Virus-cutting enzyme helps bacteria remember a threat

Bacteria may not have brains, but they do have memories, at least when it comes to viruses that attack them. Many bacteria have a molecular immune system which allows these microbes to capture and retain pieces of viral DNA that they have encountered in the past, in order to recognize and destroy it when it shows up again.

Research at Rockefeller University described in Nature offers new insight into the mysterious process by which this system works to encode viral DNA in a microbe's genome for later use as guides for virus-cutting enzymes.

"Microbes, like vertebrates, have immune systems capable of adapting to new threats. Cas9, one enzyme employed by these systems, uses immunological memories to guide cuts to viral genetic code. However, very little is known about how these memories are acquired in the first place," says Assistant Professor Luciano Marraffini, head of the Laboratory of Bacteriology. "Our work shows that Cas9 also directs the formation of these memories among certain bacteria."

These memories are embedded in the bacterial equivalent of an adaptive immune system capable of discerning helpful from harmful viruses called a CRISPR (clustered regularly interspaced short palindromic repeats) system. It works by altering the bacterium's genome, adding short viral sequences called spacers in between the repeating DNA sequences. These spacers form the memories of past invaders. They serve as guides for enzymes encoded by CRISPR-associated genes (Cas), which seek out and destroy those same viruses should they attempt to infect the bacterium again.

Cas9's ability to make precision cuts within a genome -- viral or otherwise -- has caught the attention of researchers who now use it to alter cells' genetics for experimental or therapeutic purposes. But it is still not well understood just how this CRISPR system works in its native bacteria.

Some evidence suggested that other Cas enzymes managed the memory-making process on their own, without Cas9. But because of the way Cas9 goes about identifying the site at which to make a cut, the researchers, including co-first authors Robert Heler, a graduate student, and Poulami Samai, a postdoc in the lab, suspected a role for Cas9 in memory making.

In addition to matching its CRISPR guide sequence up with the DNA of the virus, Cas9 needs to find a second cue nearby: a PAM (protospacer adjacent motif) sequence in the viral DNA. This is a crucial step, since it is the absence of a PAM sequence that prevents Cas9 from attacking the bacterium's own memory-containing DNA.

"Because Cas9 must recognize a PAM sequence before cutting the viral DNA, it made sense to us that Cas9 would also recognize the PAM sequence when the system is forming a memory of its first encounter with a virus," Heler says. "This is a new and unexpected role for Cas9."

To test their hypothesis, Heler swapped the Cas9 enzymes between the immune systems of Streptococcus pyogenes and Streptococcus thermophilus, each of which recognizes a different PAM sequence. As a result, the PAM sequences followed, swapping between the two bugs -- evidence that Cas9 is responsible for identifying the PAM during memory formation. In another experiment, he altered the part of Cas9 that binds to the PAM sequence, and found the microbes then began acquiring the target viral sequences randomly, making them unusable.

Samai, meanwhile, looked at the relationship between Cas9 and three other Cas enzymes: Cas1, Cas2 and Csn2. Components of the same CRISPR system, these enzymes were already suspected to play a role in memory making without help from Cas9.

Read more at Science Daily

Ancient and modern cities aren't so different

Despite notable differences in appearance and governance, ancient human settlements function in much the same way as modern cities, according to new findings by researchers at the Santa Fe Institute and the University of Colorado Boulder.

Previous research has shown that as modern cities grow in population, so do their efficiencies and productivity. A city’s population outpaces its development of urban infrastructure, for example, and its production of goods and services outpaces its population. What's more, these patterns exhibit a surprising degree of mathematical regularity and predictability, a phenomenon called "urban scaling."

But has this always been the case?

SFI Professor Luis Bettencourt researches urban dynamics as a lead investigator of SFI's Cities, Scaling, and Sustainability research program. When he gave a talk in 2013 on urban scaling theory, Scott Ortman, now an assistant professor in the Department of Anthropology at CU Boulder and a former Institute Omidyar Fellow, noted that the trends Bettencourt described were not particular to modern times. Their discussion prompted a research project on the effects of city size through history.

