The idea that comets delivered the chemical "seeds" for life to the early Earth has been given a big boost.

Scientists studying the tiny grains of material recovered from Comet Wild-2 by Nasa's Stardust mission have found large, complex carbon-rich molecules.

They are of the type that could have been important precursor components of the initial reactions that gave rise to the planet's biochemistry.

The first full analysis of the Wild-2 grains is reported in Science magazine.

At home: AIDS now threatens tens of thousands of African-Americans, many of them women, in big cities and small towns alike. A community in peril tries to save itself.

A sharp drop in breast cancer cases in 2003 has many researchers pointing to the fact that millions of women quit hormone replacement therapy in 2002.

But others have doubts that quitting HRT could alone produce such a steep drop.

The 7 percent drop in breast cancer cases between 2002 and 2003 means about 14,000 fewer women in the United States were diagnosed with the disease. Most of these women were between 50 and 69 years old.

"It's very, very compelling that this is not random variability, that there is something very clear and dramatic that happened," said Dr. Donald Berry, professor and chairman of biostatistics at the M.D. Anderson Cancer Center, during an interview with ABC News correspondent John McKenzie.

McKenzie also talked to Dr. Eric Winer of the Dana Farber Cancer Institute, who said, "Any downward trend would be important. But this drop, and a drop this size in a couple of years, is really very major news."

The drop is significant in that it could be the single largest year-on-year reduction in new breast cancer cases ever recorded.

"It is biologically plausible, and there is no other glaring change in public health to explain the change," said Dr. Clifford Hudis, chief of the Breast Cancer Medicine Service at Memorial Sloan-Kettering Cancer Center in New York. "This is more evidence that HRT is risky in terms of breast cancer."

According to the "Strange Matter Hypothesis," which gained popularity in the paranormal 1980's, nuclear matter, too, can be strange. The hypothesis suggests that small conglomerations of quarks, the infinitesimally tiny particles that attract by a strong nuclear force to form neutrons and protons in atoms, are the true ground state of matter. The theory has captivated particle physicists worldwide, including one of Washington University's own.

Mark Alford, Ph.D., Washington University in St. Louis assistant professor of physics in Arts & Sciences, and collaborators from MIT and the Lawrence Berkeley National Laboratory and Los Alamos National Laboratory, have used mathematical modeling to discover some properties of theoretical "strange stars," composed entirely of quark matter. Alford and his colleagues have found that under the right conditions the surface of a strange star could fragment into blobs of quark material called "strangelets," forming a rigid halo that contradicts traditional strange star models. This means that collapsed stars' nuclear leftovers, like the famously resplendent Crab Nebula, could be stranger than physicists think.

Alford and his colleagues recently published their findings in Physical Review D 73, 114016 (2006). The standard account of the dramatic death of a heavy star is that, after exploding in a supernova that rivals a whole galaxy in brightness, what is left is a "neutron star," a profoundly dense remnant, made mostly of neutrons, with a mass one and a half times that of our sun, crammed into an area with the radius of Saint Louis.

A strange star is an alternate ending of this story. If the Strange Matter Hypothesis is correct, then what is left behind is not a neutron star but an even denser strange star, made of quark matter rather than neutrons. And until recently, physicists thought that the two presented very different faces to the world.

A neutron star has a complicated multilayered surface. According to a description by M. Coleman Miller, Ph.D., of the University of Maryland, the deeper portions of the crust have voids that can be likened to Swiss cheese, overlaid by regions with sheets like lasagna, rods like spaghetti, and finally blobs like sprinklings of meatballs on the outside.

A strange star, on the other hand, was generally assumed to have a much simpler surface, consisting of a sharp interface between strange matter and the vacuum of surrounding space.

"A sharp interface between quark matter and the vacuum would have very different properties from the surface of a neutron star," noted Alford. But couldn't strange stars also have complicated surfaces? And if they did, could we even tell neutron stars and strange stars apart?

