betsymccall.net Lifelong Learning Astronomy Planets Moons

While the Earth has a moon, not every planet does. Mars' moons are captured asteroids and are destined eventually to impact the surface if left alone. This means that Earth is unique among the terrestrial planets of having one that was formed along with it in the early stages of the solar system. The larger, jovian planets all have large moons, as well as smaller, captured ones. Each is unique. While it's impossible to list links for every single moon here, I've done my best to provide a broad selection of the most interesting.

I've been working on Triton recently and a few papers and presentations have come out of that, and probably more are coming. Here's a taste.

Subsurface Oceans

Short Presentation 1 (pdf)
Short Presentation 2 (pdf)
Long Presentation (pdf)
Paper
- Some responses to the comments my prof made on the paper:
  - If this is for an audience like my class, in Columbus, Ohio, physics majors in their senior year, why exactly do I have to explain that when water freezes, ice is less dense and so it floats (thus freezing from the top down and not the bottom up), and so the layer of ice conducts heat to the exterior more slowly than evaporative cooling, etc.? Surely, everyone here has seen rivers and puddles freeze and knows the water underneath stays liquid, right? But if you want me to say this, just don't ask me "why are we looking for subsurface oceans?". That's too vague. I mean, you know surface oceans don't exist in the solar system except for here, right?
  - If my audience can't be assumed to know the above, why exactly is the "Nova-style writing" not appropriate?
  - The tidal forces we are talking about are the tidal forces on moons that are tidally locked to their parent body, not the tides on objects that are not tidally locked. Tidally locked bodies always have the force vector pointing in the same direction, and so only the magnitude can change, not the direction. On a body like the Earth, the objects causing the tides are not always pointing in the same direction, and so the tidal forces are calculated differently because the minimum and maximum are achieved by a change in geometry more than just a change in distance. The only parent body the formula in my paper applies to is Pluto, but all the objects I am talking about are moons.
  - Water is most abundant among all ices because it's made of hydrogen and oxygen. Oxygen is the third (?) most abundant molecule after hydrogen and helium, and since hydrogen is most abundant, you get a lot of water. Secondly, we know we are dealing with water ice because of the temperature range we are talking about, and because the surfaces of the two primary bodies we discuss in the paper are covered in water ice at the surface. Since water has a relatively high freezing temperature, this also plays a role. We know the water is not liquid nitrogen because at the surface temperatures of the bodies we considered (as well as on many we didn't), the temperature is well above the boiling point of nitrogen. To liquefy nitrogen you have to get it much colder than 100K. And as you get closer to the interior of the body, the temperature climbs. Only Triton could possibly have a liquid nitrogen layer because its surface temperature is below the freezing point of nitrogen (and its surface is covered in nitrogen and methane ice). Do I really need to say it's not cold enough for liquid nitrogen when I gave the surface temps of the bodies in question? Do I really need to say we think the ocean is water when I said the surface is covered with water ice? You know, you guys did take basic chemistry, yes?
- Yeah, just a bit annoyed. :) But there it is in case anyone else feels something is missing.