If you follow astronomy or planetary science news, chances are you’ve seen images of the plumes of material spouting from Enceladus’s southern regions. But what causes them? I’m going to lead you through the process scientists use to find answers: something you might have learned in high school called the scientific method. But this tool is used far beyond high school. You might even use it in your daily life without realizing it.
Enceladus is Saturn’s sixth largest moon, its “ocean moon.” It is covered entirely with ice, giving it a cracky appearance. Scientists have observed these plumes of material coming from Enceladus’s south pole region for a little while now, and have been trying to figure out what is causing them. This brings up a topic that more people need to learn about, in order to make sense of things in the world, whether it’s biology or astronomy, or even something that happens on the news. Something called the Scientific Method.
Scientists have been using the scientific method since the 17th century, but really, they’ve been using it a lot longer than that. They just didn’t have a name for it, and hadn’t come to the conclusion that using steps in a method would come to more consistent and reliable results. Once they did, however, it became pretty standard operating procedure. It works. It allows experiments to be replicated, to be studied, and to be shared. It gives people a way to see if what they think is going on actually makes logical sense. And it provides a framework for them to explain it to others.
The scientific method consists of specific steps after making an initial observation: 1) Ask a question. 2) Form a hypothesis or an educated guess as to what you THINK the answer could be. 3) Predict what would happen if your hypothesis is correct, come up with a few different possibilities. 4) Gather data by performing experiments, reading literature on the topic, consulting colleagues, etc. 5) EITHER refine your hypothesis to reflect the data you have collected and observed and test that NEW hypothesis, OR if your data suggests your hypothesis was correct, get others to see if they can replicate your experiments and so forth so that you can then form a theory. A theory is a hypothesis that has been tested over and over again, and that has been reviewed by many scientists, and is the closest thing to an answer that we have to many things. When something reaches theory status, it means we can’t prove it wrong, yet we can’t prove it as law yet. A scientific theory isn’t the same thing as a dictionary definition of theory, though. When people say, “Evolution is just a theory,” they are incorrect. Evolution is a scientific theory, which means it’s basically as close to the truth as we can get. It’s not just something that someone came up with on a whim. It’s something that has gone through the most rigorous testing we can do.
Here is a nifty graphic I made all by myself that explains it as well, in some different words, to show how the scientific method is cyclic. We come up with answers and from those answers we come up with more questions, etc.:
So where does Enceladus fit into all of this? Well, scientists observed these plumes coming from the ice. This prompted them to ask, What were they? What caused them? And then they made an educated guess to answer their questions. Their guesses also led to other questions as well, such as, “Could Enceladus host life?” Before we get to the potential answers, though, let’s look at how scientists came to them.
1. Observation: Scientists observed giant plumes of material spewing from Enceladus’s south pole.
2. Questions: What’s causing these eruptions? Could this mean Enceladus could sustain life, if it is active in this way?
3. Hypothesis: Scientists think the plumes are caused by Saturn’s strong gravitational pull.
4. Prediction: The gravity from Saturn is pulling on Enceladus and causing a tidal effect.
5. Gather Data: Scientists looked at what they had observed from other bodies in our solar system, as well as our own planet. The moon causes tidal forces on our planet. Saturn is much stronger and could easily cause the effects seen on Enceladus. The Cassini spacecraft also made observations of Saturn’s icy moon… and found that the moon is still extremely active. Too active for it to just be caused by Saturn’s gravity effect. Soooooooooo, it’s back to:
3. Hypothesis: Decay from radioactive material causes temperatures on Enceladus to be high enough to spew material.
4. Prediction: The natural decay of radioactive isotopes beneath Enceladus’s icy crust in conjunction with Saturn’s tidal forces heat things up enough so there is a global ocean under the 25-27-mile-thick crust of ice, and there is pressure that causes the liquid to escape in the southern region.
5. Gather Data: Once again, Cassini helps scientists out. The spacecraft reported evidence that hydrothermal activity was taking place in Enceladus. Hot water was reacting with rock under the crust, and some of these tiny rock particles were being spewed into space from the vents along with water vapor. When scientists looked at the info collected by Cassini, they inferred that temperatures within Enceladus must be reaching upwards of 194 degrees F! That’s much too hot to be explained by just radioactive decay and gravitational pull. So, AGAIN, back to…
3. Hypothesis: “Where Enceladus gets the sustained power to remain active has always been a bit of mystery, but we’ve now considered in greater detail how the structure and composition of the moon’s rocky core could play a key role in generating the necessary energy,” scientist Gaël Choblet says.
This is where we are currently at. After studying all the info that has come back from Cassini, now there is a new hypothesis: The core of Enceladus is made of porous rock or perhaps a sandy substance, something that can be easily deformed that water can get through. As the rock fragments move together constantly, the friction creates heat. As the cool liquid water flows down from the oceans into the rock, it heats up from the heat made by this friction. As it heats up, it starts to rise when it gets hotter than its surroundings. Then, it reacts with the rocks because of the heat, and they form hotspots. When they reach the floor of the ocean above, the difference in temperatures causes the water and rock particles to shoot upward, and with enough energy, out through the icy crust. This hypothesis explains how Enceladus can be so hot and active after so many billions of years.
“Our simulations can simultaneously explain the existence of an ocean at a global scale due to large-scale heat transport between the deep interior and the ice shell, and the concentration of activity in a relatively narrow region around the south pole, thus explaining the main features observed by Cassini,” says Choblet.
But what about life on Enceladus? Well, we aren’t there yet. Though we have tested for organic compounds and have found a lot of those, we haven’t had the opportunity to study much more than that. But someday, possibly soon, we might be.
“Future missions capable of analyzing the organic molecules in the Enceladus plume with a higher accuracy than Cassini would be able to tell us if sustained hydrothermal conditions could have allowed life to emerge,” says Nicolas Altobelli, the European Space Agency’s Cassini project scientist.
So you can kind of see how this cycle works. People see things, come up with questions, and then try to answer them with data they collect. The data either proves or disproves their guesses, and also provides opportunities for them to ask MORE questions. Curiosity never ends, and if you keep asking questions and searching for answers, both on your own and in cooperation with others, the world holds no limits.
The scientific method isn’t just good for astronomy or biology. You can use it in many areas of life from child-rearing to fact checking news sources. The most important thing is to make sure you collect data—LOTS of data from as many sources as you can. You want to make sure you aren’t just seeing what you want to see, but seeing what is really there. Remember, if you are curious and active about seeking answers, you are a scientist, too!