To test their ideas, the team examined archaeological data from the Basin of Mexico (what is now Mexico City and nearby regions). In the 1960s — before Mexico City’s population exploded — surveyors examined all its ancient settlements, spanning 2000 years and four cultural eras in pre-contact Mesoamerica.

Using this data, the research team analyzed the dimensions of hundreds of ancient temples and thousands of ancient houses to estimate populations and densities, size and construction rates of monuments and buildings, and intensity of site use.

Their results indicate that the bigger the ancient settlement, the more productive it was.

“It was shocking and unbelievable,” says Ortman. “We were raised on a steady diet telling us that, thanks to capitalism, industrialization, and democracy, the modern world is radically different from worlds of the past. What we found here is that the fundamental drivers of robust socioeconomic patterns in modern cities precede all that.”

Read more at Science Daily

Ancient Shrines Used for Predicting Future Discovered

Three shrines, dating back about 3,300 years, have been discovered within a hilltop fortress at Gegharot, in Armenia.

Local rulers at the time likely used the shrines for divination, a practice aimed at predicting the future, the archaeologists involved in the discovery say.

Each of the three shrines consists of a single room holding a clay basin filled with ash and ceramic vessels. A wide variety of artifacts were discovered including clay idols with horns, stamp seals, censers used to burn substances and a vast amount of animal bones with markings on them. During divination practices, the rulers and diviners may have burnt some form of substances and drank wine, allowing them to experience "altered" states of mind, the archaeologists say.

"The logic of divination presumes that variable pathways articulate the past, present and future, opening the possibility that the link between a current situation and an eventual outcome might be altered," write Adam Smith and Jeffrey Leon, in an article published recently in the American Journal of Archaeology. Smith is a professor at Cornell University, and Leon is a graduate student there.

The fortress at Gegharot is one of several strongholds built at around this time in Armenia. "Evidence to date suggests that this coordinated process of fortress construction was part of the emergence of a single polity that built and occupied multiple sites in the region," write Smith and Leon.

Smith believes that Gegharot would have been used as an occult center for the rulers. "I would think that this is probably a cult center largely specializing in servicing the emerging rulers from the ruling class," he told Live Science in an interview.

At the time, writing had not yet spread to this part of Armenia so the name of the polity, and its rulers, are unknown.

Predicting the future

Smith and Leon found evidence for three forms of divination at Gegharot. One form was osteomancy, trying to predict the future through rituals involving animal bones, in this case the knucklebones of cows, sheep and goat.

The knucklebones, which were covered in burns and other markings, would have been rolled like dice in rituals attempting to predict the future, Smith said. "You would roll them and depending upon whether the scorched side or the marked side came up you would a different interpretation," Smith said.

Lithomancy, trying to predict the future through the use of stone, also appears to have been practiced at Gegharot. Inside a basin at one shrine, archaeologists found 18 small pebbles. "These stones appear to have been selected for their smooth, rounded shape and their color palette, which ranged from black and dark gray to white, green and red," Smith and Leon write. How exactly these unmarked stones would have been used in rituals is unknown.

Flour for the future?

At one shrine, on the fortress' east citadel, the archaeologists found an installation used to grind flour. Smith and Leon think that this flour could have been used to predict the future in a practice called aleuromancy.

"What is conspicuous about the grinding installation in the east citadel shrine is the lack of a formal oven for bread baking," Smith and Leon write. The shrine's basin "was clearly used for burning materials and certainly could have been used to bake small balls of dough, but it is unlikely that it would have been used to cook loaves of bread."

Stamp seals found at the shrine would have allowed people to punch a variety of shapes into dough. "One possibility (admittedly among many others) is that the stamps marked the dough that was then used for aleuromancy."

Future's end

The shrines were in use for a century or so until the surrounding fortress, along with all the other fortresses in the area, were destroyed. The site was largely abandoned after this, Smith said.

At the time, there was a great deal of conflict in the south Caucasus with a number of regional polities fighting against each other, Smith said. The polity that controlled Gegharot seems to have been wiped out in one of those conflicts.

Although the rulers who controlled Gegharot put great effort into trying to predict and change the future, it was to no avail — their great fortresses being torched in a cataclysm they could not avoid.

