[X] My Assistant

[Guest_AlexBlackwell_*]

There is an interesting Spitzer-based paper by Richardson et al. ("A spectrum of an extrasolar planet") in the February 22, 2007, issue of Nature. See the Editor's Summary for a synopsis and links.

See also:

NASA's Spitzer First to Crack Open Light of Far Away Worlds
NASA/JPL
RELEASE: 07-48
February 21, 2007

Clouds, But No Water, Detected On Distant Planet
By Ker Than
Staff Writer, Space.com
posted: 21 February 2007
01:01 pm ET

[Mongo]

This paper, Albedo and Reflection Spectra of Extrasolar Giant Planets, is the fundamental paper on Jovian exoplanetary cloud decks. In it, Jovian planets are divided into 5 classes:

Class I planets are those with low effective temperatures (less than about 150K) and have tropospheric ammonia clouds. They would have fairly high Bond albedos. Jupiter and Saturn are example of class I Jovians.

Class II planets are those with water clouds as their upper cloud deck, and have the highest Bond albedos of any class -- Venus would be a (terrestrial) analog, in appearance at least.

Class III planets are too hot to allow water clouds and are clear to great depths, allowing radiation to penetrate quite deeply until they are absorbed by (typically) sodium and potassium. In the near infrared, absorption by CH4 and H2O, as well as by H2, makes for a very low albedo.

Class IV planets are hotter still (900K to 1500K), with a tropospheric silicate cloud deck expected. However, this cloud deck is expected to be so low in the atmosphere that absorption by sodium and potassium above it is considerable.

Class V planets have an effective temperature above 1500K, and the silicate cloud deck is high enough to greatly increase the Bond albedo.

A more detailed paper is Theoretical Spectra and Atmospheres of Extrasolar Giant Planets by the same authors.

Bill