Can signs of life be detected from Saturn's frigid moon?

As astrophysics technology and research continue to advance, one question persists: is there life elsewhere in the universe? The Milky Way galaxy alone has hundreds of billions of celestial bodies, but scientists often look for three crucial elements in their ongoing search: water, energy and organic material. Evidence indicates that Saturn's icy moon Enceladus is an 'ocean world' that contains all three, making it a prime target in the search for life.

During its 20-year mission, NASA's Cassini spacecraft discovered that ice plumes spew from Enceladus' surface at approximately 800 miles per hour (400 m/s). These plumes provide an excellent opportunity to collect samples and study the composition of Enceladus' oceans and potential habitability.

However, until now it was not known if the speed of the plumes would fragment any organic compounds contained within the ice grains, thus degrading the samples.

Now researchers from the University of California San Diego have shown unambiguous laboratory evidence that amino acids transported in these ice plumes can survive impact speeds of up to 4.2 km/s, supporting their detection during sampling by spacecraft.

Their findings appear in The Proceedings of the National Academy of Sciences (PNAS).

Beginning in 2012, UC San Diego Distinguished Professor of Chemistry and Biochemistry Robert Continetti and his co-workers custom-built a unique aerosol impact spectrometer, designed to study collision dynamics of single aerosols and particles at high velocities.

Although not built specifically to study ice grain impacts, it turned out to be exactly the right machine to do so.

"This apparatus is the only one of its kind in the world that can select single particles and accelerate or decelerate them to chosen final velocities," stated Continetti.

"From several micron diameters down to hundreds of nanometers, in a variety of materials, we're able to examine particle behavior, such as how they scatter or how their structures change upon impact."

In 2024 NASA will launch the Europa Clipper, which will travel to Jupiter.

Europa, one of Jupiter's largest moons, is another ocean world, and has a similar icy composition to Enceladus.

There is hope that the Clipper or any future probes to Saturn will be able to identify a specific series of molecules in the ice grains that could point to whether life exists in the subsurface oceans of these moons, but the molecules need to survive their speedy ejection from the moon and collection by the probe.

Although there has been research into the structure of certain molecules in ice particles, Continetti's team is the first to measure what happens when a single ice grain impacts a surface.

To run the experiment, ice grains were created using electrospray ionization, where water is pushed through a needle held at a high voltage, inducing a charge that breaks the water into increasingly smaller droplets.

The droplets were then injected into a vacuum where they freeze.

The team measured their mass and charge, then used image charge detectors to observe the grains as they flew through the spectrometer.

A key element to the experiment was installing a microchannel plate ion detector to accurately time the moment of impact down to the nanosecond.

The results showed that amino acids -- often called the building blocks of life -- can be detected with limited fragmentation up to impact velocities of 4.2 km/s.

"To get an idea of what kind of life may be possible in the solar system, you want to know there hasn't been a lot of molecular fragmentation in the sampled ice grains, so you can get that fingerprint of whatever it is that makes it a self-contained life form," said Continetti.

"Our work shows that this is possible with the ice plumes of Enceladus."

Continetti's research also raises interesting questions for chemistry itself, including how salt affects the detectability of certain amino acids.

It is believed that Enceladus contains vast salty oceans -- more than is present on Earth.

Because salt changes the properties of water as a solvent as well as the solubility of different molecules, this could mean that some molecules cluster on the surface of the ice grains, making them more likely to be detected.

"The implications this has for detecting life elsewhere in the solar system without missions to the surface of these ocean-world moons is very exciting, but our work goes beyond biosignatures in ice grains," stated Continetti.

"It has implications for fundamental chemistry as well. We are excited by the prospect of following in the footsteps of Harold Urey and Stanley Miller, founding faculty at UC San Diego in looking at the formation of the building blocks of life from chemical reactions activated by ice grain impact."

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Drops of seawater contain traces of an ancient world

Sea salt hides a secret: tiny droplets of the seawater from which it came, preserving geologic history.

Using specializing equipment obtained from National Science Foundation grant funds, Mebrahtu Weldeghebriel, PhD '22, a postdoctoral fellow at Princeton University, and Binghamton University Distinguished Professor of Earth Sciences Tim Lowenstein were able to reconstruct changes in seawater chemistry over the last 150 million years, also gaining insight into related geological processes and climate changes. Their article, "Seafloor Hydrothermal Systems Control Long-Term Changes in Seawater [Li+]: Evidence from Fluid Inclusions," was recently published in the journal Science Advances.

