Ancient Mars impacts created tornado-like winds that scoured surface


Scienceadaily.com - In looking at NASA images of Mars a few years ago, Brown University geologist Peter Schultz noticed sets of strange bright streaks emanating from a few large-impact craters on the planet's surface. The streaks are odd in that they extend much farther from the craters than normal ejecta patterns, and they are only visible in thermal infrared images taken during the Martian night.

Using geological observation, laboratory impact experiments and computer modeling, Schultz and Brown graduate student Stephanie Quintana have offered a new explanation for how those streaks were formed. They show that tornado-like wind vortices -- generated by crater-forming impacts and swirling at 500 miles per hour or more -- scoured the surface and blasted away dust and small rocks to expose the blockier surfaces beneath.


"This would be like an F8 tornado sweeping across the surface," Schultz said. "These are winds on Mars that will never be seen again unless another impact."

The research is published online in the journal Icarus.

Schultz says he first saw the streaks during one of his "tours of Mars." In his downtime between projects, he pulls up random images from NASA's orbital spacecraft just to see if he might spot something interesting. In this case, he was looking at infrared images taken during the Martian nighttime by the THEMIS instrument, which flies aboard the Mars Odyssey orbiter.

The infrared images capture contrasts in heat retention on the surface. Brighter regions at night indicate surfaces that retain more heat from the previous day than surrounding surfaces, just as grassy fields cool off at night while buildings in the city remain warmer.

"You couldn't see these things at all in visible wavelength images, but in the nighttime infrared they're very bright," Schultz said. "Brightness in the infrared indicates blocky surfaces, which retain more heat than surfaces covered by powder and debris. That tells us that something came along and scoured those surfaces bare."

And Schultz had an idea what that something might be. He has been studying impacts and impact processes for years using NASA's Vertical Gun Range, a high-powered cannon that can fire projectiles at speeds up to 15,000 miles per hour.

"We had been seeing some things in experiments we thought might cause these streaks," he said.

When an asteroid or other body strikes a planet at high speed, tons of material from both the impactor and the target surface are instantly vaporized. Schultz's experiments showed that vapor plumes travel outward from an impact point, just above the impact surface, at incredible speeds. Scaling laboratory impacts to the size of those on Mars, a vapor plume's speed would be supersonic. And it would interact with the Martian atmosphere to generate powerful winds.

The plume and its associated winds on their own didn't cause the strange streaks, however. The plumes generally travel just above the surface, which prevents the kind of deep scouring seen in the streaked areas. But Schultz and Quintana showed that when the plume strikes a raised surface feature, it disturbs the flow and causes powerful tornadic vortices to form and drop to the surface. And those vortices, the researchers say, are responsible for scouring the narrow streaks.

Schultz and Quintana showed that the streaks are nearly always seen in conjunction with raised surface features. Very often, for example, they are associated with the raised ridges of smaller impact craters that were already in place when the larger impact occurred. As the plume raced outward from the larger impact, it encountered the small crater rim, leaving bright twin streaks on the downwind side.

"Where these vortices encounter the surface, they sweep away the small particles that sit loose on the surface, exposing the bigger blocky material underneath, and that's what gives us these streaks," Schultz said.

Schultz says the streaks could prove useful in establishing rates of erosion and dust deposition in areas where the streaks are found.

"We know these formed at the same time as these large craters, and we can date the age of the craters," Schultz said. "So now we have a template for looking at erosion."

But with more research, the streaks could eventually reveal much more than that. From a preliminary survey of the planet, the researchers say the streaks appear to form around craters in the ballpark of 20 kilometers across. But they don't appear in all such craters. Why they form in some places and not others could provide information about the Martian surface at the time of the impact.

The researchers' experiments reveal that the presence of volatile compounds -- a thick layer of water ice on the surface or subsurface, for example -- affect the amount the vapor that rushes out from an impact. So in that way, the streaks might serve as indicators of whether ice may have been present at the time of an impact, which could lend insight into reconstructions of past climate on Mars. Equally possible, the streaks could be related to the composition of the impactor, such as rare collisions by high-volatile objects, such as comets.

"The next step is to really dig into the conditions that cause the streaks," Schultz said. "They may have a lot to tell us, so stay tuned."

Source : Brown University

The Mysterious Powers of Spider Silks

Scienceadaily.com - Spider silks, the stuff of spider webs, are a materials engineer’s dream: they can be stronger than steel at a mere fraction of weight, and also can be tougher and more flexible. Spider silks also tend not to provoke the human immune system. Some even inhibit bacteria and fungi, making them potentially ideal for surgery and medical device applications. Exploitation of these natural marvels has been slow, due in part to the challenges involved in identifying and characterizing spider silk genes, but researchers from the Perelman School of Medicine at the University of Pennsylvania have now made a major advance with the largest-ever study of spider silk genes.

As they report today in an advance online paper in Nature Genetics, Penn scientists and their collaborators sequenced the full genome of the golden orb-weaver spider (Nephila clavipes), a prolific silk-spinner that turns out to produce 28 varieties of silk proteins. In addition to cataloguing new spider silk genes, the researchers discovered novel patterns within the genes that may help to explain the unique properties of different types of silk.


