Sometimes body armor just isn’t enough. A car-sized dinosaur covered in bony plates may have sported camo, too, researchers report online August 3 in Current Biology. That could mean the Cretaceous-period herbivore was a target for predators that relied on sight more than smell to find prey.

The dinosaur, dubbed Borealopelta markmitchelli, has already made headlines for being one of the best preserved armored dinosaurs ever unearthed. It was entombed on its back some 110 million years ago under layers of fine marine sediments that buried the animal very quickly — ideal preservation conditions, says study coauthor Caleb Brown, a paleontologist at the Royal Tyrrell Museum of Palaeontology in Drumheller, Canada. The fossil, found in Alberta in 2011, captured not only large amounts of skin and soft tissue but also the animal’s three-dimensional shape.
“Most of the other armored dinosaurs are described based on the skeleton. In this case, we can’t see the skeleton because all the skin is still there,” Brown says.

That skin contains clues to the dinosaur’s appearance, including its coloration. “We’re just beginning to realize how important color is, and we’re beginning to have the methods to detect color” in fossils, says Martin Sander, a paleontologist at Bonn University in Germany who wasn’t part of the study.

But despite ample tissue, the researchers didn’t find any melanosomes, cellular structures that often preserve evidence of pigment in fossilized remains. Instead, Brown and colleagues turned to less direct evidence: molecules that appear when pigments break down. The researchers found about a dozen types of those molecules, including substantial amounts of benzothiazole, a by-product of the reddish pigment pheomelanin. That might mean the dinosaur was reddish-brown.
The distribution of pigment by-products also gives clues about the dinosaur’s appearance. B. markmitchelli had a thin film of pigment-hinting organic molecules on its back, but that layer disappeared on the belly. That pattern is reminiscent of countershading, when an animal is darker on its back than its underside, Brown says. Countershading is a simple form of camouflage that helps animals blend in with the ground when seen from above or with the sky when seen from below.
This is not the first time countershading has been proposed for a dinosaur (SN: 11/26/16, p 24). But finding the camouflage on such a large herbivore is somewhat surprising, Brown says. Modern plant eaters that don similar camouflage tend to be smaller and at greater risk of becoming someone’s dinner. B. markmitchelli’s skin patterning suggests that at least some top Cretaceous predators might have relied more on eyesight than today’s top carnivores, which often favor smell when hunting, Brown says.

Some experts, however, want stronger evidence for the coloration claims. Molecules like benzothiazole can come from melanin, but they can also come from a number of other sources, such as oils, says Johan Lindgren, a paleontologist at Lund University in Sweden. “What this paper nicely highlights is how little we actually know about the preservation of soft tissues in animal remains. There’s definitely something there — the question is, what are those [molecules], and where do they come from?”

Sander does buy the evidence for the reddish tint, but it might not be the full story, he says. The dino could have displayed other colors that didn’t linger in the fossil record. But the countershading findings “point out the importance of vision” for dinosaurs, he says. Sharp-eyed predators might have made camouflage a perk for herbivores — even ones built like tanks.

A 13-million-year-old infant’s skull, discovered in Africa in 2014, comes from a new species of ape that may not be far removed from the common ancestor of living apes and humans.

The tiny find, about the size of a lemon, is one of the most complete skulls known of any extinct ape that inhabited Africa, Asia or Europe between 25 million and 5 million years ago, researchers report in the Aug. 10 Nature. The fossil provides the most detailed look to date at a member of a line of African primates that are now candidates for central players in the evolution of present-day apes and humans.
Most fossils from more than 40 known extinct ape species amount to no more than jaw fragments or a few isolated teeth. A local fossil hunter spotted the nearly complete skull in rock layers located near Kenya’s Lake Turkana. Members of a team led by paleoanthropologist Isaiah Nengo estimated the fossil’s age by assessing radioactive forms of the element argon in surrounding rock, which decay at a known rate.

Comparisons with other African ape fossils indicate that the infant’s skull belongs to a new species that the researchers named Nyanzapithecus alesi. Other species in this genus, previously known mainly from jaws and teeth, date to as early as around 25 million years ago.

“This skull comes from an ancient group of apes that existed in Africa for over 10 million years and was close to the evolutionary origin of living apes and humans,” says Nengo, of Stony Brook University in New York and De Anza College in Cupertino, Calif.

He and colleagues looked inside the skull using a powerful type of 3-D X-ray imaging. This technique revealed microscopic enamel layers that had formed daily from birth in developing adult teeth that had yet to erupt. A count of those layers indicates that the ape was 16 months old when it died.