The ocean "is like a giant soup of different elements," Lowenstein explained. "Sodium and chloride are the most common ones, but there are dozens of others dissolved in seawater in trace amounts such as lithium."

They looked at sea salt (halite) formed at various times over the past 150 million years in geographically diverse sedimentary basins in the United States, Europe, Asia and Africa. Within the salt samples were tiny pockets containing a bit of ancient seawater.

To access the tiny droplets, the researchers used a laser to drill holes into the salt crystals and then a mass spectrometer to analyze the different trace elements present. In this research, they focused specifically on the concentration of lithium, a trace element that sustained a seven-fold decrease over the past 150 million years, paralleled by a rise in magnesium to calcium ratios.

But why?

The cause for the long-term variations in seawater composition has been debated for the past two decades. The researchers proposed that the decline in lithium concentration in seawater is mainly associated with reduced production of oceanic crust and decreased seafloor hydrothermal activity, both of which are influenced by the movements of tectonic plates. The slowdown in plate activity over the past 150 million years led to less lithium being added to the ocean and reduced amounts of carbon dioxide released into the atmosphere, which ultimately led to global cooling and the present ice age. Turning back the clock 150 million years, the earth was a warmer place with more carbon dioxide in the atmosphere and more lithium in the sea.

"There is a close link between ocean chemistry and atmospheric chemistry," Weldeghebriel said. "Whatever changes happen in the ocean also reflect what's happening in the atmosphere."

Overall, Weldeghebriel and Lowenstein's research has made a significant advance in understanding the chemistry of Earth's ancient oceans and how the movement of tectonic plates has influenced the composition of our Earth's hydrosphere and atmosphere. Such chemical changes impact biology, as well, such as the marine creatures that build their shells out of calcium carbonate.

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Wobbling droplets in space confirm late professor's theory

At a time when astronomers around the world are reveling in new views of the distant cosmos, an experiment on the International Space Station has given Cornell researchers fresh insight into something a little closer to home: water.

Specifically, the space station's microgravity environment illuminated the ways that water droplets oscillate and spread across solid surfaces -- knowledge that could have very earthbound applications in 3D-printing, spray cooling, and manufacturing and coating operations.

The team's paper, "Oscillations of Drops with Mobile Contact Lines on the International Space Station: Elucidation of Terrestrial Inertial Droplet Spreading," published Aug. 16 in Physical Review Letters. The lead author is Joshua McCraney, M.S. '19, Ph.D. '21.

The experiment and its findings, while successful, are also bittersweet. The paper's co-senior author Paul Steen, the Maxwell M. Upson Professor in the Smith School of Chemical and Biomolecular Engineering in the College of Engineering, died in September 2020, just before the experiment was conducted.

"It's sad that Paul didn't get to see the experiments launch into space," said co-senior author Susan Daniel, the Fred H. Rhodes Professor in the Smith School of Chemical and Biomolecular Engineering, and Steen's longtime collaborator. "We hope that we did right by him in the end, and that the paper that we produced from the work would make him proud."

Daniel began collaborating with Steen shortly after she first came to Cornell as an assistant professor in 2007. While her current research is focused on the biological interface of the coronavirus, her graduate work was in chemical interfaces and fluid mechanics -- a field in which Steen was advancing a number of theoretical predictions based upon how droplets resonate when subjected to vibrations. The two researchers instantly connected.

"He knew the theory and made predictions, and I knew how to execute the experiments to test them," Daniel said. "Basically, from the moment I got here in 2007 until he passed away, we worked on trying to understand how liquids and surfaces interact with each other, and how the contact line at the interface between them behaves under different conditions."

Their collaboration resulted in a "photo album" of the dozens of possible shapes that an oscillated drop of water can take. Steen later expanded on that project by cataloging the droplets' energy states as evidenced by those resonant shapes, organizing them into a "periodic table" classification.

In 2016, Steen and Daniel received a four-year grant from the National Science Foundation (NSF) and NASA's Center for the Advancement of Science in Space to conduct fluid dynamics research aboard the International Space Station U.S. National Laboratory.

Space is an ideal place to study the behavior of fluids because of the radical reduction of gravity, which on the ISS is about one-millionth of its terrestrial level. This means that fluid-surface interactions which are so small-scale and speedy on Earth that they are practically invisible can be, in space, nearly 10 times larger -- from microns to centimeters -- and their duration slows nearly 30-fold.

