Unexplained dark spots raise questions about Venus’ surface

One theory suggests that metallic compounds have condensed on Venus’ surface like frost.

The surface of Venus may be more complex than previously thought. Elise Harrington, an SFU earth sciences undergraduate student and intern at the Lunar and Planetary Institute, has made new discoveries as to how radar properties change along Venus’ mountain ranges.

Venus has been thought of by researchers as a very homogenous planet, but Harrington, who revisited spacecraft data collected by Magellan two decades ago, noticed unconventional variations in the planet’s landscape.

Alongside her supervisor, Allan Treiman, she noticed unexplained dark spots present on only one of two mountain ranges on the planet’s surface. The team thinks these new discoveries may inspire renewed interest in Venus, which has not been visited since the Magellan journey.

In conducting their observations, Harrington’s team used the property called radar reflectivity, rather than emissivity — which was used by previous researchers — in order to look at the ranges in higher resolution. Although these radar properties are very closely related, the new method was able to provide a higher spatial resolution than that of the past.

In observing Ovda Regio, the mountain range near Venus’ equator, Harrington said, “We noticed that, like the previous researchers saw, the reflectivity increased with elevation [as expected].”

However, she said that there were some observations that diverged from the expected trend. She explained that her research team noticed some anomalous dark spots occurring at the highest elevations. “We expected it to keep getting brighter and brighter, and then suddenly it got dark,” remarked Harrington.

One theory to explain why the surface brightens as elevation increases is the metal frost hypothesis, which attributes the brightness to Venus’ metallic compounds. These metallic compounds are volatile in the atmosphere, but would condense on the surface like frost on earth.

Harrington explained, “[Metal Frost] theory would explain why the surface would get brighter, but not explain the dark spots we noticed.”

Later, her research team observed Maxell Montes, located in the poles of Venus, a very different area than Ovda Regio. They wanted to see if the Maxwell mountains were showing dark spots as well.

Using the same procedure, they noticed that there were no dark spots. The mountains on Maxwell kept getting brighter, eventually reaching a stable level of luminosity. Harrington said, “That is very different from what we saw in the first mountain range.”

Although the implications of the discovery are unclear as of yet, Harrington said that this new research may inspire greater interest in the planet: “The fact that we noticed something different [. . .] raises additional questions for future researchers.”