When the sun shines on a planet, the planet’s surface reflects some of the sunlight back into space. Other sunlight gets absorbed and warms the planet. Light-colored surfaces, such as white ice caps, reflect more sunlight than dark surfaces do. By contrast, dark surfaces absorb more of the sun’s radiation, which makes them get hotter.

These pictures of the southern half of Mars show that the planet got darker between the late 1970s (left) and 2000 (right). At the center of each image, in white, is the ice cap at the planet’s south pole.

U.S. Geological Survey

Scientists who’ve compared pictures of Mars taken by satellites in the 1970s to images taken more recently have noticed that the Red Planet’s surface looks different than it used to. In some areas, the landscape looks much darker, while in others, it looks lighter. Overall, the surface of Mars—especially in the planet’s southern hemisphere—has grown darker over the past 30 years.

Most of those changes probably occurred because Martian winds blew away light-colored dust that had covered many regions. That exposed darker rocks that had been covered with dust.

The darkening of Mars has caused the planet to get warmer, a new study suggests. Scientists calculated how much more sunlight and heat Mars absorbs now. They compared that to how much it absorbed in the late 1970s. They estimate that the planet’s atmosphere is almost 1°C warmer, on average, than it was 30 years ago.

Some areas of Mars have warmed more than average. For example, the planet’s south pole may be 4°C warmer than it was in the late 1970s. That could explain why the ice cap at that pole has been melting recently, scientists say. Until now, they didn’t know why that was happening.

Like climate change on Earth, the change in Mars’ climate isn’t due to increases in the sun’s radiation, scientists say.—C. Gramling

Going Deeper:

Perkins, Sid. 2007. No escape: There’s global warming on Mars too. Science News 171(April 7):214. Available at http://sciencenews.org/articles/20070407/fob7.asp .

Sohn, Emily. 2005. Evidence of a wet Mars. Science News for Kids (Dec. 14)
http://sciencenewsforkids.org/articles/20051214/Note2.asp .

Our human ancestors came from eastern Africa. They started leaving that area around 60,000 years ago. Until recently, scientists weren’t sure when these roving humans first arrived in the area now known as China. Only one human skull that was more than 39,000 years old had ever been found in that part of the world.

This jawbone came from a 40,000-year-old human skeleton found in China. The find means that humans may have been traveling from Africa to eastern Asia much earlier than scientists once thought.

Hong Shang, et al.

But in 2001, local workers discovered some ancient human bones in a Chinese cave near Beijing. Paleontologists later excavated the site. Studies showed that the bones were 40,000 years old, leading the scientists conclude that people had made the long trek from Africa to China by that time.

The presence of those bones could also mean that humans and now-vanished humanlike species were interbreeding at that time. The scientists who’ve studied the Chinese skeleton say that it has features of both humans and humanlike Neandertals, which lived from 130,000 to 30,000 years ago in Europe and western Asia. The skeleton’s jaw, leg, and arm bones look like those of people today, but the teeth and hand bones are more like those of Neandertals, they say.

The idea of such interbreeding is controversial. Some scientists aren’t convinced. There just aren’t enough fossils from modern humans at that time to say for sure.

Although it was a very long walk from east Africa to China, the ancient people who made the trip may at least have had sturdy shoes. The skeleton has strong legs but delicate toes, and that means the ancient human probably wore some type of shoes—the oldest evidence of footwear ever found.—C. Gramling

Going Deeper:

Bower, Bruce. 2007. Asian trek: Fossil puts ancient humans in Far East. Science News 171(April 7):211. Available at http://www.sciencenews.org/articles/20070407/fob1.asp .

Sohn, Emily. 2006. Stone Age sole survivors. Science News for Kids (Jan. 11). Available at http://sciencenewsforkids.org/articles/20060111/Note2.asp .

This new, ring-shaped invisibility device is 1 centimeter tall and about the size of a drink coaster.

David Schurig et al./Science

When a person “sees” an object, his or her eye senses many different waves of visible light as they bounce off the object. The eye and brain then work together to organize these sensations and reconstruct the object’s original shape.

So, to make an object invisible, scientists have to keep waves from bouncing off it. And they have to make sure the object casts no shadow. Otherwise, the absence of reflected light on one side would give the object away.

