Tuesday, September 22, 2009

WILL KEPLER FIND HABITABLE MOONS?

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Since the launch of the NASA Kepler Mission earlier this year, astronomers have been keenly awaiting the first detection of an Earth-like planet around another star. Now, in an echo of science fiction movies a team of scientists led by Dr David Kipping of University College London thinks that they may even find habitable ‘exomoons’ too. The new results will appear in a paper in Monthly Notices of the Royal Astronomical Society.

Kepler’s primary mission is to monitor thousands of stars looking for characteristic dips in their brightness as orbiting planets pass in front of them in so-called ‘transit’ events. The orbiting observatory should be able to time these transits to an extremely high accuracy.

Dr Kipping has already devised a method for detecting exomoons but no-one was sure whether it could really be used with current technology. He and his team have now modelled the properties of the instruments on Kepler, simulating the expected signal strength that a habitable moon would generate. An exomoon’s gravity tugs on the planet it orbits, making the planet wobble during its orbit around its host star. The resulting changes in the position and velocity of the planet should be detectable by Kepler through accurate timing of the transits.

The scientists considered a wide range of possible planetary systems and found that a fluffy Saturn-like planet (the ringed world is extremely low in mass for its size) gives the best possible chance for detecting a moon, rather than a denser Jupiter-like world. This is because planets like Saturn are large – blocking out a lot of light as they pass in front of their star – but very light, meaning they will wobble much more than a heavy planet.

If the Saturn-like planet is at the right distance from its star, then the temperature will allow liquid water to be stable on any sufficiently large moons in orbit around it and these could then be habitable.

The team found that habitable exomoons down to 0.2 times the mass of the Earth are readily detectable with Kepler. Potentially the observatory could look for Earth-mass habitable moons around 25,000 stars up to 500 light-years away from the Sun. In the whole sky, there should be millions of stars which could be surveyed for habitable exomoons with present technology.

Whether or not such bodies are common in the Galaxy is unknown but astronomers now have the tools and the methodology to find out.

Dr Kipping says, "For the first time, we have demonstrated that potentially habitable moons up to hundreds of light years away may be detected with current instrumentation"

‘As we ran the simulations, even we were surprised that moons as small as one-fifth of the Earth's mass could be spotted.

‘It seems probable that many thousands, possibly millions, of habitable exomoons exist in the Galaxy and now we can start to look for them."

(Photo: Dan Durda)

Royal Astronomical Society

A VIRAL CAUSE OF PROSTATE CANCER?

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In a finding with potentially major implications for identifying a viral cause of prostate cancer, researchers at the University of Utah and Columbia University medical schools have reported that a type of virus known to cause leukemia and sarcomas in animals has been found for the first time in malignant human prostate cancer cells.

If further investigation proves the virus, XMRV (Xenotropic murine leukemia virus-related virus), causes prostate cancer in people, it would open opportunities for developing diagnostic tests, vaccines, and therapies for treating the cancer, according to the study published Sept. 7 online in the Proceedings of the National Academy of Sciences. Prostate cancer is expected to strike nearly 200,000 U.S. males this year, making it the second most common form of cancer, outside of skin cancers, among men.

"We found that XMRV was present in 27 percent of prostate cancers we examined and that it was associated with more aggressive tumors," said Ila R. Singh, M.D., Ph.D., associate professor of pathology at University of Utah and the study's senior author. "We still don't know that this virus causes cancer in people, but that is an important question we're going to investigate."

Singh, also a member of the U of U's Huntsman Cancer Institute and associate medical director at ARUP Laboratories, moved to Utah from Columbia University Medical Center in 2008, where she began this research. She remains an adjunct faculty member at Columbia.

Along with providing the first proof that XMRV is present in malignant cells, the study also confirmed that XMRV is a gammaretrovirus, a simple retrovirus first isolated from prostate cancers in 2006 by researchers at the University of California, San Francisco (UCSF), and the Cleveland Clinic. Gammaretroviruses are known to cause cancer in animals, but have not been shown to do so in humans. The UCSF study did not examine benign (non-malignant) prostate tissues, so could not link XMRV to prostate cancer. They also did not find the virus in malignant cells.

