Five of the new planet discoveries were based on observations made by the W.M. Keck Observatory in Hawaii.
Just a decade ago, scientists knew of only the nine planets - those in our local solar system. In 1995, improved detection techniques produced the first solid evidence of a planet circling another star. A proliferation of discoveries followed, and now dozens of ongoing search efforts around the globe add steadily to the roster of worlds. Most of these planets differ markedly from the planets in our own solar system. They are more similar to Jupiter or Saturn than to Earth, and are considered unlikely to support life as we know it.
The news of the past four weeks has included:
All were discovered as part of the High Accuracy Radial velocity Planet Search (HARPS), an ongoing search program based at La Silla Observatory in Chile.
The U.S. team based its finding on observations obtained at the W.M. Keck Observatory in Hawaii, which is jointly operated by the University of California and Caltech. Observation time was granted by both NASA and the University of California.
A pulsar is a dense and compact star that forms from the collapsing core left over from the death of a massive star. The new pulsar planet is the fourth to be discovered; all orbit the same pulsar, named PSR B1257+12.
Because the planets around the pulsar are continually strafed by high-energy radiation, they are considered extremely inhospitable to life.
Two methods of detection
The pulsar planet was discovered by observing the neutron star's pulse arrival times, called pulsar timing. Variations in these pulses give astronomers an extremely precise method for detecting the phenomena that occur within a pulsar's environment.
The gas-giant planets were detected using the radial velocity method, which infers the presence of an unseen companion because of the back-and-forth movement induced in the host star. This movement is detectable as a periodic red shift and blue shift in the star's spectral lines. (For more about this method, see the article Finding Planets.)
Information about NASA's hunt for extrasolar planets is available at http://planetquest.jpl.nasa.gov.