Invisibility isn’t possible yet with waves of light that the human eye can see. But it is now possible with microwaves.

Like visible light, microwaves are a form of radiant energy. They are part of the electromagnetic spectrum, which also includes radio waves, infrared light, ultraviolet rays, X rays, and gamma rays. The wavelengths of microwaves are shorter than those of radio waves but longer than those of visible light.

Microwaves bent by the walls of this 1-centimeter-tall invisibility device skip the center area and come out the other side on their original paths as if nothing had been in the way.

David Schurig et al./Science

The scientists’ new “invisibility device” is the size of a drink coaster and shaped like a ring. The ring is made of a special material with unusual abilities. When microwaves strike the ring, very few bounce off it. Instead, they pass through the ring, which bends the waves all the way around until they reach the opposite side. The waves then return to their original paths.

To a detector set up to receive microwaves on the other side of the ring, it looks as if the waves never changed their paths—as if there were no object in the way! So, the ring is effectively invisible.

When the researchers put a small copper loop inside the ring, it, too, is nearly invisible.

However, the cloaking device and anything inside it do cast a pale shadow. And the device works only for microwaves, not for visible light or any other kind of electromagnetic radiation.

So, Harry Potter’s invisibility cloak doesn’t have any real competition yet.—C. Gramling

Going Deeper:

Weiss, Peter. 2006. Vanishing actor: Physicists unveil first invisibility cloak. Science News 170(Oct. 21):261. Available at http://www.sciencenews.org/articles/20061021/fob6.asp .

______. 2006. Out of sight. Science News 170(July 15):42-43. Available at http://www.sciencenews.org/articles/20060715/bob9.asp .

Peterson, Ivars. 2004. Invisible man. Science News for Kids (July 28). Available at http://www.sciencenewsforkids.org/articles/20040728/SciFiZone.asp .

Science project idea:
Making glass objects disappear.
www.exploratorium.edu/snacks/disappearing_glass_rods.html (Exploratorium).

A crocodile’s heart may help it digest large, bony meals.

U.S. Fish & Wildlife Service

Like mammal and bird hearts, a crocodile’s heart is a muscle that pumps blood. One side of the heart sends blood that is full of oxygen out to most of the body. The other side pulls blood back toward the lungs to give it an oxygen refill.

But crocodile (and alligator) hearts have an extra valve that mammal and bird hearts don’t have. The extra valve is a flap that the animal can close in order to keep blood from flowing toward the lungs. This means that the blood goes right back into the body instead.

Although scientists have known about the crocodile heart’s extra valve for many years, they haven’t known what it was for. Some scientists thought that it might help crocodiles and alligators stay underwater longer, making them better, more deadly hunters.

Like that of a crocodile, an alligator heart may send blood to the animal’s stomach to help with digestion.

Ginger L. Corbin, U.S. Fish & Wildlife Service

Now, scientists have a new idea about what a crocodile’s heart can do. By studying captive alligators, scientists discovered that the extra valve can reroute some of the blood normally pumped to its lungs to its stomach instead. This diversion lasts about the same amount of time that it takes an alligator to digest a big meal.

To see if the valve is really connected to digestion, the scientists used surgery to close the valve in some captive alligators but left it working in others. They then fed each alligator a meal of hamburger meat and an oxtail bone. Alligators with a working valve digested the tough meal quicker.

This X ray shows a bone in the stomach of an alligator. An alligator’s heart may help it digest this meal.

Colleen G. Farmer, University of Utah

Blood returning from the body to the heart has extra carbon dioxide. Carbon dioxide is also a building block of stomach acid, which helps digest food. So, when blood rich with carbon dioxide goes to the stomach instead of the lungs, it can aid digestion.

Whether it helps alligators and crocodiles pursue their underwater prey or helps them digest it, the heart’s special valve does seem to give these hunters a leg up on the competition.—C. Gramling

Going Deeper:

Harder, Ben. 2006. Quirky cardiology: Crocs’ hearts may aid their digestion. Science News 170(Oct. 21):260-261. Available at http://www.sciencenews.org/articles/20061021/fob5.asp .

