evidence that life exists elsewhere in the solar system. But as we learn more about how "extreme" microbes live in underwater volcanic vents or in frozen environments, more possibilities open up for where they could live on other planets. These aren't the aliens people once feared lived on Mars, but microbial life in the solar system is a possibility.
Microbial life is now considered so likely on Mars that scientists take special precautions to sterilize spacecraft before sending them over there. That's not the only place, though. With several icy moons scattered around the solar system, it's possible there are microbes somewhere in the oceans of Jupiter's Europa, or perhaps underneath the ice at Saturn's Enceladus, among other locations.
Mercury is still shrinking
For many years, scientists believed that Earth was the only tectonically active planet in the solar system. That changed after the Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft did the first orbital mission at Mercury, mapping the entire planet in high definition and getting a look at the features on its surface.
In 2016, data from MESSENGER (which had crashed into Mercury as planned in April 2015) revealed cliff-like landforms known as fault scarps. Because the fault scarps are relatively small, scientists are sure that they weren't created that long ago and that the planet is still contracting 4.5 billion years after the solar system was formed.
There are mountains on Pluto
Pluto is a tiny world at the edge of the solar system, so at first it was thought that the dwarf planet would have a fairly uniform environment. That changed when NASA's New Horizons spacecraft flew by there in 2015, sending back pictures that altered our view of Pluto forever.
Among the astounding discoveries were icy mountains that are 11,000 feet (3,300 meters) high, indicating that Pluto must have been geologically active as little as 100 million years ago. But geological activity requires energy, and the source of that energy inside Pluto is a mystery. The sun is too far away from Pluto to generate enough heat for geological activity, and there are no large planets nearby that could have caused such disruption with gravity.
Pluto has a bizarre atmosphere
Pluto's observed atmosphere broke all the predictions. Scientists saw the haze extending as high as 1,000 miles (1,600 km), rising higher above the surface than the atmosphere on Earth. As data from New Horizons flowed in, scientists analyzed the haze and discovered some surprises there, too.
Scientists found about 20 layers in Pluto's atmosphere that are both cooler and more compact than expected. This affects calculations for how quickly Pluto loses its nitrogen-rich atmosphere to space. NASA's New Horizons team found that tons of nitrogen gas escape the dwarf planet by the hour, but somehow Pluto is able to constantly resupply that lost nitrogen. The dwarf planet is likely creating more of it through geological activity.
Rings are everywhere in the solar system
While we've known about Saturn's rings since telescopes were invented in the 1600s, it took spacecraft and more powerful telescopes built in the last 50 years to reveal more. We now know that every planet in the outer solar system – Jupiter, Saturn, Uranus and Neptune – each have ring systems. That said, rings are very different from planet to planet. Saturn's spectacular rings, which may have come from a broken-up moon, are not repeated anywhere else.
Rings aren't limited to planets, either. In 2014, for example, astronomers discovered rings were discovered around the asteroid Chariklo. Why such a small body would have rings is a mystery, but one hypothesis is perhaps a broken-up moonlet created the fragments.
Jupiter's Great Red Spot is shrinking
Along with being the solar system's largest planet, Jupiter also hosts the solar system's largest storm. Known as the Great Red Spot (since it's big and ruddy-colored), it's been observed in telescopes since the 1600s. Nobody knows exactly why the storm has been raging for centuries, but in recent decades another mystery emerged: the spot is getting smaller.
In 2014, the storm was only 10,250 miles (16,500 km) across, about half of what was measured historically. The shrinkage is being monitored in professional telescopes and also by amateurs, as telescope and computer technology allow high-powered photographs at an affordable cost. Amateurs are often able to make more consistent measurements of Jupiter, because viewing time on larger, professional telescopes is limited and often split between different objects.
Most comets are spotted with a sun-gazing telescope
Comets used to be the province of amateur astronomers, who spent night after night scouring the skies with telescopes. While some professional observatories also made discoveries while viewing comets, that really began to change with the launch of the Solar and Heliospheric Observatory (SOHO) in 1995.
Since then, the spacecraft has found more than 2,400 comets, which is incredible considering its primary mission is to observe the sun. These comets are nicknamed "sungrazers" because they come so close to the sun. Many amateurs still participate in the search for comets by picking them out from raw SOHO images. One of SOHO's most famous observations came when it watched the breakup of the bright Comet ISON in 2013.
There may be a huge planet at the edge of the solar system
In January, 2015, California Institute of Technology astronomers Konstantin Batygin and Mike Brown announced - based on mathematical calculations and on simulations - that there could be a giant planet lurking far beyond Neptune. Several teams are now on the search for this theoretical "Planet Nine," which could take decades to find (if it's actually out there.)
This large object, if it exists, could help explain the movements of some objects in the Kuiper Belt, an icy collection of objects beyond Neptune's orbit. Brown has already discovered several large objects in that area that in some cases rivaled or exceeded the size of Pluto. (His discoveries were one of the catalysts for changing Pluto's status from planet to dwarf planet in 2006.)
Neptune radiates more heat than it gets from the sun
Neptune is far away from Earth, and you can bet that scientists would love to get another spacecraft out there sometime soon. Perhaps today's technology could better answer some Neptunian mysteries, such as why the blue planet is giving off more heat than it receives. It's bizarre, considering that Neptune is so far away from the faint sun.
