Venus is one of the most inhospitable places in the Solar System, with temperatures hot enough to melt lead, crushing air pressure on the surface, and thick, toxic clouds perpetually hiding the planet itself from view. Now new research is helping to solve a long-standing mystery by showing that there may be frost on the surface. Not water frost, of course, given the conditions, but rather a bizarre frost composed of heavy metals.
The new findings come from the continued study of 20-year-old data from the old Magellan spacecraft, which mapped Venus a couple of decades ago. Back then, Magellan revealed some surprises which had remained mysteries all this time—radio waves being reflected differently at different elevations and radio dark spots at the highest elevations. Explanations had eluded planetary scientists, but now they think they may have the answer.
According to Elise Harrington, an Earth sciences undergraduate at Simon Fraser University, in British Columbia, “There is general brightening upward trend in the highlands and then dark spots at the highest locations.” The “brightening” is where radio waves are reflected well off the surface, while the dark areas are where there is little or no reflection. Oddly, the ground becomes more radio reflective (brighter) the higher in elevation you go, until it goes “black” in the dark spots.
Harrington continued, “Like on Earth, the temperature changes with elevation. Among the possibilities on Venus are a temperature dependent chemical weathering process or heavy metal compound precipitating from the air – a heavy metal frost.” Previously, it was thought that some kind of ferro-electric compound might cause the brightening and the dark spots, but no such compounds have ever been found.
It’s an intriguing possibility. Venusian “frost” on mountains at higher elevations, but created by heat instead of cold, the opposite of what happens on planets like Earth or Mars. For a world almost exactly the same size as Earth, Venus couldn’t be more different in many ways.
The researchers only had older Magellan data to work with, so they made use of more recent stereo radar elevation data from Dr. R. Herrick at the University of Alaska. This was higher resolution than the older Magellan radar data, enabling them to find darker patches which were as small as 1,968 x 1,968 feet (600 x 600 meters) instead of just 5 x 7.5 miles (8 x 12 kilometers) like before. By also using Magellan’s Synthetic Aperture Radar (SAR), they could look at radio emissions with a footprint of 246 x 246 feet (75 x 75 meters), much better than the radio emissions from the surface, which were only 9.3 x 14 miles (15 by 23 kilometers) in resolution.
They focused on an area known as the Ovda Regio highlands, where the same kind of brightening and dark spots had been seen before. The radar reflection at the 7,900 foot (2,400 meter) elevation was low, but then rapidly brightened going up to 14,700 feet (4,500 meters). A bit higher still, there were a lot more of the odd black spots at 15,400 feet (4,700 meters) elevation.
As Harrington noted, “The previous author saw a few dark spots. But we see hundreds of them.” She added, “No one knows what explains the sudden darkness. We think this might spur some more interest in Venus.”
Hopefully this will indeed help to make the case for continued exploration of our hellish neighbour. Previous landers could only survive a very short time in the heat and pressure, but if future landers or even rovers could be sent there, they could do in-situ investigations of some of these puzzling phenomena and help answer some of the lingering questions as to what Venus used to be like and how it became the way it is now.
The findings were presented on Oct. 20 at The Geological Society of America conference in Vancouver, B.C., and the abstract of the paper is available here.