Venus had Oceans and Continents

The planet Venus, now hellishly hot and dry, may have once have been far more like Earth, with oceans and continents. That is the implication of new research claiming to see evidence for granite highlands on the planet in data almost two decades old.

In 1990, NASA's Galileo spacecraft detected nighttime infrared emissions coming from Venus' surface. Analysing these data, an international team led by planetary scientist George Hashimoto, now at Okayama University, Japan, found that Venus's highland regions emitted less infrared radiation than its lowlands.

One interpretation of this lower infrared emission from the highlands, say the authors, is that they are composed largely of 'felsic' rocks, particularly granite. Granite, which on Earth is found in continental crust, requires water for its formation. The results are published in the Journal of Geophysical Research1.

And their abstract:

Felsic highland crust on Venus suggested by Galileo Near-Infrared Mapping Spectrometer data
Felsic highland crust on Venus suggested by Galileo Near-Infrared Mapping Spectrometer data

George L. Hashimoto

Laboratory for Earth and Planetary Atmospheric Science, Organization of Advanced Science and Technology, Kobe University, Kobe, Japan

Maarten Roos-Serote

Lisbon Astronomical Observatory, Lisbon, Portugal

Seiji Sugita

Department of Complexity Science and Engineering, Graduate School of Frontier Science, University of Tokyo, Kashiwa, Japan

Martha S. Gilmore

Department of Earth and Environmental Sciences, Wesleyan University, Middletown, Connecticut, USA

Lucas W. Kamp

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

Robert W. Carlson

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

Kevin H. Baines

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA

We evaluated the spatial variation of Venusian surface emissivity at 1.18 μm wavelength and that of near-surface atmospheric temperature using multispectral images obtained by the Near-Infrared Mapping Spectrometer (NIMS) on board the Galileo spacecraft. The Galileo NIMS observed the nightside thermal emission from the surface and the deep atmosphere of Venus, which is attenuated by scattering from the overlying clouds. To analyze the NIMS data, we used a radiative transfer model based on the adding method. Although there is still an uncertainty in the results owing to the not well known parameters of the atmosphere, our analysis revealed that the horizontal temperature variation in the near-surface atmosphere is no more than ±2 K on the Venusian nightside and also suggests that the majority of lowlands likely has higher emissivity compared to the majority of highlands. One interpretation for the latter result is that highland materials are generally composed of felsic rocks. Since formation of a large body of granitic magmas requires water, the presence of granitic terrains would imply that Venus may have had an ocean and a mechanism to recycle water into the mantle in the past.

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