Few people can add numbers in their heads that quickly. If someone showed you a set of 845 dots next to a set of 289 dots, however, you’d probably be able to tell right away which set has more dots. You could probably also tell that 845 dots is more than 100 dots plus 189 dots, even if you saw all three sets of dots separately.

How quickly can you solve this problem?

By giving tests like these to kids and adults, scientists are discovering that we develop a sense for large numbers long before we learn how to count or talk. Our brains seem to come equipped with systems for estimating amounts and doing arithmetic, says Elizabeth Spelke. She’s a psychologist at Harvard University in Cambridge, Mass.

Spelke’s work adds to a growing body of research showing that young children and even animals have some inborn sense of number, long before they ever receive a formal math lesson (see “It’s a Math World for Animals“).

Spelke’s goal is to answer one basic question. “What abilities do children have when they start school that support the learning of mathematics?” she asks.

The answer, Spelke says, could help teachers find better ways to teach math by tapping into skills that their students bring with them.

Learning what skills children already have when they start school could help teachers find better ways to teach math.

Artville

“The premise of my work is that all learning in school builds on systems we already have,” Spelke says. “My goal is to figure out what those systems are, how they work, and how they come together for mathematical thinking.”

Flash math

To add, subtract, multiply, or divide, you need to understand that numbers are symbols that can be used in a variety of settings. The symbol 11, for instance, can refer to your age, the number of days left before vacation, the number of chimes you hear when the clock strikes 11 a.m., or the total number of cookies left over in three different boxes.

That’s a tricky concept, and the ability to understand numbers as symbols is one thing that separates people from other animals. Unlike other animals, people can figure out exactly what amount you get when you add 32 and 16, without even having to know whether the numbers refer to coins, apples, or anything else.

Spelke and her coworkers have done various experiments to find out how well young children can estimate quantities and add large numbers—even before they’re taught arithmetic in school.

Their most recent attempt to uncover the foundations of our mathematical abilities involved five experiments. In each experiment, preschoolers sat in front of computers watching animations that briefly flashed various sets of dots on the screen. Each set contained from 10 to 58 dots.

In the first experiment, children saw a set of blue dots, then a set of red dots on a computer screen. They had to decide whether there were more blue dots or red dots.

Proceedings of the National Academy of Sciences (PNAS)

First, Spelke and her colleagues presented a group of 5-year-olds with one set of blue dots and one set of red dots. The sets of dots appeared one at a time, and they flashed by too quickly to be counted.

The results showed that the children were usually able to pick the larger set, even if the dots were different sizes and took up different amounts of space.

In the second experiment, five-year-olds had to decide whether the total number of blue dots in two sets was larger or smaller than the number of red dots.

Proceedings of the National Academy of Sciences (PNAS)

For the second experiment, the 5-year-olds saw one group of blue dots, which was followed by a second group of blue dots, which was followed by a group of red dots. This setup was more complicated than the first, but the kids were still able to say whether there were more blue dots altogether or red dots, suggesting that they could both add and compare amounts.

In the third experiment, the children had to compare a group of dots that they saw to a certain number of tones that they heard. They could still pick the larger group. In the fourth, they successfully chose the largest grouping, given two sets of dots of the same color and one set of tones.

In the third experiment, young children briefly saw a set of blue dots, then heard a certain number of tones (one tone for each red dot). They had to decide whether there were more blue dots or tones (red dots).

Proceedings of the National Academy of Sciences (PNAS)

These results suggest that kids have an ability to add and compare numbers in different settings.

Word problems

In the fifth set of experiments, the researchers used words instead of dots or tones to present comparison problems.

Here’s an example that’s like the second experiment with just dots. Suppose you have 15 pennies. Your Mom gives you about 10 more. Your sister has about 40. Who has more pennies: you or your sister?

When given in words, the 5-year-olds couldn’t answer the question correctly. Most of them, however, could answer the question when it was given as sets of dots.

Overall, Spelke concluded that a child’s sense of number doesn’t depend on his or her ability to use language. Other studies with adults, she says, have shown that we use one part of our brains when doing arithmetic, such as adding 43 plus 72, and another part when estimating and comparing sets of dots.

