Science News

Headlines
. How to stop a speeding bullet
. Could a planet be made of diamond?
. Watching our seas rise
. Shoulder bones fuel debate about human ancestors
. Hind wings helped a small 4-winged dinosaur make tight turns in midair

For more details, read on.

How to stop a speeding bullet

A new experiment showed how a popular plastic called polyurethane can stop a speeding bullet. A polyurethane is a polymer composed of a chain of organic units. Each molecular unit is called a monomer. Monomers are joined together or linked by carbamate (urethane) links with the chemical formula NH-(C=O)-O- (see figure). The chain of molecules strung together this way is called a polymer. This polyurethane is a kind of plastic and is popularly used in the base of sports shoes (and also paints and varnishes).
A bullet fired into a disk of polyurethane may not burst out the other side. In some instances, the bullet will stop in its tracks, frozen by the plastic and sealed inside. How a simple plastic can do this has left researchers scratching their heads. Until now.
In a new experiment, Rice research scientist Jae-Hwang Lee designed a modified version of the plastic to show what's happening inside the material when it stops a bullet. The bullets in these tests are glass beads traveling at the breakneck speed of about 5,000 km/hr!
Lee developed a newer version of hardened polyurethane which is solid and looks like a jumble of hard and soft components under a microscope. His creation resembled a miniature plastic sandwich, alternating thin slices of a glassy polymer with thin slices of a rubbery polymer. Then he and his collaborators used a device to fire tiny glass beads into the sandwich. On impact, the material went through a weird transformation.
First the layers pressed together under the impact, as you might expect. Instead of breaking, however, they seemed to melt and mix like liquids. Then, a millionth of a second later, they were solid again -- and the bead was locked inside. Scientists are still working on how to control this behaviour. Right now, Lee's fantastic plastic remains in the lab. But one day, it might find use protecting things that could be targeted by powerful projectiles.

Could a planet be made of diamond?
A planet orbiting a distant star is probably unlike any of the hundreds yet discovered. Scientists say that about one-third of this incredibly hot, barren world -- larger than Earth -- could be made from diamonds.
The planet, known as 55 Cancri e, is one of five circling the star 55 Cancri. This star lies about 40 light-years from Earth. A light-year is the distance that light travels in one year, about 9.5 trillion kilometers. The distant solar system lies within the constellation Cancer (see star chart). 55 Cancri can be seen from Earth, but only in dark skies far from cities. (The yellow star is slightly smaller and slightly less massive than the Sun, so overall the star is cooler and a little bit dimmer than the Sun.)
Although planets orbiting 55 Cancri remain completely invisible to astronomers, the scientists know that they are there: The planets are so big that their gravitational pull tugs on their parent star, causing it to wobble back and forth in ways that can be seen from Earth.
The innermost of these planets, 55 Cancri e, passes across the face of the star during each orbit, says Nikku Madhusudhan. He's an astrophysicist at Yale University. During each pass, the planet blocks a small fraction of the starlight streaming toward Earth. Using very sensitive instruments, including some that detect changes in starlight, Madhusudhan and his colleagues learned a lot about 55 Cancri e.
For one thing, this planet passes in front of its parent star, as seen from Earth, once every 18 hours. (Just imagine if a year on Earth, or the time it takes us to circle the Sun once, was less than a day long!) Using that figure, the researchers estimate that 55 Cancri e orbits just 2.2 million kilometers away from its star. That would give the planet a blazing hot surface temperature of about 2,150° Celsius. (Earth, by comparison, orbits about 150 million kilometers from the Sun.)
Based on the amount of light that 55 Cancri e blocks when it passes in front of its parent star, the planet must be just over twice the diameter of Earth. That's what Madhusudhan and his team report in a recent issue of Astrophysical Journal Letters. Additional information, some gathered previously by other scientists, suggests that the planet has about 8.4 times the mass of Earth. This makes it a "super-Earth," meaning its mass is between 1 and 10 times that of Earth's. Using the size and mass of the planet, the researchers can estimate what sort of materials 55 Cancri e is made from.
Other scientists had previously suggested that 55 Cancri e, discovered in 2004, was covered with a light material, such as water. But that's not likely, concludes Madhusudhan. That's because analyses of light from the parent star suggest that its chemical composition, as well as that of the planet, is carbon-rich and oxygen-poor. Instead of accumulating water (a substance whose molecules contain one atom of oxygen and two atoms of hydrogen) when it formed, this planet probably accumulated other light materials, such as carbon and silicon.
The core of 55 Cancri e might be made of iron, the same substance as Earth's core. But the faraway planet's outer layers could be a mixture of carbon, silicates (minerals that contain silicon and oxygen) and silicon carbide (an extremely hard mineral with a very high melting point). At the very high pressures inside this planet -- and maybe even near its surface -- much of the carbon could be in the form of diamond. (Diamond is just a special (crystalline) form of carbon.) In fact, diamond could account for up to one-third of the entire planet's weight.
Because there are several uncertainties about the new study, "we can't say that we've found a carbon planet yet," says Marc Kuchner. He's an astrophysicist at NASA's Goddard Space Flight Center in the USA. However, he adds, if there are diamond planets, "55 Cancri e is a very strong candidate."
"Carbon can exist in many forms on Earth, and there are likely even more types on a carbon planet," says Kuchner. "Diamond might be just one of the types of carbon that you'd see." The common graphite in lead pencils is another. So, thinking of 55 Cancri e only as a "diamond planet" doesn't show a lot of imagination, Kuchner suggests. So it's too early to call 55 Cancri e a diamond in the sky!

