A Tiger-Striped Surprise: Ice Volcanoes on Enceladus

I wrote this piece as part of my grad school applications last fall.

At first glance, Saturn’s tiny moon Enceladus appears to be nothing like its namesake, the giant of Greek mythology whose breath caused volcanic eruptions. Enceladus (the moon) is a frozen celestial body smaller than the state of Arizona. No one would have guessed that its name would turn out to be serendipitously appropriate.

When the Cassini spacecraft arrived at Saturn in 2005, scientists didn’t intend to conduct more than a quick flyby of Enceladus. But any expectations of Enceladus as an inert, cratered moon were soon dismantled as Cassini captured images of four large, hot fissures sliced across the south pole, like the jagged claw marks of a tiger. And so it was revealed that Enceladus truly is living up to its mythological namesake: from these so-called “tiger stripes” spewed at least 100 ice volcanoes, jetting particles and water vapor far out into space.

The discovery of these plumes was a shock. One wouldn’t initially expect moons to have active processes like violent geysers of particles — moons are usually too small and cold to produce much energy. Craters on our own Moon indicate that its surface hasn’t changed for three billion years. For tiny Enceladus to have such vigorous volcanoes, something must be happening internally to generate heat and energy.

The most natural explanation for such a small moon to be producing so much power is a process called tidal flexing. Tidal flexing occurs because Enceladus’ orbit around Saturn is not perfectly circular, so the huge planet gravitationally squeezes and stretches its tiny moon as it orbits. This constant exercise of the moon’s rocky interior causes it to heat up. But scientists expect that this tidal flexing can only generate about 10% of the power that the plumes output, so Enceladus must have some sort of other unexpected internal heat storage.

Chemical analyses of the plumes hint at more subsurface secrets. Samples of the plumes reveal “salty” sodium particles, indicating the presence of silicate rocks. Along with the abundance of water vapor particles, this data paints an image of a deep subsurface ocean with a solid rock bottom.

Liquid water, heat, and a water-rock interface are a crucial combination of ingredients for the chemistry of life that has made the once nondescript Enceladus a prime target in our search for extraterrestrial life. The idea that life could potentially arise under a crust of ice on a tiny moon of Saturn has revolutionized concepts of habitable environments. Enceladus is an embodiment of the surprises of our solar system that we have yet to uncover.

What you’ve all been waiting for: The Experiment

After several weeks of soldering wires and sealing leaks, Rita and I were finally ready to get some Martian simulation going. Because the scientific process should always be transparent, here’s your personal guide to making those lovely irradiated magnetite samples you’ve always wanted.

Now don’t try this at home, kids.

1. Flush the glove box with nitrogen, three times for 15 minutes each. By filling the glove box with nitrogen, we ensured that in the unlikely case of a leak in the chamber, the surrounding atmosphere was unreactive. Rita and I made sure to stand in the hallway when the nitrogen was on, to avoid any unintended unconsciousness.

2. Put the magnetite on the tray and place it into the transfer chamber. We created a vacuum in the chamber, then filled it with nitrogen from the glove box. We did this vacuum-and-fill process three times to make sure no external atmosphere got into the glove box when we transferred in the sample tray. This is important – it’s not a very good Mars simulation chamber if there’s a ton of Earth’s atmosphere in it. We used a glove box that looks like the one below. (Image from Wikimedia Commons.)

 

  • How do you move things around when they’re already in the glove box? The glove box is totally sealed, so we use these awesome built-in gloves to handle the samples once they’re inside. But use caution: wearing these seemingly-invincible contraptions may make you feel and act like a true mad scientist.

3. Take the samples from the transfer chamber, and put them into the simulation chamber. Using our invincibility gloves, we sealed the sample tray inside the small Mars chamber. These are the magnetite samples we used: a chunk from Greenland, a chunk with olivine inclusions, and a very fine powder.

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4. Suffocate the samples. We vacuumed the chamber using first the back pump, and then the turbomolecular pump, so it’s nice and airless. We then let in 18 millibars of CO2 (a millibar is a unit of pressure – one millibar is about the pressure exerted by a penny lying flat). Remember, only the chamber that becomes a vacuum – the surrounding glove box is still filled with nitrogen.

5. Turn on the UV light. You wouldn’t bake a cake without turning on the oven, so why would you even think about doing this experiment without the radiation?

6. SCIENCE HAPPENS! We left the samples under the radiation for two weeks, checking the pressure and UV lights daily to make sure everything was working properly.

On August 11, we removed the samples to be analyzed. I know you’re dying to find out if the radiation mutated our magnetite into miniature Martians, but you’ll just have to wait for the next blog post.

Mechanical Mars – An Interactive Post

When I first saw the Mars chamber I would be working with, I felt just the tiniest sense of utter bewilderment, and possibly a hint of panic. I am not an engineer, and this thing looks mega intimidating.

Thanks to the awesome Rita Kajtar, who made major contributions to the chamber’s construction as part of her masters thesis, I began to understand its various bits and pieces. But still, I knew I’d have a hard time explaining it to you without some visuals. And so, since hands-on learning is the best learning, I made you an interactive photo! Mouseover for some enlightenment.

And here’s the sample tray that goes inside of the Chamber. 

Since science and technology are ever-updating fields, there are of course a few improvements that still need to be made. For example, even though experiments are run under a near-perfect vacuum and condensation is unlikely, a humidity sensor needs to be added. And even though we can use the ideal gas law to make a rough estimate of the temperature during the experiments, it would also be helpful to have a temperature sensor.