Based on a presumably rapid growth rate, the scientists calculated that the ancient ape would have weighed about 11.3 kilograms as an adult. Its adult brain volume would have been almost three times larger than that of known African monkeys from the same time, the researchers estimate.
N. alesi’s tiny mouth and nose, along with several other facial characteristics, make it look much like small-bodied apes called gibbons. Faces resembling gibbons evolved independently in several extinct monkeys, apes and their relatives, the researchers say. The same probably held for N. alesi, making it an unlikely direct ancestor of living gibbons, they conclude.
No lower-body bones turned up with the new find. Even so, it’s possible to tell that N. alesi did not behave as present-day gibbons do. In gibbons, a part of the inner ear called the semicircular canals, which coordinates balance, is large relative to body size. That allows the apes to swing acrobatically from one tree branch to another. N. alesi’s small semicircular canals indicate that it moved cautiously in trees, Nengo says.

Several of the infant skull’s features, including those downsized semicircular canals, connect it to a poorly understood, 7-million- to 8-million-year-old ape called Oreopithecus. Fossils of that primate, discovered in Italy, suggest it walked upright with a slow, shuffling gait. If an evolutionary relationship existed with the older N. alesi, the first members of the Oreopithecus genus probably originated in Africa, Nengo proposes.

Without any lower-body bones for N. alesi, it’s too early to rule out the possibility that Nyanzapithecus gave rise to modern gibbons and perhaps Oreopithecus as well, says paleontologist David Alba of the Catalan Institute of Paleontology Miquel Crusafont in Barcelona. Gibbon ancestors are thought to have diverged from precursors of living great apes and humans between 20 million and 15 million years ago, Alba says.

Despite the age and unprecedented completeness of the new ape skull, no reported tooth or skull features clearly place N. alesi close to the origins of living apes and humans, says paleoanthropologist David Begun of the University of Toronto.

Further studies of casts of the inner braincase, which show impressions from surface features of the brain, may help clarify N. alesi’s position in ape evolution, Nengo says. Insights are also expected from back, forearm and finger fossils of two or three ancient apes, possibly also from N. alesi, found near the skull site in 2015. Those specimens also date to around 13 million years ago.

On the morning of August 21, a pair of jets will take off from NASA’s Johnson Space Center in Houston to chase the shadow of the moon. They will climb to 15 kilometers in the stratosphere and fly in the path of the total solar eclipse over Missouri, Illinois and Tennessee at 750 kilometers per hour.

But some of the instruments the jets carry won’t be looking at the sun, or even at Earth. They’ll be focused on a different celestial body: Mercury. In the handful of minutes that the planes zip along in darkness, the instruments could collect enough data to answer this Mercury mystery: What is the innermost planet’s surface made of?
Because it’s so close to the sun, Mercury is tough to study from Earth. It’s difficult to observe close up, too. Extreme heat and radiation threaten to fry any spacecraft that gets too close. And the sun’s brightness can swamp a hardy spacecraft’s efforts to send signals back to Earth.

NASA’s Messenger spacecraft orbited Mercury from 2011 to 2015 and revealed a battered, scarred landscape made of different material than the rest of the terrestrial planets (SN: 11/19/11, p. 17).
But Messenger only scratched the surface, so to speak. It analyzed the planet’s composition with an instrument called a reflectance spectrometer, which collects light and then splits that light into its component wavelengths to figure out which elements the light was reflected from.
Messenger took measurements of reflected light from Mercury’s surface at wavelengths shorter than 1 micrometer, which revealed, among other things, that Mercury contains a surprising amount of sulfur and potassium (SN: 7/16/11, p. 12). Those wavelengths come only from the top few micrometers of Mercury. What lies below is still unknown.

To dig a few centimeters deeper into Mercury’s surface, solar physicist Amir Caspi and planetary scientist Constantine Tsang of the Southwest Research Institute in Boulder, Colo., and colleagues will use an infrared camera, specially built by Alabama-based Southern Research, that detects wavelengths between 3 and 5 micrometers.

