Apr 26, 2018

Magma ocean may be responsible for the moon's early magnetic field

The bottom-most layer of the moon's mantle melts to form a metal-rich "basal magma ocean" that sits on top of the moon's metal core. Convection in this layer may have driven a dynamo, creating a magnetic field which would have been recorded at the surface by the cooling lunar crust, including the samples brought back by Apollo astronauts.
Around four billion years ago, the Moon had a magnetic field that was about as strong as Earth's magnetic field is today. How the Moon, with a much smaller core than Earth's, could have had such a strong magnetic field has been an unsolved problem in the history of the Moon's evolution.

Scientist Aaron Scheinberg of Princeton, with Krista Soderlund from the University of Texas Institute for Geophysics, and Linda Elkins-Tanton of Arizona State University, set out to determine what may have powered this early lunar magnetic field. Their results and a new model for how this may have happened, have been recently published in Earth and Planetary Science Letters.

A new model

Earth's magnetic field protects our planet by deflecting most of the solar wind, whose charged particles would otherwise strip away the ozone layer that protects the Earth from harmful ultraviolet radiation.

While Earth's magnetic field is generated by the motions of its convecting liquid metal outer core, known as the dynamo, the Moon's core is too small to have produced a magnetic field of that magnitude.

So, the research team proposed a new model for how the magnetic field could have reached Earth-like levels. In this scenario, the dynamo is powered not by the Moon's small metal core, but by a heavy layer of molten (liquid) rock that sits on top of it.

In this proposed model, the bottom-most layer of the Moon's mantle melts to form a metal-rich "basal magma ocean" that sits on top of the Moon's metal core. Convection in this layer then drives the dynamo, creating a magnetic field.

"The idea of a basal magma ocean dynamo had been proposed for the early Earth's magnetic field, and we realized that this mechanism may also be important for the Moon," says co-author Soderlund.

Soderlund further explains that a partially molten layer is thought to still exist at the base of the lunar mantle today. "A strong magnetic field is easier to achieve at the Moon's surface if the dynamo operated in the mantle rather than in the core," she says, "because magnetic field strength decreases rapidly the farther away it is from the dynamo region."

In simulations of the core dynamo of the Moon conducted by the team, they kept finding that the lower layer of the Moon's mantle was overheating and melting. Initially, they tried to focus on cases without melting that were easier to model, but eventually considered that the melting process was the key to their new model.

"Once we started thinking of that melting as a feature, instead of a bug," says Scheinberg, "the pieces started fitting together and we wondered if the melting that we saw in the models could produce a metal-rich magma ocean to power the strong early field."

A later weak magnetic field

Further along in the evolution of the Moon (around 3.56 billion years ago), there is also evidence that the strong magnetic field that existed around the Moon eventually became a weak magnetic field, one that continued until relatively recently. The team's new model may also help explain this phenomenon as well.

"Our model provides an elegant potential solution," says Scheinberg. "As the Moon cooled, the magma ocean would have solidified, while the core dynamo would have continued to create the later weak field."

"We're excited by this result because it explains fundamental observations about the Moon -- its early, strong magnetic field and its subsequent weakening and then disappearance -- using first-order processes already supported by other observations," adds co-author Elkins-Tanton.

Beyond providing a new model to build from, this research may also provide a better understanding of planetary magnetic field generation elsewhere in our solar system and beyond.

Read more at Science Daily

Molecular evolution: How the building blocks of life may form in space

Star forming region (Pillars of Creation) in the Eagle Nebula. Low-energy electrons, created in matter by space radiation (e.g., galactic cosmic rays, GCR, etc.), can induce formation of glycine (2HN-CH2-COOH) in astrophysical molecular ices; here, icy grains of interstellar dust (or ices on planetary satellites) are simulated by ammonia, methane and carbon dioxide condensed at 20 K on Pt in UHV, and irradiated by 0-70 eV LEEs.
In a laboratory experiment that mimics astrophysical conditions, with cryogenic temperatures in an ultrahigh vacuum, scientists used an electron gun to irradiate thin sheets of ice covered in basic molecules of methane, ammonia and carbon dioxide. These simple molecules are ingredients for the building blocks of life. The experiment tested how the combination of electrons and basic matter leads to more complex biomolecule forms -- and perhaps eventually to life forms.

"You just need the right combination of ingredients," author Michael Huels said. "These molecules can combine, they can chemically react, under the right conditions, to form larger molecules which then give rise to the bigger biomolecules we see in cells like components of proteins, RNA or DNA, or phospholipids."

The right conditions, in space, include ionizing radiation. In space, molecules are exposed to UV rays and high-energy radiation including X-rays, gamma rays, stellar and solar wind particles and cosmic rays. They are also exposed to low-energy electrons, or LEEs, produced as a secondary product of the collision between radiation and matter. The authors examined LEEs for a more nuanced understanding of how complex molecules might form.

