The Electric Sands Of A Misty Moisty Moon Of Saturn
By Judith E Braffman-Miller
The outer Solar System is enshrouded in the perpetual semi-darkness that exists far from the brilliant light and warmth of our Sun. Here, in this cold, shadowy outer kingdom, a quartet of gaseous, giant, majestic planets reign supreme–Jupiter, Saturn, Uranus, and Neptune–all circled by most of the many moons inhabiting our Sun’s family. Saturn is perhaps the most beautiful planet in our Solar System, surrounded by its fascinating, fabulous rings composed of sparkling frozen icy bits, for which it has long been famous. This second-largest planet in our Star’s family–after the incredible banded behemoth, Jupiter–Saturn also possesses what is arguably the most interesting moon in our Solar System, as well as the second-largest–the hydrocarbon-slashed, moon-world Titan, veiled as it is in a heavy orange smog that has hidden its mysterious face for centuries from the prying eyes of curious observers. Titan is an eerily familiar, but nevertheless tantalizingly alien, moon-world. In March 2017, a team of planetary scientists proposed that Titan possesses yet another of a myriad of truly bizarre features–electric sands that cover its mysterious misty moisty surface.
Experiments led by planetary scientists at the Georgia Institute of Technology (Georgia Tech) in Atlanta suggest that the particles that coat the surface of Titan are “electrically charged”. When the winds of Titan roar at speeds of almost 15 miles per hour, Titan’s non-silicate grains get kicked upwards, and then begin to do a wild hopping dance in a motion that is termed saltation. As the tiny grains bump into one another, they become frictionally charged, in a manner that has been likened to the way a balloon being swept against your hair becomes frictionally charged. The grains clump together in a way that has never been observed for sand dune grains on Earth–the electrically charged grains of sand on Titan become resistant to further motion. The sand grains can maintain that charge for days–or even months–and cling to other hydrocarbon substances. These findings have been published in the March 27, 2017 issue of the journal Nature Geoscience.
“If you grabbed piles of grains and built a sand castle on Titan, it would perhaps stay together for weeks due to their electrostatic properties. Any spacecraft that lands in regions of granular material on Titan is going to have a tough time staying clean. Think of putting a cat in a box of packing peanuts,” commented geophysicist Dr. Josef Dufek in a March 27, 2017 Georgia Tech Press Release. Dr. Dufek is a professor at Georgia Tech who co-led the study.
Misty Moisty Moon
Until the Cassini spacecraft–carrying the Huygens probe piggyback–arrived at the Saturn system in 2004, very little was known about Titan. All that planetary scientists then knew about Titan was that it was a Mercury-sized moon whose surface was heavily enshrouded beneath a nitrogen-rich, thick atmosphere. However, Cassini successfully mapped Titan’s long-veiled surface, studied its atmospheric reactions, discovered seas of liquid hydrocarbons, and even detached and dispatched the Huygens probe to the misty moon’s surface, where it landed on January 14, 2005–completely rewriting our scientific understanding of this eerily Earth-like and, yet, at the same time, hauntingly alien world.
Before Cassini-Huygens began its intense study of Saturn’s largest moon, planetary scientists only knew Titan as an approximately Mercury-sized hazy orange sphere, blanketed by a fascinating but frustratingly heavy and impenetrable mist. The scientists had also determined that Titan sports a nitrogen atmosphere–the only known world with a dense nitrogen atmosphere besides Earth. However, what might be hidden beneath the smoggy orange shroud of bizarre clouds was still a beckoning, bewitching mystery.
Data derived from Cassini-Huygens reveals that Titan is slashed by lakes and seas of liquid methane and ethane–that are constantly being replenished by large, lazy drops of hydrocarbon rain. On Titan, the hard rain that falls is composed of gasoline-like liquids. The mission also provided new and exciting information that Titan is hiding a subsurface liquid ocean beneath its strange surface. The internal liquid ocean is thought to be composed of water and ammonia.