Read more at Discovery News

Why It's So Freakin' Cold: Here's the Science

As if the outdoors weren't harsh enough with Boston buried under ungodly amounts of snow and the rest of the Northeast unable to shake the bitter cold, more winter weather is on the way. So what's behind this extreme chill?

Parts of the United States are expected to have historic lows this week, as temperatures in the Southeast, Mid-Atlantic and central Appalachians may drop to the coldest they've been since the mid-1990s, according to the National Weather Service (NWS).

"Get ready for an even more impressive surge of Arctic air later this week as another cold front drops south from Canada," the NWS said in a statement.

That Arctic air in the form of a polar vortex eddy is dropping temperatures with a burst of bitterly cold air, the NWS said.

The freezing weather is part of a weather pattern that began last year, when the polar vortex, a system of cold air swirling around the Arctic, began pushing cold air into the United States. This pattern continued on and off throughout the summer, explaining the cooler temperatures in the eastern United States, said Bob Oravec, a forecaster at the National Weather Service.

This cold weather can take hold, thanks to flows in the middle and upper levels of the atmosphere that travel from northwest to southeast.

"They form at different times of the year, and they tend to go farther south during the winter," Oravec said. "Right now, we have that favorable weather pattern — a northwest flow from Alaska across a big part of Canada into the United States."

He called it one of the more persistently cold winters in the United States. "Especially this month, the temperature anomalies are way below average across a big part of the central to eastern United States," Oravec said.

Highs in the Southeast, Mid-Atlantic and central Appalachians will likely stay below 20 degrees Fahrenheit (minus 6 degrees Celsius) for much of today (Feb. 19) and Friday, and overnight lows may dip below 0 degrees F (minus 17 degrees C) in some places. A wind chill advisory is also in effect for these places, the NWS said.

Why Boston has record snow

A separate repeating weather system is to blame for the record snow levels in Boston and other parts of New England.

"Boston is now in the top two or three snowiest winters," said David Roth, a meteorologist at the National Weather Service's Weather Prediction Center in College Park, Maryland. "I'm pretty sure parts of Maine are getting there, too."

Similar weather conditions that support the polar vortex are pushing cold air toward New England. This winter, "they've been sweeping across or south of the Great Lakes, been coming off the East Coast and then strengthening as ocean storms," Roth said.

Southern New England falls right in its path, "so you end up having this big comma head of snow that ends up falling over the region," Roth said. "That's usually good for a foot [0.3 meters] or so of snow."

In warmer seasons, the same weather pattern would likely cause rain and thunderstorms.

The storm system will continue to repeat until another storm or weather system changes it, he added. For instance, coastal storms can drag weather systems north or northeast, he said.

Many New Englanders are looking forward to a break from the snow. They've had four significant snowstorms since Thanksgiving, amounting to 96.3 inches (245 centimeters) of snow accumulation at Logan Airport, according to the NWS. The average snowfall for this time of year is 30.2 in (77 cm). The average for large snowfalls in 2015, some of which last two days, is almost 20 inches, the NWS found.

The rest of February will be cold in the eastern United States, the NWS predicts. From Feb. 24 to Feb. 28 the NWS has predicted that the eastern half of the country will have below-normal temperatures, and the West Coast will have above-normal temperatures.

But the days are getting longer as winter nears its end.

"No matter where you are in the eastern United States, the averages are coming up," Roth said. "The local sun angle is coming up each day. You're getting longer days."

Read more at Discovery News

Hubble Watches Massive Exoplanet Stir Stellar Dust

Owed to its long-duration mission, Hubble can spot short-duration changes in celestial objects, revealing unprecedented detail in an otherwise ‘unchanging’ sky. Take Beta Pictoris for example. This 20 million year-old star sports an extensive edge-on protoplanetary disk and Hubble has been watching motion in this dust, stirred up by the presence of a massive exoplanet.

This is yet another cosmic first for the veteran space telescope; astronomers have been able to compare Hubble observations of Beta Pictoris 1997 and 2012 and would therefore be able to track any morphological changes in its protoplanetary disk.