"It's harder to study these drop motions, experimentally and fundamentally, when you have gravity in your way," Daniel said.

Steen and Daniel selected a few resonance shapes from their photo album that they wanted to explore in detail, with a focus on how a water droplet's contact line -- or outer edge -- slides back and forth across a surface, driving the way the liquid will spread, a phenomenon that can be controlled by varying vibration frequencies.

The team prepared meticulous instructions for the astronauts to follow, compressing four years of planning into a several-minute experiment in which every second was tightly choreographed.

With the researchers monitoring and providing feedback in real time on the ground, the astronauts deposited 10 mL water droplets via a syringe onto nine different hydrophobic surfaces with varying degrees of roughness. They also forced pairs of droplets to coalesce together, and placed droplets onto an oscillator and tuned its vibrations to achieve the targeted resonance shapes. The water droplets' wobbling and jiggling movements were filmed, and the researchers spent the next year analyzing the data.

That analysis ultimately confirmed Steen's theories about the way a liquid's density and surface tension control the contact line's mobility, overcoming a surface's roughness.

Daniel credits co-author Joshua Bostwick, Ph.D. '11, a former student of Steen's and now the Stanzione Collaboration associate professor at Clemson University, with ensuring that the experiment results squared with Steen's theoretical predictions.

"Josh was able to carry on with the theoretical side of this work in Paul's absence, which was not something I was ready to step into and do. It was nice to have him rejoin the team and help us make sure that we were able to extract everything we could from the data we collected," Daniel said. "Now we can essentially use the theory that Paul created to make predictions, for example, in processes where you're spraying droplets on surfaces, or in 3D-printing, or where liquids spread across a surface really quickly."

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Researchers film human viruses in liquid droplets at near-atomic detail

A pond in summer can reveal more about a fish than a pond in winter. The fish living in icy conditions might remain still enough to study its scales, but to understand how the fish swims and behaves, it needs to freely move in three dimensions. The same holds true for analyzing how biological items, such as viruses, move in the human body, according to a research team led by Deb Kelly, Huck Chair in Molecular Biophysics and professor of biomedical engineering at Penn State, who has used advanced electron microscopy (EM) technology to see how human viruses move in high resolution in a near-native environment. The visualization technique could lead to improved understanding of how vaccine candidates and treatments behave and function as they interact with target cells, Kelly said.

In an effort to expand the tools scientists have to study the microscopic world, researchers recorded live, 20-second-long movies of human viruses floating in liquid at near-atomic detail in an electron microscope. The same degree of information, immediately available as they record, may take up to 24 hours to acquire using traditional static imaging methods. Their approach and results were made available online July 24 in Advanced Materials.

"The challenge remained to view biological materials in dynamic systems that reflects their authentic performance in the body," said Kelly, who also directs the Penn State Center for Structural Oncology. "Our results show new structures and active insights of human viruses contained in minute volumes of liquid -- the same size as respiratory droplets that spread SARS-CoV-2."

Cryogenic electron microscopy (cryo-EM) is becoming the field's gold standard for observing samples at or beyond atomic resolution, according to Kelly. The technique involves flash freezing the sample and focusing a beam of electrons through it. The electrons and the sample's components interact, which is captured by detectors embedded in the instrument. Thousands of images can be processed to calculate what the item looks like in 3D -- but more is needed to fully understand how the item functions in a more natural setting.

"While cryo-EM can tell us a lot of information, it still produces a static image," said GM Jonaid, the paper's first author and a student in the Bioinformatics and Genomics Graduate Program in the Huck Institutes of the Life Sciences. Jonaid is conducting his doctoral dissertation research in Kelly's lab. "With improved chips and a powerful direct detector on the microscope, we can accumulate a lot of movie frames to view how the sample acts in real time. We can see things how they exist -- not just how we prepared them."

The researchers used adeno-associated virus (AAV) as a model system to demonstrate their approach. AAV is a biological nanoparticle that can be used to help deliver vaccines or treatments directly to cells. The platform is based on a hijacked adenovirus, which can easily enter several kinds of cells. The ease with which it interacts with cells makes it a useful capsule to transport its engineered payload.

"AAV is a well-known, gene therapy vehicle with current applications involved in drug delivery and vaccine development for COVID-19," Kelly said. "This model system is already well-studied so we can use it to validate our approach with the goal of seeing biological entitles in a liquid state, as maintained in the human body."

