Planets Orbiting Stars Is the Milky Way Standard
An international collaboration involving Livermore astrophysicist Kem Cook has found that planetary systems resemble our solar system more often than they differ. The team’s research results also indicate that, on average, every star in the Milky Way hosts one or more planets in an orbital-distance range of 0.5 to 10 times the distance between the Sun and Earth.

For this project, researchers analyzed microlensing data collected between 2002 and 2007 by the Optical Gravitational Lensing Experiment and the Probing Lensing Anomalies Network. Gravitational microlensing occurs when light from a source star is bent and focused by gravity as a second object (called the lens star) passes between the source star and an observer on Earth. A planet rotating around the lens star will produce an additional deviation in the microlensing.

Over the past 16 years, astronomers have detected more than 700 confirmed extrasolar planets. Most of these planets, discovered using the Doppler-shift technique, are gas giants similar to Jupiter and Saturn, and their parent stars are much closer to them than the Sun is to Earth. Although microlensing events are rare, they allow researchers to probe planets with greater orbital-distance ranges.

According to Cook, the team’s measurements confirm that low-mass planets are very common. Approximately 17 percent of the Milky Way’s stars host Jupiter-mass planets. Cool, Neptune-type planets and super-Earths are even more prevalent, occurring 52 percent and 62 percent of the time, respectively. The team also found that the number of planets increases with decreasing planet mass, in agreement with predictions of the core-accretion scenario for planet formation. Says Cook, “Planets around stars in our galaxy appear to be the rule rather than the exception.” Results from the team’s research appeared in the January 12, 2012, edition of Nature.
Contact: Anne Stark (925) 423-9799 (stark8@llnl.gov).

Livermore System Monitors Mars Launch
When the Mars Science Laboratory lifted into space on November 26, 2011, a comprehensive radiological emergency preparedness system monitored the launch from the ground. The Livermore-designed system uses environmental continuous air monitors (ECAMs) to collect samples and analyze suspended particles for radioactivity that might result in the unlikely event of a launch accident.

Onboard the spacecraft is the largest, most advanced rover ever sent to another planet. Named Curiosity, the rover relies on a radioisotope thermoelectric generator—essentially a nuclear battery with 4.8 kilograms of plutonium-238 dioxide that converts heat into electricity. The battery powers the rover and keeps its internal systems warm during frigid Martian nights, where temperatures can dip as low as –150°C.

Prior to the launch, the National Aeronautics and Space Administration installed 30 ECAMs on and around the Kennedy Space Center. The monitors send real-time data via satellite to the Kennedy Space Center’s Radiological Control Center and to the National Atmospheric Release Advisory Center (NARAC) at Livermore. NARAC scientists then quickly combine the ECAM data with weather, wind, and other information to develop detailed plume models for radiological contingency planning. Two Laboratory scientists, Steve Homann and Ron Baskett, were deployed to the Kennedy Space Center for the launch.

Curiosity will visit regions of Mars not previously explored to collect and analyze rock samples. Its mission is to study the geologic record on Mars and help determine whether conditions are or have ever been favorable for microbial life. More information about the Mars Science Laboratory is available online at www.nasa.gov/msl.
Contact: Steve Homann (925) 423-4962 (shomann@llnl.gov).

Researcher Clarifies Water’s Ionic Conductivity
Livermore scientist Sebastien Hamel and collaborators from the Institut für Physik at Universität Rostock in Germany have resolved a long-standing problem in using quantum molecular-dynamics simulations to calculate ionic conductivity in fluids. The researchers combined two well-established techniques—density functional theory molecular-dynamics simulations and polarization theory—to determine electrical conductivity directly, without making assumptions about the effective charge transported by protons.

Quantum simulations have provided insight into the dynamics of proton transport at the microscopic level, including how the involved molecular and ionic species interact. For example, simulations revealed that as pressure and temperature in water increase, molecules dissociate, allowing more protons to contribute to charge transport and thus increasing conductivity.

The team’s simulations with the combined techniques indicate that the effective charge of protons fluctuates on a femtosecond (10^–15-second) timescale and is crucial to charge transport in water. The new approach can now be applied to study the ionic conductivities of electronically insulating materials of arbitrary composition, such as complex molecular mixtures under the extreme conditions deep inside giant planets. Results from the team’s research appeared in the October 25, 2011, issue of Physical Review Letters.
Contact: Sebastien Hamel (925) 423-8048 (hamel2@llnl.gov).