Singh and her fellow researchers examined more than 200 human prostate cancers, and compared them to more than 100 non-cancerous prostate tissues. They found 27 percent of the cancers contained XMRV, compared to only 6 percent of the benign tissues. The viral proteins were found almost exclusively in malignant prostatic cells, suggesting that XMRV infection may be directly linked to the formation of tumors.

Retroviruses insert a DNA copy of their genome into the chromosomes of the cells they infect. Such an insertion sometimes occurs adjacent to a gene that regulates cell growth, disrupting normal cell growth, resulting in more rapid proliferation of such a cell, which eventually develops into a cancer. This mechanism of carcinogenesis is followed by gammaretroviruses in general. Singh is currently examining if a similar mechanism might be involved with XMRV and prostate cancer.

In another important finding of the study, Singh and her colleagues also showed that susceptibility to XMRV infection is not enhanced by a genetic mutation, as was previously reported. If XMRV were caused by the mutation, only the 10 percent of the population who carry the mutated gene would be at risk for infection with virus. But Singh found no connection between XMRV and the mutation, meaning the risk for infection may extend to the population at large.

While the study answers important questions about XMRV, it also raises a number of other questions, such as whether the virus infects women, is sexually transmitted, how prevalent it is in the general population, and whether it causes cancers in tissues other than the prostate.

"We have many questions right now," Singh said, "and we believe this merits further investigation."

Viruses have been shown to cause cancer of the cervix, connective tissues (sarcomas), immune system (lymphoma), and other organs. If the retrovirus is shown to cause prostate cancer, this could have important implications for preventing viral transmission and for developing vaccines to prevent XMRV infection in people.

(Photo: U of U Health Sciences Public Affairs)

University of Utah

SCIENTISTS USE MICRORNAS TO TRACK EVOLUTIONARY HISTORY FOR FIRST TIME

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The large group of segmented worms known as annelids, which includes earthworms, leeches and bristle worms, evolved millions of years ago and can be found in every corner of the world. Although annelids are one of the most abundant animal groups on the planet, scientists have struggled to understand how the different species of this biologically diverse group relate to each other in terms of their evolutionary history. Now a team of scientists from Yale University and Dartmouth College has used a groundbreaking method to untangle some of that history.

The researchers used a novel source of data—the presence and absence of different microRNA genes—to investigate the evolutionary relationships of annelids. MicroRNAs are small, non-coding genes that have long been known to play an important role in developmental biology but which have never before been used to study the evolutionary relationships between organisms. The team’s findings appear online September 9 in the journal Proceedings of the Royal Society B.

“These genes are excellent evolutionary markers,” said lead author Erik Sperling, a graduate student in Yale’s Department of Geology and Geophysics. “Once a microRNA gene is fixed in a species, it is very rarely lost. As such, organisms with similar microRNAs are closely related to one another.”

Building on previous work done at Kevin Peterson’s lab at Dartmouth, which demonstrated the potential of using microRNAs to decipher evolutionary history, the team applied a form of high-throughput sequencing technology at the Yale Center for Genomics and Proteomics that uses a novel strategy to reveal the microRNA complement of an organism.

They discovered that certain groups of organisms previously shown by molecular analyses to lie within the annelid family, such as mollusks and peanut worms, could not have evolved from the same branch of the evolutionary tree as the rest of the annelids. Instead, the team’s results demonstrate that annelids represent a unique evolutionary branch separate from these other organisms. They also show that the ancestral annelid more closely resembled a kind of bristle worm that lived on the seafloor, as opposed to the classical belief that it was a kind of burrowing worm that lived in the ocean mud.

The team’s microRNA sequencing results also agree with the order in which the different annelids and their relatives appear in the fossil record—something that previous hypotheses about their relationships had failed to do, said co-author Derek Briggs, Yale’s Frederick William Beinecke Professor of Geology and Geophysics.

“This study is an elegant example of how new methods can reconcile results from molecular sequencing of living animals with information from the fossil record,” he said.

(Photo: Yale U.)

Yale University

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