The researchers applied minute volumes of liquid solution containing AAV to the wells of specialized silicon nitride microchips, commercially supplied by Protochips Inc. They then placed the microchip assemblies in the EM to examine the viruses in action.

"The images are very comparable to cryo-EM data, but the preparation was less complex, less technically involved," Jonaid said. "Once we had the images, taken rapidly, like frames of a movie, we processed them just like we would any other high-resolution data."

The results were videos of AAV moving in liquid, with subtle changes in the particle's surface, suggesting that the particle's physical properties change as it explores its environment, Kelly said. The resolution was close to three to four Angstroms (a single atom is measured as one Angstrom).

Once they proved the imaging strategies worked, the researchers set their sights on a smaller target: antibodies produced by COVID-19 patients.

"We saw how antibodies contained in the serum of COVID-19 patients interacted with the remaining SARS-CoV-2 particles," Kelly said, noting that the ability to observe such interactions would be especially useful when assessing the viability of vaccine candidates prior to clinical trials.

Kelly and her team plan to continue investigating the molecular underpinnings of SARS-CoV-2 and host-receptor proteins using liquid phase-EM, as a complement to the information garnered from cryo-EM results.

"You really need data from both techniques to understand how viruses look and behave in the living body," Kelly said. "Visualizing the dynamic movement in solution complements high-resolution snapshots to reveal more complete information."

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Flushing a public toilet? Don't linger, because aerosolized droplets do

 Flushing a toilet can generate large quantities of microbe-containing aerosols depending on the design, water pressure or flushing power of the toilet. A variety of pathogens are usually found in stagnant water as well as in urine, feces and vomit. When dispersed widely through aerosolization, these pathogens can cause Ebola, norovirus that results in violent food poisoning, as well as COVID-19 caused by SARS-CoV-2.

Respiratory droplets are the most prominent source of transmission for COVID-19, however, alternative routes may exist given the discovery of small numbers of viable viruses in urine and stool samples. Public restrooms are especially cause for concern for transmitting COVID-19 because they are relatively confined, experience heavy foot traffic and may not have adequate ventilation.

A team of scientists from Florida Atlantic University's College of Engineering and Computer Science once again put physics of fluids to the test to investigate droplets generated from flushing a toilet and a urinal in a public restroom under normal ventilation conditions. To measure the droplets, they used a particle counter placed at various heights of the toilet and urinal to capture the size and number of droplets generated upon flushing.

Results of the study, published in the journal Physics of Fluids, demonstrate how public restrooms could serve as hotbeds for airborne disease transmission, especially if they do not have adequate ventilation or if toilets do not have a lid or cover. Most public restrooms in the United States often are not equipped with toilet seat lids and urinals are not covered.

For the study, researchers obtained data from three different scenarios: toilet flushing; covered toilet flushing and urinal flushing. They examined the data to determine the increase in aerosol concentration, the behavior of droplets of different sizes, how high the droplets rose, and the impact of covering the toilet. Ambient aerosol levels were measured before and after conducting the experiments.

"After about three hours of tests involving more than 100 flushes, we found a substantial increase in the measured aerosol levels in the ambient environment with the total number of droplets generated in each flushing test ranging up to the tens of thousands," said Siddhartha Verma, Ph.D., co-author and an assistant professor in FAU's Department of Ocean and Mechanical Engineering. "Both the toilet and urinal generated large quantities of droplets smaller than 3 micrometers in size, posing a significant transmission risk if they contain infectious microorganisms. Due to their small size, these droplets can remain suspended for a long time."

The droplets were detected at heights of up to 5 feet for 20 seconds or longer after initiating the flush. Researchers detected a smaller number of droplets in the air when the toilet was flushed with a closed lid, although not by much, suggesting that aerosolized droplets escaped through small gaps between the cover and the seat.

"The significant accumulation of flush-generated aerosolized droplets over time suggests that the ventilation system was not effective in removing them from the enclosed space even though there was no perceptible lack of airflow within the restroom," said Masoud Jahandar Lashaki, Ph.D., co-author and an assistant professor in FAU's Department of Civil, Environmental and Geomatics Engineering. "Over the long-term, these aerosols could rise up with updrafts created by the ventilation system or by people moving around in the restroom."