Watching our seas rise
Scientists these days are worried about sea level. As Earth warms, the surface of the ocean is creeping upward. This creep is happening partly because saltwater expands a tiny bit as it warms. "Warmer water literally is taller," explains Josh Willis. He's a climate scientist at the NASA Jet Propulsion Laboratory in Pasadena, USA.
Sea level also is rising because warm temperatures have prompted glaciers in Antarctica, Greenland and other usually cold places to melt more quickly. Glaciers are essentially rivers of ice, and their melting adds freshwater to the ocean. Antarctica and Greenland are together losing about 350 cubic kilometers of ice per year. Spread over the world's oceans, that meltwater alone raises sea level about 1 millimeter or so each year.
Scientists have long known that sea level changes over time. Scientists have found dead coral reefs buried 150 meters beneath the sea. When that coral was alive, it grew just below the water's surface. Today, those coral skeletons provide evidence that sea level was once much lower, too.
The big challenge for scientists has been how to measure changes to sea level throughout the past 50 to 100 years. Bruce Douglas, a retired scientist who worked for 20 years at the National Oceanic and Atmospheric Administration, or NOAA, in the USA, spent years working on this. During the 1980s and 1990s he measured sea level rise by studying records from tide gauges. Harbor operators have relied on these devices for more than 200 years to monitor the water level in coastal areas in order to alert ships at risk of running aground. But the gauges gave a limited picture: They measured the level of the world's oceans, which cover 360 million square kilometers, in only 20 or 30 places!
Scientists have gradually solved that problem as satellites have become accurate enough to monitor sea level. Several satellites, including the Jason-2 satellite, are observing the sea levels constantly. This flies 1,340 kilometers high and travels 25,000 kilometers per hour, 27 times as fast as a commercial jet. And it circles Earth a little over 12 times a day.
So, two thousand times per second, Jason-2's spotlight -- pointed down at Earth -- flashes on for an instant. It isn't a flash that you could see even if you were looking. The spotlight is throwing off radio waves, which are invisible to the eyes of humans and other animals. Those waves ripple down to Earth and bounce off of its surface, back into space. A computer aboard the satellite times exactly how long those reflected radio waves take to return -- usually, about nine-thousandths of a second.
By measuring how long the signal takes to bounce back, Jason-2 can measure the distance between itself and Earth's surface. The satellite was launched into space to measure sea-surface heights. Or, more to the point, Jason-2 is measuring how quickly the planet's seas are rising. Jason-2 has shown that overall, sea level is currently rising about 2.4 millimeters per year. That may not sound like much -- but this number will slowly start adding up.
This slow rise is expected to cause flooding in many of the world's coastal cities in the next 50 to 100 years. Worse yet, the speed of sea level rise is also expected to grow. Seas may eventually rise four to eight times faster than they are today.
The big question for scientists like NASA's Willis is: Has sea level been rising that fast for millennia? Or did this rate of sea level rise begin much more recently? In the past century or two, humans began spewing more carbon dioxide into the air through the burning of fossil fuels such as coal, oil and natural gas. And as a type of greenhouse gas, carbon dioxide helps warm Earth's atmosphere -- and its seas. So it would make sense that the seas started rising more quickly in the last few hundred years.
Archeologists studying ancient fishponds built by the Romans 2,000 years ago have now helped to answer this important question.
The Romans built dozens of saltwater ponds in southern Europe, along the edge of the Mediterranean Sea. Their goal was to farm fish for dinner. Channels connected the sea to the ponds, which were replenished during high tides. So the ponds had to be built right at sea level. But today, they sit 1 meter under water. They were submerged by rising seas.
Those ponds show that sea level has risen by no more than 1 meter in the last 2,000 years -- less than one-tenth of a millimeter per year. If sea level is currently rising 2.4 millimeters per year, then it is rising at least 20 times as fast as it has, on average, since the fishponds were built!
Concludes Willis, "The last 150 years have seen much more rapid rise than at any other time in the last 2,000 years."
A rise in sea level of just 1 meter would cause sea water to enter towns all over the world during ordinary high tides that happen every month. But the worst effects will happen during large storms called hurricanes or cyclones that form over the ocean. As a hurricane comes ashore, its howling winds push a pile of seawater forward. These water piles, called storm surges, can tower as much as 8 meters above normal sea level.
Storm surges as high as 3.3 meters swept over New Jersey and New York coastlines when Hurricane Sandy came ashore in the eastern coast of the USA on October 29. Storm surges occur regularly in India as well, especially in Kanyakumari, the tip of South India. The sea level and its possible rise will become a critical issue for large numbers of people. So NASA scientists are making sure that there is a replacement for Jason-2 (called Jason-3) ready to go whenever Jason-2 wears out.