Kaleidoscopic aura of matter

Earlier this year, Alford's colleagues concocted a radical proposal. If blobs of quark matter (strangelets) have the right properties, maybe the strange star crust is something more like a kaleidoscopic aura of matter than a melon rind. "The idea was that the surface of a quark star might be as complicated as that of a neutron star, with a sort of crystalline halo or crust of strangelets," Alford explained. "If strangelets exist in reality, they will have a preferred size. If small strangelets are preferable, then big ones will split up into smaller ones. Conversely, if big strangelets are more stable, then small ones could fuse with other small ones--if they happened to bump in to each other--to make big ones."

If strangelets prefer to be big, then the strange star's surface will be the conventional simple sharp interface, with particles fused into the main body of the star. But if strangelets prefer to be small, then the surface will evaporate small strangelets to form a crystalline aura of strangelets floating in a sea of electrons.

His colleagues found that if surface tension along the interface and electrical forces within the charge distribution were neglected, then strangelets prefer to be small, and the strange star's surface indeed fragments into strangelets.

To follow, Alford joined the researchers in a more definitive investigation, addressing key parameters like surface tension and electrical forces that were neglected in the original study. Their results show that as long as the surface tension is below a low critical value, the large strangelets are indeed unstable to fragmentation and strange stars naturally come with complex strangelet crusts, analogous to those of neutron stars.

Their results will fuel the ongoing debate among astrophysicists about the nature and existence of strange stars. "A strange star believer would say: See, they showed that if the quark matter surface tension was low, then a strange star would have this strangelet crust, so perhaps some of the objects we think are neutron stars could actually be strange stars," Alford explained. "A strange star skeptic would say: Oh well, but the surface tension would have to be absurdly low for that to happen. These results basically show that for any reasonable value of the surface tension there is no crust, and strange stars are completely different."

Both conclusions are valid.

The strange star theory has its staunch defenders, but most physicists think it's merely an interesting, though improbable idea. But Alford and his colleagues are keeping its possibility afloat.

"There is still enough doubt about our understanding of these things," he said, "to leave room for speculation that there may be strange stars out there."

More than a decade of searching for factors that make the common parasite Toxoplasma gondii dangerous to humans has pinned 90 percent of the blame on just one of the parasite's approximately 6,000 genes.

The finding, reported in this week's issue of Science by researchers at Washington University School of Medicine in St. Louis and elsewhere, should make it easier to identify the parasite's most virulent strains and treat them. The results suggest that when a more harmful strain of T. gondii appears, approximately 90 percent of the time it will have a different form of the virulence gene than that found in the more benign strains of the parasite.

Working at the frontier between chemistry and physics, the University of Nebraska-Lincoln's Xiao Cheng Zeng usually finds his reward in discovering the unexpected through computer modeling.

Zeng and his colleagues regularly find new and often unanticipated behaviors of matter in extreme environments, and those discoveries have been published several times in major international scientific journals. Their findings, though, have been so far ahead of existing technology that their immediate practical impact was essentially nil -- until now.

Breast cancer could be sexually transmitted, says a researcher who has found the same virus that causes cervical cancer in breast cancer tumours from Australian women.

Emeritus Professor James Lawson of the University of New South Wales and colleagues have found the same form of the human papillomavirus (HPV) associated with cervical cancer in almost half the breast tumour samples they tested.

It's the first study of its kind in Australia, although international studies have also found cervical cancer-related HPV in breast cancer cells.

WASHINGTON - The Bush administration is clamping down on scientists at the U.S. Geological Survey, the latest agency subjected to controls on research that might go against official policy.

New rules require screening of all facts and interpretations by agency scientists who study everything from caribou mating to global warming. The rules apply to all scientific papers and other public documents, even minor reports or prepared talks, according to documents obtained by The Associated Press.

Top officials at the Interior Department's scientific arm say the rules only standardize what scientists must do to ensure the quality of their work and give a heads-up to the agency's public relations staff.

Some 10,000 US researchers have signed a statement protesting about political interference in the scientific process.

The statement, which includes the backing of 52 Nobel Laureates, demands a restoration of scientific integrity in government policy.

According to the American Union of Concerned Scientists, data is being misrepresented for political reasons.

It claims scientists working for federal agencies have been asked to change data to fit policy initiatives.