21. 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.
22. 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.
23. 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.
24. 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 hundreds of 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.
25. 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.