"There have been previous suggestions that RCW 86 is the remains of the supernova from 185 A.D.," said Jacco Vink of University of Utrecht, the Netherlands, and lead author of the study. "These new X-ray data greatly strengthen the case."

When a massive star runs out of fuel, it collapses on itself, creating a supernova that can outshine an entire galaxy. The intense explosion hurls the outer layers of the star into space and produces powerful shock waves. The remains of the star and the material it encounters are heated to millions of degrees and can emit intense X-ray radiation for thousands of years.

In their stellar forensic work, Vink and colleagues studied the debris in RCW 86 to estimate when its progenitor star originally exploded. They calculated how quickly the shocked, or energized, shell is moving in RCW 86, by studying one part of the remnant. They combined this expansion velocity with the size of the remnant and a basic understanding of how supernovas expand to estimate the age of RCW 86.

"Our new calculations tell us the remnant is about 2,000 years old," said Aya Bamba, a coauthor from the Institute of Physical and Chemical Research (RIKEN), Japan. "Previously astronomers had estimated an age of 10,000 years."

The younger age for RCW 86 may explain an astronomical event observed almost 2000 years ago. In 185 AD, Chinese astronomers (and possibly the Romans) recorded the appearance of a new bright star. The Chinese noted that it sparkled like a star and did not appear to move in the sky, arguing against it being a comet. Also, the observers noticed that the star took about eight months to fade, consistent with modern observations of supernovas.

RCW 86 had previously been suggested as the remnant from the 185 AD event, based on the historical records of the object's position. However, uncertainties about the age provided significant doubt about the association.

"Before this work I had doubts myself about the link, but our study indicates that the age of RCW 86 matches that of the oldest known supernova explosion in recorded history," said Vink. "Astronomers are used to referencing results from 5 or 10 years ago, so it's remarkable that we can build upon work from nearly 2000 years ago."

The smaller age estimate for the remnant follows directly from a higher expansion velocity. By examining the energy distribution of the X-rays, a technique known as spectroscopy, the team found most of the X-ray emission was caused by high-energy electrons moving through a magnetic field. This is a well-known process that normally gives rise to low-energy radio emission. However, only very high shock velocities can accelerate the electrons to such high energies that X-ray radiation is emitted.

"The energies reached in this supernova remnant are extremely high," said Andrei Bykov, another team member from the Ioffe Institute, St. Peterburg, Russia. "In fact, the particle energies are greater than what can be achieved by the most modern particle accelerators."

The difference in age estimates for RCW 86 is due to differences in expansion velocities measured for the supernova remnant. The authors speculate that these variations arise because RCW 86 is expanding into an irregular bubble blown by a wind from the progenitor star before it exploded. In some directions, the shock wave has encountered a dense region outside the bubble and slowed down, whereas in other regions the shock remains inside the bubble and is still moving rapidly. These regions give the most accurate estimate of the age.

The study describing these results appeared in the Sepember 1 issue of The Astrophysical Journal Letters. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the agency's Science Mission Directorate. The Smithsonian Astrophysical Observatory, Cambridge, Mass., controls science and flight operations from the Chandra X-ray Center, Cambridge, Mass. XMM-Newton is an European Space Agency science mission managed at the European Space Research and Technology Centre, Noordwijk, the Netherlands for the Directorate of the Scientific Programme.

Atlantis commander Brent Jett described the newest objects as two rings and a piece of fabric. He told mission control the first object, about 30 metres from the shuttle, was "a reflective cloth or a mechanic looking-cloth ... It's not a solid metal structure."

"It doesn't look like anything I've seen outside the shuttle," Jett said.

He suggested the three objects might have come from the Russian Soyuz vehicle, which docked with the international space station early Wednesday.

The astronauts are continuing to inspect the shuttle's heat shield for damage. They're using a boom equipped with cameras and sensors, attached to the craft's robotic arm.

Atlantis flight director Steve Stitch said all appears normal and, "so far, the inspections are going well."

Stitch said it's common to see pieces of floating debris when astronauts open the payload bay doors at the beginning of the mission, although "it is a little bit unusual to maybe see objects this late in the mission."