Information about alligators and crocodiles can be found at www.sandiegozoo.org/animalbytes/t-crocodile.html (San Diego Zoo).

You can learn more about the American crocodile at www.kidsplanet.org/factsheets/american_crocodile.html (Defenders of Wildlife).

A swath of seafloor beneath the Pacific Ocean (outlined in orange) has little or no sediment. This area is about the size of the Mediterranean Sea.

E. Roell

The rocks that form Earth’s surface beneath the oceans are usually covered with a thick layer made up of sand or dirt and the skeletons of tiny ocean creatures called plankton.

Plankton are microscopic plants that spend their lives drifting in the ocean. When they die, their skeletons sink to the seafloor. Some parts of the oceans contain abundant plankton, and their skeletons can eventually form a very thick layer on the ocean floor.

But one patch of ocean floor is missing this layer entirely. The patch, called the South Pacific Bare Zone, is about the size of the Mediterranean Sea. It’s located thousands of miles east of New Zealand.

Scientists found the bare zone using equipment that can detect different kinds of rocks and soils. The measurements showed that there was very little sediment, or accumulated particles, in this region.

Scientists were surprised by their discovery. But they came up with several reasons why this particular area would lack sediment.

The waters in this part of the ocean have low levels of nutrients, so there’s little food for plankton. As a result, there aren’t large quantities of plankton to die, fall to the bottom, and build up into a thick layer of sediment. Any skeletons that do reach the bottom tend to dissolve.

The bare zone is also far from any continents, which are a big source of windblown dust and other particles that drop into the sea. And it’s far from any major ocean currents, so Antarctic icebergs carrying material scraped from that continent don’t pass over the bare zone and drop sediment.

Researchers are excited by the discovery of the Pacific’s bare zone because this may be the one place on Earth where they can directly study seafloor materials that are normally hidden by sediment.—C. Gramling

Going Deeper:

Perkins, Sid. 2006. Nearly naked: Large swath of Pacific lacks seafloor sediment. Science News 170(Oct. 14):246. Available at http://www.sciencenews.org/articles/20061014/fob7.asp .

Ramsayer, Kate. 2004. Deep drilling at sea. Science News for Kids (Sept. 8). Available at http://www.sciencenewsforkids.org/articles/20040908/Feature1.asp .

Scientists who spent years studying a colony of about 100 prairie dogs in Utah discovered that when it’s time to court females, males become too distracted to pay attention to anything else—including predators.

The Utah prairie dog is the rarest of five species of prairie dogs found in the United States.

iStockphoto

The mating season for Utah prairie dogs lasts only 17 days, and each female is ready to breed for only 5 hours once a year. This means that males don’t have much time to mate, so they tend to focus all their attention on breeding.

The researchers watched prairie dogs from sunup to sundown for several months each year for 10 years. When they arrived in 2005, they saw something new. A fox was hanging around trying to catch the prairie dogs.

Foxes are normally very shy around people. So, it’s unusual to catch sight of a fox hunting. This particular fox, however, must have gotten used to people, and the researchers had a front-row seat as it went after prairie dogs. The researchers also spied at least one goshawk—a bird that swoops out of the sky to snag prey—in the hunt.

In 4 months, the researchers observed these predators kill 26 prairie dogs. Many of the victims were adult males who were apparently too busy paying special attention to the females to avoid capture.

Predators often prey on the old and weak, the scientists say. But the prairie-dog study shows that, at certain times of the year, healthy adult males can be at risk, too.—C. Gramling

Going Deeper:

Milius, Susan. 2006. Courting costs: Male prairie dogs seem too busy mating to dodge predators. Science News 170(Oct. 14):245-246. Available at http://www.sciencenews.org/articles/20061014/fob6.asp .

You can learn more about Utah prairie dogs at www.r6.fws.gov/species/mammals/utprairiedog/ (U.S. Fish & Wildlife Service), www.prairiedogcoalition.org/map/utah-prairie-dog.shtml (Prairie Dog Coalition), or www.nps.gov/archive/brca/utah_prairiedog.html (National Park Service).

Scientists have now found that some spiders can also make silk in their feet, which may sometimes help them get a firmer grip on a surface.

A zebra tarantula can produce silk from its feet.

