Helena Puumala’s SF Romance series features a planet with seven moons. This rather unusual setting gives me the opportunity to talk about some of the remarkable moons in our solar system, as I test different moons for the cover of book 2 of the series. This blog is about Europa, one of the four large moons of Jupiter, and one of the most interesting, as there is intense speculation that it could harbor life in its deep ocean.
Here are a few facts about Europa, courtesy of Wiki:
- It's the smallest of Jupiter’s four Galilean moons, but still the sixth largest in the solar system.
- As noted above, it is one of the four original moons discovered by Galileo in 1610 (thus, referred to a Galilean moon).
- It is the second farthest from Jupiter of the four Galilean moons. It is easy to find in a small telescope.
- It participates in a 1:2:4 orbital resonance with the two Galilean moons that it is between, Io (closest to Jupiter) and Ganymede(third from Jupiter). That means, for every one time Ganymede goes around Jupiter, Europa goes around twice and Io goes around four times.
- Europa’s orbit takes about three and a half days. It is tidally locked with Jupiter (its rotation rate is the same as its orbit rate), so at a certain point on Europa, Jupiter would always be directly overhead.
- The orbit is slightly eccentric (non-circular), so sometimes it is a little farther from Jupiter and sometimes it is a little closer. This causes the planet’s shape to change slightly, elongating when closest to Jupiter and becoming more spherical when farther away. The flexing of the planet creates heat (friction, basically), which keeps the liquid ocean under the ice from freezing.
- The orbital resonance with Io “pumps” its orbit, so that it remains elliptical and does not completely circularize over time. Thus, the moon continues flexing every 3.5 days, supplying a constant source of heat for the buried ocean.
- An ocean exists many kilometers underneath Europa’s icy crust, which acts as an insulating blanket. Due to the temperature at the surface (-160 Celsius) that surface ice would be as hard as granite.
- Some researchers think certain “chaotic” surface features indicate that this ocean may occasionally break through in places to the surface. This is an area of intense debate.
- Europa has a small magnetic moment, probably caused by the salty subsurface ocean, which can act a conductor, and induces the magnetic field.
- Water vapor plumes have been spotted by the Hubble Space Telescope.
- It is not known exactly how far down the liquid ocean is, but speculations range from a few kilometers to tens of kilometers.
- Life could cluster around features equivalent to the “black smokers” of Earth’s oceans, where heat and matter from the crust and mantle below escape into the ocean. Europa might have similar hydrothermal vents.
- Alternatively, primitive life, like bacterial mats on Earth, might exist near the bottom of this ocean, which would be warmer than the higher levels.
- There may even be a relatively high oxygen content in this ocean, due to the breakdown of hydrogen peroxide, which seems to exist on the surface. This could then be absorbed into the ocean below.
- Free oxygen might also come from water ice being broken down at the surface of Europa, by cosmic rays, that is then absorbed into the deep ocean.
- A high oxygen content could mean complex life (fish?).
- Its albedo is about 64% (about 64% of the light falling on it is reflected). This is one of the highest albedos in the solar system.
- The surface is smooth and bright, due to the constant reworking of it by the tidal energies noted above.
- There are plans to land a probe on Europa and drill into the surface. That would be difficult and expensive; among other things, the surface has high levels of radiation (via Jupiter’s effect on the solar wind).
Here's a picture of Europa, taken by a NASA probe.
Now, here’s a well-deserved pitch for Helena Pummala’s latest SF Romance series, The Witches’ Stones:
Helena Puumala's SF Romance series features the planet Kordea, home to a race of beautiful and powerful psychic aliens, known as the Witches of Kordea. The planet has seven moons, an extraordinary arrangement for a terrestrial sized planet in its star's habitable zone, as is noted in Book 1, which you can get from the link below: :).
In fact, the moons of Kordea become a central element in Book 2, soon to come out. The cover below actually borrows the moon Europa, one of the moons of Jupiter. I will by testing out different moons for the cover of the Witches' Stones Book 2, so, as noted above, this gives me the opportunity to do a mini-tour of some of the major moons of our solar system. Moons, including our own, are fascinating. A terrestrial planet with seven moons would be cool (though it would probably be a very unstable arrangement).