Stitch said there are two windows of opportunity for the shuttle to land on Thursday: 6:21 a.m. ET and 7:51 a.m. ET.

"The forecast for tomorrow looks very good," he said.

Col. Chris Hadfield, a Canadian who took part in two previous shuttle missions, said objects floating in the blackness of space stand out when they catch the sunlight.

"It's a little bit the case of the more you look at something, the more you see," he said, adding that he'd seen space debris during both of his missions.

Hadfield said the current mission's astronauts are confident in the health of the shuttle, and are pleased to have an extra day in space.

"We're all very sure this little piece of stuff floating is just normal operations for a vehicle as big and complex and multi-faceted as the shuttle," he said.

Figures released by Zhejiang and Guangdong provinces in advance of the publication of national figures by the Ministry of Health next week show alarming rises in the number of birth defects.

In Zhejiang, the incidence of babies with birth defects was 1.15 percent in 2003 -- the year compulsory pre-marital health checks were scrapped -- rising to 1.33 percent in 2004 and 1.47 percent last year.

About 480,000 babies are born in Zhejiang each year, which means about 7,200 babies were born with defects in 2005.

In the southern province of Guangdong, the incidence has risen from 0.96 percent ten years ago to 2.12 percent today.

In Shanghai, birth defects have been reported as the top killer of babies for the past 10 years.

Cleft palette, neural tube defects, hyperdactylia (excessive numbers of fingers or toes), congenital heart disease and hydrocephalus (water on the brain) are the top five birth defects among Chinese babies.

Experts said hereditary diseases, viral infections, environmental pollution, unhealthy lifestyles and poor nutrition were among the main known causes.

Duan Tao, deputy head of the No. 1 Maternity and Children Care Center affiliated to the Tongji University in Shanghai, said the treatment of chronic diseases, the prohibition of marriage between close relatives and discouraging pregnant women from drinking alcohol and smoking could help reduce birth defects.

Pre-marital tests could also prevent the transmission of hereditary diseases and pre-pregnancy health checks could detect viruses that caused birth defects, said Gu Peibao, an obstetrician at Zhejiang Maternal and Children Health Hospital.

"Some would-be parents pay more attention to smoking and drinking and even avoid living in newly-renovated apartments, but forget or ignore pre-marital tests," Gu said.

The number of would-be couples undergoing the checks has dropped drastically since they were made optional in 2003, after previously being a legal prerequisite for obtaining a marriage license.

Pan Guiyu, deputy director of the State Population and Family Planning Commission, called for the resumption of compulsory pre-marital tests, saying their cancellation in 2003 was a major cause of the rise in birth detects and could affect the "quality" of the population.

To reverse the situation, some local health authorities have begun providing free pre-marital tests to encourage more people to go through the health check, but the outcome was not promising.

However, some experts argued it was uncertain if lack of pre-marital tests had significantly contributed to the rising incidence of birth defects.

"Currently we have no concise figures to support this claim, so the resumption of compulsory pre-marital tests needs more consideration," said Ma Huaide, professor of the China University of Political Science and Law, in an interview with major Chinese Internet portal Sina.com.

According to professor Wang Yifei, of the Shanghai Jiaotong University, 50 to 60 percent of birth defects in humans occurred for no obvious reason.

Chromosomal abnormality contributed to six to seven percent, genetic mutation contributed seven to eight percent, environmental factors seven to 10 percent and the comprehensive effect of hereditary and environmental factors 20 to 25 percent, according to a research revealed by Wang.

He called for the establishment of a monitoring system on birth defects in China linked with international network, while stepping up research on hereditary and environmental factors.

China has about one million to 1.2 million babies born with defects each year, accounting for four to six percent of births, latest official figures show.

Birth defects, also called congenital anomalies, are a major cause of infant mortality and childhood morbidity, affecting two to three percent of all babies around the globe, according to the World Health Organization.

In countries where infant mortality has been reduced to less than 50 per 1,000 births, birth defects are emerging as the most common cause of neonatal deaths. These deaths account for 30 to 50 percent of perinatal mortality and 20 to 30 percent of infant mortality, according to figures released at the second International Conference on Birth Defects and Disabilities in the Developing World held in September 2005.