There was a 69.5 percent increase in measured levels for particles sized 0.3 to 0.5 micrometers, a 209 percent increase for particles sized 0.5 to 1 micrometers, and a 50 percent increase for particles sized 1 to 3 micrometers. Apart from the smallest aerosols, comparatively larger aerosols also pose a risk in poorly ventilated areas even though they experience stronger gravitational settling. They often undergo rapid evaporation in the ambient environment and the resulting decreases in size and mass, or the eventual formation of droplet nuclei, can allow microbes to remain suspended for several hours.

"The study suggests that incorporation of adequate ventilation in the design and operation of public spaces would help prevent aerosol accumulation in high occupancy areas such as public restrooms," said Manhar Dhanak, Ph.D., co-author, chair of FAU's Department of Ocean and Mechanical Engineering, and professor and director of SeaTech. "The good news is that it may not always be necessary to overhaul the entire system, since most buildings are designed to certain codes. It might just be a matter of redirecting the airflow based on the restroom's layout."

During the 300-second sampling, the toilet and urinal were flushed manually five different times at the 30-, 90-, 150-, 210-, and 270-second mark, with the flushing handle held down for five consecutive seconds. The restroom was deep cleaned and closed 24 hours prior to conducting the experiments, with the ventilation system operating normally. The temperature and relative humidity within the restroom were 21 degrees Celsius (69.8 degrees Fahrenheit) and 52 percent, respectively.

"Aerosolized droplets play a central role in the transmission of various infectious diseases including COVID-19, and this latest research by our team of scientists provides additional evidence to support the risk of infection transmission in confined and poorly ventilated spaces," said Stella Batalama, Ph.D., dean of the College of Engineering and Computer Science.

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Inexpensive, accessible device provides visual proof that masks block droplets

 

  Duke physician Eric Westman was one of the first champions of masking as a means to curtail the spread of coronavirus, working with a local non-profit to provide free masks to at-risk and under-served populations in the greater Durham community.

But he needed to know whether the virus-blocking claims mask suppliers made were true, to assure he wasn't providing ineffective masks that spread viruses along with false security. So he turned to colleagues in the Duke Department of Physics: Could someone test various masks for him?

Martin Fischer, Ph.D., a chemist and physicist, stepped up. As director of the Advanced Light Imaging and Spectroscopy facility, he normally focuses on exploring new optical contrast mechanisms for molecular imaging, but for this task, he MacGyvered a relatively inexpensive apparatus from common lab materials that can easily be purchased online. The setup consisted of a box, a laser, a lens, and a cell phone camera.

In a proof-of-concept study appearing online Aug. 7 in the journal Science Advances, Fischer, Westman and colleagues report that the simple, low-cost technique provided visual proof that face masks are effective in reducing droplet emissions during normal wear.

"We confirmed that when people speak, small droplets get expelled, so disease can be spread by talking, without coughing or sneezing," Fischer said. "We could also see that some face coverings performed much better than others in blocking expelled particles."

Notably, the researchers report, the best face coverings were N95 masks without valves -- the hospital-grade coverings that are used by front-line health care workers. Surgical or polypropylene masks also performed well.

But hand-made cotton face coverings provided good coverage, eliminating a substantial amount of the spray from normal speech.

On the other hand, bandanas and neck fleeces such as balaclavas didn't block the droplets much at all.

"This was just a demonstration -- more work is required to investigate variations in masks, speakers, and how people wear them -- but it demonstrates that this sort of test could easily be conducted by businesses and others that are providing masks to their employees or patrons," Fischer said.

"Wearing a mask is a simple and easy way to reduce the spread of COVID-19," Westman said. "About half of infections are from people who don't show symptoms, and often don't know they're infected. They can unknowingly spread the virus when the cough, sneeze and just talk.

"If everyone wore a mask, we could stop up to 99% of these droplets before they reach someone else," Westman said. "In the absence of a vaccine or antiviral medicine, it's the one proven way to protect others as well as yourself."

Westman and Fischer said it's important that businesses supplying masks to the public and employees have good information about the products they're providing to assure the best protection possible.

"We wanted to develop a simple, low-cost method that we could share with others in the community to encourage the testing of materials, masks prototypes and fittings," Fischer said. "The parts for the test apparatus are accessible and easy to assemble, and we've shown that they can provide helpful information about the effectiveness of masking."

Westman said he put the information immediately to use: "We were trying to make a decision on what type of face covering to purchase in volume, and little information was available on these new materials that were being used."

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