Satellites take center stage today
Planets and stars receive a lot of our attention, but we think that there is still plenty to go around. The natural satellites of planets are called moons and they can be just as interesting (sometimes more) as planets. We have a ton of bizarre phenomena and weird geological activity in the solar system and most of it takes place not on planets, but on the moons around them. So today we are looking at a few facts about them.
1. There are a lot of them. But how many are there exactly? It’s pretty hard to tell. We are still discovering new ones because moons can be pretty tiny. Right now we’re at 173. Just for the sake of clarity, we are only referring to moons that orbit planets, not satellites orbiting dwarf planets or any other kind of minor celestial objects. If we included these, you’d have to add about 200 more.
2. Where are they all? Most of these moons aren’t particularly significant because they are very tiny and they are orbiting really big things like the gas giants. We are likely to find more each time we send a probe past the asteroid belt. Out of the total 173 moons, most of them can be found around Jupiter and Saturn. Jupiter has the most moons with 67 and Saturn is close behind with 62.
Jupiter and four Galilean Moons
3. Almost all planets have moons. Natural satellites are not uncommon and, as we can see above, the bigger the objects the more satellites it’s bound to have. Out of the eight planets in our solar system, six of them have moons. All the gas giants have them in the double digits while Mars has two and we have one which we call the Moon…which isn’t confusing at all. If you want to be fancy, you could refer to it by its Latin name, Luna. Venus and Mercury don’t have any satellites. In case you are wondering about our notorious ex-planet Pluto (or is it?), it has five moons.
4. They are not as small as you would think. The size of the moons can really vary wildly since what matters most is their size in comparison to whatever object they are orbiting. If they are orbiting a really huge planet, they can get pretty big too since that planet will have the gravitational pull necessary in order to keep its satellites in orbit. Ganymede is the largest moon in our planet, a satellite a Jupiter. It is followed pretty close by Titan, a moon of Saturn. Both of these are actually larger than the planet Mercury.
Biggest moons and the Earth for scale
5. Our Moon is pretty weird. We’ve talked about the Moon already so we won’t go into too much detail, but the size of our Moon really is surprising. It’s not that it’s very big (although it is; it’s the fifth largest moon in the solar system), it’s more of how big it is compared to its primary (which is us). Mars has two teeny-tiny moons called Phobos and Deimos, Venus and Mercury have nothing and Pluto has one reasonably big moon called Charon (although nowhere near the size of the Moon) and four tiny ones. We really don’t have anything similar to compare it to. All the other similarly sized moons orbit giants like Saturn and Jupiter.
6. They have volcanoes. We were pretty shocked when we found volcanic activity in other places other than Earth. So far, we know for certain of five places in the solar system with volcanoes: one is us, another is Venus and three are moons: Enceladus, Io and Triton. Out of them all, Io is the most volcanically active object in the solar system. So far we’ve detected about 150 volcanoes on the Jovian moon and astronomers approximate that there could be around 400 total.
7. Some volcanoes shoot ice. On an even cooler note, some of the aforementioned moons don’t just have volcanoes, but cryovolcanoes. This is something which isn’t found on Earth. Basically, when the volcanoes erupt, they spit out a mixture of volatiles such as water, methane and ammonia. This phenomenon was first observed on Neptune’s moon Triton and then on Enceladus. Circumstantial evidence point to other moons such as Ganymede and Titan having cryovolcanoes, as well.
Cryovolcanoes on Enceladus
8. Mimas is weird. Mimas is a small moon of Saturn which has become something of a nerd favorite on the Internet. It is relatively unremarkable except for the fact that from a certain angle it looks an awful lot like the Death Star from Star Wars. Not only that, but if you look at a temperature map of the moon, it gets even better. Again, this only works from a particular angle, but Mimas looks just like Pac Man and it even has a crater to symbolize a power pellet.
Deimos, moon of Mars
9. They have weird shapes. If you’ve ever wondered why most objects in the Universe eventually become round, the short answer is gravity. However, you’ll probably also know that objects like asteroids or comets are not typically round because they are not large enough. There is a point when an object becomes sufficiently large that it starts to shape itself but, until then, it can take a lot of weird shapes. Since many moons are quite tiny, they take on many bizarre forms. For example, Pan kinda looks like a flying saucer from a cheesy 60s sci-fi movie. Deimos looks like a smooth stone you’d throw across the surface of a lake. Methone looks like an egg.
10. They could have life on them. This isn’t just guesswork here. Several moons are genuine candidates for extraterrestrial life. They have suitable conditions to support or have supported primitive life at some point. As we’ve talked before, Jupiter’s moon Europa is seen as the likeliest candidate, but Titan also makes a good case for itself. Until recently, we didn’t really know what Titan actually looked like thanks to its very thick atmosphere, but now we can see that it looks surprisingly a lot like Earth.