Copies of the instrument will fly on the two NASA WB-57 research jets, whose altitude and speed will give the observers two advantages: less atmospheric interference and more time in the path of the eclipse. Chasing the moon’s shadow will let the planes stay in totality — the region where the sun’s bright disk is completely blocked by the moon — for a combined 400 seconds (6.67 minutes). That’s nearly three times longer than they would get by staying in one spot.
Mercury’s dayside surface is 425° Celsius, and it actually emits light at 4.1 micrometers — right in the middle of the range of Caspi’s instrument. As any given spot on Mercury rotates away from the sun, its temperature drops as low as ‒179° C. Measuring how quickly the planet loses heat can help researchers figure out what the subsurface material is made of and how densely it’s packed. Looser sand will give up its heat more readily, while more close-packed rock will hold heat in longer.

“This is something that has never been done before,” Caspi says. “We’re going to try to make the first thermal image heat map of the surface of Mercury.”

Unfortunately for Caspi, only two people can fly on the jet: The pilot and someone to run the instrument. Caspi will remain on the ground in Houston, out of the path of totality. “So I will get to watch the eclipse on TV,” Caspi says.

Every few years, for a handful of minutes or so, science shines while the sun goes dark.

A total eclipse of the sun is, for those who witness it, something like a religious experience. For those who understand it, it is symbolic of science’s triumph over mythology as a way to understand the heavens.

In ancient Greece, the pioneer philosophers realized that eclipses illustrate how fantastic phenomena do not require phantasmagoric explanation. An eclipse was not magic or illusion; it happened naturally when one celestial body got in the way of another one. In the fourth century B.C., Aristotle argued that lunar eclipses provided strong evidence that the Earth was itself a sphere (not flat as some primitive philosophers had believed). As the eclipsed moon darkened, the edge of the advancing shadow was a curved line, demonstrating the curvature of the Earth’s surface intervening between the moon and sun.

Oft-repeated legend proclaims that the first famous Greek natural philosopher, Thales of Miletus, even predicted a solar eclipse that occurred in Turkey in 585 B.C. But the only account of that prediction comes from the historian Herodotus, writing more than a century later. He claimed that during a fierce battle “day suddenly became night,” just as Thales had forecast would happen sometime during that year.

There was an eclipse in 585 B.C., but it’s unlikely that Thales could have predicted it. He might have known that the moon blocks the sun in an eclipse. But no mathematical methods then available would have allowed him to say when — except, perhaps, a lucky coincidence based on the possibility that solar eclipses occurred at some regular cycle after lunar eclipses. Yet even that seems unlikely, a new analysis posted online last month finds.

“Some scholars … have flatly denied the prediction, while others have struggled to find a numerical cycle by means of which the prediction could have been carried out,” writes astronomer Miguel Querejeta. Many such cycles have already been ruled out, he notes. And his assessment of two other cycles concludes “that none of those conjectures can be regarded as serious explanations of the problematic prediction of Thales: in addition to requiring the existence of long and precise eclipse records … both cycles that have been examined overlook a number of eclipses which match the visibility criteria and, consequently, the patterns suggested seem to disappear.”

It’s true that the ancient Babylonians worked out methods for predicting lunar eclipses based on patterns in the intervals between them. And the famous Greek Antikythera mechanism from the second century B.C. seems to have used such cycle data to predict some eclipses.

Ancient Greek astronomers, such as Hipparchus (c. 190–120 B.C.), studied eclipses and the geometrical relationships of the Earth, moon and sun that made them possible. Understanding those relationships well enough to make reasonably accurate predictions became possible, though, only with the elaborate mathematical description of the cosmos developed (drawing on Hipparchus’ work) by Claudius Ptolemy. In the second century A.D., he worked out the math for explaining the movements of heavenly bodies, assuming the Earth sat motionless in the center of the universe.

His system specified the basic requirements for a solar eclipse: It must be the time of the new moon — when moon and sun are on the same side of the Earth — and the positions of their orbits must also be crossing the ecliptic, the plane of the sun’s apparent orbital path through the sky. (The moon orbits the Earth at a slight angle, crossing the plane of the ecliptic twice a month.) Only precise calculations of the movements of the sun and moon in their orbits could make it possible to predict the dates for eclipsing alignments.

Predicting when an eclipse will occur is not quite the same as forecasting exactly where it will occur. To be accurate, eclipse predictions need to take subtle gravitational interactions into account. Maps showing precisely accurate paths of totality (such as for the Great American Eclipse of 2017) became possible only with Isaac Newton’s 17th century law of gravity (and the further development of mathematical tools to exploit it). Nevertheless Ptolemy had developed a system that, in principle, showed how to anticipate when eclipses would happen. Curiously, though, this success was based on a seriously wrong blueprint for the architecture of the cosmos.

