We’ve put men on the moon and car-sized robots on Mars. We’ve also discovered nearly 1,800 planets around other stars. It would be easy to think that we’ve got a pretty good handle on what’s out there. Then you find out that there’s a bizarre giant hexagon on Saturn, and you realize that we don’t understand half of what’s going on with our closest neighbors. These mysteries make it clear we’re going to need a lot more robots.
10 The Venus Vortex
A giant vortex near the Venus’s south pole behaves like a storm but without rain or lightning. It’s about 1,800 kilometers (1,200 mi) across, 18 kilometers (12 mi) tall, and takes place 41 kilometers (26 mi) above the planet’s surface. We used to think it was an oval, but in 2011, scientists discovered it regularly changes shape. Sometimes it looks like an “S” or an “8,” but often, it’s just an irregular blob. It’s about three degrees off from the south pole, which it orbits every 5 to 10 days.
In 2013, we discovered it isn’t a single vortex at all. It’s actually two vortices, with two centers of rotation at different altitudes. They break up and merge but rarely line up. Scientists studying the pair would have expected them to move as one feature and are unsure why they don’t. This may have something to do with how Venus’s atmosphere rotates 60 times faster than the planet itself, but scientists haven’t figured out the connection yet.
9 The Very Mysterious Iapetus
Iapetus, Saturn’s third-largest moon, has been a source of mystery ever since Giovanni Cassini discovered it in 1671. The Italian astronomer noticed that the moon’s forward face, which leads the orbit, is darker than the trailing hemisphere. In fact, the back is 10 times brighter.
This oddity remained unexplained for 336 years, until we sent a probe past Saturn—a probe fittingly named after Cassini. Scientists discovered that the moon originally swept up dust as it moved. This darkened the front, which then absorbed more sunlight, causing ice there to melt. This darkened it further, absorbing still more sunlight, and so the spiral continued.
The Cassini probe may have solved that mystery but not before discovering a new one. An 18-kilometer-tall (12 mi) ridge runs around most of the moon’s equator—that’s over twice the height of Everest on a moon one-ninth Earth’s diameter. One theory says Iapetus had a ring which fell to the surface, forming the ridge. Another suggests that a 1,000-kilometer-wide (650 mi) asteroid crashed into Iapetus and suddenly slowed the moon’s spin. The resulting stress flattened the moon at the poles, creating a central bulge.
Not content with simply providing its own mysteries, Iapetus may also help solve those on other planets. A sturzstrom is a type of landslide found on Earth and Mars that travels about 15 times further than most, and we have no idea why. One theory suggests that sound waves make rock particles act like a fluid. These landslides appear to be extremely common on Iapetus, so the more we learn about its surface, the closer we may be to figuring out what causes sturzstroms.
8 The Spider On Mercury
When NASA’s MESSENGER probe made a pass on Mercury in January 2011, it photographed an impact crater different from any other we’ve found in the solar system. It’s been nicknamed “the spider” as around 50 troughs branch out from the basin in all directions. A scientist from the laboratory that helped build the probe called it “a real mystery” and suggested volcanic activity may be behind it. The structure has since received the official name “Pantheon Fossae,” named after the Pantheon domed temple in Rome, withFossae being the Latin word for “trenches.” The central crater has been called Apollodorus, after the Pantheon’s chief architect.
High-resolution images suggest that the 41-kilometer-wide (27 mi) crater may have nothing to do with the trenches at all, as it’s slightly off-center. A meteor may have struck close to the bull’s-eye after the pattern had already formed.
