New molecules found on Venus
A research team at the Department of Chemistry, University of Copenhagen, has found a mechanism for the formation of significant amounts of two new sulfur oxide molecules, both form when two sulfur monoxide molecules collide. The near-UV absorption of these molecules matches that of the missing absorber on Venus.
A solution is proposed to a long standing problem of a missing near-UV absorber in the Venusian atmosphere. The team from Copenhagen, PhD student Benjamin Normann Frandsen and Professor Henrik Grum Kjaergaard, and Caltech Professor Paul Ottolenghi Wennberg (currently on sabbatical), have published their research in the Geophysical Research Letters, a flagship journal of the American Geophysical Union.
The sulfur oxides have been observed in the atmosphere of Venus. However, neither of these molecules absorb in the near-UV region of 320-400 nanometres (nm). This new research suggests that two new sulfur oxides are formed in significant amounts in the top-cloud layer on Venus. In this region, the calculated concentrations of sulfur oxides are similar to those of the other known sulfur compounds.
"It’s cool that we are able to explain the UV absorbtion on Venus", says Henrik Kjaergaard. "As a scientist this is real fun. In the big picture, I reckon that the atmospferic models of Venus will have to be revised as a consequence of our research.”
The planet Venus exhibits atmospheric absorption in the 320-400 nanometres wavelength range produced by unknown chemistry. The team has identified two different isomers, which are formed in significant amounts and are destroyed following absorption of sunlight in a process known as photolysis. Based on their formation and photolysis rates, the research team found that the molecules are good candidates to explain the enigmatic 320-400 nm near-UV absorption.
Visit to Venus?
The project began when Kjaergaard and Frandsen read that the sulfur oxides are prevalent on Venus but hardly existing on Earth. While not responsible for the near-UV absorption, sulfur oxides are the key ingredients in the chemical process, forming the two new molecules that cause absorption. The reason that sulfur oxide molecules are formed on Venus and not Earth, is mainly due to the oxidizing nature of Earth’s atmosphere, in which sulfur oxide would quickly oxidize to sulfur dioxide and trioxide, and after combination with water, H2O, to sulfuric acid. The atmosphere of Venus contains vanishingly little oxygen. This makes Venus a natural laboratory for sulfur chemistry, which can create a number of compounds that do not occur naturally on Earth.
The discovery has already aroused interest among Venus experts abroad, and, it is hoped, will spur ESA/NASA interest in future Venus missions. If proven correct, this will solve a 40-year old Venus mystery.
Professor Henrik Grum Kjærgaard