As the exoplanet’s orbit is predicted to have an orbital period of between 18-20 years, over the 15 years between observations, the exoplanet would have shifted considerably, but Hubble has noticed little change in the distribution of dust in the protoplanetary disk, confirming some models about how protoplanetary disks mingling with exoplanets work.

“Some computer simulations predicted a complicated structure for the inner disk due to the gravitational pull by the short-period giant planet,” said Daniel Apai of the University of Arizona. “The new images reveal the inner disk and confirm the predicted structures. This finding validates models, which will help us to deduce the presence of other exoplanets in other disks.”

From these observations, astronomers can see that the circumstellar dust is orbiting in unison with the exoplanet “like a carousel,” according to a Hubble news release. This suggests that the inner dusty disk is “smooth and continuous” as it orbits the star.

Beta Pictoris, however, isn’t believed to be a ‘typical’ young star with a protoplanetary disk.

“The Beta Pictoris disk is the prototype for circumstellar debris systems, but it may not be a good archetype,” said co-author Glenn Schneider of the University of Arizona.

Beta Pictoris was the first star to be discovered to have a bright circumstellar disk. It’s believed that asteroids and comets in the system are continuously colliding, populating the disk with copious quantities of dust. Also, a lobe-like feature in the disk is thought to be the dusty remains of a pulverized Mars-sized body.

Read more at Discovery News

The Tough-as-Hell Antarctic Fish With Antifreeze for Blood

This fish shouldn’t be alive. Though I dunno, maybe it isn’t. Hard to tell with fish sometimes. Gotta get them some eyelids.

Last week I wrote about a snail with an iron-plated shell that lives around deep-sea hydrothermal vents, where the water tops 750 degrees F and toxic chemicals swirl. They’re about as close to hell as you can get on Earth. But down in Antarctica, there’s a polar-opposite (yeesh) ecosystem of brutally low temperatures, damn near 28.4 degrees F—the freezing point of seawater.

Yet even there, life flourishes. And one group of fishes, the notothenioids, swims in those frigid waters nearly carefree, thanks to very special blood loaded with antifreeze. Some of these fish have even done away with oxygen-carrying red blood cells altogether, adopting thin, crystal-clear blood that doesn’t get as viscous as the temperatures drop. These fishes are tougher than you. So much tougher than you.

Studying these critters is evolutionary biologist Paul Cziko of the University of Oregon, who happily drills through Antarctic sea ice and jumps into the water. Cziko is tougher than you. So much tougher than you. “It’s not that brave,” he says, “in part because the water is amazingly clear.” So at least there’s that.

Cziko cutting a hole in 12-foot-thick sea ice. You know, like ya do.

Cziko has a fancy dive suit to protect him, but most fish will get ice crystals in their blood, which grow and grow until the creature freezes solid. “We think the ice comes predominantly from the outside,” says Cziko. “The fishes are drinking and eating and rubbing up against ice, and there are lots of little ice crystals in the water column that they’re bringing into their bodies.” But the notothenioids (which I will henceforth refer to as the notoes, because it’s cute and I feel like it) have developed remarkable proteins that imprison individual crystals. “The antifreeze proteins recognize the surface of ice crystals and stick to them extremely tightly,” Cziko says, “and they apparently bind essentially irreversibly to the ice crystal surface. Once an ice crystal gets into a fish, it’ll get covered with the antifreeze proteins that are in the fish’s blood and stop growing.”

Here’s the problem, though. That irreversibility means that over time the crystals build up inside the fish, and having lots of foreign objects in your blood is usually something best avoided. But these fishes live for up to 30 years without obvious ill effects, so somehow they’re dealing with the accumulation of crystals. Scientists who study notoes once thought slightly warmer water temperatures in the summer allowed the crystals to melt, but Cziko and his colleagues measured temperatures around Antarctica for more than a decade and found the summers don’t get warm enough to help any. It could be that the spleen is somehow filtering the imprisoned crystals somehow, but no one really knows. “There’s no free lunch in evolution,” Cziko says. “The evolution of antifreeze proteins comes with a tradeoff, where you now have to figure out what to do with the ice crystals once they get into the body.” Conversely, it could be that the crystals aren’t that dangerous after all. “It’s really hard to prove that internal ice crystals are actually bad for the fishes. Having ice crystals in your body that could clog blood vessels certainly seems like it would cause problems. But if they didn’t have the antifreeze proteins they’d be frozen solid, and they wouldn’t survive at all.”