Building blocks

So, certain building blocks for learning math seem to be in place before kids start school, Spelke says. It then takes years of math class for the brain to learn how to combine its inborn number sense with its language and other symbolic skills. High grades on algebra tests are the final result.

Learning elementary arithmetic is surprisingly hard for lots of kids.

If you’re trying hard and still getting B’s and C’s in math, though, you’re not alone.

“Learning elementary arithmetic is surprisingly hard for all children,” Spelke says. Her research shows, however, that you might be better at certain types of math than you think you are. That should give you hope.

“It is both surprising and encouraging to see,” Spelke says, “that if you engage kids in thinking about number outside of symbolism, they understand a lot.”

Even then, most kids need to take classes and do lots of homework to learn arithmetic.

The effort is worth it, Spelke says, because without math, our culture couldn’t function. “So much of our understanding of the world depends on mathematics,” she says.

“Math is fundamental to measurement,” Spelke says. “It’s fundamental to technology. It’s fundamental to science.”

Additional Information

Questions about the Article

Word Find: Math Skills

Going Deeper:

The bands of brilliant color on this butterfly’s wing are produced from tiny scales on the wing’s surface.

Image courtesy of Peter Vukusic/University of Exeter

Swallowtails that belong to a group called Princeps nireus actually have fluorescent wings. This means that when the wings absorb a special type of light, called ultraviolet light (or “black light”), they give off a bright blue-green glow. The glow that they give off has a longer wavelength than the ultraviolet light they absorb.

Physicist Peter Vukusic of Exeter University wanted to figure out why the wings are unusually bright. So, he took a close-up look.

Butterfly wings are covered with hundreds of thousands of colored scales, like tiles covering a roof. The scales are made of cuticle, a material that is similar to human fingernails. Vukusic and his colleagues used highly sensitive microscopes to look at individual scales.

Optical microscope image of a single scale from a butterfly wing.

Image courtesy of Peter Vukusic/University of Exeter

Their pictures show that each scale has three vertical levels. The bottom level is itself split up into three more layers, like an Oreo cookie, with an air space sandwiched between two layers of cuticle. Each layer is about 90 nanometers thick. One nanometer is one-billionth of a meter. A human hair is about 80,000 nanometers wide.

The middle level is a 1.5-micrometer-thick air space, held together by columns of cuticle. One micrometer is one-millionth of a meter, or 1,000 nanometers.

Finally, the top level is made of cuticle arranged in a sort of honeycomb pattern, 2 micrometers thick. The honeycomb holds tiny cylinders of air, measuring 240 nanometers across. The walls of these cylinders hold the pigments that cause the wings to glow, or fluoresce.

The wings seem to achieve their bright glow in two ways, the scientists conclude. First, the pigment-filled cylinders in the top level and the Oreo sandwich in the bottom level cause all of the fluorescence to reflect out of the top of the wing. Second, the bottom level adds even more blue-green light by reflecting sunlight that filters down and hits it.

Peter Vukusic with several different butterflies that have wings covered with special scales that brighten the color.

Image courtesy of Peter Vukusic/University of Exeter

Some electronic devices called light-emitting diodes (LEDs) work in a remarkably similar way. LEDs light up the numbers on clocks and watches and show when appliances are on, among many other jobs.

It’s another amazing example of technology imitating nature, whether intended or not.—E. Sohn

Going Deeper:

Cunningham, Aimee. 2005. Way to glow: Butterfly-wing structure matches high-tech lights’ design. Science News 168(Nov. 19):324. Available at http://www.sciencenews.org/articles/20051119/fob3.asp .

Recent analyses of fossilized dino droppings unearthed in India have turned up at least five types of grasses. The discovery is thrilling to paleontologists because it’s the first evidence that some dinosaurs actually ate grass. The remains also suggest that grass had evolved into different types much earlier than scientists had thought.

This glassy fragment (about 100 micrometers long) was extracted from fossilized dinosaur dung unearthed in India. Its presence shows that the reptiles dined on grass.

© Science

Titanosaurs probably produced the fossilized poop pellets 65 million years ago. Each piece of fossilized dung, called a coprolite, was shaped like a sphere and measured up to 10 centimeters (4 inches) across.

When the researchers looked closely at the coprolites, they were able to identify tiny fragments of glass called phytoliths. These little bits of silica form inside the cells of many plants, and they are especially common in grasses.

