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Webb’s Titan Forecast: Partly Cloudy With Occasional Methane Showers
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By NASA
Hydrocarbon lake and methane rain clouds on Titan Jenny McElligott/eMITS NASA research has shown that cell-like compartments called vesicles could form naturally in the lakes of Saturn’s moon Titan.
Titan is the only world apart from Earth that is known to have liquid on its surface. However, Titan’s lakes and seas are not filled with water. Instead, they contain liquid hydrocarbons like ethane and methane.
On Earth, liquid water is thought to have been essential for the origin of life as we know it. Many astrobiologists have wondered whether Titan’s liquids could also provide an environment for the formation of the molecules required for life – either as we know it or perhaps as we don’t know it – to take hold there.
New NASA research, published in the International Journal of Astrobiology, outlines a process by which stable vesicles might form on Titan, based on our current knowledge of the moon’s atmosphere and chemistry. The formation of such compartments is an important step in making the precursors of living cells (or protocells).
The process involves molecules called amphiphiles, which can self-organize into vesicles under the right conditions. On Earth, these polar molecules have two parts, a hydrophobic (water-fearing) end and a hydrophilic (water-loving) end. When they are in water, groups of these molecules can bunch together and form ball-like spheres, like soap bubbles, where the hydrophilic part of the molecule faces outward to interact with the water, thereby ‘protecting’ the hydrophobic part on the inside of the sphere. Under the right conditions, two layers can form creating a cell-like ball with a bilayer membrane that encapsulates a pocket of water on the inside.
When considering vesicle formation on Titan, however, the researchers had to take into account an environment vastly different from the early Earth.
Uncovering Conditions on Titan
Huygens captured this aerial view of Titan from an altitude of 33,000 feet. ESA/NASA/JPL/University of Arizona Titan is Saturn’s largest moon and the second largest in our solar system. Titan is also the only moon in our solar system with a substantial atmosphere.
The hazy, golden atmosphere of Titan kept the moon shrouded in mystery for much of human history. However, when NASA’s Cassini spacecraft arrived at Saturn in 2004, our views of Titan changed forever.
Thanks to Cassini, we now know Titan has a complex meteorological cycle that actively influences the surface today. Most of Titan’s atmosphere is nitrogen, but there is also a significant amount of methane (CH4). This methane forms clouds and rain, which falls to the surface to cause erosion and river channels, filling up the lakes and seas. This liquid then evaporates in sunlight to form clouds once again.
This atmospheric activity also allows for complex chemistry to happen. Energy from the Sun breaks apart molecules like methane, and the pieces then reform into complex organic molecules. Many astrobiologists believe that this chemistry could teach us how the molecules necessary for the origin of life formed and evolved on the early Earth.
Building Vesicles on Titan
The new study considered how vesicles might form in the freezing conditions of Titan’s hydrocarbon lakes and seas by focusing on sea-spray droplets, thrown upwards by splashing raindrops. On Titan, both spray droplets and the sea surface could be coated in layers of amphiphiles. If a droplet then lands on the surface of a pond, the two layers of amphiphiles meet to form a double-layered (or bilayer) vesicle, enclosing the original droplet. Over time, many of these vesicles would be dispersed throughout the pond and would interact and compete in an evolutionary process that could lead to primitive protocells.
If the proposed pathway is happening, it would increase our understanding of the conditions in which life might be able to form.
“The existence of any vesicles on Titan would demonstrate an increase in order and complexity, which are conditions necessary for the origin of life,” explains Conor Nixon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We’re excited about these new ideas because they can open up new directions in Titan research and may change how we search for life on Titan in the future.”
NASA’s first mission to Titan is the upcoming Dragonfly rotorcraft, which will explore the surface of the Saturnian moon. While Titan’s lakes and seas are not a destination for Dragonfly (and the mission won’t carry the light-scattering instrument required to detect such vesicles), the mission will fly from location to location to study the moon’s surface composition, make atmospheric and geophysical measurements, and characterize the habitability of Titan’s environment.
News Media Contacts
Karen Fox / Molly Wasser
Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
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By NASA
6 min read
NASA’s Dragonfly Mission Sets Sights on Titan’s Mysteries
When it descends through the thick golden haze on Saturn’s moon Titan, NASA’s Dragonfly rotorcraft will find eerily familiar terrain. Dunes wrap around Titan’s equator. Clouds drift across its skies. Rain drizzles. Rivers flow, forming canyons, lakes and seas.
Artist’s concept of NASA’s Dragonfly on the surface of Saturn’s moon Titan. The car-sized rotorcraft will be equipped to characterize the habitability of Titan’s environment, investigate the progression of prebiotic chemistry in an environment where carbon-rich material and liquid water may have mixed for an extended period, and even search for chemical indications of whether water-based or hydrocarbon-based life once existed on Titan. NASA/Johns Hopkins APL/Steve Gribben But not everything is as familiar as it seems. At minus 292 degrees Fahrenheit, the dune sands aren’t silicate grains but organic material. The rivers, lakes and seas hold liquid methane and ethane, not water. Titan is a frigid world laden with organic molecules.
Yet Dragonfly, a car-sized rotorcraft set to launch no earlier than 2028, will explore this frigid world to potentially answer one of science’s biggest questions: How did life begin?
Seeking answers about life in a place where it likely can’t survive seems odd. But that’s precisely the point.