To say the waters around Antarctica are bizarre would be an understatement. Anchor ice forms on the seafloor when saltwater is cooled slightly below its freezing point. This anchor ice formed on a steel cable, floating up into an arch and confusing the living daylights out of that seal, who’s like lol wut.

As for the notoes with clear blood, a group known as the icefish, they have another problem entirely. They have no red blood cells or hemoglobin, and therefore have no efficient way to shuttle oxygen around their bodies. But a species like the crocodile icefish also lacks scales, and in fact its skin is translucent, so it could be that it’s absorbing oxygen through its skin like an amphibian. In addition, the fish has relatively large blood vessels and a bigger stroke volume through the heart, so it drives more blood with each pump. This may seem like a dangerous evolutionary game, but thinner blood that lacks red blood cells could be invaluable. Liquids get more viscous as their temperature drops, and blood is no exception, so maybe this clear version is easier to pump around.

I know I mentioned earlier that these fish are tougher than you, and that’s true in the sense that they can survive when temperatures dip below 30 degrees F. But the icefish are also in their way quite vulnerable. “You catch them on a hook and line, maybe catch them in a trawl, and bring them up to the surface and they are essentially catatonic for half an hour,” Cziko says. “They’re pretty beat up. Without hemoglobin, they don’t easily recover from acute stresses like that.”

That syringe is indeed filled with blood—the clear variety.

The icefish, though, are voracious predators when we’re not ruining their day, mostly hanging out on the seafloor targeting things like worms, shrimp, other fish, and, at least in captivity, each other. (Behavior in captivity can get a bit…eccentric, so this may never actually happen in the wild.) “You can put two crocodile icefishes of almost equal size—maybe they’re a foot long or a foot and a half long, something like that—in the tank,” says Cziko, “and you turn around and one of them is gone.”

Life is rough, and it don’t get much rougher than life in the Antarctic. But why would a creature even bother? Why not head north and find some kind of tropical paradise? Well, first of all the notoes wouldn’t be able to take the heat. As with the scaly-foot snail and its hellish environment, by adapting to the hardships they’ve been able to make a good living because so few creatures dare join them. The living may be rough, but it’s a profitable one.

Read more at Wired Science

Humans, Other Animals Are Evolving Larger Bodies

Humans and many other animals tend to evolve larger body sizes over time, suggests an extensive new study that provides strong evidence for a theory known as “Cope’s Rule.”

Cope’s Rule holds that there is active selection for increasing body size in nature. The new study, published in the journal Science, finds this to be true. It appears that evolution follows certain rules and can, at least to some extent, be predicted.

“We’ve known for some time now that the largest organisms alive today are larger than the largest organisms that were alive when life originated or even when animals first evolved,” co-author Jonathan Payne, a paleobiologist at Stanford’s School of Earth, Energy & Environmental Sciences, said in a press release.

This is not to say that huge animals didn’t existed in the past. The gigantic dinosaur Dreadnoughtus, for example, measured 85 feet long and weighed about 65 tons. The point is that, as many animal lineages evolve, there is a tendency toward larger sizes, particularly if food resources, the environment and other factors remain relatively stable.

The effect has been dramatic for animals like horses. As seen in the accompanying image, the earliest horses were much smaller than those alive today. Humans, in general, are also growing larger. In Britain, for example, the average height of a 21-year-old man increased from 5’5” in the 1870s to 5’10” as of the 1970s, according to researchers from the University of Essex and the National University in Canberra.

For the latest study, Payne and his team tested out Cope’s Rule on marine animals. The scientists compiled a dataset that included adult body size measurements for individual species within more than 17,000 groups, or genera, of marine animals spanning five major phyla: Arthropods, Brachiopods, Chordates, Echinoderms and Mollusks.

“Our study is the most comprehensive test of Cope’s Rule ever conducted,” said lead author Noel Heim of Stanford University. “Nearly 75 percent of all of marine genera in the fossil record and nearly 60 percent of all the animal genera that ever lived are included in our dataset.”