As Copernicus persuasively demonstrated in the 16th century, the Earth orbits the sun, not vice versa. Ptolemy’s geometry may have been sound, but his physics was backwards. While demonstrating that mathematics is essential to describing nature and predicting physical phenomena, he inadvertently showed that math can be successful without being right.

It’s wrong to blame him for that, though. In ancient times math and science were separate enterprises (science was then “natural philosophy”). Astronomy was regarded as math, not philosophy. An astronomer’s goal was to “save the phenomena” — to describe nature correctly with math that corresponded with observations, but not to seek the underlying physical causes of those observations. Ptolemy’s mathematical treatise, the Almagest, was about math, not physics.

One of the great accomplishments of Copernicus was to merge the math with the physical realty of his system. He argued that the sun occupied the center of the cosmos, and that the Earth was a planet, like the others previously supposed to have orbited the Earth. Copernicus worked out the math for a sun-centered planetary system. It was a simpler system than Ptolemy’s. And it was just as good for predicting eclipses.

As it turned out, though, even Copernicus didn’t have it quite right. He insisted that planetary orbits were circular (modified by secondary circles, the epicycles). In fact, the orbits are ellipses. It’s a recurring story in science that mathematically successful theories sometimes are just approximately correct because they are based on faulty understanding of the underlying physics. Even Newton’s law of gravity turned out to be just a good mathematical explanation; the absolute space and invariable flow of time he believed in just aren’t an accurate representation of the universe we live in. It took Einstein to see that and develop the view of gravity as the curvature of spacetime induced by the presence of mass.
Of course, proving Einstein right required the careful measurement by Arthur Eddington and colleagues of starlight bending near the sun during a solar eclipse in 1919. It’s a good thing they knew when and where to go to see it.

A single genetic mutation made the Zika virus far more dangerous by enhancing its ability to kill nerve cells in developing brains, a new study suggests.

The small change — which tweaks just one amino acid in a protein that helps Zika exit cells — may cause microcephaly, researchers report September 28 in Science. The mutation arose around May 2013, shortly before a Zika outbreak in French Polynesia, the researchers calculate.

Zika virus was discovered decades ago but wasn’t associated with microcephaly — a birth defect characterized by a small head and brain — until the 2015–2016 outbreak in Brazil. Women who had contracted the virus while pregnant started giving birth to babies with the condition at higher-than-usual rates (SN: 4/2/16, p. 26).
Researchers weren’t sure why microcephaly suddenly became a complication of Zika infections, says Pei-Yong Shi, a virologist at the University of Texas Medical Branch at Galveston. Maybe the virus did cause microcephaly before, scientists suggested, but at such low rates that no one noticed. Or people in South America might be more vulnerable to the virus. Perhaps their immune systems don’t know how to fight it, they have a genetic susceptibility or prior infections with dengue made Zika worse (SN: 4/29/17, p. 14). But Shi and colleagues in China thought the problem might be linked to changes in the virus itself.
The researchers compared a strain of Zika isolated from a patient in Cambodia in 2010 with three Zika strains collected from patients who contracted the virus in Venezuela, Samoa and Martinique during the epidemic of 2015–2016. The team found seven differences between the Cambodian virus and the three epidemic strains.

Researchers engineered seven versions of the Cambodian virus, each with one of the epidemic strains’ mutations, and injected the viruses into fetal mouse brains. Viruses with one of these mutations, dubbed S139N, killed brain cells in fetal mice and destroyed human brain cells grown in lab dishes more aggressively than the Cambodian strain from 2010 did, the researchers found.
“That’s pretty convincing evidence that it at least plays some role in what we’re seeing now,” says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

The mutation changes an amino acid in a Zika protein called prM. That protein helps the virus mature within infected cells and get out of the cells to infect others. Shi and colleagues don’t yet know why tweaking the protein makes the virus kill brain cells more readily.

The alteration in that protein probably isn’t the entire reason epidemic strains cause microcephaly, Shi says. The Cambodian strain also led to the death of a few brain cells, but perhaps not enough to cause microcephaly. “We believe there are other changes in the virus that collectively enhance its virulence,” he says. In May in Nature, Shi and colleagues described a different mutation that allows the virus to infect mosquitoes more effectively.

Brain cells from different people vary in their susceptibility to Zika infections, says infectious disease researcher Scott Weaver, also at the University of Texas Medical Branch but not involved in the study. He says more work on human cells and in nonhuman primates is needed to confirm whether this mutation is really the culprit in microcephaly.

