Mega-laser to Probe Secrets of Exoplanets

Artist's impression of a gas giant planet circling the star Gliese 436. The new laser will investigate the internal chemistry of these vast planets (Image: NASA)

Sunday, March 01, 2009

AN AWESOME laser facility, built to provide fusion data for nuclear weapons simulations, will soon be used to probe the secrets of extrasolar planets.

The National Ignition Facility (NIF) at the Lawrence Livermore National Laboratory in California was declared ready for action earlier this month. Its vital statistics reveal it to be a powerful beast: its ultraviolet lasers can deliver 500 trillion watts in a 20-nanosecond burst. That power opens up new scientific possibilities.

For instance, Raymond Jeanloz, an astronomer at the University of California, Berkeley, will use the device to recreate the conditions inside Jupiter and other larger planets, where pressures can be 1000 times as great as those at the centre of the Earth.

Jeanloz will fire the lasers at an iron sample 800 micrometres in diameter. The intense heat will vaporise the metal, generating a gas jet so powerful it will send a shock wave through the iron, compressing it to over a billion times atmospheric pressure. By measuring how the metal's crystalline structure and melting point change at these pressures, Jeanloz hopes to shed light on the formation of the hundreds of giant exoplanets that we have discovered in the last two decades. "The chemistry of these planets is completely unexplored," says Jeanloz. "It's never been accessible in the laboratory before."

Next year, Livermore teams will start work on experiments that could ultimately have an even bigger impact. They will use the lasers to ignite a fusion reaction in a ball of hydrogen isotopes. Other labs have triggered fusion, but not a self-sustaining reaction. The Livermore facility should deliver a big enough jolt of energy to trigger a reaction that burns until the fuel is used up. The data produced will feed into attempts to design a commercial fusion power plant.

The same reaction will also aid the management of the US nuclear weapons stockpile. It is more than 15 years since the US tested a nuclear weapon. Engineers use computer simulations to determine if warheads are in working order, but the models need to be calibrated using data from experiments like NIF's fusion reactions.