Analysis of the massive dataset revealed that, over the past 542 million years, the mean size of marine animals has increased 150-fold.

“That’s the size difference between a sea urchin that is about 2 inches long versus one that is nearly a foot long,” Heim explained. “This may not seem like a lot, but it represents a big jump.”

The researchers additionally found that the increase in body size, which has occurred since animals first appeared in the fossil record around 550 million years ago, is not due to every animal lineage steadily growing bigger. It’s instead due to the diversification of groups of organisms that were already larger than other groups early in the history of animal evolution.

“That’s also something we didn’t know before,” Payne said. “For reasons that we don’t completely understand, the classes with large body size appear to be the ones that over time have become differentially more diverse.”

They suspect this is because of advantages associated with a larger size, such as the ability to move faster, to burrow more deeply and efficiently in sediment or to capture larger prey.

“It’s really a story of the survival and diversification of big things relative to small things,” Heim said.

Small things aren’t all staying small either. Yet another recent study found that certain spiders are growing bigger in urban areas.

There’s no need to fear monster-sized ants, termites or other such things in our lifetimes, though. Growth within a species — if it happens at all — occurs slowly and over many generations.

Read more at Discovery News

Largest Trove of Gold Coins Found off Israel

A group of amateur scuba divers uncovered Israel’s largest trove of gold coins on the seabed of the ancient Mediterranean harbor of Caesarea, the country’s antiquities authority said Tuesday.

The treasure, probably exposed during recent storms, wasn’t immediately recognized by the divers.

“At first they thought they had spotted a toy coin from a game and it was only after they understood the coin was the real thing that they collected several coins and quickly returned to the shore in order to inform the director of the dive club about their find,” Israel Antiquities Authority (IAA) said in a statement.

Using metal detectors, marine archeologists uncovered nearly 2,000 coins that sat on the bottom of the Roman-era port for about 1,000 years. The coins came in different denominations, dimensions and weight: a dinar, half dinar and quarter dinar.

“The earliest is a quarter dinar minted in Palermo, Sicily, in the second half of the ninth century AD,” the IAA said.

Most of the pieces circulated by the Fatimid Caliphate, the Muslim dynasty that ruled an empire in large parts of North Africa and the Middle East from 909 to 1171. The coins also remained in circulation after the Crusader conquest, particularly in port cities.

According to Kobi Sharvit, director of the Marine Archaeology Unit of the Israel Antiquities Authority, there is probably a shipwreck of an official treasury boat on the seabed.

“The boat was on its way to the central government in Egypt with taxes that had been collected. Perhaps the treasure of coins was meant to pay the salaries of the Fatimid military garrison which was stationed in Caesarea and protected the city,” Sharvit said.

Another theory is that the coins belonged to a large merchant ship that traded among Mediterranean coastal cities and sank in the port.

Further excavations might help “answer the many questions that still remain unanswered about the treasure,” the IAA said.

No restoration is needed for the coins, which are perfectly preserved despite laying on the seafloor for about a millennium.

“This is because gold is a noble metal and is not affected by air or water,” Robert Cole, an expert numismaticist with the Israel Antiquities Authority said.

He added that several coins were bent and show teeth and bite marks, evidence they were “physically” inspected by their owners or the merchants.

Read more at Discovery News

Some Rain Falls Faster than Physics Says It Should

Some radical raindrops are flouting the rules: The wet-weather drips seem to be breaking a physical speed limit, sometimes falling 10 times faster than they should, scientists have found.

Like all objects in free fall, raindrops move according to the laws of physics. One of those laws puts a barrier on how fast a free-falling object can travel. This terminal velocity is reached when the downward tug of gravity equals the opposing force of air resistance.

In 2009, physicists reported that they had discovered small raindrops falling faster than this terminal velocity. In that study, detailed in the journal Geophysical Research Letters, Alexander Kostinski and Raymond Shaw of Michigan Technological University, along with Guillermo Montero-Martinez and Fernando Garcia-Garcia of the National University of Mexico, measured 64,000 raindrops, and found clusters of "superterminal" drops falling faster than they should based on their size and weight, especially as the rain became heavier.