Each type of grass produces its own uniquely shaped phytolith. So, by analyzing phytoliths left behind in the dino excrement, the scientists were able to identify a variety of grasses that had passed through the digestive tracts of the animals. They also found evidence of other plants, including palm trees, conifers, and cycads.

Until now, the earliest known fossils of grass leaves and stems dated back just 56 million years. The new find pushes the date when grasses were flourishing back at least 9 million years, probably more.

The research could “completely revise what we’ve thought about the origin of grasses,” says Elizabeth A. Kellogg. She’s an evolutionary biologist at the University of Missouri-St. Louis. “This isn’t that much older than the oldest previous grass fossils, but to find such diversity at that time is surprising.”

Other evidence suggests grasses could have first appeared as far back as 80 million years ago.

Knowing that grasses arose so early might help explain a long-standing animal mystery. Just before the dinosaurs died out about 65 million years ago, mammals called gondwanatheres appeared on Earth.

Gondwanatheres were as big as groundhogs with long, flat teeth. Their teeth were similar to those of horses and other modern grass-eaters. Scientists have been puzzling about what these animals ate. Now they know that it might have been grass.—E. Sohn

Going Deeper:

Perkins, Sid. 2005. Ancient grazers: Find adds grass to dinosaur menu. Science News 168(Nov. 19):323. Available at http://www.sciencenews.org/articles/20051119/fob1.asp .

TV crews wait for Mount St. Helens to erupt. Sound at low frequencies that people can’t hear could provide a warning that such a volcanic eruption is about to occur.

Kate Ramsayer

These silent sounds, or infrasound, are calling to some scientists. These researchers are using special microphones to eavesdrop on infrasound created by the world around us. The noisemakers include volcanoes, tsunamis, hurricanes, and even the turbulence that shakes airplanes.

“We’re learning more about how the planet operates by listening,” says Michael A. Hedlin. He studies sounds at the Scripps Institution of Oceanography in La Jolla, Calif.

Low notes

Like all types of sound, infrasound travels in waves. The sound waves have different heights, or amplitudes, which make them louder or softer. They also have different wavelengths, measured from the crest of one wave to the top of the next. And they have different frequencies, measured by the number of crests that pass by a particular position per second.

Short, rapid waves make high-pitched sounds, like a teapot’s whistle. Long, slow waves make low-pitched sounds, like a bass guitar in a rock band. And below the lowest note on a bass, below what people can hear, there’s infrasound.

An elephant generates and probably detects infrasound.

Infrasound is created when something, such as a bomb explosion or an earthquake, sets a large amount of air in motion. The resulting sound waves travel through the air, sometimes for thousands of kilometers.

Scientists originally started studying infrasound to make sure faraway countries weren’t testing nuclear bombs. Now, they’re using infrasound to check for natural events.

“We’re finding all these exotic sources [of infrasound] that we hadn’t thought of before,” Hedlin says.

Tsunami sounds

One of those infrasound sources is a gigantic wave called a tsunami. “We didn’t know that a tsunami produces infrasound,” says Milton Garcés. He runs the infrasound laboratory at the University of Hawaii, Manoa.

Earthquakes under the ocean can generate tsunamis. Special instruments on buoys, such as this one, can detect the resulting waves.

National Oceanic and Atmospheric Administration

When a massive earthquake occurred off the coast of Indonesia in December 2004, for example, it sent a deadly wave across the Indian Ocean. When Garcés looked at infrasound data that were recorded near the tsunami, he found a big signal that corresponded to the wave. “It produced a wallop,” he says.

In the last year, Garcés and his colleagues have picked up sounds from two more tsunamis. One was a Japanese tsunami that produced “beautiful infrasound,” he says.

The researchers recently set up a tsunami infrasound project in Hawaii. “Whenever there’s a tsunami, we’re going to be looking at it very carefully,” Garcés says. The scientists hope to learn how the giant waves produce infrasound, which is currently a mystery.

Volcano rumbles

Garcés and others are also using infrasound to listen in on volcanoes.

On the Sakurajima volcano in Japan, Garcés discovered that stronger and stronger infrasound signals led up to the volcano’s eruption in 1998. If this happens all the time, scientists could use infrasound patterns to warn people if a nearby volcano is about to blow, he says.