In their paper, in the Journal of Chemical Physics, from AIP Publishing, the authors exposed multilayer ice composed of carbon dioxide, methane and ammonia to LEEs and then used a type of mass spectrometry called temperature programmed desorption (TPD) to characterize the molecules created by LEEs.

In 2017, using a similar method, these researchers were able to create ethanol, a nonessential molecule, from only two ingredients: methane and oxygen. But these are simple molecules, not nearly as complex as the larger molecules that are the stuff of life. This new experiment has yielded a molecule that is more complex, and is essential for terrestrial life: glycine.

Glycine is an amino acid, made of hydrogen, carbon, nitrogen and oxygen. Showing that LEEs can convert simple molecules into more complex forms illustrates how life's building blocks could have formed in space and then arrived on Earth from material delivered via comet or meteorite impact.

In their experiment, for each 260 electrons of exposure, one molecule of glycine was formed. Seeking to know how realistic this rate of formation was in space, not just in the laboratory, the researchers extrapolated out to determine the probability that a carbon dioxide molecule would encounter both a methane molecule and ammonia molecule and how much radiation they, together, might encounter.

Read more at Science Daily

Archaeologists on ancient horse find in Nile River Valley

The Tombos horse was discovered in 2011. The ancient horse is dated to the Third Intermediate Period, 1050-728 B.C.E., and it was found more than 5 feet underground in a tomb. The horse, with some chestnut-colored fur remaining, had been buried in a funeral position with a burial shroud. The discovery provides a window into human-animal relationships more than 3,000 years ago.
An ancient horse burial at Tombos along the Nile River Valley shows that a member of the horse family thousands of years ago was more important to the culture than previously thought, which provides a window into human-animal relationships more than 3,000 years ago.

The research findings are published in Antiquity. The Tombos horse was discovered in 2011, and members of the Purdue team -- professor Michele Buzon and alumna Sarah Schrader -- played a part in the excavation and analysis. The horse is dated to the Third Intermediate Period, 1050-728 B.C.E., and it was found more than 5 feet underground in a tomb. The horse, with some chestnut-colored fur remaining, had been buried in a funeral position with a burial shroud.

"It was clear that the horse was an intentional burial, which was super fascinating," said Buzon, a professor of anthropology. "Remnants of fabric on the hooves indicate the presence of a burial shroud. Changes on the bones and iron pieces of a bridle suggest that the horse may have pulled a chariot. We hadn't found anything like this in our previous excavations at Tombos. Animal remains are very rare at the site."

Buzon, a bioarchaeologist, has worked with Stuart Tyson Smith, anthropology professor at the University of California, Santa Barbara, for 18 years at this site in modern-day Sudan, and both are principal investigators on the project. Buzon uses health and cultural evidence from more than 3,000-year-old burial sites to understand the lives of Nubians and Egyptians during the New Kingdom Empire. This is when Egyptians colonized the area in about 1500 B.C. to gain access to trade routes on the Nile River. Over the years, hundreds of artifacts, including pottery, tools, carvings and dishes were unearthed at this burial site for about 200 individuals.

"Finding the horse was unexpected," Schrader said. "Initially, we weren't sure if it was modern or not. But as we slowly uncovered the remains, we began to find artifacts associated with the horse, such as the scarab, the shroud and the iron cheekpiece. At that point, we realized how significant this find was. Of course, we became even more excited when the carbon-14 dates were assessed and confirmed how old the horse was."

Schrader, who graduated from Purdue in 2013 with a doctoral degree in anthropology, is an assistant professor of human osteoarchaeology at Leiden University in The Netherlands. Schrader is lead author on this article, and she helped frame this find within the context of Nubian history.

Once the archaeologists discovered the horse, Sandra Olsen, curator-in-charge at the Biodiversity Institute and Natural History Museum at the University of Kansas and a well-known ancient horse expert, was invited to Purdue to analyze the horse skeleton. Buzon coordinated the analysis between the team, and she established the chronology of the horse via radiocarbon dating.

Read more at Science Daily

Projectile cannon experiments show how asteroids can deliver water

Special delivery. Experiments using a high-powered projectile cannon suggest that asteroids can deliver surprising amounts of water when they smash into planetary bodies.
Experiments using a high-powered projectile cannon show how impacts by water-rich asteroids can deliver surprising amounts of water to planetary bodies. The research, by scientists from Brown University, could shed light on how water got to the early Earth and help account for some trace water detections on the Moon and elsewhere.

"The origin and transportation of water and volatiles is one of the big questions in planetary science," said Terik Daly, a postdoctoral researcher at Johns Hopkins University who led the research while completing his Ph.D. at Brown. "These experiments reveal a mechanism by which asteroids could deliver water to moons, planets and other asteroids. It's a process that started while the solar system was forming and continues to operate today."

