[ad_1]
<! –
->
Infrared view of the seas and lakes of Titan's northern hemisphere, taken by Cassini in 2014. You can see sunlight shining south of Titan's largest sea, Kraken Mare. Scientists now believe that "bath rings" on the shores of seas and lakes are composed of organic crystals. Image via NASA / JPL-Caltech / University of Arizona / University of Idaho / AGU 100.
The moon of Saturn Titan is the only other body in the solar system, apart from Earth, known to have liquids on its surface. These rains, rivers, lakes and seas are very similar to those of the Earth, but are composed of liquid methane and ethane (hydrocarbons) instead of water. Now, scientists have found another way to differ from their terrestrial counterparts: the shores of lakes and seas could be encrusted with "bathtub rings" composed of organic crystals not found on Earth.
The new research was published in a new article and presented on June 24 at the 2019 Scientific Conference on Astrobiology (AbSciCon 2019) in Bellevue, Washington.
New paper:
We discovered a third stable molecular mineral under the same conditions as those present on the surface of Titan, a moon of Saturn. This molecular mineral consists of acetylene and butane, two organic molecules produced in the atmosphere of Titan and falling to the surface. We call these "molecular minerals" because they behave exactly like minerals on Earth, but instead of being composed of carbonates or silicates, they are composed of organic molecules. The two molecular minerals we discovered previously were composed of benzene and ethane, acetylene and ammonia. The most recent is probably much more abundant on the surface of Titan, because acetylene and butane would be very common. In particular, we believe that the "bath rings" around Titan's lakes could be made of this material because acetylene and butane dissolve well in liquid methane and ethane compared to other molecules .
Artist concept of a hydrocarbon lake on Titan seen from the ground. Image via Steven Hobbs (Brisbane, Queensland, Australia / NASA).
The intriguing results come from laboratory tests in which conditions similar to those of Titan were recreated. Scientists have discovered compounds and minerals that do not exist on Earth. One of the co-crystals consisted of solid acetylene and butane, which exist on Earth, but only in the form of gas. Titan is so cold, however, that acetylene and butane freeze and combine to form crystals.
So how did the scientists create conditions similar to those of Titan in a laboratory on Earth? Titan is extremely cold, about -290 degrees Fahrenheit (-179 degrees Celsius). So they used a custom built cryostat, a device that keeps things cold. Since Titan's atmosphere is mainly composed of nitrogen, like that of the Earth, they filled the cryostat with liquid nitrogen. But they needed the nitrogen to be a gas, as on Titan, so they warmed the room slightly. Methane and ethane were then added, which is also very common on Titan. They are both in liquid form on the moon, in the rain, rivers, lakes and seas. The result was a "soup" rich in hydrocarbons.
Map of Titan seas and lakes in the northern hemisphere. Image via JPL-Caltech / NASA / ASI / USGS / EarthSky.
The surface of Titan seen by the Huygens lander in 2005. Huygens found wet sand landing near a riverbed evaporating. The liquid was methane / ethane, but the "rocks" turned out to be solid ice. Image via ESA / NASA / University of Arizona / EarthSky.
The benzene crystals were the first to form in this soup. Benzene is present in gasoline on Earth. It is a snowflake-shaped molecule composed of a hexagonal ring of carbon atoms. But something amazing happened in the simulated conditions of Titan: the benzene molecules rearranged in such a way as to let the ethane molecules pass, thus creating a co-crystal. The researchers also later discovered a co-crystal of acetylene and butane, which would probably be more common on Titan.
These are the acetylene and butane co-crystals that probably create the bathtub rings – evaporated minerals – around lakes and seas. The minerals would fall to the surface when the liquid hydrocarbons begin to evaporate. The Cassini probe made it possible to see some lakes on Titan when they were full of liquid and at other times when they had partially evaporated. This evaporation process is similar to the way salts can form crusts around the lakes and seas of the Earth.
The bathtub rings on Titan are believed to exist on the basis of Cassini's evidence, but have not yet been fully confirmed, as noted by Morgan Cable at the Jet Propulsion Laboratory:
We do not know yet if we have these bathtub rings … It's hard to see through the foggy atmosphere of Titan.
An acid salt lake south of Beacon, Western Australia. The incrustations of salt on its edges resemble the rings of the bathtub which border the lakes and the seas of Titan. Image via Suzanne M. Rea / ResearchGate.
The rivers, lakes and seas of Titan, mainly near the North Pole, give this moon an appearance strangely similar to that of the Earth. There are also methane showers and massive sand dunes near the equator, as in the deserts of the Earth, but composed of hydrocarbon particles. The thick and foggy atmosphere obscures the ground, but Cassini could use a radar to see the characteristics of the surface. The Huygens spacecraft, part of the Cassini mission, also sent back Titan's first photos taken in 2005, showing a riverbed evaporating with "rocks" made up of solid water ice. . Behind all this lies an underwater ocean. Titan can look looks a lot like Earth in many ways, but in terms of composition, it's a totally foreign world.
Unfortunately, with Cassini's mission ending at the end of 2017, new observations of the bath rings will have to await the return of a mission to Titan. Probes that could float or swim in one of the lakes or seas have been proposed, but are still on the drawing boards right now. However, NASA's new Dragonfly mission, which was just announced last week, will send a drone-like rotorcraft flying into Titan's skies, making many landings at various interesting places. Dragonfly should be launched in 2026 and land in 2034. Exciting!
Conclusion: By simulating Titan's conditions in a terrestrial laboratory, scientists have discovered that unusual shapes of organic crystals can create bath rings around lakes and seas of the moon.
Source: Acetylene-butane co-crystal: a potentially abundant molecular mineral on Titan
Via AGU 100
[ad_2]
Source link