Milky Way brims with planets

Carl Sagan would have loved it: not only are there billions and billions of stars in our galaxy, but every star may also harbour a planet. Millions of these could be like the fictional planet Tatooine in Star Wars, which orbits two stars.

About 700 extrasolar planets have been found in the Milky Way, a small number compared with the number of stars present. To find out whether such planets are truly rare or just hard to find, Arnaud Cassan of the Pierre and Marie Curie University in Paris, France, and colleagues turned to gravitational microlensing, in which one star focuses the light from a more distant star.

While other techniques are best at finding planets around nearby sun-like stars, gravitational microlensing can study any star up to 20,000 light years away.

The Optical Gravitational Lensing Experiment (OGLE) observes millions of stars every night with telescopes in Chile to find microlensing events. Then the Probing Lensing Anomalies Network (PLANET) follows up on intriguing signals using a global network of telescopes.

The researchers studied six years of microlensing data from the two projects and estimated that extrasolar planets are the rule rather than the exception, with each star in the galaxy hosting an average of 1.6 planets. More specifically, 17 per cent of the stars host a Jupiter-like planet, 52 per cent have a Neptune-like planet, and 62 per cent harbour a super-Earth – a rocky planet up to 10 times as massive as Earth.

Super-Earths

The seeming abundance of rocky super-Earths lends support to the core accretion model of planet formation, in which small rocky bodies collide and clump together to grow into these objects.

"Our results suggest that Earths should be even more common than super-Earths, if the mechanism to build an Earth is similar to that of building a super-Earth," says Cassan.

Meanwhile, William Welsh of San Diego State University in California and colleagues studied 750 stars observed by NASA's Kepler satellite. Based on their findings, they reckon several million planets in our galaxy orbit two stars, like the Star Wars planet Tatooine.

"Nature seems to like forming planets. The more carefully we look, the more of them we find," says Welsh.

Millions of planets orbit two stars (Illu

The End Of The Space Shuttle Era

Doomsday Clock Moved 1 Minute Closer to Midnight

In a sign of pessimism about humanity's future, scientists today set the hands of the infamous "Doomsday Clock" forward one minute from two years ago.

"It is now five minutes to midnight," Bulletin of the Atomic Scientists (BAS) director Kennette Benedict announced today (Jan. 10) at a press conference in Washington, D.C.

That represents a symbolic step closer to doomsday, a change from the clock's previous mark of six minutes to midnight, set in January 2010. 

The clock is a symbol of the threat ofhumanity's imminent destruction from nuclear or biological weapons, climate change and other human-caused disasters. In making their deliberations about how to update the clock's time, the Bulletin of the Atomic Scientists focused on the current state of nuclear arsenals around the globe, disastrous events such as the Fukushima nuclear meltdown, and biosecurity issues such as the creation of an airborne H5N1 flu strain.

The Doomsday Clock came into being in 1947 as a way for atomic scientists to warn the world of the dangers of nuclear weapons. That year, the Bulletin set the time at seven minutes to midnight, with midnight symbolizing humanity's destruction. By 1949, it was at three minutes to midnight as the relationship between the United States and the Soviet Union deteriorated. In 1953, after the first test of the hydrogen bomb, the doomsday clock ticked to two minutes until midnight.

The Bulletin — and the clock ­— were at their most optimistic in 1991, when the Cold War thawed and the United States and Russia began cutting their arsenals. That year, the Bulletin set the clock at 17 minutes to midnight.

From then until 2010, however, it was a gradual creep back toward destruction, as hopes of total nuclear disarmament vanished and threats of nuclear terrorism and climate change reared their heads. In 2010, the Bulletin found some hope in arms reduction treaties and international climate talks and nudged the minute hand of the Doomsday Clock back to six minutes from midnight from its previous post at five to midnight.

With today's decision, the Bulletin repudiated that optimism. The panel considers a mix of long-term trends and immediate events in the decision-making process, said Benedict. Trends might include factors like improved solar energy technology to combat climate change, she said, while political events such as the recent United Nations climate meeting in Durban play a role as well. This year, the Fukushima nuclear disaster made a big impression.

"We're trying to weight whether that was a wake-up call, whether it will make people take a closer look at this new and very powerful technology, or whether people will go on with business as usual," Benedict told LiveScience on Monday in an interview before the announcement of the "doomsday time" decision. [Top 10 Alternative Energy Bets]

Other factors that played into the decision included the growing interest in nuclear power from countries such as Turkey, Indonesia and the United Arab Emirates, Benedict said.

The Bulletin panel found that despite hopes of global agreements about nuclear weapons, nuclear power and climate change in 2010, little progress has been made. 

"The world still has approximately over 20,000 deployed nuclear weapons with enough power to destroy the world's inhabitants many times over," said Lawrence Krauss, an Arizona State University professor and the co-chair of the BAS Board of Sponsors. "We also have the prospect of nuclear weapons being used by terrorist non-state actors."

Likewise, talks on climate change have resulted in little progress, the panel found. In fact, politics seemed to trump science in discussions over the last two years, said Robert Socolow, a Princeton professor of mechanical and aerospace engineering and a member of the Bulletin's Science and Security board. 

"We need the political leadership to affirm the primacy of science as a way of knowing, or problems will be far worse than they are already," Socolow said.