Mercury’s rotation around the sun is unique. Due to their closeness, it is gravitationally locked: for every two orbits around the sun, Mercury completes three rotations of its axis. Mercury’s relationship with the sun is currently stable. But when the sun burns out in about five billion years, resulting in it becoming a red giant, it will devour Mercury. And Venus, too, because – why not? Earth and Mars will have to watch out as they’re going to get displaced.

Venus takes about 243 Earth days to complete a single rotation. So one day on Venus is longer than on any other planet in our solar system. This is even more amazing compared to its year, roughly 224 Earth days. No wonder Venus appears to be pretty peeved. Potential visitors should be prepared for rain made of sulphuric acid and will be crushed and burned simultaneously – hey, two for the price of one. The air pressure is like being 1000 km below sea on Earth but with temperatures high enough to melt lead.

Humanity was once very attracted by our nightly companion. But manned missions became refocused on Earth’s orbit once the race to the Moon was decided in 1969 with Apollo 11. We’re really sorry, Moon. Adding up all the time spent on the lunar surface, humans have spent less than two weeks on the moon, who probably feels very ignored now that today’s spacefaring nations and private corporations are dreaming of the first manned flights to Mars.

The dark side of the Moon … is just called that because it’s not visible from Earth. The Moon rotates around its axis in about the same time it takes to orbit Earth (i.e. synchronous rotation). That's why we always see the same side. The Moon used to rotate at a faster rate, but its rotation slowed and became tidally locked in this orientation.  

Mars‘ atmosphere was much denser 2-4 billion years ago offering plenty of liquid water on its surface which was very active due to erosion and volcanism. Was there life during those earth-like conditions? Scientist simply don’t know. (No, the internet doesn‘t, either.) Mars lost its atmosphere, grew cold and (probably) geological inactive, almost any water left is frozen at the poles and below surface.

The four inner planets have a hard surface of rock covering a metal core. This seems to have been caused during the formation of our solar system, when objects closer to the newly formed star could only form from elements with high melting points (iron, nickel, silicates). More volatile components like water and methane could only stabilise at a certain distance – thus forming gas giants, comets and cool rocks like Pluto.

Jupiter’s Great Red Spot is an enormous storm, which was first documented in 1831 (or possibly 1665). Nobody knows exactly how long the storm has been raging or if it’s permanent. But we do know it’s large enough for about three Earths to fit inside of it!
Jupiter has a very turbulent atmosphere, divided into zones and cloud belts, and its different colours are due to a mixture of               ammonia crystals and sulphur. Jupiter also has a faint ring system, but as it’s almost black and with particles as small as those in cigarette smoke, it means it’s very hard to observe. So maybe don’t bother. trying.

Jupiter has the largest number of moons with secure orbits of any planet in our solar system. Most of these objects are captured flybys from outer regions like the comet Shoemaker-Levy 9, which impacted in Jupiter’s southern hemisphere in 1994. So Jupiter’s collection isn’t very well kept. Even the largest moons are permanently stressed by its gravitational field, causing icy Europa’s surface to wrinkle (liniae) and even to partially vaporise and become fluid underneath. Which doesn’t sound like fun.

Saturn’s 95 Earth masses are not what you’d call “lightweight”. But its low density of 0.69 g/cm³ means it could float on water (good luck trying to find a pool large enough). However, thanks to this low density and fast rotation, it’s actually pretty flat, with a polar diameter of only 90% of its equatorial diameter. Saturn’s rings don’t help at all in slimming down its frame. But does that diminish its attractiveness? Over 60 moons would dare to disagree, so #stopbodyshaming.

Uranus’ axis is tilted almost 98°, so, effectively, it rotates on its side. This means Uranus’ north pole points at the sun for half of its 84 Earth-year-long rotation, while the south pole points at the sun the other half of its year. Kind of like being in Norway. Like every oddball with an embarrassing name, Uranus must have been bullied by at least one large object to achieve that level of skew. It also has the solar system´s coldest atmosphere, measuring about -224° C, which is globally constant even in sunlit areas. Again, kind of like Norway.

Neptune, (so far) the farthest planet from the sun, has an almost perfectly circular orbit with an eccentricity of only 0.0113. Neptune’s gravitational force has a profound impact on the region directly beyond it, forcing Pluto and similar objects to synchronize, completing two orbits for every three of Neptune. However, the control freak doesn’t quite have that kind of grip on itself, unleashing storms of up to 1,300 mph in its atmosphere.

Sunlight travelling to Pluto needs 5 ½ hours to arrive. The sun’s perceived radius in these outer regions is only 1/50 of what it appears on Earth. But the daylight is actually still bright enough to be compared to earthly twilight. So Pluto and its five moons are not alone in the dark. 

Pluto hasn’t been the ninth planet of the solar system since 2006. Deal with it. A planet is defined as “a rounded object in a stable orbit around a star with enough gravitational force to clear its neighbouring region of similar objects”. Pluto doesn’t quite fit two of these three requirements.
We all love Pluto despite of that. So it’s time to #stopbullying.