Auroras are eerie, undulating bands and sheets of light that, on Earth, are formed from interactions between charged particles streaming out from the Sun, called the solar wind, and atoms and molecules in the upper layers of the planet's atmosphere where the magnetosphere is weak.

In the Northern Hemisphere, these light displays are known as aurora borealises or northern lights; in the south, they're called aurora australises.

The magnetosphere is an invisible shield that protects Earth from the solar wind and other types of radiation that could otherwise fry satellites and sensitive electronics. The shield is made up of magnetic field lines that radiate out from the poles and is shaped like a donut, with Earth in the middle.

Auroras on Jupiter are up to a hundred times brighter than those on Earth, but until now, scientists had thought the solar wind had very little to do with these Jovian light shows. Instead, it was believed that they were created from material spewed by Jupiter's volcanic moon Io being churned about by the planet's rapidly spinning magnetosphere.

Another way to make auroras

Io is the most volcanically active body in the solar system. The moon expels a stream of sulfur and sulfur dioxide into space at the rate of about one ton per second, forming a large gas cloud that trails behind the moon as it orbits Jupiter.

The inner portions of Jupiter's rotating magnetosphere contain a hot gas-like mixture of charged particles and electrons called plasma. When Io's ejected material interacts with this plasma, it gets ionized and becomes plasma itself.

"As soon as the material gets turned into plasma, it suddenly feels Jupiter's magnetic field which is spinning a lot faster," explained Jonathan Nichols at the University of Leicester.

This process is responsible for some of the luminous auroras seen on Jupiter, but not all. Nichols and colleagues recently compared ultraviolet images of Jupiter's auroras taken by NASA's Hubble Space Telescope with simultaneous measurements collected by Cassini of the solar wind during the spacecraft's flyby of the giant planet in December 2000 and January 2001.

They found a strong correlation between the strength of the solar wind and the behavior of auroras at Jupiter's poles. This suggests that Earth-like processes are responsible for some of the planet's auroras, Nichols said.

Nichols will present the team's findings at the Royal Astronomical Society's National Astronomy Meeting on April 4.

At the same meeting, Sarah Badman, also from the University of Leicester, will present results showing that the solar wind also plays a role in the light shows on Saturn. Using a similar combination of Hubble and Cassini information as Nichols' team, Badman found that Saturnian auroras are caused by the explosive release of solar wind energy collected over time and stored in the planet's magnetic field.

Solving an old mystery

The new results from Nichols' team could help explain why Jupiter is significantly warmer than it should be, a mystery that has puzzled scientists for decades.

"We know that the Earth is the temperature it is because of its distance from the Sun, and Mars is colder and Jupiter should be even colder," Nichols told SPACE.com. "But Jupiter is a bit warmer than predicted. It gives out more energy than it receives in terms of solar radiation."

Nichols thinks the energy imparted to the planet by the solar wind is partly responsible for this imbalance.

"That's an energy source which hasn't been taken into account by people when they're trying to calculate what Jupiter's temperature should be," he said.

The findings help explain one mystery, but they also raise another one. Jupiter's auroras appear as concentric ovals near the planet's poles. The researchers found that Jupiter's outer oval auroras - which shouldn't be affected by the solar wind - got brighter the stronger the solar wind blew, which is completely opposite from what is predicted by theory.

"The main aurora oval on Jupiter we think should dim when the solar wind blows harder, but what we see is that actually gets brighter, which is totally counter intuitive and we still don't know why," Nichols said.

The teams are respectively led by Alcatel Alenia Space, Qinetiq of Britain and EADS Astrium, each of which has long experience in European space projects, ESA said in a press release on Monday.

ESA, helped by an independent panel of experts, will assess their submissions in October, and the outcome will be made public in 2007.

The Don Quijote mission will comprise two spacecraft.

One of them, called Hidalgo, will smash into the asteroid at relatively high speed, while a second one, Sancho, will arrive earlier at the same asteroid to measure the variation on the asteroid's orbital parameters after the impact.

The risk of an asteroid collision with Earth is extremely remote.

But if such an event were to occur, and the rock were big, the immediate devastation could be continent-wide and there could be lasting changes to the planet's weather system.

The long reign of the dinosaurs is believed to have come to an abrupt end 65 million years ago when an asteroid or comet smashed into modern-day Mexico.

The collision kicked up so much dust that heat and light from the Sun were diminished, destroying much of Earth's vegetation and the larger species of land animals that depended on it.

Deflection is considered a safer bet than blowing up a dangerous asteroid with nuclear bombs. An explosion would break the asteroid into chunks, with the risk these pieces could hit Earth in turn.

The U.S. Geological Survey didn't register anything in the immediate area.

"We felt something shake our building," said Lt. Jim Bolwerk at the sheriff's communication center in Kearny Mesa, where dispatchers immediately fielded phone calls from concerned residents.

Cpl. K.T. Tran, spokesman for Camp Pendleton north of Oceanside, said he didn't feel any shaking in his building. The base started training at 6 a.m. with 81mm mortars that can sometimes be heard up to 50 miles away.