Shoulder bones fuel debate about human ancestors
A fossil is the remains or impression of a prehistoric organism preserved in rock. It may also be petrified or saved as a mould. Study of fossils has taught us a great deal about how life has evolved on Earth.
Fossil shoulder blades suggest an ancient humanlike species may have been at home in the trees as well as on the ground. This was concluded by examining a shoulder blade from a 3-year-old humanlike female who lived more than 3 million years ago. Scientists are studying the fossil to learn whether the creature climbed trees. Nicknamed Selam by her discoverers, this individual belonged to a long-gone species known as Australopithecus afarensis (AU stral oh PITH i kus AF a REN sis).
Shoulder blades are the triangular bones that stick out of your back like small wings. Also known as scapulas, they connect different parts of the body. Many species have scapulas, although their shapes and sizes can differ. Without these bones, you couldn't climb a tree. The surprising presence of them in a now-extinct humanlike species suggests it may have been a tree climber.
Selam's shoulder blades resemble those from an ape. That connection led the researchers to conclude that this ancient species both climbed trees and walked on the ground. That conclusion reignites a controversy: Scientists disagree about whether this species lived only on the ground or could climb trees as well. The disagreement has been ongoing for more than 30 years, since another member of the same species -- an individual nicknamed Lucy -- was discovered in Ethiopia in 1974.
Paleontologist David Green of Midwestern University in Downers Grove, Ill., and anthropologist Zeresenay Alemseged of the California Academy of Sciences in San Francisco worked on the new study. Paleontologists study fossil organisms and anthropologists study humankind.
Lucy and Selam spent time on the ground but probably scaled trees for food and safety, Green says. His group's new study of Selam's shoulder blades also suggests that this species would have learned to climb trees early in life.
"Juvenile members of A. afarensis may have been more active climbers than adults," Green told Science News.
Modern humans are born with shoulder sockets that point downward. (Later, they shift to point outward, away from the torso.) Today's apes have shoulder sockets that point upward, which makes it easier for these primates to swing from branch to branch. Green, Alemseged and their coworkers noted that the skeletons of both Selam and Lucy have upward-pointing shoulder sockets -- like tree-swinging apes. Selam's shoulder blades also have a ridge that can be found in the bones of modern apes.
Other scientists say it's too soon to declare that members of the A. afarensis species mixed walking and climbing. In 2010, anthropologist Yohannes Haile-Selassie of the Cleveland Museum of Natural History studied the fossil remains of Big Man, yet another member of A. afarensis. Haile-Selassie told Science News that Big Man's skeleton points to a creature for whom climbing trees wasn't very important. Instead, the animal walked on the ground in way that closely resembles how humans walk.
Haile-Selassie says that if future studies of Selam also show that the creature climbed trees, it may cast doubt on whether the new fossil belonged to A. afarensis. It may instead belong to a new species that's never been documented before.

Hind wings helped a small 4-winged dinosaur make tight turns in midair
For some animals, two wings just won't do -- as was the case for a four-winged dinosaur that lived 130 million years ago. Fossils of the creature were unearthed in China about 10 years ago. Since then, scientists have puzzled over how this dino used its two bonus wings. Now researchers report a likely answer.
In a new study, scientists Justin Hall and Michael Habib and their collaborators suggest the dino tucked its hind wings under its body most of the time. It brought the extra wings out only when it needed to make tricky turns in midair. To make a right turn, the dino would lift its left hind wing, for example.
Hall and Habib, who work at the University of Southern California in Los Angeles, presented the new idea about these dinos at a recent meeting of scientists who research prehistoric animals.
Other scientists had suggested that the dinosaur glided through the air either with all four wings out or with one pair positioned beneath the other, like the wings on a biplane. Scientists are still arguing over whether the dinosaur could flap its wings and stay in the air like birds or just glide gently downward.
The new study suggests a simpler solution to the mysterious function of the four wings. Keeping the back wings tucked away most of the time would have made it easier for the animal to remain aloft, Hall finds. He notes that the feathers on the back legs were arranged in a shape that probably didn't add much lift. Lift is an upward force that acts against gravity.
Keeping two wings hidden away when moving straight ahead would have made the dinosaur more aerodynamic, meaning it would have had a shape that let air flow past more freely. Extended all the time, the extra wings would have slowed the dino by creating resistance from the air. Air resistance, or drag, is the enemy of flight: A raindrop falls faster than a feather because air resistance doesn't slow the drop down as much as the feather.
Hall and his collaborators studied the dinosaur Microraptor gui. It was the first found to have four wings. But it's no longer the only one: Since M. gui's discovery, other four-winged dinos have turned up. And their hind wings probably worked the same way, says dinosaur expert Luis Chiappe at the Natural History Museum of Los Angeles.

--Compiled from several sources