Rivers of molten rock slither across the surface, sulfuric acid rains down, and all beneath an ocean of toxic carbon dioxide. The planet Venus, in contradiction to its namesake, is a hateful place, and though it is now a hellscape, Venus probably started out like Earth. Understanding how these sister planets diverged so radically is one focus of NASA’s recently selected VERITAS mission. As it turns out, Venus’ violent past may be Earth’s future.
From Heavenly to Hadean
Imagine an Earth-like world: an ocean laps gently on a rocky shore under a Sun shining with an unfamiliar intensity. In the distance, you glimpse a volcano steadily erupting, creating an island chain and spewing gases high into the sky.
Fast forward perhaps billions of years, and the waxing Sun has vaporized most of the ocean, while the volcano inexorably churns out hot greenhouse gases. The resulting feedback — volcanism releases more gases, which produces more warming, vaporizing more water, which gives even more warming — dries out all the oceans and turns the world, Venus, into the fierce planetary oven we see today. Indeed, surface temperatures on Venus today are high enough to bake chemicals out of the very rocks, giving rise to the thick layer of sulfuric acid clouds that globally enshroud Venus’ surface.
This story represents our current best understanding of Venus’ history, but we only know it in broad strokes. Filling in the individual chapters requires a closer examination of Venus’ geophysical activity, both ancient and ongoing.
In Venere, VERITAS
On June 2, NASA selected the VERITAS Mission as one of its Discovery Program missions. VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) will use radar, infrared, and gravitational measurements to probe Venus’ geology. Following the highly successful Magellan mission, which ended in 1994, VERITAS will launch in 2028 and operate for about five years.
VERITAS will use radio waves to cut through the thick clouds and measure elevations on Venus’ surface to better than 5 meters (15 feet). Repeat passes over the same regions will allow VERITAS to detect changes as small as 2 millimeters (< 1/10 of an inch). Such changes could result from, for example, volcanic eruptions or Venus-quakes. For example, the 2020 Stanley earthquake produced groundshifts of about 3 centimeters (1 inch).
VERITAS will also use infrared observations to pierce the clouds and explore the surface mineralogy. Different rocks emit light differently in infrared wavelengths, so comparing VERITAS’s infrared observations to the radio elevation maps will tell us something about Venus’ surface mineralogy, which is almost entirely speculative. Active volcanoes on the surface should also stand out like infrared beacons for VERITAS.
Two Roads Diverged … and Then Came Together Again
Stars like our Sun brighten as they age. Eventually, the intensifying sunlight will drive Earth’s climate over a tipping point, producing the same runaway greenhouse effect that Venus experienced long ago. Fortunately, this apocalypse won’t occur for billions of years, long after humanity has found other planetary refuges.
But our current rampant fossil fuel usage is reproducing, in miniature, the eruption of Venusian volcanoes and the resulting greenhouse warming. Hopefully, we can display more intelligence than Venusian volcanoes and avoid the same climatic catastrophe.
Dr. David Grinspoon provides a whirlwind tour of Venus in Venus Revealed and a sobering but optimistic look at climate change in Earth in Human Hands.