Physicists often ponder small things, but probably not the ones on Kerwyn Casey “KC” Huang’s mind. He wants to know what it’s like to be a bacterium.

“My motivating questions are about understanding the physical challenges bacterial cells face,” he says. Bacteria are the dominant life-forms on Earth. They affect the health of plants and animals, including humans, for good and bad. Yet scientists know very little about the rules the microbes live by. Even questions as basic as how bacteria determine their shape are still up in the air, says Huang, of Stanford University.

Huang, 38, is out to change that. He and colleagues have determined what gives cholera bacteria their curved shape and whether it matters (a polymer protein, and it does matter; the curve makes it easier for cholera to cause disease), how different wavelengths of light affect movement of photosynthetic bacteria (red and green wavelengths encourage movement; blue light stops the microbes in their tracks), how bacteria coordinate cell division machinery and how photosynthetic bacteria’s growth changes in light and dark.

All four of these findings and more were published in just the first three months of this year.
Huang also looks for ways to use tools and techniques his team develops to solve problems unrelated to bacteria. Computer programs that measure changes in bacterial cell shape can also track cells in plant roots and in developing zebrafish embryos. He’s even helped determine how a protein’s activity and stability contribute to a human genetic disease.

A physicist by training, Huang delves into biology, biochemistry, microbial ecology, genetics, engineering, computer science and more, partnering with a variety of scientists from across those fields. He’s even teamed up with his statistician sister. He’s an “all-in-one scientist,” says longtime collaborator Ned Wingreen, a biophysicist at Princeton University.

When Huang started his lab at Stanford in 2008, after getting his Ph.D. at MIT and spending time at Princeton as a postdoctoral fellow, his background was purely theoretical. He designed and ran the computer simulations and then his collaborators carried out the experiments. But soon, he wanted to do hands-on research too, to learn why cells are the way they are.
Such a leap “is not trivial,” says Christine Jacobs-Wagner, a microbiologist at Yale University who also studies bacterial cell shape. But Huang is “a really, really good experimentalist,” she says.

Jacobs-Wagner was particularly impressed with a “brilliant microfluidics experiment” Huang did to test a well-established truism about how bacteria grow. Researchers used to think that turgor pressure — water pressure inside a cell that pushes the outer membrane against the cell wall — controlled bacterial growth, just like it does in plants. But abolishing turgor pressure didn’t change E. coli’s growth rate, Huang and colleagues reported in 2014 in Proceedings of the National Academy of Sciences. “This result blew my mind away,” Jacobs-Wagner says. The finding “crumbled the foundation” of what scientists thought about bacterial growth.

“He uses clever experiments to challenge old paradigms,” Jacobs-Wagner says. “More than once he has come up with a new trick to address a tough question.”
Sometimes Huang’s tricks require breaking things. Zemer Gitai, a microbiologist at Princeton, remembers talking with Huang and Wingreen about a question that microbiologists were stuck on: How are molecules oriented in bacterial cell walls? Researchers knew that the walls are made of rigid sugar strands connected by flexible proteins, like a chain link fence held together by rubber bands. What they didn’t know was whether the rubber bands circled the bacteria like the hoops on a wine barrel, ran in stripes down the length of the cell or stuck out like hairs.

If bacteria were put under pressure, the cells would crack along the weak rubber band–like links, Huang and Wingreen reasoned. If the cells split like hot dogs on a grill, it would mean the links ran the length of the cells. If they opened like a Slinky, it would suggest a wine-barrel configuration. The researchers reported the results — opened like a Slinky — in 2008. Another group, using improved microscope techniques, got the same result.

Huang teamed up with other researchers to do microfluidics experiments, growing bacteria in tiny chambers and tracking individual cells to learn how photosynthetic bacteria grow in light and dark.

But in nature, bacteria don’t live alone. So Huang has also worked with Stanford colleague Justin Sonnenburg to answer a basic question: “Where and when are bacteria in the gut growing? No one knows,” Huang says. “How can we not know that? It’s totally fundamental.” Without that information, it’s impossible to know, for example, how antibiotics affect the microbial community in the intestines, he says.

Stripping fiber from a mouse’s diet not only changes the mix of microbes in the gut, it alters where in the intestines the microbes grow, the researchers discovered. Bacteria deprived of fiber’s complex sugars began to munch on the protective mucus lining the intestines, bumping against the intestinal lining and sparking inflammation, Huang, Sonnenburg and colleagues reported in Cell Host & Microbe in 2015.

