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September 09, 2011

Invisible World Discovered using gravitational effect on another exoplanet

NASA's Kepler spacecraft has spotted a planet that alternately runs late and early in its orbit because a second, "invisible" world is tugging on it. This is the first definite detection of a previously unknown planet using this method. No other technique could have found the unseen companion.

Both the seen and unseen worlds orbit the Sun-like star Kepler-19, which is located 650 light-years from Earth in the constellation Lyra. The 12th-magnitude star is well placed for viewing by backyard telescopes on September evenings.

Kepler locates planets by looking for a star that dims slightly as a planet transits the star, passing across the star's face from our point of view. Transits give one crucial piece of information - the planet's physical size. The greater the dip in light, the larger the planet relative to its star. However, the planet and star must line up exactly for us to see a transit.




The Kepler spacecraft will continue to monitor Kepler-19 throughout its mission. Those additional data will help nail down the orbit of Kepler-19c. Future ground-based instruments like HARPS-North will attempt to measure the mass of Kepler-19c. Only then will we have a clue to the nature of this invisible world.

Harps North

The search for planets outside our solar system continues to heat up. NASA's Kepler spacecraft has located more than 1,200 planetary candidates, however confirming them remains a challenge. A new instrument called HARPS-North (HARPS stands for High-Accuracy Radial velocity Planet Searcher.) will help confirm the exoplanets. This precision spectrograph is designed to detect the tiny radial-velocity signal induced by planets as small as Earth, if they orbit close to their star.

A spectrograph operates by splitting the light from a star into its component wavelengths or colors, much like a prism. Chemical elements absorb light of specific colors, leaving dark lines in the star's spectrum. Those lines shift position slightly due to the Doppler shift created by the gravitational tug of an orbiting planet on its star.

HARPS-N will essentially duplicate the successful design of an existing instrument in the Southern Hemisphere, the original HARPS. It will be augmented by technology now under development, such as a laser comb for wavelength calibration, which will allow it to detect subtle radial-velocity signals.

The original HARPS operates on the 3.6-meter European Southern Observatory telescope at La Silla, Chile. HARPS-N will be installed on the 3.6-meter Telescopio Nazionale Galileo (TNG) in the Canary Islands. From this location, it will be able to study the same region of the sky viewed by the Kepler spacecraft, within the northern constellations of Cygnus and Lyra.

"We have set up an enthusiastic collaboration among various institutions to build a northern copy of HARPS. We all expect HARPS-N to be as successful as its southern 'brother,'" said HARPS-N principal investigator Francesco Pepe of the Astronomical Observatory of Geneva.

"HARPS-N will pursue the most interesting targets found by Kepler, at a level that no one else in the world can do," said Dimitar Sasselov, Director of the Harvard Origins of Life Initiative. "HARPS-N will partner with Kepler to characterize worlds enough like Earth that they might be able to support life as we know it."

First light for HARPS-N is anticipated in April 2012.

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