NASA’s Cassini spacecraft would eventually complete over 100 targeted flybys above Titan, dispatching the European Space Agency’s (ESA’s) Huygens probe down, down, down to the strange and long-hidden surface of the secretive, hydrocarbon-tormented moon-world. This historic descent represented the first landing on the surface of a world inhabiting the outer Solar System. As it floated down to Titan’s surface for two and a half hours, Huygens took measurements of the composition of Titan’s atmosphere, as well as some very revealing pictures of its long-hidden surface. The heroic little probe not only managed to survive the remarkable descent and landing, but went on to transmit important new data for over an hour on Titan’s frigid surface–until its batteries finally were drained.
Since that historic first in 2005, planetary scientists from all over the world have studied volumes of new data about Titan, dispatched back to Earth by Huygens and Cassini. This very important information, collected by the hardy spacecraft, revealed many details of a surprisingly Earth-like–as well as unEarthly–moon, and in the process raised intriguing new questions to be answered in the future.
Scientists now know that Titan is a moon-world with seas and lakes composed of liquid methane and ethane located near its poles, with extensive arid regions of hydrocarbon-laden dunes girdling its equator. And hidden deep below Titan’s surface, there is a large liquid ocean.
The great variety of features on Titan’s strange surface has both delighted and surprised planetary scientists–as well as the public. “I am intrigued by how many features on Titan’s surface are remarkably Earth-like, including hydrocarbon rivers, lakes and seas, and equatorial dunes, with liquid methane playing the role on Titan that water plays on Earth,” noted Dr. Linda Spilker in a NASA Jet Propulsion Laboratory (JPL) report on the mission. Dr. Spilker is Cassini project scientist at the JPL, located in Pasadena, California.
Wavelets of ruffling sand dunes, similar to those seen in Earth’s Arabian desert, have been observed in the dark equatorial regions of Titan. However, the “sands” on Titan are not composed of silicates like the sand on our own planet. Many planetary scientists propose that Titan’s sand is composed of water ice within a shell of hydrocarbons that tumble down from the atmosphere. Images reveal that Titan’s alien, icy dunes are enormous, extending, on average, 0.6 to 1.2 miles wide, hundreds of miles long, and around 300 feet high.
Titan is the only other world in our Solar System known to possess an Earth-like cycle of liquids streaming across its surface as the planet experiences changing seasons. Each season on Titan lasts for about 7.5 Earth years. Since 2011, Cassini has glimpsed the transition from fall to winter on Titan’s south pole–marking the first time anyone has observed the beginning of a Titan winter. Cassini has also watched summer marching in to Titan’s north. “We’re monitoring the weather on Titan, watching for predicted methane rainstorms at the north pole,” Dr. Spilker noted in the JPL report.
The Huygens probe also successfully made the very first direct measurements of Titan’s lower atmosphere, and also directly sampled aerosols in the atmosphere, confirming that carbon and nitrogen are primary constituents. Cassini followed up Huygens’ measurements from space, spotting other chemicals that include propylene, which is a chemical used to make household plastic, as well as poisonous hydrogen cyanide. This variety of chemicals suggests a complex and rich chemistry, originating from methane and nitrogen, and evolving into complex molecules–eventually creating the heavy orange hydrocarbon smog that blankets the icy moon. Many planetary scientists think that methane and ethane rain pours down from clouds to Titan’s surface, but the ultimate origin of the methane is still not well understood. “The most interesting question is why is there still lots of methane in the atmosphere of Titan? Where’s it coming from?” noted Dr. Jonathan Lunine in the JPL report. Dr. Lunine is a Cassini interdisciplinary scientist from Cornell University in Ithaca, New York.
Cassini’s many gravity measurements of Titan revealed the existence of the liquid water and ammonia subsurface ocean hidden about 35 to 50 miles beneath its surface.