S. Niederegger and S. Gorb, Max Planck Society

Spiders are good at gripping walls with their legs. Thousands of little hairs on their feet make it possible. To test whether spiders also make these hairs wet to improve grip, scientists watched zebra tarantulas crawl up glass slides.

When they tilted a glass slide until it was almost vertical, the spider slipped a few millimeters before attaching itself again. The scientists were surprised to see little threads stretching from its feet to the slide. When they studied the spider’s feet under a special microscope, they found tiny silk-shooting spouts among the hairs.

This was a surprise because scientists had previously thought spiders only use special organs near their stomachs to make silk.

A zebra tarantula from Costa Rica.

S. Niederegger and S. Gorb, Max Planck Society

It’s possible that, a long time ago, feet were the first body parts of spiders to produce silk. Only later in their evolutionary history did spiders develop spinnerets on their abdomens to produce silk for webs.

If so, the researchers say, this could mean that the silk’s original purpose was to help spiders climb and stick, rather than to build homes or trap prey.—C. Gramling

Going Deeper:

Cunningham, Aimee. 2006. Silky feet. Science News 170(Oct. 7):238. Available at http://www.sciencenews.org/articles/20061007/note14.asp .

Jaffe, Eric. 2006. Not slippery when wet. Science News for Kids (June 14). Available at http://www.sciencenewsforkids.org/articles/20060614/Note2.asp .

Sohn, Emily. 2003. How a gecko defies gravity. Science News for Kids (Nov. 19). Available at http://www.sciencenewsforkids.org/articles/20031119/Feature1.asp .

LabZone
Spy on a Spider
http://www.sciencenewsforkids.org/articles/20040519/LZActivity.asp

Now, astronomers have given another dwarf planet an official name. Once known as Xena, the dwarf planet’s new name is Eris, after the Greek goddess of discord and strife. Eris’ moon also has a new name: Dysnomia, the Greek goddess of lawlessness.

In this artist’s illustration, the sun is a small spot (lower right), as seen from behind the newly named dwarf planet Eris. Eris’ moon, Dysnomia, is near the top middle.

Robert Hunt/IPAC, Caltech

Xena and its moon, once called Gabrielle, were originally named after a popular TV show about a warrior princess and her companion. The names were never meant to be permanent, however. But astronomers took a long time to decide what to call the objects officially, and the popular names began to stick.

Astronomer Mike Brown, who discovered both objects in 2005, gave them their temporary names and their new names. He thinks Eris is a fitting name for the new dwarf planet because astronomers have argued for so long over how to define a planet.

With Pluto’s demotion, there are now four known dwarf planets in the solar system: Pluto, Pluto’s moon Charon, asteroid Ceres, and Eris. Eris is the largest of these objects.

But the debate continues. Some scientists are now saying that Pluto should regain its status as a planet.—C. Gramling

Going Deeper:

Cowen, Ron. 2006. A discordant name for a dwarf planet. Science News 170(Oct. 7):237. Available at http://www.sciencenews.org/articles/20061007/note9.asp .

You can learn more about the naming of 2003 UB 313 at www.iau2006.org/mirror/www.iau.org/iau0605/index.html (International Astronomical Union).

Sohn, Emily. 2006. Pluto and the plutons. Science News for Kids (Aug. 23). Available at http://www.sciencenewsforkids.org/articles/20060823/Note3.asp .

______. 2006. Xena’s mysterious sparkle. Science News for Kids (April 19). Available at http://www.sciencenewsforkids.org/articles/20060419/Note2.asp .

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

SciFiZone
The Name’s the Thing
http://www.sciencenewsforkids.org/articles/20060906/SciFiZone.asp

Name the Eleventh Planet
http://www.sciencenewsforkids.org/articles/20040407/SciFiZone.asp

A seedling of a vine known as dodder attaches to a tomato plant.

Photo by Justin Runyon (courtesy of De Moraes and Mescher Labs)

When a dodder seed sprouts, it doesn’t grow roots to seek its own food. Instead, it grows a shoot that reaches out to other plants, tapping them for food. The baby vine needs to find a host within a week to survive. It then grows into a spaghetti tangle that can even ensnare more than one plant.

