There's Sand on Titan, Where Does it Come From?

Even though the

Cassini orbiter

ended its mission on of September 15th, 2017, the data it gathered on Saturn and its largest moon,

Titan

, continues to astound and amaze. During the thirteen years that it spent orbiting Saturn and conducting flybys of its moons, the probe gathered a wealth of data on Titan's atmosphere, surface, methane lakes, and rich organic environment that scientists continue to pore over.

For instance, there is the matter of the mysterious "sand dunes" on Titan, which appear to be organic in nature and whose structure and origins remain have remained a mystery. To address these mysteries, a team of scientists from

John Hopkins University

(JHU) and the research company

Nanomechanics

recently conducted

a study

of Titan's dunes and concluded that they likely formed in Titan's equatorial regions.

Their study, "

Where does Titan Sand Come From: Insight from Mechanical Properties of Titan Sand Candidates

", recently appeared online and has been submitted to the

Journal of Geophysical Research: Planets.

The study was led by Xinting Yu, a graduate student with the Department of Earth and Planetary Sciences (EPS) at JHU, and included EPS Assistant Professors Sarah Horst (Yu's advisor) Chao He, and Patricia McGuiggan, with support provided by Bryan Crawford of Nanomechanics Inc.

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To break it down, Titan's sand dunes were

originally spotted by Cassini's radar instruments

in the Shangri-La region near the equator. The images the probe obtained showed long, linear dark streaks that looked like wind-swept dunes similar to those found on Earth. Since their discovery, scientists have theorized that they are comprised of grains of hydrocarbons that have settled on the surface from Titan's atmosphere.

In the past, scientists have conjectured that they form in the northern regions around Titan's methane lakes and are distributed to the equatorial region by the moon's winds. But where these grains actually came from, and how they came to be distributed in these dune-like formations, has remained a mystery. However, as Yu explained to Universe Today via email, that is only part of what makes these dunes mysterious:

[caption id="attachment_117282" align="aligncenter" width="580"]

Dunes on Titan seen in Cassini's radar (top) that are similar to Namibian sand dunes on Earth. The features that appear to be clouds in the top picture are actually topographic features. Credit: NASA

[/caption]

To shed light on this, Yu and her colleagues conducted a series of experiments to simulate materials being transported on both terrestrial and icy bodies. This consisted of using several natural Earth sands, such as silicate beach sand, carbonate sand and white gyspum sand. To simulate the kinds materials found on Titan, they used laboratory-produced tholins, which are molecules of methane that have been subjected to UV radiation.

The production of tholins was specifically conducted to recreate the kinds of organic aerosols and photochemistry conditions that are common on Titan. This was done using the Planetary HAZE Research (PHAZER) experimental system at Johns Hopkins University - for which the Principal Investigator is Sarah Horst. The last step consisted of using a nanoidentification technique (overseen by Bryan Crawford of Nanometrics Inc.) to study the mechanical properties of the simulated sands and tholins.

This consisted of placing the sand simulants and tholins into a wind tunnel to determine their mobility and see if they could be distributed in the same patterns. As Yu explained:

[caption id="attachment_92932" align="aligncenter" width="580"]

Radar image of sand dunes on Titan. Credit: NASA/JPL–Caltech/ASI/ESA and USGS/ESA

[/caption]

In the end, the team determined that the organic molecules found on Titan are much softer and more brittle when compared to even the softest sands on Earth. Simply put, the tholins they produced did not appear to have the strength to travel the immense distance that lies between Titan's northern methane lakes and the equatorial region. From this, they concluded that the organic sands on Titan are likely formed near where they are located.

"And their formation may not involve liquids on Titan, since that would require a huge transportation distance of over 2000 kilometers from the Titan's poles to the equator," Yu added. "The soft and brittle organic particles would be grinded to dust before they reach the equator. Our study used a completely different method and reinforced some of results inferred from Cassini observations."

In the end, this study represents a new direction for researchers when it comes to the study of Titan and other bodies in the Solar System. As Yu explained, in the past, researchers were mostly constrained with

Cassini

data and modelling to answer questions about Titan's sand dunes. However, Yu and her colleagues were able to use laboratory-produced analogs to address these questions, despite the fact that the

Cassini

mission is now at an end.

What's more, this most recent study is sure to be of immense value as scientists continue to pore over

Cassini's

data in anticipation of future missions to Titan. These missions aim to study Titan's sand dunes, methane lakes and rich organic chemistry in more detail. As Yu explained:

[caption id="attachment_135310" align="aligncenter" width="580"]

Artist's concept of the dragonfly being deployed to Titan and commencing its exploration mission. Credit: APL/Michael Carroll

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In addition, this study has implications for the study of bodies other than Titan. "We have found organics on many other solar system bodies, especially icy bodies in the outer solar system, such as Pluto, Neptune's moon Triton, and comet 67P," said Yu. "And some of the organics are photochemically produced similarly to Titan. And we do found wind blown features (called aeolian features) on those bodies as well, so our results could be applied to these planetary bodies as well."

In the coming decade, multiple missions are expected to explore the moons of the outer Solar System and reveal things about their rich environments that could help shed light on the origins of life here on Earth. In addition, the

James Webb Space Telescope

(now expected to be deployed in 2021) will also use its advanced suit of instruments to study the planets of the Solar System in the hopes of address these burning questions.