The eruption of the Fuego volcano in Guatemala in 2003 generated strong infrasound, mostly below a frequency of 10 hertz (cycles per second). The pressure readings show that the strength of these sound waves can reach the equivalent of 120 decibels (rough

Jeffrey B. Johnson, University of Hawaii at Manoa

Detecting volcanic eruptions with infrasound would also be a useful tool for airplane pilots, because ash from an erupting volcano can dangerously damage a plane’s engines.

Infrasound stations are also keeping an ear on Mount St. Helens in Washington State. Hedlin can tell that gas is bubbling up in the volcano just by looking at the infrasound recordings.

The recordings also detect small earthquakes inside the volcano that push air around, as well as other events whose causes are yet unknown. Infrasound gives researchers a more complete picture of how volcanoes work, Hedlin says.

And scientists are always listening for new things to investigate, Hedlin adds.

Hedlin has recorded infrasound coming from sprites, which are short flashes of light in the atmosphere above thunderclouds. He’s also planning to set up a station to study winds off the coast of Africa, where hurricanes begin to form. To listen to the speeded-up sound of a sprite (so that you can hear it), click here.

The northern lights (auroras) generate infrasound by pushing the surrounding air outward.

Collection of Dr. Herbert Kroehl, NGDC, National Oceanic and Atmospheric Administration

Other researchers are using infrasound to detect avalanches, the northern lights, ocean waves, bumpy air that causes airplane turbulence, and mountains shaking from earthquakes.

Animal calls

While people are deaf to infrasound, other animals appear to use it to communicate. When elephants trumpet, for example, they also produce infrasound that can reach other elephants as far as 10 kilometers away, researchers discovered.

Elephants might even pick up these low rumblings through their feet, says Caitlin E. O’Connell-Rodwell. She’s a scientist at Stanford University in California.

Other researchers have suggested that whales, rhinos, and big birds called cassowaries can create or pick up infrasound. Even some dinosaurs might have had this ability.

A cassowary might pick up ultrasonic signals with its casque, a mysterious structure on top of its head. No one is yet sure what this structure is for.

Andrew L. Mack, Wildlife Conservation Society

In addition, it’s possible that people can detect infrasound in special ways. When elephants trumpet, “it’s such a powerful, low-frequency sound,” O’Connell-Rodwell says. “You really feel it resonating in your chest.”

In one experiment, researchers in England played infrasound during a music performance. Although listeners couldn’t hear the super-low notes, they seemed to have stronger emotions during the performance than did people who heard music without infrasound.

There certainly seems to be more to infrasound than meets the ear.

Going Deeper:

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Word Find: Infrasound

In the movies, a daring hero comes up with a crazy plan to destroy or divert the asteroid and save the day. In real life, scientists have come up with more reasonable plans that might actually work if this rare situation ever comes up.

A massive spacecraft could use its gravity to divert an asteroid headed for Earth.

D. Durda, FIAAA/B612 Foundation

One solution, say two NASA scientists and astronauts, is a 20-ton spacecraft called a gravitational tractor. First, the tractor would zoom up to the threatening asteroid and stop a short distance away. It would hover there, firing its thrusters just enough to overcome the force of gravity between the spacecraft and the asteroid.

The tractor could then use its own gravity to tug the asteroid off course. It would take about a year for the spacecraft to drag a medium-sized asteroid that measures 200 meters (660 feet) across and weighs 60 million tons away from Earth’s path.

An asteroid this large could cause major damage to our planet. Some asteroids are even larger than this, and it would require bigger tractors to pull them enough to remove the threat.

The tricky part is that the spacecraft would have to arrive at the Earth-bound asteroid about 20 years before the asteroid was due to hit Earth. It would take a much smaller nudge then to move the asteroid out of the way than it would take if the asteroid were closer to its impact time.

Still, the tractor idea is better than many previously proposed strategies for asteroid avoidance. Blowing up asteroids, for example, wouldn’t work because the rocky bodies are too full of air holes to burst apart.

Nor is it reasonable to have a spacecraft attach itself to an asteroid and use its engines to steer the object away. That’s because asteroids spin. Unless the craft stopped the asteroid from spinning, each thrust would push the asteroid in a different direction. A gravitational tractor could get around these problems.