The research is published in Science Advances.

The source of Earth's water remains something of a mystery. It was long thought that the planets of the inner solar system formed bone dry and that water was delivered later by icy comet impacts. While that idea remains a possibility, isotopic measurements have shown that Earth's water is similar to water bound up in carbonaceous asteroids. That suggests asteroids could also have been a source for Earth's water, but how such delivery might have worked isn't well understood.

"Impact models tell us that impactors should completely devolatilize at many of the impact speeds common in the solar system, meaning all the water they contain just boils off in the heat of the impact," said Pete Schultz, co-author of the paper and a professor in Brown's Department of Earth, Environmental and Planetary Sciences. "But nature has a tendency to be more interesting than our models, which is why we need to do experiments."

For the study, Daly and Schultz used marble-sized projectiles with a composition similar to carbonaceous chondrites, meteorites derived from ancient, water-rich asteroids. Using the Vertical Gun Range at the NASA Ames Research Center, the projectiles were blasted at a bone-dry target material made of pumice powder at speeds around 5 kilometers per second (more than 11,000 miles per hour). The researchers then analyzed the post-impact debris with an armada of analytical tools, looking for signs of any water trapped within it.

They found that at impact speeds and angles common throughout the solar system, as much as 30 percent of the water indigenous in the impactor was trapped in post-impact debris. Most of that water was trapped in impact melt, rock that's melted by the heat of the impact and then re-solidifies as it cools, and in impact breccias, rocks made of a mish-mash of impact debris welded together by the heat of the impact.

The research gives some clues about the mechanism through which the water was retained. As parts of the impactor are destroyed by the heat of the collision, a vapor plume forms that includes water that was inside the impactor.

"The impact melt and breccias are forming inside that plume," Schultz said. "What we're suggesting is that the water vapor gets ingested into the melts and breccias as they form. So even though the impactor loses its water, some of it is recaptured as the melt rapidly quenches."

The findings could have significant implications for understanding the presence of water on Earth. Carbonaceous asteroids are thought to be some of the earliest objects in the solar system -- the primordial boulders from which the planets were built. As these water-rich asteroids bashed into the still-forming Earth, it's possible that a process similar to what Daly and Schultz found enabled water to be incorporated in the planet's formation process, they say. Such a process could also help explain the presence of water within the Moon's mantle, as research has suggested that lunar water has an asteroid origin as well.

The work could also explain later water activity in the solar system. Water found on the Moon's surface in the rays of the crater Tycho could have been derived from the Tycho impactor, Schultz says. Asteroid-derived water might also account for ice deposits detected in the polar regions of Mercury.

Read more at Science Daily

Apr 25, 2018

To see the first-born stars of the universe

The galaxy cluster Abell 2744 lies at a distance of about 3.5 billion light-years and contains more than 400 member galaxies. The combined gravity of all the galaxies makes the cluster act as a lens to magnify the light from stars beyond including, the team hopes, the first stars to form in the universe.
About 200 to 400 million years after the Big Bang created the universe, the first stars began to appear. Ordinarily stars lying at such a great distance in space and time would be out of reach even for NASA's new James Webb Space Telescope, due for launch in 2020.

However, astronomers at Arizona State University are leading a team of scientists who propose that with good timing and some luck, the Webb Space Telescope will be able to capture light from the first stars to be born in the universe.

"Looking for the first stars has long been a goal of astronomy," said Rogier Windhorst, Regents' Professor of astrophysics in ASU's School of Earth and Space Exploration. "They will tell us about the actual properties of the very early universe, things we've only modeled on our computers until now."

Windhorst's collaborator, Frank Timmes, professor of astrophysics at the School of Earth and Space Exploration, adds, "We want to answer questions about the early universe such as, were binary stars common or were most stars single? How many heavy chemical elements were produced, cooked up by the very first stars, and how did those first stars actually form?

Duho Kim, a School of Earth and Space Exploration graduate student of Windhorst's, worked on modeling star populations and dust in galaxies.

The other collaborators on the paper are J. Stuart B. Wyithe (University of Melbourne, Australia), Mehmet Alpaslan (New York University), Stephen K. Andrews (University of Western Australia), Daniel Coe (Space Telescope Science Institute), Jose M. Diego (Instituto de Fisica de Cantabria, Spain), Mark Dijkstra (University of Oslo), and Simon P. Driver and Patrick L. Kelly (both University of California, Berkeley).

The team's paper, published in the Astrophysical Journal Supplement, describes how the challenging observations can be done.

Gravity's magnifying lens

The first essential step in the task relies on the infrared sensitivity of the Webb Telescope. While the first stars were large, hot and radiated far-ultraviolet light, they lie so far away that the expansion of the universe has shifted their radiation peak from the ultraviolet to much longer infrared wavelengths. Thus their starlight drops into the Webb Telescope's infrared detectors like a baseball landing in a fielder's mitt.

