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New planet may have Earth-like neighbor

Another planet has been added to the list of 100 or so worlds that astronomers have discovered around distant stars _ but unlike all those other planets, this one is in a solar system that may be capable of supporting another Earth.

The discovery, which was announced Wednesday at a conference in Paris and is to be published in an upcoming issue of the Astrophysical Journal, marks the first time that the search for extrasolar worlds has produced a planet orbiting in a system so strikingly similar to our own.

"This planet and its orbit are quite reminiscent of Jupiter," said Brad Carter, an astronomer at the University of Southern Queensland and lead author of the upcoming article.

The planet, which is a gas giant about twice the size of Jupiter, travels around a star very much like our own sun in a nearly circular orbit about three-fifths the size of our solar system's resident giant.

What is most interesting about this system, though, is what astronomers didn't find.

Unlike other systems with Jupiter-like planets orbiting at Jupiter-like distances, this system does not have any other gas giants closer to its sun in the region where liquid water could exist _ the so-called habitable zone. The finding suggests that this void could be filled by smaller rocky planets.

"If we see a big empty gap," said astronomer Debra A. Fischer, co-author of the article, "we have to wonder if it's really empty."

Mixed-gender embryos produced

Scientists in Chicago have for the first time made human embryos that are part male and part female, raising novel ethics questions and prompting calls for more oversight of the rapidly evolving field of human embryo manipulation.

The experiments, described at a meeting of the European Society of Human Reproduction and Embryology in Madrid, aimed to answer basic questions about human embryo development and develop therapies for congenital diseases.

The hybrid embryos were destroyed after six days, when they had grown to a few hundred cells organized into a microscopic, mixed-gender ball, according to a written synopsis of the work submitted by the research leader, Norbert Gleicher of the Foundation for Reproductive Medicine.

"I don't know if this work is "right' or "wrong,' but it should be reviewed and discussed long and hard before it's done," said George Annas, a professor of health law and bioethics at Boston University.

New study suggests cosmic brake

Pulsars are the fastest spinning stars in the universe _ rotating at hundreds of revolutions per second _ and they could go twice as fast before flying apart. A new study suggests these exotic stars are held together by gravitational radiation that puts on the brakes.

Observations by NASA's Rossi X-ray Timing Explorer of 11 pulsars found there seems to be a natural limit on how fast the stars can spin, astronomers said Wednesday.

"The fastest-spinning pulsars could technically go twice as fast, but something stops them before they break apart," said Deepto Chakrabarty, a Massachusetts Institute of Technology astronomer and the lead author of a study appearing in the journal Nature.

Chakrabarty called the natural brake "a cosmic speed limit" and said it may be the result of rotational energy being emitted from the stars as gravitational waves.