Don’t spend too much time worrying about asteroids falling on your house, however. The chances of a collision occurring in your lifetime are very slim. If it does happen, though, scientists will do everything they can to keep you from getting hurt. Sounds pretty heroic to me!—E. Sohn

Going Deeper:

Cowen, Ron. 2005. Protecting Earth: Gravitational tractor could lure asteroids off course. Science News 168(Nov. 12):310. Available at http://www.sciencenews.org/articles/20051112/fob8.asp .

Sohn, Emily. 2005. Killers from outer space. Science News for Kids (May 18). Available at http://www.sciencenewsforkids.org/articles/20050518/Feature1.asp .

Since then, the Great Lakes Fishery Commission has spent many millions of dollars on attempts to control lampreys in the Great Lakes. The fish are a hearty bunch. Now, scientists from the University of Minnesota have found a new way to keep the destructive creatures at bay. They’re tapping into a lamprey’s sense of smell.

Two sea lampreys cling to the glass wall of a laboratory tank.

University of Minnesota

As larvae, sea lampreys spend up to 20 years in freshwater streams, where they eat and grow. Then, nearing adulthood, they move to a larger body of water, where they feed off one fish after another, for about a year. Finally, they swim to streams to mate. After a few weeks of breeding and laying eggs, they die.

Scientists have long suspected that lampreys follow the scent of each other’s pheromones, or body chemicals, to find suitable streams for mating.

An adult sea lamprey, about 1 meter long, swims to a spawning site.

University of Minnesota

To sort out which particular chemicals attract lampreys, the University of Minnesota researchers began with 8,000 liters (210 gallons) of water that had contained about 35,000 baby lamprey larvae. The scientists concentrated the liquid until they had just a few grams of gunk. They separated the gunk into individual chemical components, or compounds. Then, they tested each compound to see how lampreys responded to it.

The study turned up three compounds that both affected the lamprey’s sense of smell and attracted the fish. It was the first time that scientists have identified pheromones that affect migration in any vertebrate (animal with a backbone).

University of Minnesota researcher Peter Sorensen holds a sea lamprey.

David Hansen

After the researchers figured out which chemicals matter, they were able to create one of the compounds in the lab. If they can find a way to make the compound in large quantities, the scientists hope they’ll be able to use it to attract lampreys away from their breeding grounds. This would prevent the lampreys from reproducing, which would reduce their numbers and their impact.

Mimicking the lamprey’s scent could be a cheap and efficient way to reclaim the Great Lakes from a pesky parasite.—E. Sohn

Going Deeper:

Cunningham, Aimee. 2005. Whiff weapon: Pheromone might control invasive sea lampreys. Science News 168(Nov. 12):308-309. Available at http://www.sciencenews.org/articles/20051112/fob4.asp .

You can learn more about the sea lamprey at www.seagrant.wisc.edu/greatlakesfish/sealamprey.html (Wisconsin Sea Grant) and www.science.mcmaster.ca/Biology/Harbour/
SPECIES/SEALAMP/TITLE.HTM (McMaster University).

“Its head,” Sandved says, “was sticking out and looking at me.”

A viper has coiled itself around a branch.

© Kjell Sandved

Instead of reacting with terror and panic, like most people would, Sandved noticed something remarkable. Resting in this position, the snake looked like the letter “Q.”

It wasn’t the first letter of the alphabet that Sandved had picked out while observing nature. In 1975, the talented photographer had published a poster displaying every letter in the alphabet, each one found somewhere on the wings of butterflies and moths. Later, he finished a colorful collection of letters, numbers, and symbols found throughout the natural world. Completing both alphabets consumed him for 24 years.

Now 83 years old, Sandved has continued his quest. Recent photographs include patterns that resemble faces, eyes, ampersands, the Greek letter pi, and the shapes of cats and mice.

Unusual quest

Sandved’s unusual quest began when he first traveled to the United States from his native Norway in 1960. He was 38 years old, and he was working on an encyclopedia about the natural world. He had already written encyclopedias about classical music and European art.

Up nearly to his neck in water, Kjell Sandved films butterfly behavior in Maryland wetlands.

