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.

Mars may harbor subsurface liquid water

I wrote this piece as my “Discovery Story” assignment for En84, “Writing About Science,” at Caltech, and got an A. The press release I drew information from is here and the original paper is here.

 

Ancient Mars was a warm and wet place, coursing with rivers and lakes. Though the lakebeds are now dusty and the water long gone, researchers have recently discovered evidence that the present-day Mars may not be as dry as we thought. The evidence suggests that a thin layer of salty liquid water may exist just under the Martian surface, condensing in the cool hours of night and evaporating in the morning.

Conditions on Mars are not favorable for liquid water — Martian temperatures and atmospheric pressures only allow water to exist as ice or vapor. However, the Curiosity rover recently detected a chemical compound in the Martian soil that could make it possible for water to exist in a liquid form.

The compound, called calcium perchlorate, lowers the freezing point of water, acting like an anti-freeze by allowing water to exist in a liquid state even under temperatures where it would normally form ice. Under particular humidity and temperature conditions, perchlorates can also absorb water vapor from the atmosphere, forming salty liquid solutions called brines that can then trickle down into the soil.

While perchlorates are abundant in many places on Mars, this is the first time they have been detected along with the right humidity and temperature for brines to form. Additionally, these conditions were detected at the equator — the driest and hottest region of Mars. If the delicate brine-forming conditions can exist even on the harshest region of the planet, it’s likely that milder regions can stably support brines as well.

The authors measured air humidity and temperature at the equator using Curiosity’s Rover Environmental Monitoring Station (REMS) over a Martian year. They describe the brines as “transient” because the proper humidity and temperatures for brine formation don’t last throughout a full Martian day. The salty solutions only have one night to condense before evaporating with the sunlight.

Liquid water is considered a crucial building block for life, but these brines are unlikely to harbor it — they are simultaneously too short-lived, too cold, and too exposed to solar radiation to support terrestrial organisms.

“Conditions near the surface of present-day Mars are hardly favorable for microbial life as we know it, but the possibility for liquid brines on Mars has wider implications for habitability and geological water-related processes,” says the lead author on the study, Javier Martin-Torres of the Spanish Research Council in Spain and Sweden’s Lulea University of Technology. He is also a member of Curiosity’s science team.

Though for now this finding seems to have few extraterrestrial implications, it is part of a collection of Curiosity’s discoveries that are transforming our perception of Mars. Last year, Curiosity measured sharp spikes and drops in atmospheric methane concentration, implying that somewhere on Mars is a source producing the organic chemical. Scientists have also observed dusty geysers of carbon dioxide erupting from the polar ice caps in the warming of spring. Mars is turning out to be a much more diverse and dynamic planet than we thought.

The Rusted Red Planet

It is a well-known nuisance that when you leave a freshly sliced apple exposed to air, it quickly turns brown. It’s a nuisance of the same kind that must frustrate the Statue of Liberty—her once-coppery skin turned green from only two years of exposure to air. The process that causes these seemingly dissimilar metamorphoses is called oxidation. Oxidation occurs when an atoms in a substance lose electrons, changing the overall chemical makeup and structure. It doesn’t necessarily cause decay; oxidation is essentially just atomic reshuffling. Key to oxidation processes are atmospheric elements like water and oxygen.

Another common kind of oxidation is rust. Rust occurs when iron metals oxidize to form other compounds. Hematite is one of these results of oxidation, rust-red in powdered form and created by the oxidation of other iron-containing compounds, like magnetite. When magnetite rusts, one of its iron atoms loses an electron, chemically changing into hematite. The presence of water is an important catalyst for this reaction—if you’ve ever left an old bike out in the rain, you’ll notice it gets rusty pretty fast.

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Hematite is the abundant mineral that gives Mars its distinctive reddish color. The planet is covered by a layer of fine red hematite powder, so much so that you can see the hue from Earth on a clear night. But there are no oceans or lakes of water on Mars, and the Martian atmosphere is practically parched. Without water to facilitate rusting and oxidation, the origins of this ubiquitous mineral are unknown. NASA’s Martian rovers have found no indication of rusty Martian bicycle tracks, so there’s one scenario we can rule out.

