Researchers Wonder if Pluto’s Moon Charon is Cracked

One of NASA’s most recent news stories features work performed at Goddard Space Flight Center, where researchers are trying to develop mathematical models that will help us understand the results from New Horizons, a spacecraft on its way to Pluto (arriving in July of 2015). While Pluto may have been demoted from “planet” to “dwarf planet,” it can still teach us many things about the history of our Solar System.

What might New Horizons see when it reaches Pluto and its moon, Charon? What will those observations tell us about the histories of these two planetary bodies? Like all good scientists, this team of researchers at NASA are developing detailed hypotheses about the places the spacecraft will visit.

First: will Charon be fractured? Many icy moons are crisscrossed by patterns of huge cracks, or faults like California’s San Andreas. For example, Jupiter’s moon Europa has so many long, dark linea (linear features) that there’s an entire wikipedia article dedicated to a list of them! Many researchers believe that these giant fractures are the product of gravitational tides, which repeatedly bend and eventually fracture the ice shell. At Saturn’s moon Enceladus it is thought that tides continue to open and close the moon’s “Tiger Stripes,” causing jets of water vapor to spew out of the moon’s south pole at regular intervals – a space version of Yellowstone’s Old Faithful. It’s possible that Pluto’s moon, Charon, experienced tides like this soon after its formation, perhaps leading to fractures across its icy surface. By building a mathematical model of Charon and Pluto which examines the strength of their gravitational interaction, these researchers have described the conditions under which Charon’s surface would have fractured, and if New Horizons sees linea on Charon, this research may explain how they formed.

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 Plumes erupt from huge fractures in the surface of Enceladus, a moon of Saturn. Image courtesy NASA.

     But the picture gets even more detailed: the location and orientation of these fractures depends on the thickness and viscosity of the ice enveloping Charon. The viscosity (how easily the ice flows when pushed by, for example, gravity) depends on many things – temperature, pressure, the purity of the ice, and even the size of each individual ice crystal –  so it is a major “unknown” in models of icy moons. These scientists, however, recognized that because fractures are driven by stresses, which are in turn affected by the deep structure of the moon, the patterns of fractures we (might) see on the surface tells us about what is happening deep below the surface.

     To explore this idea, they envisioned many different potential thicknesses and viscosities of Charon’s ice layer and subjected these hypothetical ice shells to tides using computer models, then observed the resulting fractures (or lack thereof). Their results are, in a sense, a picture book of fractures on Charon, each with their own back story, which scientists can consult once they have images from New Horizons – see the fractures, find the matching model, and voila: a theory on the orbital history of Pluto and Charon! The photos from New Horizons will be a great test of these scientists’ hypotheses.

  So when New Horizons reaches the end of its long journey, keep an eye out for photos. Grab this paper off of Google Scholar and see if you can figure out how thick the ice shell is!

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Read the original article here, on NASA’s website.

This post summarizes an article in press:

Rhoden, A. R., Henning, W., Hurford, T. A., & Hamilton, D. P. (2014). The interior and orbital evolution of Charon as preserved in its geologic record.Icarus.

Saturn’s Rings: A Busy Place for Ice

Icy moons aren’t the only place in the Outer Solar System where ice takes center stage. Saturn’s rings are almost entirely composed of water ice, and are seen here in a mosaic of photos taken by NASA’s Cassini Spacecraft:

Cassini Ring Mosaic

Saturn’s rings are formed from the debris of ancient moons that drifted too close to the planet, past an invisible barrier known as the Roche Limit, and were torn apart by Saturn’s gravitational tides (yes – dissipation of tidal energy is important here, too)! The rings do not spin around the planet entirely peacefully, either. Icy pillars rise up from the rings, visible only at the planet’s Equinox:Columns of Ice Rise from Saturn's Rings

The conditions required to take this photo occur only once every 15 years… so mark your calendar for 2024, when the next sighting opportunity arises!

The rings also swirl with turbulence as pieces of debris collide and swarm around one another:Turbulence in Saturn's F Ring

But the rings are not only places of turbulence and destruction: Cassini recently captured this image of the birth of a new moon amid the debris.

Cassini Sees New Moon Forming

 

Saturn’s rings may be beautiful, but they certainly aren’t passive …and to fully understand their dynamics, we must understand the physics of ice!

For more cool images (pun intended), check out the Cassini Mission’s website.