Saturn is orbited by more than 60 known moons, as well as a dazzling multitude of tiny, twirling icy moonlets that are only about 2 to 3 kilometers across. The objects that circle Saturn are mostly icy bodies, sparkling both within and outside of Saturn’s system of gossamer rings.
The Electric Sands Of A Misty Moisty Moon Of Saturn
The electrification findings of Dr. Dufek and his colleagues could possibly explain a bizarre phenomenon observed on Titan. The prevailing winds of this misty moisty moon-world blow from east to west across its surface. However, sandy dunes that are nearly 300 feet tall apparently form in the opposite direction.
“These electrostatic forces increase frictional thresholds. This makes the grains so sticky and cohesive that only heavy winds can move them. The prevailing winds aren’t strong enough to shape the dunes,” explained Josh Mendez Harper in the March 27, 2017 Georgia Tech Press Release. Mendez Harper is a Georgia Tech geophysics and electrical engineering doctoral student.
In order to test the particle flow that would exist under Titan-like conditions, the scientists constructed a small experiment in a modified pressure vessel in their lab at Georgia Tech. They then inserted grains of naphthalene and biphenyl–two toxic, carbon and hydrogen-bearing compounds thought to exist on Titan’s surface–into a small cylinder. The scientists then rotated the tube for 20 minutes in a dry, pure nitrogen environment. They did this because Titan’s atmosphere is composed of 98 percent nitrogen. Afterwards, the scientists measured the electric properties of each grain as it somersaulted out of the tube.
“All of the particles charged well, and about 2 to 5 percent didn’t come out of the tumbler. They clung to the inside and stuck together. When we did the same experiment with sand and volcanic ash using Earth-like conditions, all of it came out. Nothing stuck,” Mendez Harper continued to explain in the Georgia Tech Press Release.
Our planet’s sand does pick up electrical charge when it’s moved. However, the charges are smaller and dissipate rapidly. This is one reason why water is necessary to hold Earth’s sand together to create a structure, such as when a child builds a sand castle by the sea. However, the sands of Titan behave differently.
“These non-silicate, granular materials can hold their electrostatic charges for days, weeks or months at a time under low gravity conditions,” explained George McDonald in the March 27, 2017 Georgia Tech Press Release. McDonald is a graduate student in the School of Earth and Atmospheric Sciences who also co-authored the paper.
Titan, at least at first glance, is the world in our Solar System that most resembles Earth. Data collected from many flybys by Cassini since 2005 have unveiled large liquid lakes at the poles, as well as rivers, mountains, and possible volcanoes. However, a closer look reveals that instead of water-filled oceans and seas, such as those on our own planet, Titan’s oceans and seas are brimming with methane and ethane, and are replenished by alien rains pouring down from hydrocarbon saturated clouds. The surface pressure on Titan is a little higher than that of Earth. If a visiting Earthling stood on this misty moisty moon she would feel like she was standing 15 feet underwater here on our own planet.
“Titan’s extreme physical environment requires scientists to think differently about what we’ve learned of Earth’s granular dynamics. Landforms are influenced by forces that aren’t intuitive to us because those forces aren’t so important on Earth. Titan is a strange electrostatically sticky world,” Dr. Dufek commented in the March 27, 2017 Georgia Tech Press Release.
Scientists from the Jet Propulsion Lab, University of Tennessee-Knoxville and Cornell University also-co-authored the paper, which is titled Electrification of Sand on Titan and its influence on Sediment Transport.
The highly productive Cassini mission will end in September 2017, when the spacecraft makes its grand finale exit, crashing down into the clouds of the beautiful ringed gas-giant planet that it has been observing for more than a decade.
Judith E. Braffman-Miller is a writer and astronomer whose articles have been published since 1981 in various magazines, journals, and newspapers. Although she has written on a variety of topics, she particularly loves writing about astronomy because it gives her the opportunity to communicate to others the many wonders of her field. Her first book, “Wisps, Ashes, and Smoke,” will be published soon.