Mars has a very sparse atmosphere, about 1/100th of Earth’s, and so the surface receives very little protection from solar ultraviolet (UV) radiation. UV light is very powerful: it can split apart molecules to create extremely reactive new molecules called radicals, and it can even interact with our genes to cause mutations. Perhaps the abundance of UV light on Mars, in the absence of water, can facilitate the oxidation of magnetite into hematite.

To test this hypothesis, I placed a few magnetite samples into a chamber with a simulated Martian atmosphere: a very cold, low-pressure CO2 atmosphere with no water vapor. Then I switched on a powerful UV lamp and waited for two weeks. I carried out this research with the Mars Group at the Niels Bohr Institute at Copenhagen University.

There were two possible outcomes.

Possibility 1: Oxidation was detected on the samples at the end of the experiment. This could imply:

  • UV radiation can physically knock electrons off of iron, and alter the ratios of iron and oxygen from magnetite to hematite. No water is necessary. This could mean that the dust on Mars is actively, however slowly, being formed. Mars may not be such a static “dead” planet as we may have thought.
  • UV radiation can interact with CO2 to create an oxidant which then oxidizes iron, changing magnetite to hematite. No water is necessary. Again, this could mean that the dust on Mars is actively, however slowly, being formed.
  • The magnetite in our samples had already been oxidized through exposure to Earth’s atmosphere before we introduced them to our chamber. I’ll explain this more in the results section.

Possibility 2: No oxidation was detected on the samples at the end of the experiment. This could imply:

  • UV radiation cannot induce oxidation alone. It may have no role in converting magnetite to hematite. Alternatively, it may have a partial role combined with mechanical weathering, or other processes. Perhaps the only way UV radiation could have played a role in oxidation is under a completely different set of atmospheric conditions. If Mars previously had an Earth-like atmosphere containing more water and oxygen, UV radiation could photolyze H2O or O2 to create radicals that would steal an electron from iron atoms.
  • UV radiation can indeed induce oxidation without the presence of water, but over very long timescales—the experiment did not run for enough time. This would imply that the dust on Mars could be very old, which suggests that the planet has been unchanging for millions of years.
  • The analysis did not catch the oxidation.

The results are now in.

After the experiment, the samples were analyzed using x-ray photoelectron spectroscopy (XPS). This mouthful is a technique sensitive to the surfaces of materials, giving the chemical composition of the top 10 nanometers. This means that the results we found were only for the surfaces of our samples, not the bulk. XPS can also tell us the chemical environment of an atom, meaning we can determine the oxidation state of elements. The analysis was carried out by Dr. Nico Bovet at Copenhagen University’s NanoGeoScience Center.

The powder samples showed signs of oxidation even before they went in the chamber. The little bump in the graph around 719 eV indicates iron in the oxidized state. After the experiment, they didn’t show any noticeable change.

 

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The spectrum of the powdered magnetite sample before the experiment.

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The spectrum of the powdered magnetite sample after the experiment.

As for the solid samples, neither of them show that same bump around 719 eV — indicating that no iron oxidized after the experiment.

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The spectrum of the solid magnetite sample from Greenland.

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The spectrum of the solid magnetite sample that also included olivine.

So there you have it. Our results indicate that UV radiation cannot, in two weeks, induce the oxidation of magnetite to hematite in an atmosphere analogous to Mars’.

In science, getting “no” for an answer is common, and it’s not necessarily a bad thing. Any result of the scientific process is important, and leads to new questions and new directions of research. It’s possible that UV radiation does play a role in oxidation on longer timescales, or in combination with other Martian processes. We will just have to ask more questions and do more science to find out.

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.