In the new study, Kostinski and his colleagues verified that initial finding using completely different instruments. The researchers clocked the speeds of 1.5 million raindrops passing through a laser beam during six rainstorms at a site near Charleston, South Carolina. All of the raindrops measuring 0.8 millimeters (0.03 inches) and larger fell to the ground at predicted speeds, but 30 to 60 percent of the smaller drops (those measuring about 0.3 millimeters, or about 0.01 inches) traveled faster than their terminal velocity.

"Occasionally, smaller drops (less than a millimeter) fall more than 10 times faster than expected," Kostinski told Live Science in an email. "On average, small drops move about 30 percent faster than expected, but it depends on rain type and strength."

The superterminal drops may be the result of fragmenting, in which a "parent" droplet breaks up into smaller droplets. "Right after the breakup, fragments move approximately with the speed of mother drops," Kostinski wrote. "The mother drop is large, and its terminal speed is much higher than the one of smaller drops. This is one possible reason for smaller drops (fragments), breaking the speed limit."

So-called turbulent wakes that form behind the raindrops may also explain the odd behavior. In those wakes, air resistance that's opposing gravity's downward pull would decrease. "If they fall behind another drop, air drag decreases (like a group of bikers behind a leader)," Kostinski wrote.

By using 21 laser precipitation monitors and a video device, the researchers also ruled out the idea that the speedy raindrops were the result of droplets splashing off the instruments or some kind of measurement error.

"The fact that a substantial fraction of drizzle-sized drops are moving faster than their terminal velocities suggest that we are not just seeing an outlier effect here," lead author Michael Larsen, an assistant professor of physics and astronomy at the College of Charleston, said in a statement. "That was a bit surprising to me and helped me realize that there's more science to be done."

Read more at Discovery News

Pluto's Tiny Moons Spied by Incoming NASA Probe

A NASA spacecraft speeding toward an epic flyby of Pluto on July 14 has beamed home its first good looks at two moons of the dwarf planet.

The New Horizons probe captured images of Nix and Hydra, two of Pluto's five known satellites, from Jan. 27 through Feb. 8, at distances ranging from 125 million miles to 115 million miles (201 million to 186 million kilometers), NASA officials said. The photos have been spliced together to create a short movie showing Nix and Hydra circling Pluto.

ANALYSIS: Pluto and Moon Charon May Share Same Atmosphere

NASA released the new footage Wednesday (Feb. 18), 85 years to the day after American astronomer Clyde Tombaugh discovered Pluto at the Lowell Observatory in Flagstaff, Arizona.

"It’s thrilling to watch the details of the Pluto system emerge as we close the distance to the spacecraft’s July 14 encounter," New Horizons science team member John Spencer, of the Southwest Research Institute in Boulder, Colorado, said in a statement. "This first good view of Nix and Hydra marks another major milestone, and a perfect way to celebrate the anniversary of Pluto’s discovery."

New Horizons team members discovered Nix and Hydra in 2005 using NASA's Hubble Space Telescope. Scientists think both moons are between 25 miles and 95 miles (40 to 153 km) wide; New Horizons should nail down their sizes when it zooms through the Pluto system this summer.

Hydra is Pluto’s outermost known moon and circles the dwarf planet every 38 days, at a distance of about 40,200 miles (64,700 km). Nix lies 30,260 miles (48,700 km) from Pluto and completes one orbit every 25 days.

Two other Pluto moons, Styx and Kerberos, are smaller than Nix and Hydra, and are too faint to show up in the latest New Horizons images, NASA officials said. The dwarf planet's other known moon, Charon, blends into Pluto in the photos, creating a fuzzy white blob. (Charon is about 750 miles, or 1,207 km, in diameter — about half as wide as Pluto itself.)

The new photos were captured by New Horizons' Long-Range Reconnaissance Imager (LORRI), to help improve team members' understanding of the orbits of Nix and Hydra. The right-hand images have been processed to remove the Pluto-Charon glare and that of background stars, making Nix and Hydra easier to see, NASA officials said.

The streak extending to the right of Pluto and Charon is a result of overexposure, they added. (LORRI took the photos in a special mode that sacrifices resolution to boost sensitivity.)

Read more at Discovery News