Huang’s breadth of research — from deciphering the nanoscale twists of proteins to mapping whole microbial communities — is sure to lead to many more discoveries. “He’s capable of making contributions to any field,” Jacobs-Wagner says, “or any research question that he’s interested in.”

Many people may be fuzzy on the details of North America’s colonial history between Columbus’ arrival in 1492 and the Pilgrims’ landing on Plymouth Rock in 1620. But Europeans were actively attempting to colonize North America from the early 16th century onward, even though few colonies survived.

As historian Sam White explains in A Cold Welcome, most early attempts were doomed by fatally incorrect assumptions about geography and climate, poor planning and bad timing.
White weaves together evidence of past climates and written historical records in a comprehensive narrative of these failures. One contributing factor: Explorers assumed climates at the same latitude were the same worldwide. But in fact, ocean currents play a huge role in moderating land temperatures, which means Western Europe is warmer and less variable in temperature from season to season than eastern North America at the same latitude.

On top of that, explorations occurred during a time of global cooling known as the Little Ice Age, which stretched from the 13th to early 20th centuries. The height of exploration may have occurred at the peak of cooling: Starting in the late 16th century, a series of volcanic eruptions likely chilled the Northern Hemisphere by as much as 1.8 degrees Celsius below the long-term average, White says.

This cooling gave Europeans an especially distorted impression of their new lands. For instance, not long after Spanish explorer Sebastián Vizcaíno landed in California’s Monterey Bay in December 1602, men’s water jugs froze overnight — an unlikely scenario today. Weather dissuaded Spain from further attempts at colonizing California for over a century.
Harsh weather also heightened conflict when underprepared Europeans met Native Americans, whose own resources were stretched thin by unexpectedly bad growing seasons.

A Cold Welcome is organized largely by colonial power, which means findings on climate are repeated in each chapter. But White’s synthesis of climate and history is novel, and readers will see echoes of today’s ignorance about the local consequences of climate change. “Human psychology may be both too quick to grasp at false patterns and yet too slow to let go of familiar expectations,” White writes.

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A proposed form of ice acts like a cross between a solid and a liquid. Now, a new study strengthens the case that the weird state of matter really exists.

Hints of the special phase, called superionic ice, appeared in water ice exposed to high pressures and temperatures, researchers report February 5 in Nature Physics. Although such unusual ice isn’t found naturally on Earth, it might lurk deep inside frozen worlds like Uranus and Neptune (SN Online: 3/5/12).
Normal ice is composed of water molecules, each made of an oxygen atom bonded to two hydrogen atoms. As water freezes, those molecules link up to form a solid. But superionic ice is made up of ions, which are atoms with a positive or negative electric charge. Within the material, hydrogen ions flow freely through a solid crystal of oxygen ions.

“That’s really strange behavior for water,” says study coauthor Marius Millot, a physicist at Lawrence Livermore National Laboratory in California. Although the superionic state was first predicted 30 years ago, “up until now we didn’t really know whether this was something that was real.”

At extremely high pressures, familiar substances like water can behave in unusual ways (SN: 1/14/12, p. 26). Working with a sample of ice that was crushed between two diamonds, Millot and colleagues used a laser to create a shock wave that plowed through the ice, boosting the pressure even more. At first, the density and temperature of the ice ramped up smoothly as the pressure increased. But at around 1.9 million times atmospheric pressure and 4,800 kelvins (about 4,500° Celsius), the scientists observed a jump in density and temperature. That jump, the researchers say, is evidence that superionic ice melted at that point. Although we normally think of ice as being cold, at high pressures, superionic ice can form even when heated. The melting occurred at just the conditions that theoretical calculations predict such ice would melt. The physicists didn’t measure the pressure at which the superionic phase first formed.

The electrical conductivity of the material provided another hint of superionic ice: The level of conductivity was consistent with expectations for that phase of matter. Whereas metals conduct electricity via the motion of electrons, in superionic ice, the flowing hydrogen ions transmit electricity.
The researchers “provide quite good evidence” of the new phase, says Alexander Goncharov, a physicist at the Carnegie Institution for Science in Washington, D.C., who was not involved with the study.

Others are more cautious about the significance of the work. “It’s definitely providing more insight into water at these conditions,” says physicist Marcus Knudson of Washington State University in Pullman. But, he says, “I don’t see strong evidence that there’s a melting transition in their data.”

So more work remains before this weird kind of ice is fully understood. For now, the superionic state of water seems likelier, but still on thin ice.