“Dragonfly isn’t a mission to detect life — it’s a mission to investigate the chemistry that came before biology here on Earth,” said Zibi Turtle, principal investigator for Dragonfly and a planetary scientist at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. “On Titan, we can explore the chemical processes that may have led to life on Earth without life complicating the picture.”
On Earth, life has reshaped nearly everything, burying its chemical forebears beneath eons of evolution. Even today’s microbes rely on a slew of reactions to keep squirming.
“You need to have gone from simple to complex chemistry before jumping to biology, but we don’t know all the steps,” Turtle said. “Titan allows us to uncover some of them.”
Titan is an untouched chemical laboratory where all the ingredients for known life — organics, liquid water and an energy source — have interacted in the past. What Dragonfly uncovers will illuminate a past since erased on Earth and refine our understanding of habitability and whether the chemistry that sparked life here is a universal rule — or a wonderous cosmic fluke.
Before NASA’s Cassini-Huygens mission, researchers didn’t know just how rich Titan is in organic molecules. The mission’s data, combined with laboratory experiments, revealed a molecular smorgasbord — ethane, propane, acetylene, acetone, vinyl cyanide, benzene, cyanogen, and more.
These molecules fall to the surface, forming thick deposits on Titan’s ice bedrock. Scientists believe life-related chemistry could start there — if given some liquid water, such as from an asteroid impact.
Enter Selk crater, a 50-mile-wide impact site. It’s a key Dragonfly destination, not only because it’s covered in organics, but because it may have had liquid water for an extended time.
Selk crater, a 50-mile-wide impact site highlighted on this infrared image of Titan, is a key Dragonfly destination. Landing near Selk, Dragonfly will explore various sites, analyzing the surface chemistry to investigate the frozen remains of what could have been prebiotic chemistry in action. NASA/JPL-Caltech/University of Nantes/University of Arizona The impact that formed Selk melted the icy bedrock, creating a temporary pool that could have remained liquid for hundreds to thousands of years under an insulating ice layer, like winter ponds on Earth. If a natural antifreeze like ammonia were mixed in, the pool could have remained unfrozen even longer, blending water with organics and the impactor’s silicon, phosphorus, sulfur and iron to form a primordial soup.
“It’s essentially a long-running chemical experiment,” said Sarah Hörst, an atmospheric chemist at Johns Hopkins University and co-investigator on Dragonfly’s science team. “That’s why Titan is exciting. It’s a natural version of our origin-of-life experiments — except it’s been running much longer and on a planetary scale.”
For decades, scientists have simulated Earth’s early conditions, mixing water with simple organics to create a “prebiotic soup” and jumpstarting reactions with an electrical shock. The problem is time. Most tests last weeks, maybe months or years.
The melt pools at Selk crater, however, possibly lasted tens of thousands of years. Still shorter than the hundreds of millions of years it took life to emerge on Earth, but potentially enough time for critical chemistry to occur.
“We don’t know if Earth life took so long because conditions had to stabilize or because the chemistry itself needed time,” Hörst said. “But models show that if you toss Titan’s organics into water, tens of thousands of years is plenty of time for chemistry to happen.”
Dragonfly will test that theory. Landing near Selk, it will fly from site to site, analyzing the surface chemistry to investigate the frozen remains of what could have been prebiotic chemistry in action.
Morgan Cable, a research scientist at NASA’s Jet Propulsion Laboratory in Southern California and co-investigator on Dragonfly, is particularly excited about the Dragonfly Mass Spectrometer (DraMS) instrument. Developed by NASA’s Goddard Space Flight Center in Greenbelt, Maryland, with a key subsystem provided by the CNES (Centre National d’Etudes Spatiales), DraMS will search for indicators of complex chemistry.
“We’re not looking for exact molecules, but patterns that suggest complexity,” Cable said. On Earth, for example, amino acids — fundamental to proteins — appear in specific patterns. A world without life would mainly manufacture the simplest amino acids and form fewer complex ones.
Generally, Titan isn’t regarded as habitable; it’s too cold for the chemistry of life as we know it to occur, and there’s is no liquid water on the surface, where the organics and likely energy sources exist.
Still, scientists have assumed that if a place has life’s ingredients and enough time, complex chemistry — and eventually life — should emerge. If Titan proves otherwise, it may mean we’ve misunderstood something about life’s start and it may be rarer than we thought.
“We won’t know how easy or difficult it is for these chemical steps to occur if we don’t go, so we need to go and look,” Cable said. “That’s the fun thing about going to a world like Titan. We’re like detectives with our magnifying glasses, looking at everything and wondering what this is.”
Dragonfly is being designed and built under the direction of the Johns Hopkins Applied Physics Laboratory (APL), which manages the mission for NASA. The team includes key partners at NASA’s Goddard Space Flight Center and NASA’s Jet Propulsion Laboratory. Dragonfly is managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate at NASA Headquarters in Washington.
For more information on Dragonfly, visit:
https://science.nasa.gov/mission/dragonfly/
By Jeremy Rehm
Johns Hopkins Applied Physics Laboratory, Laurel, Md.
Media Contacts:
Karen Fox / Molly Wasser
Headquarters, Washington
202-358-1600
karen.c.fox@nasa.gov / molly.l.wasser@nasa.gov
Mike Buckley
Johns Hopkins Applied Physics Laboratory
443-567-3145
michael.buckley@jhuapl.edu
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