The second essential step is to use the combined gravity of an intervening cluster of galaxies as a lens to focus and magnify the light of the first generation stars. Typical gravitational lensing can magnify light 10 to 20 times, but that's not enough to make a first-generation star visible to the Webb Telescope. For Webb, the candidate star's light needs boosting by factor of 10,000 or more.

To gain that much magnification calls for "caustic transits," special alignments where a star's light is greatly magnified for a few weeks as the galaxy cluster drifts across the sky between Earth and the star.

Caustic transits occur because a cluster of galaxies acting as a lens doesn't produce a single image like a reading magnifier. The effect is more like looking through a lumpy sheet of glass, with null zones and hot spots. A caustic is where magnification is greatest, and because the galaxies in the lensing cluster spread out within it, they produce multiple magnifying caustics that trace a pattern in space like a spider web.

Playing the odds

How likely is such an alignment? Small but not zero, say the astronomers, and they note the spider web of caustics helps by spreading a net. Moreover each caustic is asymmetrical, producing a sharp rise to full magnification if a star approaches from one side, but a much slower rise if it approaches from the other side.

"Depending on which side of the caustic it approaches from, a first star would brighten over hours -- or several months," Windhorst explained. "Then after reaching a peak brightness for several weeks, it would fade out again, either slowly or quickly, as it moves away from the caustic line."

A key attribute of the first stars is that they formed out of the early universe's mix of hydrogen and helium with no heavier chemical elements such as carbon, oxygen, iron, or gold. Blazingly hot and brilliantly blue-white, the first stars display a textbook simple spectrum like a fingerprint, as calculated by the ASU team using the open software instrument Modules for Experiments in Stellar Astrophysics.

Another object potentially visible by the same magnifying effect is an accretion disk around the first black holes to form after the Big Bang. Black holes would be the final evolutionary outcome of the most massive first stars. And if any such stars were in a two-star (binary) system, the more massive star, after collapsing to a black hole, would steal gas from its companion to form a flat disk feeding into the black hole.

An accretion disk would display a different spectrum from a first star as it transits a caustic, producing enhanced brightness at shorter wavelengths from the hot, innermost part of the disk compared to the colder outer zones of it. The rise and decay in brightness would also take longer, though this effect would likely be harder to detect.

Accretion disks are expected to be more numerous because solitary first stars, being massive and hot, race through their lives in just a few million years before exploding as supernovas. However, theory suggests that an accretion disk in a black hole system could shine at least ten times longer than a solitary first star. All else being equal, this would increase the odds of detecting accretion disks.

It's educated guesswork at this stage, but the team calculates that an observing program which targets several galaxy clusters a couple of times a year for the lifetime of the Webb Telescope could find a lensed first star or black hole accretion disk. The researchers have selected some target clusters, including the Hubble Frontier Fields clusters and the cluster known as "El Gordo."

"We just have to get lucky and observe these clusters long enough," Windhorst said. "The astronomical community would need to continue to monitor these clusters during Webb's lifetime."

On beyond Webb

Which raises a point. While the Webb Space Telescope will be a technical marvel, it will not have a long operational lifetime like the Hubble Space Telescope. Launched in 1990, the Hubble Telescope is in low Earth orbit and has been serviced by astronauts five times.

The Webb Space Telescope, however, will be placed at a gravitationally stable point in interplanetary space, 1.5 million kilometers (930,000 miles) from Earth. It has been designed to operate for 5 to 10 years, which might with care stretch to about 15 years. But there's no provision for servicing by astronauts.

Accordingly, Windhorst notes that ASU has joined the Giant Magellan Telescope Organization. This is a consortium of universities and research institutions that will build its namesake telescope on a high and dry mountaintop at Las Campanas Observatory in Chile. The site is ideal for infrared observing.

Upon completion in 2026, the GMT will have a light-collecting surface 24.5 meters (80 feet) in diameter, built from seven individual mirrors. (The Webb Space Telescope's main mirror has 18 sections and a total diameter of 6.5 meters, or 21 feet.) The GMT mirrors are expected to achieve a resolving power 10 times greater than that of the Hubble Space Telescope in the infrared region of the spectrum.

There will be a period during which the Webb Telescope and the Giant Magellan Telescope will both be in operation.

"We're planning to make observations of first-generation stars and other objects with the two instruments," Windhorst said. "This will let us cross-calibrate the results from both."

The overlap between the two telescopes is important in another way, he said.

Read more at Science Daily

First Footprint Evidence of Human Hunting Discovered

Human footprint inside a sloth track. This composite track is part of a trackway in which the human appears to have stalked the sloth
Fossilized tracks — footprints created thousands of years ago — provide some of the best evidence for past behaviors. Sometimes they show animal predators hunting, but none have ever been from humans hunting, until now.