“There were so many surprises that emerged from our study: new silk genes, new DNA sequences that presumably confer strength, toughness, stretchiness and other properties to silk proteins; and even a silk protein made in venom glands rather than silk glands,” said senior author Benjamin F. Voight, PhD, an associate professor in the departments of Genetics and Systems Pharmacology and Translational Therapeutics. “All this new information should greatly advance our efforts to capture the extraordinary properties of these silks in man-made materials.”

Even though spider silks have been studied for more than 50 years, earlier foundational work had identified only a comparative handful of spider silk genes. Even recent work from species with smaller silk repertoires than the golden orb-weaver’s were incomplete. To find all of the silk genes hidden across the golden orb-weaver’s genome—the veritable “lab rat” of spider silk science—required the construction of the entire genome, a daunting task in itself.

In the new study, Voight and his colleagues began with the herculean task of sequencing and reassembling the genome of the golden orb-weaver: a task comparable to solving a multimillion-piece jigsaw puzzle, with few clues as to how these pieces fit together.

In the golden orb-weaver’s genome—which turns out to be about as large as the human genome—the researchers identified more than 14,000 likely genes, including 28 that appear to encode spider silk proteins, known as spidroins.

Spidroins have been classified into seven categories according to their protein sequences and functions; these categories include aciniform silk for wrapping prey (and tying down partners for mating); and the super-strong major ampullate silk from which spiders (and Spider-Man) swing while at work. However, some of the newly discovered spidroins have sequences that do not fit neatly into any of these categories—suggesting that the encoded silk proteins may have novel functions, or that the existing categories need to be redefined.

An extensive computational analysis of the orb-weaver’s spidroin genes revealed nearly 400 short sequences—many never before described—that appear repeatedly in these genes with small variations and in different combinations. These repetitive spidroin “motifs” are of great interest to biologists and engineers because they are likely to confer the key properties of a given spider silk, such as high tensile strength, flexibility, or stickiness. The analysis also revealed novel, higher-order organizations of these motifs into groups of motifs (“cassettes”) and groups of groups (“ensembles”).
Voight’s team also examined gene transcripts from different orb-weaver silk glands and in each case found transcripts belonging to more than one spidroin class, suggesting that these glands are not strictly specialized for producing one type of silk. “We found significantly more complexity in silk production than we expected,” Voight said.

The biggest surprise was the discovery that one of the orb-weaver’s spidroins—FLAG-b, a novel discovery by the group—appears to be produced primarily in the orb-weaver’s venom gland rather than in any silk gland, hinting at intriguing new functions for silk connected to prey capture, immobilization, or preservation.

In their analyses of the genome data, Voight and colleagues also identified 649 likely genes that are not spidroin genes but are highly expressed in silk glands, and thus probably have roles in converting the liquid silk from spider cells into solid, spinnable threads—a tricky process that biotech engineers are just beginning to achieve outside of spiders.

Voight and his team are now following up with a genome-sequencing study of Darwin’s bark spider, which makes the strongest known silks, and has been known to span rivers with them.
The scientists are also at work on technology for the rapid production of silks in the lab starting from their spidroin DNA sequences, to better understand how these sequences and their motifs encode silks’ biological and physical properties.

“When I say that we’d like to build a ‘web-shooter’ like Spider-Man’s in the lab, I’m only half joking” Voight said.

Source :  University of Pennsylvania School of Medicine

Oxford Student Creates First Synthetic Retina

Scienceadaily.com - A synthetic, soft tissue retina developed by an Oxford University student could offer fresh hope to visually impaired people.

Until now, all artificial retinal research has used only rigid, hard materials. The new research, by Vanessa Restrepo-Schild, a 24 year old Dphil student and researcher at the Oxford University, Department of Chemistry, is the first to successfully use biological, synthetic tissues, developed in a laboratory environment. The study could revolutionise the bionic implant industry and the development of new, less invasive technologies that more closely resemble human body tissues, helping to treat degenerative eye conditions such as retinitis pigmentosa.


Just as photography depends on camera pixels reacting to light, vision relies on the retina performing the same function. The retina sits at the back of the human eye, and contains protein cells that convert light into electrical signals that travel through the nervous system, triggering a response from the brain, ultimately building a picture of the scene being viewed.

Vanessa Restrepo-Schild led the team in the development of a new synthetic, double layered retina which closely mimics the natural human retinal process. The retina replica consists of soft water droplets (hydrogels) and biological cell membrane proteins. Designed like a camera, the cells act as pixels, detecting and reacting to light to create a grey scale image.  The Colombian native said: ‘The synthetic material can generate electrical signals, which stimulate the neurons at the back of our eye just like the original retina.’

The study, published in the journal Scientific Reports, shows that unlike existing artificial retinal implants, the cell-cultures are created from natural, biodegradable materials and do not contain foreign bodies or living entities. In this way the implant is less invasive than a mechanical devise, and is less likely to have an adverse reaction on the body.  Miss Restrepo-Schild added: ‘The human eye is incredibly sensitive, which is why foreign bodies like metal retinal implants can be so damaging, leading to inflammation and/or scaring. But a biological synthetic implant is soft and water based, so much more friendly to the eye environment.’