© Butterfly Alphabet, Inc.

When he arrived in Washington, D.C., for what he thought would be a 6-month visit, the director of the city’s Smithsonian Institution agreed to let him look through the museum’s collections.

“Then, one day, it happened,” Sandved says. “My meeting with destiny. It was a Cuban cigar box, full of butterflies and moths. There, on the wing, I saw a beautiful letter ‘F.’ I’ll never forget it. I thought, ‘My God, how can nature put something so beautiful on a butterfly’s wing?’”

Inside boxes, the butterflies had lost much of their color. So, Sandved taught himself how to take photographs. Then, he began traveling around the world, looking for more letters.

His adventures have taken him to more than 30 countries, including Brazil, Papua New Guinea, and the Philippines. He still lives in the United States.

Shapes in nature

The easiest shapes and symbols to find in nature, Sandved says, are the symmetrical ones. O’s, X’s, and I’s, for example, are more common than R’s, F’s, and G’s. “Design elements in nature,” he says, “tend to go toward symmetry.”

A spider waits for prey atop a sticky, white cross made of spider silk.

© Kjell Sandved

Eye-like shapes are also easy to find, Sandved says. Many creatures, including butterflies, fish, and peacocks, have eye-shaped markings on their bodies as a strategy for defense. Often, the markings fool a predator into thinking that its prey is moving in one direction, when it’s actually moving in another.

Intricate patterns can also help animals attract mates, just as people might dress up or wear makeup to impress each other.

It’s probably just a coincidence that the designs we see in nature look like the letters we use. After all, our brains are trained to recognize particular patterns.

The arms of a sea creature known as a brittlestar form an “R.”

© Kjell Sandved

We’re especially quick to pick out shapes that we see all the time, such as letters and numbers. Butterflies themselves don’t see K’s and Q’s. They simply see other butterflies that they want either to approach or stay away from.

Adventures in nature

For Sandved, the search for letters in nature has inspired a huge appreciation for the environment and everything in it. He marvels at the creatures, plants, and objects he discovers in the course of his adventures.

A moth’s wings bear a pattern resembling the figure “8.”

Credit: © Kjell Sandved

“All finite things reveal infinitude,” reads a poem by Theodore Roethke. The poem is printed on many of Sandved’s posters.

“This is one of the deepest statements I can think of that has ever been uttered in science and life,” Sandved says. “The more I learn, the more I see that I’m totally ignorant.”

Our brains are like boxes, he says, and it can be hard to think outside of what we are comfortable with.

After many years spent observing and photographing spiders mating and then eating each other, butterflies flitting around, and other intricacies of nature, Sandved has given up on trying to understand it all. Instead, he lives his life with a sense of wonder and amazement.

A flamingo’s neck forms a graceful “S.”

Credit: © Kjell Sandved

Sandved has also been lucky enough to dedicate his life to something he loves.

“All of these things have been so much fun,” he says. And his work has paid off. His images are fascinating to look at, and they’ve become a popular tool for teaching numbers and letters to kids.

You might want to start your own quest. What letters, numbers, and other symbols can you find in the natural world around you?

Kjell Sandved’s famous butterfly alphabet.

© Butterfly Alphabet, Inc.

Going Deeper:

Additional Information

Questions about the Article

Word Find: Nature’s Alphabet

Rodents will probably never sing their way to Broadway, but researchers from Washington University in St. Louis have found evidence that mice do, in fact, sing. Until now, crooning mice have starred in cartoons, but never before have they been heard belting it out in real life.

Mice appear to string together “chirplike” ultrasonic noises (shown as a plot in yellow) to create songs.

Timothy E. Holy and Zhongsheng Guo

Scientists already knew that mice make ultrasonic sounds—noises that are too high-pitched for people to hear without special equipment. Mouse babies cry out when they lose their mothers. Male mice make noise when they smell females.

To find out whether mice put such sounds together in song-like patterns, the researchers recorded the sounds of 45 male mice. They put each mouse in its own chamber with a urine-soaked cotton swab. The smell of the urine inspired them to make noise. Microphones recorded the sounds.

Using computer software, the researchers were able to separate the squeaks into specific types of syllables, based on how quickly the pitch rose or fell. The mice produced about 10 syllables per second.