Prehistoric footprints for both humans and giant ground sloths have just been discovered at White Sands National Monument in New Mexico. The trackways are interpreted as being the first-known footprint evidence for people hunting. The footprints, described in the journal Science Advances, suggest people 11,000 years ago stalked a giant ground sloth, which was a strong and sharp-clawed animals that could grow up to about 9 feet long.

"Sloth anatomy is not built for speed, but strength," co-author Sally Reynolds of Bournemouth University's Institute for Studies in Landscapes and Human Evolution told Seeker.

"The sloth would have raised itself up to full height and attempted to keep the attackers at bay with its long forearms and large sharp claws," she added. "The hunters would have needed to wait patiently to get the right opportunity to strike the killing blow in a vulnerable part of the sloth anatomy, such as the heart, underbelly, neck, or eyes. The hunters would have been at significant physical risk to themselves while the animal was defending itself."

General view of Alkali Flat at White Sands National Monument (New Mexico) showing a series of excavated footprints in the foreground
Researchers are still dating the tracks and haven't ruled out that the prints could be much older than 11,000 years. If that estimate holds, however, the landscape at the time included "a lake bed with patches of seasonal water," senior author Matthew Bennett, also from Bournemouth University, told Seeker.

He explained that peat and sediment were probably reactivated by water, promoting creation of the now-preserved tracks.

He said footprints from multiple people of various ages were discovered along the edge of the lake bed, which is now a playa. A small number of the prehistoric individuals went out into the drying lake bed. The tracks that they left behind show that they were barefoot, but today would have fit into men's shoes sized at about 8.5 in US size, 8 in UK.

The humans appear to have been following, and sometimes even stepping into, prints left behind by about 2–3 giant ground sloths. In the absence of human tracks, these animals tend to travel in a straight or curvilinear fashion. Here, the lumbering beasts distantly related to anteaters and armadillos made sharp changes in their direction of travel. These changes correspond to the approaching humans.

In one track, a line of human toe impressions suggests that the person approached a giant ground sloth on tiptoe while at least one other person was behind the animal.

These, and the other footprints, according the authors suggest a group of people gathered along the edge of the drying lakebed, possibly to keep the sloths out on the flat mud where they could more easily be attacked.

"One hunter stalks the sloth, harassing it so that it turns toward the stalker," Bennett said. "It rises on its hind legs and swings its forelegs around, putting its claws down to steady itself as it swings."

"While the sloth is distracted," he continued, "another hunter approached and tried to land the killing blow. If successful, the sloth would then have been killed or followed as it bled to death. Having the rest of the group as distant observers would mean that others would be on hand to deal with the carcass, if required."

Composite cast showing a range of footprints from the White Sands National Monument field site
The researchers can tell that neither the hunters nor the sloths were running, perhaps due to the challenges of navigating the muddy substrate.

If the humans were, as suspected, members of the Clovis culture from the American Southwest, they likely would have been hunting the giant sloths with long spears in hand. The researchers are not sure what specific species of giant sloth met its doom at the site, now called Alkali Flat, but Nothrotheriops and Paramylodon both lived in what is now New Mexico during the late Pleistocene.

Notably, all four species of giant ground sloths went extinct shortly afterward — approximately 10,000 years ago.

"This helps us to clarify the debate about how human hunting may have impacted these megafaunal extinctions," Reynolds said.

Read more at Seeker

If the Rotten Egg Smell Doesn’t Kill You, the Negative 200°C Temperature of Uranus Will

View of Uranus from NASA's Voyager 2 probe
There's a lot of really smelly stuff wafting around Uranus.

The clouds in Uranus' upper atmosphere are composed largely of hydrogen sulfide, the molecule that makes rotten eggs so stinky, a new study suggests.

"If an unfortunate human were ever to descend through Uranus' clouds, they would be met with very unpleasant and odiferous conditions," study lead author Patrick Irwin of Oxford University in England said in a statement.

But that wayward pioneer would have bigger problems, he added: "Suffocation and exposure in the negative 200 degrees Celsius (minus 328 degrees Fahrenheit) atmosphere, made of mostly hydrogen, helium, and methane, would take its toll long before the smell."

Researchers have long wondered about the composition of the clouds high up in Uranus's sky — specifically, whether they're dominated by ammonia ice, as at Jupiter and Saturn, or by hydrogen sulfide ice. The answer has proved elusive because it's tough to make observations with the required detail on distant Uranus. (Not only are Jupiter and Saturn closer to Earth, they have also hosted dedicated orbiter missions. Uranus has been visited just once — a brief flyby by NASA's Voyager 2 probe in January 1986.)

