In 1997 I wrote: "The problem is that the only reports available to the rest of the astronomical community by the discoverers are still not in the technical literature for other astronomers to read and evaluate. I have to point out that there have been many reports over the last 30 years of planets being discovered orbiting other stars. The most sensational of these was in the early 1960's when a nearby star called Barnards's Star was reported to 'wiggle' as it moved in the sky in a way that suggested an orbiting planet a few times bigger than Jupiter. The data, however, were faulty after other astronomers tried to reproduce the original measurements using other telescopes. I think we have to try to be a bit cautious about claims like these until the data is published and other astronomers have the chance to check the claims with new observations of these stars, using other instruments. There is too much that can go wrong, and too much at stake to believe the results as they stand today. I know that this doesn't sound in keeping with all the hoopla in the press about these new planets, but this is the way that true science operates. Any claims have to be verified by independent investigators before they are accepted as observational facts. Lets be a bit more patient and see what the outcome of this process is in a year or two!"
In May 2000 I can now say with much more confidence that 51 Pegasi's planets have been confirmed by independent studies, and in one case among the recent planetary detections, the planet was not only seen by its spectroscopic effects, but by a direct diminution in the star's light as the planet crossed the disk of the star, HD209458, as viewed from Earth. There are now 40 planets in the list of extra-solar objects, which have been detected with the same confidence as 51 Pegasi, and the list continues to grow every few months. If you want to keep up to date with new discoveries, you should visit Paul Butler's Planet Search pages at San Francisco State University.
Because of the method used to find them, the planets are all very big ( Jupiters mass or at most Saturn's mass) and on very elliptical orbits close to their parent star. The temperature of these gas giants outer atmosphere must be over 1000 K because of their proximity to their star, but the temperatures vary considerably because of the elliptical orbits. The plot above shows the locations and masses of the detected planets to scale with our solar system. Earth orbits at '1 AU' in the diagram with a period of 365 days.
Astronomers who work on the theory-side of planetary system formation are increasingly convinced that these objects were formed elsewhere in the original planetary disk, and wound up on these orbits either by planetary collisions/encounters, or by the friction in the gaseous planetary disk slowly causing them to lose energy and drift inwards to their present locations. It seems unlikely that other planets could exist in many of these systems without having been ejected as these Jupiter-sized bodies evolved in both mass and orbit properties.
Copyright 1997 Dr. Sten Odenwald
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