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The Hunt for Extrasolar Planets – Second Part

Published by Klaus Schmidt on Fri Mar 9, 2007 4:51 pm
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Searching for extrasolar planets was coined with failures and disappointments a long time. The technical challenge or just simple observation errors made the announced discoveries disappear again quite quickly.

First of all we should look what a planet is. At an interstellar distance we surely won’t have to distinguish between smaller objects like Pluto in our solar system (we couldn’t them detect anyway) and full sized planets. But there is an upper boundary concerning its mass.

Normally extrasolar planet masses are listed in parts of Jupiter masses. That has its reasons. Not only that Jupiter is the largest planet in our system and therefore the easiest to detect at interstellar distances, its mass make it also unique.

Basically planets are nothing else than stars contemplating their composition. A more ore less large solid core is encased by a gaseous shell. So if you would blow up Jupiter’s mass to a certain level, Jupiter would start a nuclear fusion process and become a star. This would happen at about 84 times the mass of Jupiter.

That sounds like quite a margin to differ planets from stars. But there is a sort of objects between 13 times the mass of Jupiter and the boundary to a „real“ star: the brown dwarfs.

While being too small to start its own nuclear fire and therefore staying as dark as a planet, they once shined even brighter than our sun in their development phase. All stars (and planets) form out of a dust cloud. While these proto-stars contract, they glow very bright and a normal star will start its nuclear fire when gravity heated up the interior to several million degrees. But brown dwarfs have not enough mass for this to happen.

When the electron pressure balances out the contraction effect, the proto-star that wasn’t able to start the hydrogen-burning nuclear fusion becomes a brown dwarf, that slowly cools down.

Back to our unsuccessful tries to find extrasolar planets. A major case was the companion around Barnards Star. In 1969 the Dutch astronomer Peter van den Kamp announced the discovery of not only one but two planets around this red dwarf.

It was in 1973 that George Gatewood and Heinrich Eichhorn published their devastating result. There were no planets around Barnards Star. The believed discovery was caused by an observation error. Van den Kamp tended to change his telescope’s configuration about every 8.3 years, the orbital period of one of the planets.

Like this case several more believed discoveries were made over the decades but none widthstand a closer examination. In most of the cases plain observation errors were responsible.

The first confirmed discovery was then made in 1991 by the Polish astronomer Alex Wolszczan. This discovery was totally unexpected. Not that an extrasolar planet was discovered but the nature and environment of this planet made this discovery extraordinary.

What was so surprising with that discovery you can read in the next part of „The Hunt for Extrasolar Planets“.

Feel free to discuss this article in the forum…

You can find the first part of “The Hunt for Extrasolar Planets” here…

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