Irwin and his colleagues studied Uranus's air using the Near-Infrared Integral Field Spectrometer (NIFS), an instrument on the 26-foot (8 meters) Gemini North telescope in Hawaii. NIFS scrutinized sunlight reflected from the atmosphere just above Uranus' cloud tops — and spotted the signature of hydrogen sulfide.

"Only a tiny amount remains above the clouds as a saturated vapor," study co-author Leigh Fletcher, from the University of Leicester in England, said in the same statement. "And this is why it is so challenging to capture the signatures of ammonia and hydrogen sulfide above cloud decks of Uranus. The superior capabilities of Gemini finally gave us that lucky break."

Neptune's clouds are likely similar to those of Uranus, the researchers said. The big difference between the clouds of these two "ice giants" and those of Jupiter and Saturn probably trace to the worlds' formation environments: Uranus and Neptune coalesced much farther from the sun than the two gas giants did.

Read more at Seeker

Experiments Confirm the Interiors of Uranus and Neptune Are Made of Superionic Ice

Uranus, on the left, Neptune, on the right
A unique form of water ice that is both solid and liquid at the same time might be found inside Uranus and Neptune, according to a recent set of experiments that mimicked the conditions inside the icy giants. 

The results, published in the journal Nature Physics, confirmed a 30-year old theory that a form of water ice called superionic ice likely exists in certain planetary conditions where liquids endure extreme heat and pressure. This includes the ice giants in our own solar system, as well as similar exoplanets discovered in other solar systems throughout our galaxy.  Superionic ice, however, is not found naturally on Earth.

“We wanted to see if we could confirm the prediction for superionic water ice and measure its properties in the laboratory,” lead author Marius Millot, a researcher at Lawrence Livermore National Laboratory, said in an email to Seeker. “It is such an unusual state of matter, we wanted to see if we could create it with shock waves.”

There are perhaps 17 — or more — types of water ice, although some remain theoretical. On Earth’s surface, only one kind of ice occurs naturally — the ice in your drink or that makes up the Antarctic ice sheets — called ice lh (pronounced “ice one h”). As water freezes and turns from a liquid into a solid, the water molecules crystalize into a hexagonal shape.

But depending on the pressure and temperature, the water molecules can line up into different shapes, creating different types of ice. Even water at high temperatures can turn solid when compressed under enough pressure. Ice of this type, called ice VII (pronounced “ice eight”), is known to exist deep within Earth, and it was recently found inside of diamonds. Ice VII has also been created in laboratories.

Superionic ice is thought to form at extreme temperatures and pressures, where oxygen atoms are locked into a crystal structure, but the hydrogen ions move around, making the ice simultaneously solid and liquid, somewhat similar to lava. Over the years, various research groups have explored the properties of water under high pressure using computer simulations of the structure of water.

“These simulations showed that when water is compressed to millions of [Earth] atmospheres and heated to thousands of degrees it forms a crystal of oxygen ions with hydrogen ions moving rapidly through the crystal in a fluid-like manner,” co-author Sebastien Hamel, also from LLNL, said in an email. “However, such simulations have been approximations and so we wanted to verify those predictions by reaching those pressure and temperature conditions for a sample of water in the lab and measuring whether or not it solidified and whether or not the hydrogen ions were fluid-like.”

Millot, Hamel, and their colleagues first created ice VII in their laboratory by putting a small, sub-millimeter-sized water sample inside a diamond anvil cell (DAC), a high-pressure device made up of two opposing diamonds, which places water under extreme pressure. They then hand-carried the sample to a laser facility at the University of Rochester.

“What was novel about our experiment was to combine the compressed ice with a laser-generated shock wave to compress and heat up the water sample to reach the conditions of pressure and temperature that we wanted,” Hamel said.

The water was pre-compressed in the DAC to about 30,000 atmospheres and the shockwave briefly increased the pressure to 2,000,000 atmospheres, while heating the sample to about 4,000 degrees Kelvin.

Over a year, the researchers conducted multiple tests and were able to confirm that the extreme pressure and temperatures created superionic ice. They measured the optical reflectivity and absorption levels, showing the samples were opaque, suggesting that the ions were moving.

“Physicist often measure the optical properties to understand the electronic structure,” Millot explained. “Superionic water ice is a semiconductor, and because there are not enough ‘free electrons’ able to carry electrical current, it is not shiny like a metal. Instead, it absorbs visible light and looks black, opaque if there is a thick enough layer.”

These results were consistent with the computer-simulated predictions and Hamel said the researchers are now working on developing a general capability for performing this type of experiment for various other materials.

Interestingly, the team brought the DAC carrying the ice sample inside a carry-on case on a commercial flight from LLNL in California to the laser facility in New York. Asked if that method of transport was nerve-wracking, Millot and Hamel said “not at all. “

“We often hand-carry our targets for laser experiments, so there is always a chance that one cell will break during the trip, but they are usually okay,” Millot said, adding that they usually bring multiple samples. “The final countdown for the laser shots is more stressful, because each cell is destroyed once we have fired the laser. So if the diagnostic did not record, the whole time preparing the target and setting up the laser shot is lost!”