The Photogenic Side of Ice

Almost all of us have interacted with ice in some way, even if it is simply clinking around in your glass. But have you ever taken a look at those ice cubes as they float? Have you ever wondered what is going on at the microscopic scale in those little cubes who sacrifice themselves to keep your beverage so deliciously cool? (Okay – so the last question may imply a high level of nerdiness, but still…) Most of us are so accustomed to the presence of ice in our daily lives that we scarcely give it a second thought, but an important aspect of my research is looking at ice. And not just giving it a casual glance, but looking at it for hours under incredibly powerful microscopes! For those of you who hardly pay your ice cube a second thought, here are some photos to help you appreciate the more photogenic side of those little crystals.

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A crystal orientation map from one of my experimental samples. Basically, the colors correspond to different tilt angles, while the solid black lines define the edges of individual crystals.

 

 

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A snow crystal photographed in a regular light (left) and in a low-temperature electron microscope (right) by the USDA’s snow research group.

 

 

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“Columnar” ice, similar to sea ice, that has been deformed experimentally. Photo credit Narayana Golding.

 

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A stereo image of snow. Cross/relax your eyes and this should end up looking like a 3D pile of crystals! (Courtesy USDA)

 

 

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FROST ON MARS – or what it might look like, anyway. On Mars, the atmosphere can get so cold that not only water freezes, but carbon dioxide… this is crystalline CO2, courtesy of the USDA. Frozen CO2, or “dry ice” is used to package frozen foods (and, incidentally, to package my ice samples during formation)!

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Planets Get Heat With a Little Help From Their Friends

How might worlds orbiting other stars stay warm enough to support life?

Tidal heating – the inspiration for my research – may be the answer!

Artist's conception of planets orbiting a low-mass star. (image courtesy of NASA/JPL)

“Let’s be honest for a second. The search for planets in the galaxy is about the search for life. It is awesome that we’re learning about thousands of other planetary systems. We’re making discoveries – some surprising, some reassuring – about the nature and evolution of the universe. This is great. But one look at the hyperbolic headlines about Earth-like planets and Earth twins reveals why, in the hearts and minds of the public, and maybe of a lot of researchers, the search for planets is the search for potential homes for life.

In that case, our understanding of exoplanets is about finding promising candidates so that, once we have the means to look for evidence of life, we’ll have a shortlist.”

Reposted from astrobites.org.

Making Ice – Mother Nature makes it look so easy!

With heaps of ice crystals falling from the sky, it seems an appropriate time to answer one of my readers’ questions: How do I make the ice that I torture during my experiments? Unfortunately, it’s not as straightforward as putting a tray in the freezer and coming back a few hours later for cubes.

Making ice for scientific experiments requires me to precisely control not only the cleanliness of the ice, but the size of the crystals, and the methods we use to control crystal size – or “grain size” in scientific lingo – are pretty exciting.

The first step in any of my experiments is to decide “how” I want my ice to deform. Ice is a non-newtonian fluid (Wikipedia has a great article for anyone who wants to delve into that) whose properties can be strongly influenced by grain size. As such, I decide what sort of properties I want to investigate, and then choose a grain size that will allow me to do so.

Choosing the grain size, in a way, determines how I will make my ice.

For large grains (that is, bigger than 100 microns or so), I use what I like to call the alien lander. It really does look like Dr. Goldsby stole this thing from the set of “War of the Worlds:”

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The process goes from frozen, deionized water, through a blender and a set of sieves (imagine a red-faced blonde leaning over into a chest freezer for about an hour, banging a set of sieves against the inside, and you’ll get the idea), packing the resulting snow into a mold and flooding it with ice-cold water. The latter process involves a small-scale “Polar Bear Plunge” where I reach into a bucket of ice water to move valves on the alien lander.

After all that, the flooded powder is left to freeze overnight. I take the frozen sample out of the mold, cut it down to size, and voila! Coarse-grained ice sample, ready to go.

If I need grains smaller than 100 microns, I have to get creative. The process involves spraying a fine mist of deionized water into a dewar filled with liquid nitrogen (at about -200⁰ C). This forms a slurry of liquid nitrogen and very small particles of ice, which I then pour through a shaker to separate. As the shaker runs, I must continually douse the mixture with liquid nitrogen to keep anything from melting or growing. Finally, the resulting powder gets packed into a mold.

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 The result of these efforts is a beautiful piece of polycrystalline ice, ready for science!

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