The results showed that nearly all of the mice repeated sequences of syllables in distinct patterns. That’s enough to meet the definition of what scientists call song. Birds, whales, and people do the same thing.

Not all scientists are convinced that what the mice are doing is actually singing. To prove it, the researchers must show that there’s learning involved. And, they need to figure out why the mice sing. One guess, the researchers say, is that male mice use songs to woo females that they admire.

Nonetheless, the discovery that mice produce such complicated sounds could have important implications for the study of communication in animals, including people.

To hear various versions of mouse songs, visit http://www.sciencenews.org/articles/20051105/mousesongs.asp .—E. Sohn

Going Deeper:

Harder, Ben. 2005. Beyond falsetto: Do mice sing at ultrasonic frequencies? Science News 168(Nov. 5):293. Available at http://www.sciencenews.org/articles/20051105/fob5.asp .

You can hear various versions of mouse songs at http://www.sciencenews.org/articles/20051105/mousesongs.asp .

To learn more about how researchers studied mice and their songs, go to mednews.wustl.edu/news/page/normal/6040.html (Washington University School of Medicine) and www.eurekalert.org/pub_releases/2005-10/plos-mha102605.php (Public Library of Science).

As soon as you’ve memorized the planet lessons in your textbook, however, you’ve got more work to do. The Hubble Space Telescope has just spotted two more moons around Pluto, adding to the one we already knew about. If the finding is true, astronomers will have to rethink what they know about the planet and about the Kuiper belt—a collection of small, icy objects that lingers way out on the edge of our solar system.

The imagined surface of one of the two newfound moons of Pluto shows the planet above the horizon. The previously known moon, Charon, lies to the right of the planet, and the other new moon is at the far left.

NASA, ESA, and G. Bacon (STScI)

Until now, scientists had supposed that Pluto had just one moon, called Charon. This object follows an orbit 19,600 kilometers (12,200 miles) from the planet and measures 1,270 kilometers (790 miles) across. Charon is about half as wide as Pluto.

The new moons have been named S/2005 P1 and S/2005 P2. The first one lies about 48,000 kilometers (30,000 miles) from Pluto and has an estimated diameter of 56 kilometers (35 miles). The second lies about 64,000 kilometers (39,800 miles) from Pluto and has a diameter of about 48 kilometers (30 miles).

For every 12 times that Charon goes around Pluto, it looks like S/2005 P1 goes around 3 times, while S/2005 P2 goes around twice. Based on this information, scientists suspect that the moons formed at the same time that Charon formed, when some massive object smashed into Pluto soon after the planet’s birth 4.5 billion years ago. Chunks that flew off in the collision then became moons when they were trapped by the planet’s gravity.

These two images from the Hubble Space Telescope show the positions of Pluto, Charon, and the two objects that may be additional moons of Pluto. The movements of these objects, shown three days apart, suggest that they orbit Pluto.

NASA, ESA, H. Weaver (JHU/APL), A. Stern (SwRI), and the Hubble Space Telescope Pluto Companion Search Team

More observations are needed to confirm that the two objects actually orbit Pluto, but astronomers have reason to believe that they do. The same two objects also appear in pictures taken by Hubble 3 years ago.

After finishing with your textbook, keep watching the news. It’s the only way to keep up with our constantly changing map of outer space.—E. Sohn

Going Deeper:

Cowen, Ron. 2005. New partners: Hubble finds more moons around Pluto. Science News 168(Nov. 5):291. Available at http://www.sciencenews.org/articles/20051105/fob1.asp .

You can learn more about the discovery of Pluto’s new moons at hubblesite.org/newscenter/newsdesk/archive/releases/2005/19/ (Space Telescope Science Institute).

Sohn, Emily. 2005. Solving a Sedna mystery. Science News for Kids (May 4). Available at http://www.sciencenewsforkids.org/articles/20050504/Note3.asp .

______. 2004. Icy orbs at the solar system’s edge. Science News for Kids (Dec. 1). Available at http://www.sciencenewsforkids.org/articles/20041201/Note2.asp .

______. 2004. Planets on the edge. Science News for Kids (April 7). Available at http://www.sciencenewsforkids.org/articles/20040407/Feature1.asp .