But the researchers said understanding superionic ice could also solve a mystery about the odd, lopsided magnetic fields of Uranus and Neptune detected by the Voyager 2 mission in the 1980’s. Planetary magnetic fields are produced by the movement of electrically conducting internal fluids at high pressures, and any unusual magnetic fields are thought to be related to the consistency of the fluids that generate them.

“Given how we think planets like Neptune and Uranus form, a large fraction of their mass is water,” Hamel said. “Under the pressures and temperatures achieved in the interior of those giant planets, water will be a fluid for the outer part of the planet and a super-ionic solid for the deeper layers of the planet.”

Read more at Seeker

Apr 24, 2018

Galaxies grow bigger and puffier as they age

A new international study involving The Australian National University (ANU) and The University of Sydney has found that galaxies grow bigger and puffier as they age.

Co-researcher Professor Matthew Colless from ANU said that stars in a young galaxy moved in an orderly way around the galaxy's disk, much like cars around a racetrack.

"All galaxies look like squashed spheres, but as they grow older they become puffier with stars going around in all directions," said Professor Colless, who is the Director of the ANU Research School of Astronomy and Astrophysics and a Chief Investigator at the ARC Centre of Excellence in All-Sky Astrophysics in 3D (ASTRO 3D).

"Our Milky Way is more than 13 billion years old, so it is not young anymore, but the galaxy still has both a central bulge of old stars and spiral arms of young stars."

To work out a galaxy's shape, the research team measured the movement of stars with an instrument called SAMI on the Anglo-Australian Telescope at the ANU Siding Spring Observatory.

They studied 843 galaxies of all kinds and with a hundred-fold range in mass.

The study, which is published in Nature Astronomy, was funded by ASTRO 3D at ANU and the ARC Centre of Excellence for All Sky Astrophysics (CAASTRO) at The University of Sydney.

Lead author Dr Jesse van de Sande, from The University of Sydney and ASTRO 3D, said that it was not obvious that galaxy shape and age had to be linked, so the connection was surprising and could point to a deep underlying relationship.

"As a galaxy ages, internal changes take place and the galaxy may collide with others," Dr van de Sande said.

"These events disorder the stars' movements."

Co-author Dr Nicholas Scott, from the University of Sydney and ASTRO 3D, said scientists measured a galaxy's age through colour.

"Young, blue stars grow old and turn red," he said.

"When we plotted how ordered the galaxies were against how squashed they were, the relationship with age leapt out. Galaxies that have the same squashed spherical shape, have stars of the same age as well."

Dr van de Sande said scientists had known for a long time that shape and age were linked in very extreme galaxies, that is very flat ones and very round ones.

"This is the first time we've shown shape and age are related for all kinds of galaxies, not just the extremes -- all shapes, all ages, all masses," he said.

University of Sydney co-author Dr Julia Bryant, lead scientist for the SAMI instrument, said the team was still searching for the simple, powerful relationships like shape and age that underlie a lot of the complexity scientists see in galaxies.

"To see those relationships, you need detailed information on large numbers of galaxies," she said.

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Did last ice age affect breastfeeding in Native Americans?

Photograph of human upper incisors with significant "shoveling," anatomical variation influenced by the EDAR V370A allele alongside an increase in mammary duct branching.
The critical role that breast feeding plays in infant survival may have led, during the last ice age, to a common genetic mutation in East Asians and Native Americans that also, surprisingly, affects the shape of their teeth.

The genetic mutation, which probably arose 20,000 years ago, increases the branching density of mammary ducts in the breasts, potentially providing more fat and vitamin D to infants living in the far north where the scarcity of ultraviolet radiation makes it difficult to produce vitamin D in the skin.

If the spread of this genetic mutation is, in fact, due to selection for increased mammary ductal branching, the adaptation would be the first evidence of selection on the human maternal-infant bond.

"This highlights the importance of the mother-infant relationship and how essential it has been for human survival," said Leslea Hlusko, an associate professor of integrative biology at the University of California, Berkeley.

As for the teeth, it just so happens that the gene controlling mammary duct growth also affects the shape of human incisors. Consequently, as the genetic mutation was selected for in an ancestral population living in the far north during the last Ice Age, shovel-shaped incisors became more frequent too. Shoveled incisors are common among Native Americans and northeastern Asian populations but rare in everyone else.

Hlusko and her colleagues outline the many threads of evidence supporting the idea in an article published this week in the journal Proceedings of the National Academy of Sciences.

The finding could also have implications for understanding the origins of dense breast tissue and its role in breast cancer.