Scientists would love to know what's going on, because it's believed that the vast temperature differential could affect weather processes on the planet. NASA estimates the temperature difference between the heat source and the cloud tops is minus 260 degrees Fahrenheit (minus 160 degrees Celsius).
Jupiter has more heavy elements (proportionally) than the sun
The sun and the planets likely formed from the same cloud of hydrogen and helium gas. This would especially be true of Jupiter, a planet 317 times the size of Earth that pulled in a lot more gas than our own planet. So if that's the case, why does Jupiter have more heavy, rocky elements than the sun?
One of the leading theories is that Jupiter's atmosphere is "enriched" by the comets, asteroids and other small rocky bodies that it pulls in with its strong gravitational field. Since amateur technology has improved, several small bodies have been seen falling into Jupiter in the past decade.
Earth's Van Allen belts are more bizarre than expected
Earth has bands of radiation belts surrounding our planet, known as the Van Allen belts (named after the discoverer of this phenomenon.) While we've known about the belts since the dawn of the space age, the Van Allen Probes (launched in 2012) have provided our best-ever view of them. They've uncovered quite a few surprises along the way.
We now know that the belts expand and contract according to solar activity. Sometimes the belts are very distinct, and sometimes they swell into one massive belt. An extra radiation belt (beyond the known two) was spotted in 2013. Understanding these belts helps scientists make better predictions about space weather, or solar storms.
Uranus has a very battered moon
One of the most bizarre moons in the outer solar system is Miranda, which, unfortunately, we saw only once when Voyager 2 passed by it in 1986. This moon of Uranus has bizarre features on its surface, with sharp boundaries separating ridges, craters and other things. It is possible that the moon could have had tectonic activity, but how that happened on a body with a diameter of 500 km is a mystery.
Scientists aren't sure how the patchwork surface came about, and we likely won't be able to tell for sure until another mission gets out there. Perhaps the moon was smashed into bits and coalesced again, or maybe meteorites struck the surface and caused temporary melts in small areas.
Saturn has a two-tone moon
Saturn's moon Iapetus is a study in contrasts, with a very dark hemisphere and a very light hemisphere. It's unlike anything else in the solar system and has sparked speculation as to what is really going on.
Some scientists believe that particles from Phoebe (another, darker moon) may be falling on its surface. Others speculate that it's due to volcanic eruptions of hydrocarbons, which would create dark patches.
Cassini's flyby of Iapetus in 2007 also postulated a third theory, which is thermal segregation. Iapetus only rotates once every 79 days or so, stretching out the daily temperature cycle. This could force icy material to move into colder regions as the dark material heats up.
Titan has a liquid cycle, but it's definitely not water
Another weird moon in Saturn's system is Titan, which hosts a liquid "cycle" that moves between the atmosphere and the surface. That sounds a lot like Earth, until you begin looking at its environment. It has lakes filled with methane and ethane, which could be reminiscent of the chemistry that occurred on Earth before life arose.
Titan also nitrogen-rich compounds known as tholins. This gives Titan its distinctive orange color. Titan's atmosphere is so thick that radar is needed to penetrate a spacecraft's view down to the surface.
Organics are commonplace in the solar system
Organics are molecules that are present both in life processes and in nonlife processes. While common on Earth, what's interesting is they're also in many places in the solar system. When scientists found organics on the surface of Comet 67P, for example, it bolstered the case that perhaps organics were brought to the surface of Earth by small bodies.
Organics have also been found on the surface of Mercury, on Saturn's moon Titan (which gives Titan its orange color) and on Mars. This makes them common in the solar system.
Mars has varying amounts of methane in its atmosphere
Methane is a substance that is produced by life (such as by microbes) or by natural processes such as volcanic activity. But why it keeps fluctuating so much on Mars is a mystery. Various telescopes and space probes have found different levels of methane on Mars over the years, making it hard to chart where this substance is coming from. It's unclear if the varying levels of methane are due to telescopic differences, or differences in the amount of methane coming from the surface.
NASA's Curiosity rover even detected a spike in methane during one Martian year that did not repeat the next, indicating whatever it saw was not seasonal. It will likely take more long-term observations of Mars to fully figure out the mystery.
Saturn has a hexagonal-shaped storm
Saturn's northern hemisphere has a raging six-sided storm nicknamed "the hexagon." Why exactly it's that shape is a mystery. But what is known is that this hexagon, which shares several features in common with hurricanes, has been there for at least decades- if not a hundred years.
Lighting conditions in Saturn's northern hemisphere began to improve in 2012, when Saturn approached its northern summer solstice. Cassini will continue observing the feature until the end of its mission in 2017, at the height of the solstice.
The solar atmosphere is much hotter than the surface
While the sun's visible surface - the photosphere - is 10,000 degrees Fahrenheit (5,500 degrees Celsius), the upper atmosphere has temperatures in the millions of degrees. It's a large temperature differential with little explanation, for now
NASA has several sun-gazing spacecraft on the case, however, and they have some ideas for how the heating is generated. One is "heat bombs," which happens when magnetic fields cross and realign in the corona. Another is when plasma waves move from the sun's surface into the corona.