Planetary Geology: An unasked for paper

My Geology class has had us researching as if we were going to do a research paper, but instead of actually writing a paper, we’re just making  a presentation. But my head is bursting with things to share, so I’m writing something anyway.Doing it on the blog means I can be a bit more informal, which is going to make this more fun, for everyone involved.

At the beginning of the semester, when we were determining our topics to study, I became curious with the question of how we know things about other planets. What is Jupiter made of, and what do we know? It wasn’t on the list, so I asked the professor, and got it approved.

It turns out the subject of planetary geology, also known occasionally as exogeolgy, had good reason for not being on the list. It is a BROAD topic and that has made writing the final presentation tricky. Sure, I could write a paper, but to condense the thought down to just a few slides, not being able to share the awesome things, that pains me.

Hence, this.

Part 1: Space is big.

“Space is big. You just won’t believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.” – Douglas Adams, The Hitchhiker’s Guide to the Galaxy

There is a problem in science that the layman doesn’t think of. It’s hard to see things that we want to see. The world is big, there is a lot happening, and we can’t be a fly on the wall in the right place at the right time, except when we’re very, very lucky. Research for a previous paper I wrote last year, on wolves in Yellowstone, showed me the difference in studying wolves. A two week trek with no results was very possible before, where as once wolves were reintroduced, observers could see wolves on the daily, and catalogue their activities and record their behaviors in ways unthinkable by researchers a decade before.

In geology itself, the Earth gets in the way of studying the Earth. We’re developing new tricks all the time, but still, there are a lot of things we know about the Earth that is made through inference, not through actual, hands on observations.

As on Earth, so in the Heavens. There are planets out there. We’ve seen them. But there is a vast difference between seeing something through a telescope and being able to state with certainty, what’s going on.

Heck, some things can’t even be seen by telescopes! In the Kuiper Belt, an asteroid belt out near Pluto, we are just now discovering objects that are smaller that 100 km across. That’s a rock that would fit in the English Channel. And until recently, we couldn’t see it.

On top of that, there are things like earthquakes that looking at via telescope can’t tell us things, even if we can detect them. On Earth, we have sensors placed everywhere, that measure temperature, humidity, Earth’s seismic movements, anything we can think of. If it would be useful, we find a way to measure it, and find away to acquire as many measurements as we can. Mass producing seismagraphs and GPS sensors tells us a lot about Earth.

But out there, in space, we don’t have that option at the moment. Our payloads to beyond are limited by what we can cram into a rocket. So instead of being able to say “This is,” a lot of planetary geology is based on “Based on [this], we guess that…” and work off of that.

Part 2: Knowledge through inference

I had underestimated how much computer simulation and data crunching was part of geology before this paper. Teams of scientists take the limited data we have and run it through whatever algorithms they can think of.  Each lab build a Model, a computer simulation that takes the data that we have, combines it with guesses at equations and unknowns, and tries to predict what would happen. These guesses are refined and rerun, until they are as solid as they can get with the information that we have. And when a space mission, an observation, or even a conclusion from another team trots out a new fact, everything is rerun with the new data and assumptions.

There are many teams of scientists, working on different things. I say teams, but that makes it sound like an organized, concerted effort. That is probably not very accurate. Instead, a group has a question, begins crunching data, and applies for grants to pay for it. Some of this money comes from public programs, others from private interests that have reasons to find some things out. But in the end, different teams do what they can to find things out about the universe. So the questions of what’s out there are studied from all directions.

And some things in the Solar system have questions that we can’t really relate to on Earth. For example, while we’re all familliar with humidity, trying to model the weather on Titan involves figuring out how humidity works when it’s not based on water, but methane. How does that differ? No idea. It might work exactly the same, or it might be different. All I know is that reading these paper has give me the chance to read some awesome things like this:

“Titan and Earth are the only worlds in the Solar System where rain reaches the surface, although the atmospheric cycles of water and methane are expected to be very different” (Hueso & Sánchez-Lavega, 2006, p. 430)

Part 3: Making the most of a mission

Missions into space are expensive. That’s why astronauts are kept busy running so many things in the ISS. There are a lot of questions to be answered out there, and they are answers we can guess at from the ground, but until we poke and prod and find out, we can’t know. So when a space mission does go up, it’s packed with as much tech to discover facts as we can. Various missions have focuses, whether that’s lading something on Mars, dropping a probe into Jupiter, or doing a few flybys of Saturn, each mission is carefully measured and planned, and devices that do everything from scan on various infrared levels, to a mass spectrometer, are loaded with enough power to record and report.

The Galileo probe had sixteen different sensors built into it. A separate part of the mission, the Galelio entry probe that was dropped into Jupiter, had seven sensors for its own brief mission, and that doesn’t count the sensors built to monitor the rate that the hull ablated as it was destroyed by the largest planet hostile atmosphere.

All of the data returned is poured over, again and again. We’re still using information from the Voyager missions to draw conclusions, even if they were launched near 50 years ago.

One of the important things that scientists do is decide what observations would be important to know, and how to acquire that information. The models made before a mission can inform the probe’s mission, giving it priorities of what to look for, and help decide what sensors to pack into their machines. Once the payload is determined, scientists return to their models, and prepare for the data that would come in. Even without knowing what it is, they can run simulations based on projected answers, preparing them to slot in actual information once they have it.

All in all, this is making me realize how amazing the ships on Star Trek are. Being able to get to other planets, to orbit and observe with their sensors, to collect and sort through information is a planetary geologist’s dream.

Part 4: Planetary Bodies share geological aspects

While planetary bodies can vary differently from Earth’s processes, there are some similarities. The moon Io has volcanoes. And while we believe that the melted rock inside comes not from internal process, but from the forces of Jupiter’s gravitational effects on the moon, we can still draw conclusions about its internal makeup from studying the lava flows, which are reminiscent of some long flowing volcanoes in Hawaii.

Pluto, the distant dwarf planet, has glaciation, as glaciers sublimate, and rebuild their depths. The patterns are familiar, even if their makeup is not water, but frozen Nitrogen. Yes, imagine liquid nitrogen that is so cold, it is actually frozen. Now imagine whole glaciers made of the stuff. That’s Pluto.

So there’s plenty of useful comparisons to make, even if the whole system doesn’t match.

Part 5: Many questions remain

There are a lot of things we know, but many more we don’t getting a mass spectrometry reading of Jupiter gave us some clues to its make up, but all we have are some ratios. The exact gases are still a mystery. Different combinations change how the planet works on subtle levels. We know it’s made of gas now, but it may have had a core that degraded over time.

Even something as simple as “How fast does Saturn spin?” is a question that we don’t know exactly. We have it narrowed down to a window, but there are error bars on it. A lot of what we can learn is limited by question marks in places where we’re used to having data.

Ignorance, as well as knowledge, can cascade. Things we’re sure of can be made unclear if some of the facts they’re built on have shaky foundations.

But, we are always moving forward. Each mission into space gives us more data, that we can use to develop more answers about the universe. And everything is connected. As we find out things about the origins of Jupiter, we learn things about the beginning of Earth. As we study weather on Neptune, we can apply modelling techniques to weather on Earth. The techniques and questions we develop about other planetary bodies can also be asked about Earth, and science will continue to march forward.


I’m so grateful for the chance I’ve had to do this research. I’ve learned a lot about many different areas of science and research. Taking the time to find an article of interest on the topic each week has been mind expanding. I may try to continue, even after this assignment is done. There are many things that are unknown about all planetary bodies that we know of. No area of research is satiated.

Leave a comment

Your email address will not be published. Required fields are marked *