For the study, Hlusko and her colleagues assessed the occurrence of shovel-shaped incisors in archeological populations in order to estimate the time and place of evolutionary selection for the trait. They found that nearly 100 percent of Native Americans prior to European colonization had shoveled incisors, as do approximately 40 percent of East Asians today.

The team then used the genetic effects that are shared with dental variation as a way to discern the evolutionary history of mammary glands because of their common developmental pathway.

"People have long thought that this shoveling pattern is so strong that there must have been evolutionary selection favoring the trait, but why would there be such strong selection on the shape of your incisors?" Hlusko said. "When you have shared genetic effects across the body, selection for one trait will result in everything else going along for the ride."

The vitamin D connection

Getting enough vitamin D, which is essential for a robust immune system and proper fat regulation as well as for calcium absorption, is a big problem in northern latitudes because the sun is low on the horizon all year long and, above the Arctic Circle, doesn't shine at all for part of the year. While humans at lower latitudes can get nearly all the vitamin D they need through exposure of the skin to ultraviolet light, the scarce UV at high latitudes forced northern peoples like the Siberians and Inuit to get their vitamin D from animal fat, hunting large herbivores and sea mammals.

But babies must get their vitamin D from mother's milk, and Hlusko posits that the increased mammary duct branching may have been a way of delivering more vitamin D and the fat that goes with it.

Hlusko, who specializes in the evolution of teeth among animals, in particular primates and early humans, discovered these connections after being asked to participate in a scientific session on the dispersal of modern humans throughout the Americas at the February 2017 American Association for the Advancement of Science meeting. In preparing her talk on what teeth can tell us about the peopling of the New World, she pulled together the genetics of dental variation with the archaeological evidence to re-frame our understanding of selection on incisor shape.

Incisors are called "shovel-shaped" when the tongue-side of the incisors -- the cutting teeth in the front of the mouth, four on top, four on the bottom -- have ridges along the sides and biting edge. It is distinctive of Native Americans and populations in East Asia -- Korea, Japan and northern China -- with an increasing incidence as you travel farther north. Unpersuaded by a previously proposed idea that shoveled incisors were selected for use softening animal hides, she looked at explanations unrelated to teeth.

The genetic mutation responsible for shoveling -- which occurs in at least one of the two copies, or alleles, of a gene called EDAR, which codes for a protein called the ectodysplasin A receptor -- is also involved in determining the density of sweat glands in the skin, the thickness of hair shafts and ductal branching in mammary glands. Previous genetic analysis of living humans concluded that the mutation arose in northern China due to selection for more sweat glands or sebaceous glands during the last ice age.

"Neither of those is a satisfying explanation," Hlusko said. "There are some really hot parts in the world, and if sweating was so sensitive to selective pressures, I can think of some places where we would have more likely seen selection on that genetic variation instead of in northern China during the Last Glacial Maximum."

The Beringian standstill

Clues came from a 2007 paper and later a 2015 study by Hlusko's coauthor Dennis O'Rourke, in which scientists deduced from the DNA of Native Americans that they split off from other Asian groups more than 25,000 years ago, even though they arrived in North American only 15,000 years ago. Their conclusion was that Native American ancestors settled for some 10,000 years in an area between Asia and North America before finally moving into the New World. This so-called Beringian standstill coincided with the height of the Last Glacial Maximum between 18,000 and 28,000 years ago.

According to the Beringian standstill hypothesis, as the climate became drier and cooler as the Last Glacial Maximum began, people who had been living in Siberia moved into Beringia. Gigantic ice sheets to the east prohibited migration into North America. They couldn't migrate southwest because of a large expanse of a treeless and inhospitable tundra. The area where they found refuge was a biologically productive region thanks to the altered ocean currents associated with the last ice age, a landmass increased in size by to the lower sea levels. Genetic studies of animals and plants from the region suggest there was an isolated refugium in Beringia during that time, where species with locally adaptive traits arose. Such isolation is ripe for selection on genetic variants that make it easier for plants, animals and humans to survive.

"If you take these data from the teeth to interpret the evolutionary history of this EDAR allele, you frame-shift the selective episode to the Beringian standstill population, and that gives you the environmental context," Hlusko said. "At that high latitude, these people would have been vitamin D deficient. We know they had a diet that was attempting to compensate for it from the archaeological record, and because there is evidence of selection in this population for specific alleles of the genes that influence fatty acid synthesis. But even more specifically, these genes modulate the fatty acid composition of breast milk. It looks like this mutation of the EDAR gene was also selected for in that ancestral population, and EDAR's effects on mammary glands is the most likely target of the selection."

The EDAR gene influences the development of many structures derived from the ectoderm in the fetus, including tooth shape, sweat glands, sebaceous glands, mammary glands and hair. As a consequence, selection on one trait leads to coordinated evolution of the others. The late evolutionary biologist and author Steven Jay Gould referred to such byproducts of evolution as spandrels.

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