"I felt it at my home, University City," said forecaster Philip Gonsalves of the National Weather Service. "All that happened was that my windows rattled. There's a lot of speculation (about the cause), but that's all it is."

The finding supports a growing consensus that birds and humans make sound in much the same way -- although it is presumed these processes evolved independently of each other in birds and hominids.

In 2004, Suthers reported in the journal Current Biology that monk parakeets use their tongues to shape sound. Other studies have implicated beaks, especially beak gape, in shaping the sound that birds produce. Similarly, humans move their tongues, alter the shape of their upper vocal tracts, and change the shape of their mouths when they sing, laugh, talk and groan.

"The bird's vocal tract, like the human vocal tract in speech, acts as a resonance filter that can control the sound coming from the mouth," Suthers said. "Beak movements during song also contribute to this filter, but are not as important as changes in the size of the internal vocal tract. Human sopranos use the same technique as the cardinal to increase the loudness of very high notes so they can be heard above the orchestra."

That birds' throats vibrate when they sing will come as no surprise to birdwatchers. The effect of these oscillations on the birds' sound production, however, was unknown.

The acoustics of sound-making are complicated. Most tones produced in nature are accompanied by a complex series of higher-pitched, quieter tones called overtones. When the loudness of these overtones is high, the tone sounds more complex. Birds can control the loudness of overtones to increase the tonal purity of their song. Humans use a similar technique to produce different vowel sounds of speech by altering the shapes of their throats, the positions of their tongues and the wideness of their mouths. The PNAS study reveals yet another parallel between birdsong production and human speech.

"At low frequencies, the bird increases the volume of its oropharyngeal cavity and even expands the top of its esophagus," Suthers said. "These air-filled structures form a single cavity with a resonant frequency that matches the main frequency of the song. This amplifies the fundamental frequency and suppresses overtones."

Suthers, biologist Tobias Riede, who is now at the National Center for Voice and Speech (Colorado), Purdue University veterinary scientist William Blevins, and Australian National University acoustic physicist Neville Fletcher used X-ray cinematography to observe and measure the shape and total volume (three-dimensional space, not loudness) of a cardinal's throat as it spontaneously sang. Explanatory video can be downloaded here - small file size or full size.:

The scientists determined that note changes in birdsong are accompanied by controlled changes in the volume of the upper esophagus as well as the positions of the bird's larynx and hyoid skeleton (a U-shaped bone formation in the bird's throat). They also found that the volume of the upper esophagus goes up whenever the main tone produced by the bird goes down, and vice versa. These alterations of shape have the effect of increasing the main tone and suppressing the loudness of overtones.

The percentage of American men, teens and children who are overweight increased significantly between 1999 and 2004, the study found.

However, the percentage of women in the U.S. who are overweight remained steady over the same time period.

The U.S. Centers for Disease Control reported the new findings in this week's issue of the Journal of the American Medical Association.

The data, from the CDC's national health and nutrition examination survey, consists of height and weight measurements from nearly 4,000 children, aged two to 19, and about 4,400 adults aged 20 and older.

The study's lead author, epidemiologist Cynthia Ogden, said actual measurements are much better than telephone surveys for this kind of data, as men tend to overestimate their height while heavy people underestimate their weight.

The survey found that the percentage of men who are overweight rose to 71 per cent in 2003-04 from 67 per cent in 1999-2000. The proportion of men who are obese rose from 27.5 per cent to 31 per cent.

For women, the proportion of the population who are overweight and obese remained steady over the same time period, at 62 per cent and 33 per cent respectively.

Among adults, the CDC says a person is overweight if his body mass index (BMI) is 25 or higher, and obese if it is 30 or higher.

The percentage of boys aged two to 19 who were obese rose to more than 18 per cent from 14 per cent in 1999-2000. For girls, the percentage rose to 16 per cent from 14 per cent.

For children, obesity was defined as having a BMI higher than 95 per cent of children the same age and sex, based on benchmark data collected between 1963 and 1994.

A similar Canadian survey recently showed that the proportion of obese Canadians is also on the rise.

Dr. William Dietz, of the CDC's divison of nutrition and physical activity, said it is good news that the proportion of overweight women is levelling off, saying it shows that women are recognizing obesity as a health threat.

However, Kelly Brownell of the Center for Eating and Weight Disorders at Yale University said the bad news about obesity in children in the survey outweighs the good.

The 5-inch-long shell exploded Monday while Robert Colla was teaching 20 to 25 students at an adult education class.

Part of Colla's right hand was severed and he suffered severe burns and minor shrapnel wounds to his forearms and torso, fire Capt. Tom Weinell said. No one else was injured. He was reported in stable condition at a hospital.

The teacher slammed the shell down in an attempt to kill something that was buzzing or crawling across the desk, said Fire Marshal Glen Albright.

Colla found the 40 mm round while hunting years ago and "obviously he didn't think the round was live," said Dennis Huston, who teaches computer design alongside Colla.