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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.
1. Uranus is tilted on its sideSlide 2 of 51
1. Uranus is tilted on its side
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.Slide 3 of 51
2. Jupiter's moon Io has towering volcanic eruptionsSlide 4 of 51
2. 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.Slide 5 of 51
3. Mars has the biggest volcano (that we know of)Slide 6 of 51
3. 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.Slide 7 of 51
4. Mars also has the longest valleySlide 8 of 51