Also known as strangleweed and witches’ shoelaces, dodders are listed among the 10 worst weeds in the United States. They can cost farmers millions of dollars by stunting their crops.

To figure out how a type of dodder vine known to prefer tomato plants finds a victim, scientists placed dodder sprouts near several possible targets. These targets included pots of moist soil, little jars of dyed water that created colored lights, young tomato plants, and even a cup of perfume made from chemicals that tomato plants give off.

A dodder tangle steals food and water from a glasswort plant.

Photo by Collin Purrington (courtesy of De Moraes and Mescher Labs)

Seedlings grew toward the tomato plant. They also reached out toward the cup of tomato perfume. They tended not to grow toward the moist soil or colored water.

The scientists then used a different setup, hiding the targets in chambers connected to dodder sprouts only by curving pipes, so the vine could find them only by smell. Dodder sprouts still grew toward their favored targets.

The tendril of a young dodder plant stretches out to entwine a tomato seedling.

Photo by Justin Runyon (courtesy of De Moraes and Mescher Labs)

By placing dodder sprouts near different plants, the scientists found that the type of dodder that they were studying prefers tomatoes and a flower called impatiens. And when given a choice between tomato and wheat, vine seedlings grow toward tomato.

The researchers then tested seven of the ingredients that make up tomato perfume separately. Dodder sprouts were attracted to three of them.

One of these ingredients turns up in wheat perfume, but the wheat perfume also contains a substance that repels dodder sprouts. This chemical could offer farmers one way to fight the vine and save their crops.—C. Gramling

Going Deeper:

Milius, Susan. 2006. Scent stalking: Parasitic vine grows toward tomato odor. Science News 170(Sept. 30):214. Available at http://www.sciencenews.org/articles/20060930/fob7.asp .

To learn more about research on dodder vines and how they respond to smell, see live.psu.edu/story/19800 (Penn State University).

To see a QuickTime movie of a dodder shoot growing toward a tomato plant, click here.

For additional information about dodder, go to
www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7496.html and
plants.usda.gov/java/profile?symbol=CUPE3.

Science project ideas: Do all types of dodder vines rely on smell to find their hosts? How do various types of dodder vines differ in their preferences for plant hosts? Do any other parasitic plants find hosts by smell?

These brain-scan images reveal that certain areas of the brain (shown in color), as seen from different angles, are active while a study participant explores a virtual environment.

PLoS Biology

Recent studies have shown that the parts of the brain that we use to learn a task become active again during sleep. This activity, scientists suggest, could be the brain transferring memories from short-term to long-term storage (see “Memories Are Made with Sleep”).

But the brain doesn’t necessarily wait until the lights are out to begin processing those memories.

To find out how the brain handles memories during waking hours, scientists gave 15 volunteers two tasks, each requiring different parts of the brain to learn. In one task, the subjects learned how to navigate a virtual town and then searched the town for an object. In the second task, they learned to predict where a sequence of dots would appear on a screen.

Using a special machine, the researchers scanned the volunteers’ brains right before and right after the tasks. They compared the two images to see whether the regions of the brain involved in learning the task were still active even after the task was completed.

After a break, the scientists took a third image of each participant’s brain. They wanted to determine whether these regions in the brain continued to be active after more time had passed.

They discovered that, for at least an hour after learning a task, the brain stays active. It appears to continue processing the new information.

Furthermore, the images showed that distracting the subjects doesn’t affect their ability to store memories. The processing continues even when they’re thinking about or doing other things.

Some scientists say this could mean that sleep isn’t essential for storing memories. Others disagree. Until that’s settled, it’s probably still better to be on the safe side, getting plenty of sleep.—C. Gramling

Going Deeper:

Gramling, Carolyn. 2006. Awake and learning: Memory storage begins before bedtime. Science News 169(April 1):197. Available at http://www.sciencenews.org/articles/20060401/fob5.asp .

Sohn, Emily. 2004. Sleep to remember places and routes. Science News for Kids (Nov. 10). Available at http://www.sciencenewsforkids.org/articles/20041110/Note3.asp .

______. 2003. Memories are made with sleep. Science News for Kids (Oct. 15). Available at http://www.sciencenewsforkids.org/articles/20031015/Note2.asp .