More than three-quarters of the planet candidates discovered by
The Kepler team today reports on four years of ground-based follow-up observations targeting Kepler's exoplanet systems at the
Included in the findings are five new rocky planets ranging in size from 10 to 80 percent larger than Earth. Two of the new rocky worlds, dubbed Kepler-99b and Kepler-406b, are both 40 percent larger in size than Earth and have a density similar to lead. The planets orbit their host stars in less than five and three days respectively, making these worlds too hot for life as we know it.
A major component of these follow-up observations was Doppler measurements of the planets' host stars. The team measured the reflex wobble of the host star, caused by the gravitational tug on the star exerted by the orbiting planet. That measured wobble reveals the mass of the planet: the higher the mass of the planet, the greater the gravitational tug on the star and hence the greater the wobble.
"This marvelous avalanche of information about the mini-Neptune planets is telling us about their core-envelope structure, not unlike a peach with its pit and fruit," said
Using one of the world's largest ground-based telescopes at the
The density measurements dictate the possible chemical composition of these strange, but ubiquitous planets. The density measurements suggest that the planets smaller than Neptune -- or mini-Neptunes -- have a rocky core but the proportions of hydrogen, helium and hydrogen-rich molecules in the envelope surrounding that core vary dramatically, with some having no envelope at all.
The ground-based observation research validates 38 new planets, six of which are non-transiting planets only seen in the Doppler data. The paper detailing the research is published in the
A complementary technique used to determine mass, and in turn density of a planet, is by measuring the transit timing variations (TTV). Much like the gravitational force of a planet on its star, neighboring planets can tug on one another, causing one planet to accelerate and another planet to decelerate along its orbit.
"Kepler's primary objective is to determine the prevalence of planets of varying sizes and orbits. Of particular interest to the search for life is the prevalence of Earth-sized planets in the habitable zone," said
The dynamical mass measurements produced by Doppler and TTV analyses will help to answer these questions. The results hint that a large fraction of planets smaller than 1.5 times the radius of Earth may be comprised of the silicates, iron, nickel and magnesium that are found in the terrestrial planets here in the solar system.
Armed with this type of information, scientists will be able to turn the fraction of stars harboring Earth-sizes planets into the fraction of stars harboring bona-fide rocky planets. And that's a step closer to finding a habitable environment beyond the solar system.
Ames is responsible for the Kepler mission concept, ground system development, mission operations and science data analysis.
For more information about the Kepler space telescope, visit: http://www.nasa.gov/kepler.
TNS 30BautistaJude 140107-4592141 30BautistaJude
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