Destination Mars

Sometimes it seems like Mars gets all the planetary love. There are currently nine active missions orbiting or trekking along the surface of the little red planet, and more than twenty have been launched internationally since the 1960’s. But why Mars in particular? Two traits make Mars an ideal target for exploration: the science it has to offer, and the relative ease of exploration.

Mars is like a giant history book, written in the language of geology and chemistry — when we can decode what it’s saying, we peer back into the past. Signatures of a long-gone magnetic field, arid riverbeds, and frozen fields of basaltic lava hint at a world that once was. What happened to this planet that seemed to once be teeming with dynamic flows of lava and liquids? Planetary scientists are hunting for evidence to put together a picture of how an active planet can become a desolate rock. Could Earth be headed towards the same cold, dry future? By studying other planets, we’re learning more about our origins, our selves, and possibly our futures. In addition, we get some inspiration as to “habitability” — potential conditions for life to arise and thrive. And then there’s the glamorous idea that we might one day send humans to visit and perhaps colonize the red planet. But that’s a discussion for another blog post.

This is an exaggerated color photo of the Martian surface from NASA’s Mars Reconnaissance Orbiter. Credit goes to NASA/JPL-Caltech/Univ. of Arizona.

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The other reason we have such a persistent interest in Mars is that it’s accessible. Jupiter and Saturn both have interesting moons of ice which probably harbor lakes and oceans, but missions to the outer planets are quite a time investment, often taking a few years to reach their targets. Venus, Earth’s other neighbor, doesn’t like visitors too much — she’s extraordinarily hostile to any sort of landing spacecraft. With a heavy lower atmosphere of sulfuric acid clouds and winds up to 220 mph, we’d be basically trying to land a rover on a surface that’s hot enough to melt lead. Though Venus may have long ago had an environment much like Earth’s, a runaway greenhouse effect [1] has led the planet to often be nicknamed “Earth’s evil twin.” Probably not a very popular destination for cute little rovers. (But hopefully we’ll send a brave one there soon.)

With NASA’s budget, it seems that Mars is an attainable goal that produces solid science. But you don’t have to go there to do Martian science — I’ve got my very own mini-Mars in the basement of the Niels Bohr Institute!

 

[1] The runaway greenhouse effect occurs when a planet’s atmosphere absorbs heat that the planet emits, and then radiates it back towards the surface, heating it even more. This usually happens with atmospheres that contain lots of water, carbon dioxide, and other gases that absorb and emit in similar wavelengths.

Science is Coming

8996 kilometers across a continent and ocean. 18 hours of sunshine per day. 10 weeks. One Mars simulation chamber.

Yep, I’m back in Copenhagen. I’m working on a project with the Mars group at the Niels Bohr Institute, using a Mars simulation chamber to examine the big question: Why is the red planet red? Or, more accurately, how is the red planet red? I’ll be determining whether UV radiation can induce the oxidation of magnetite to hematite, the mineral responsible for Mars’ distinctive shade. I’m very thankful to be funded by the Monticello Foundation at Caltech.

This is my nifty version of Mars in a box.

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Because I’m passionate about reaching a broad audience with my scientific endeavours, I’m starting this blog to document my science shenanigans, from mineralogy in the Mars chamber to my caffeinated attempts at learning Python. Science should be for everyone, so every week I’ll be updating you, and your grandma, and your dog, about what I’m currently working on.

But I’m no world-class researcher (yet). I just finished my third year of undergrad at Caltech, double-majoring in Planetary Science and Philosophy (you might think this is an odd combo — I’ll blog about it soon). I like philosophizing about alien life, experimenting with different genres of journalism, and hunting for the best cappuccinos in Denmark. As an exchange student in Copenhagen last fall, I fell in love with the city and decided to come back for this summer project.

As I’m trying my hand at this science communication thing, there will probably be some typos and inaccuracies throughout — remember, this is my journey through the dark forests of literature searches and experimental trial and error. Science communication is a two-way street, so interaction with you all is important — if you read something that makes no sense or is just plain wrong, write me a comment!

Brace yourselves — science is coming.