NRAO/Socorro Colloquium Series

William Borucki

NASA

A Sampling of Exoplanet Results from the Kepler Mission

Over 3500 planetary candidates have been found with an enormous range of sizes, temperatures, and types of stellar hosts. In particular, exoplanets near the size of Earth’s moon to those larger than Jupiter have been found orbiting stars much cooler and smaller than the Sun as well orbiting stars hotter than the Sun. Orbital periods range from 8.5 hours to over 1000 days and orbital distances range from 0.01 AU to many AU. Several planets have been discovered orbiting binary stars and one in a triple-star system. Preliminary estimates of the size distribution suggest two populations; one for large planets formed when gas and dust were abundant and another for small planets formed later and strongly influenced by collisions and scattering.

Calculated radiative equilibrium temperatures range from higher than molten lava for planets near the surface of their host star to temperatures to those as cold as -70C. One object appears to be so hot that it is leaving a tail of evaporated material stretching half way around its orbit. Dozens of planetary candidates in the habitable zone have been found. Eight have been confirmed; one is in the HZ of a binary star. Although no Earth-analogs have yet been found, improvements are being made to the data analysis algorithms to increase the chances of finding them.

Masses of those planets with large masses and/or short orbital-periods are being determined by both radial velocity observations from ground-based telescopes and by transit timing methods based on the Kepler measurements. By combining these results with the sizes obtained from transit photometry, the densities of t both large and small planets are being determined. They range from 0.2 gr/cc for Kepler-7b to 8.8 gr/cc for Kepler-10b. The results are indicative of planets that are mostly gas, to water planets, and to iron-rich rocky planets. A group of 63 stars with planets discovered by Kepler was observed by RV to determine planet densities. Analysis indicates that those smaller than 1.6 R are likely to rocky planets whereas planets substantially larger are likely to have substantial hydrogen/helium atmospheres. Model calculations indicate that “Water planets” are more accurately labeled “steam planets”.

The combination of high photometric precision and long-duration observations allow detection of many modes of stellar oscillations and thereby the resolution of the internal structure of both main-sequence and evolved stars. In particular, observations of red giants have been used to determine their internal rotation and to distinguish those that are burning hydrogen in their cores from those burning hydrogen in a shell. Main-sequence stars with white-dwarf companions or stripped-core companions have been found. Measurements of the variability of G dwarfs show that a surprising number are more variable than the Sun.

March 14, 2014
11:00 am

Array Operations Center Auditorium

All NRAO employees are invited to attend via video, available in Charlottesville 245, Green Bank Auditorium,  Tucson N525, and NTC 400.

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