January 12, 1999

Letters to the Editor
Sky & Telescope

Dear Mr. Editor

New Type of Objects?

When one reads your February newsnote "Yet More Extrasolar Planets" in the light of your January cover story on the Origin of our Solar System, there is something that does not fit. The accretion disk theory states that planetesimals close to their parent star are not able to retain the light elements H and He, because of the high temperatures. As the remaining elements are only 1% of the original nebula, these 'terrestrral' planets have small masses. The giant planets need lower temperatures to be formed, which exist only much further from the central star.

The extrasolar planets just discovered, however, usually have masses larger than Jupiter and are much closer to their central star than Mercury is to the Sun. Therefore, they must have a very different origin than our solar systems planets. Perhaps they are aborted double stars or maybe even midsized black holes. Who knows? Anyway, if they were born in a completely different way than ours, they should not be entitled to be called planets like the ones of our Solar System. Let their discoverers find a better name for them!

Eduardo Vila-Echagüe
Waterloo 421
Santiago de Chile 1