Of the motivation behind the ground-breaking study,  Miss Restrepo-Schild said: ‘I have always been fascinated by the human body, and want to prove that current technology can be used to replicate the function of human tissues, without having to actually use living cells.

I have taken the principals behind vital bodily functions, e.g. our sense of hearing, touch and the ability to detect light, and replicated them in a laboratory environment with natural, synthetic components. I hope my research is the first step in a journey towards building technology that is soft and biodegradable instead of hard and wasteful.’

Although at present the synthetic retina has only been tested in laboratory conditions, Miss Restrepo-Schild is keen to build on her initial work and explore potential uses with living tissues. This next step is vital in demonstrating how the material performs as a bionic implant.

Miss Restrepo-Schild has filed a patent for the technology and the next phase of the work will see the Oxford team expand the replica’s function to include recognising different colours. Working with a much larger replica, the team will test the material’s ability to recognise different colours and potentially even shapes and symbols. Looking further ahead the research will expand to include animal testing and then a series of clinical trials in humans.

Source : University of Oxford

Astronomers Confirm Nearby Star a Good Model of Our Early Solar System

Scienceadaily.com - NASA's SOFIA aircraft, a 747 loaded with a 2.5-meter telescope in the back and stripped of most creature comforts in the front, took a big U-turn over the Pacific west of Mexico.

The Stratospheric Observatory for Infrared Astronomy aircraft was just beginning the second half of an overnight mission on Jan. 28, 2015. It turned north for a flight all the way to western Oregon, then back home to NASA's Armstrong Flight Research Center in Palmdale, California. Along the way, pilots steered the plane to aim the telescope at a nearby star.

This is an artist's illustration of the epsilon Eridani system showing Epsilon Eridani b, right foreground, a Jupiter-mass planet orbiting its parent star at the outside edge of an asteroid belt. In the background can be seen another narrow asteroid or comet belt plus an outermost belt similar in size to our solar system's Kuiper Belt. The similarity of the structure of the Epsilon Eridani system to our solar system is remarkable, although Epsilon Eridani is much younger than our sun. SOFIA observations confirmed the existence of the asteroid belt adjacent to the orbit of the Jovian planet. Larger illustration. Illustration by NASA/SOFIA/Lynette Cook.

Iowa State University's Massimo Marengo and other astronomers were on board to observe the mission and collect infrared data about the star.

That star is called epsilon Eridani. It's about 10 light years away from the sun. It's similar to our sun, but one-fifth the age. And astronomers believe it can tell them a lot about the development of our solar system.

Marengo, an Iowa State associate professor of physics and astronomy, and other astronomers have been studying the star and its planetary system since 2004. In a 2009 scientific paper, the astronomers used data from NASA's Spitzer Space Telescope to describe the star's disk of fine dust and debris left over from the formation of planets and the collisions of asteroids and comets. They reported the disk contained separate belts of asteroids, similar to the asteroid and Kuiper belts of our solar system.

Subsequent studies by other astronomers questioned that finding.

A new scientific paper, just published online by The Astronomical Journal, uses SOFIA and Spitzer data to confirm there are separate inner and outer disk structures. The astronomers report further studies will have to determine if the inner disk includes one or two debris belts.

Kate Su, an associate astronomer at the University of Arizona and the university's Steward Observatory, is the paper's lead author. Marengo is one of the paper's nine co-authors.

Marengo said the findings are important because they confirm epsilon Eridani is a good model of the early days of our solar system and can provide hints at how our solar system evolved.

"This star hosts a planetary system currently undergoing the same cataclysmic processes that happened to the solar system in its youth, at the time in which the moon gained most of its craters, Earth acquired the water in its oceans, and the conditions favorable for life on our planet were set," Marengo wrote in a summary of the project.

A major contributor to the new findings was data taken during that January 2015 flight of SOFIA. Marengo joined Su on the cold and noisy flight at 45,000 feet, above nearly all of the atmospheric water vapor that absorbs the infrared light that astronomers need to see planets and planetary debris.

Determining the structure of the disk was a complex effort that took several years and detailed computer modeling. The astronomers had to separate the faint emission of the disk from the much brighter light coming from the star.

"But we can now say with great confidence that there is a separation between the star's inner and outer belts," Marengo said. "There is a gap most likely created by planets. We haven't detected them yet, but I would be surprised if they are not there. Seeing them will require using the next-generation instrumentation, perhaps NASA's 6.5-meter James Webb Space Telescope scheduled for launch in October 2018."

That's a lot of time and attention on one nearby star and its debris disk. But Marengo said it really is taking astronomers back in time.

"The prize at the end of this road is to understand the true structure of epsilon Eridani's out-of-this-world disk, and its interactions with the cohort of planets likely inhabiting its system," Marengo wrote in a newsletter story about the project. "SOFIA, by its unique ability of capturing infrared light in the dry stratospheric sky, is the closest we have to a time machine, revealing a glimpse of Earth's ancient past by observing the present of a nearby young sun."

Source : Iowa State University