Title: Angular Momentum in Extrasolar Planetary Systems

Sam T. Durrance
John Hopkins

Is the universe filled with Earth-like planets orbiting other stars? Since the first planetary companion to a normal star like the Sun was discovered in 1995, the detection of extrasolar planets has proceeded at a rapid pace, with over 320 found. Most of the newly discovered planets, however, are gaseous giants, like Jupiter, orbiting relatively close to their parent star--quite unlike the Solar system. They were discovered indirectly by observing an effect the planets have on their parent stars rather than observing the planets themselves. What does this tell us about the nature of planetary systems in general? Is the Solar system unique? Recently, two Earth-like planets were discovered orbiting a small nearby star; both may orbit within, or near, that star's habitable zone. Might these planets harbor life? With our ever improving ability to observe exoplanets, will we soon be able to answer the age old question: Are we alone?

This presentation investigates the distribution of angular momentum in 28 extrasolar planetary systems. Only exoplanets detected with both transit and radial velocity measurements were included in the study to remove the uncertainty associated with unknown orbital inclination angles. The distribution of angular momentum between an exoplanet and its host star and between different extrasolar systems was determined. It is clear from this study that the angular momentum per unit mass of the host stars is generally less than the average value for main-sequence stars of the same mass and that the angular momentum per unit mass of the complete extrasolar planetary system is generally greater. Also, more than 50 % of the angular momentum in these systems resides in the exoplanet and in many cases more than 80 %. To draw any general conclusions about the role of angular momentum in the planetary formation process will require additional work to understand and quantify the observational selection effects.

UT Arlington Physics