Reducing mortality by two-thirds among children under five has been set by the United Nations as one of the eight Millennium Development Goals, all 191 U.N. member nations have agreed to meet this goal by 2015.

According to Coyle, 10 percent to 15 percent of lung cancer cases occur among nonsmokers. One possible explanation: Inhalation of air pollution, especially fine particulate matter -- bits of metal that are too small to be seen with the naked eye but can still enter the lungs.

Mining, smelting and petroleum production all produce this type of pollution, Coyle said, as can motor vehicle exhaust.

But while air pollution has been directly linked to respiratory disorders and heart disease, its role in lung cancer is still under debate.

In the new study, Coyle and her colleagues tried to determine if exposure to metallic bits of air pollution was associated with higher levels of lung cancer. To find the answer, they compared lung cancer rates in 254 Texas counties from 1995-2000 to federal reports that companies filed when they released pollution between 1988 and 2000.

The researchers found an "association" between various types of lung cancer and releases of zinc, chromium and copper. When the study results were adjusted to take into account the effects of factors such as gender and race, zinc was still linked to lung cancer.

The findings of the federally funded study appear in the September issue of the Journal of Thoracic Oncology.

The study doesn't say how much more likely it is for people to develop lung cancer if they're exposed to higher levels of the pollutants.

Also, the role of smoking is unclear because the county-by-county statistics didn't reveal whether the individual lung cancer patients smoked. However, Coyle said smoking levels were consistent across the counties studied.

More research needs to be done to confirm the results and "determine who is at the greatest risk, given this exposure," Coyle said.

Dr. Michael Thun, head of epidemiologic research for the
American Cancer Society, suggested that the value of the study is limited because it didn't take into account smoking by the lung cancer patients.

"It's clear that smoking is such a powerful cause of lung cancer that it's very difficult in wealthy countries to identify any separate contributions from air pollution," Thun said. "It's extremely hard to measure, and this study doesn't solve that problem."

Vast patches of ice-free sea stretched north of Svalbard, an archipelago lying midway between Norway and the North Ple, and extended deep into the Russian Arctic, all the way to the North Pole, the agency said in a press release.

"This situation is unlike anything observed in previous record low-ice seasons," said Mark Drinkwater of ESA's Oceans/Ice Unit.

"It is highly imaginable that a ship could have passed from Spitzbergen or Northern Siberia through what is normally pack ice to reach the North Pole without difficulty."

Spitzbergen is one of the Svalbard islands, which are Norwegian.

Drinkwater added: "If this anomaly continues, the Northeast Passage, or 'Northern Sea Route' between Europe and Asia will be open over longer intervals of time, and it is conceivable we might see attempts at sailing around the world directly across the summer Arctic Ocean within the next 10 to 20 years."

The images are for late summer. In the last weeks, what was open water has begun to freeze, as the autumn air temperatures over the Arctic begin to fall, ESA said.

Regular satellite monitoring over the last 25 years shows that the northern polar ice cover has shrunk and thinned as global temperatures have risen.

But this year's images are unprecedented, and fierce storms that fragmented and scattered already thin pack ice may be to blame, the scientists believe.

The images were released less than a week after a paper, published in the US journal Science, found that year-round sea ice in the Arctic shrank by one seventh between 2004 and 2005.

Loss of sea ice does not affect global sea levels. Ice that floats in the water displaces its own volume.

However ice that is on land, as an icesheet, glacier or permanent snowcap, adds to sea level when it melts and runs off.

Retreating ice cover also creates a vicious circle, adding to the warming caused by greenhouse gases -- carbon emissions, mainly from fossil fuels, that trap the Sun's heat.

Ice, being white, reflects the Sun's rays. Less ice therefore means the sea warms, which in turn accelerates the shrinkage.

The shrinkage of the Arctic icecap is viewed with alarm by scientists, as it appears to perturb important ocean currents elsewhere, notably the Gulf Stream, which gives western Europe its balmy climate.

It also threaten animals such as polar bears and seals that depend on ice.

There are geopolitical implications, too, as Canada, Russia and the United States jockey to claim rights over transpolar passages that open up within their newly ice-free waters.