Solar system

Abstract:

Geomorphic evidence that Mars was warm enough to support flowing water about 3.8 billion years ago presents a continuing enigma that cannot be explained by conventional greenhouse warming mechanisms. Model calculations show that the surface of early Mars could have been warmed through a scattering variant of the greenhouse effect, resulting from the ability of the carbon dioxide ice clouds to reflect the outgoing thermal radiation back to the surface. This process could also explain how Earth avoided an early irreversible glaciation and could extend the size of the habitable zone on extrasolar planets around stars.

Abstract:

Measurements of the Venus mesosphere made in 1978/79 by the Pioneer Venus Orbiter Infrared Radiometer (OIR) have been reanalysed. An optimal estimation retrieval technique has been applied to data from individual orbits. These retrievals reveal the structure of transient features such as the polar dipole and polar collar and short term variations in water vapour abundance and cloud top height. High abundances of water vapour are observed at equatorial latitudes in the early afternoon with a spatial structure which appears consistent with the ultraviolet 'Y' shaped structure. Additionally a two to four day period is observed in both water vapour abundance and cloud top height which is the characteristic period of this ultraviolet feature. © 1997 COSPAR. Published by Elsevier Science Ltd.