Is Venus by Mars?

Why are we so obsessed with Mars?

That seemed to be the question posed by planetary geologist Martha Gilmore on February 4 during her Frontiers Lecture, “The Terrain of Venus” at the Museum of Natural History’s Kaufmann Theater.

Mars has captured the human imagination for generations. From sci-fi books to B-movies, the red planet has intrigued earthlings everywhere.  This fascination has even led many to ponder the question, “Is there life on Mars?” But in a sweeping exploration of another planet sometimes called “Earth’s twin,” Gilmore made the case that we should be far more curious about life on Venus. Gilmore spoke with the wonder of a child who at age seven said she changed her career choice from ballerina to planetary geologist. A professor of Earth and Environmental Sciences at Wesleyan University, Gilmore studies the surface morphology and composition of Venus, Mars and the Earth.

Gilmore probed the possibility of Venusian life from an obvious starting point. “We live in a habitable universe, right?” Right. We earthlings live in the so-called “habitable zone” of our solar system, where liquid water can exist on the surface. Within such zones, according to Gilmore, the elements that make for a habitable planet include an atmosphere, sufficient mass and liquid water.

With a surface temperature of 864 degrees Fahrenheit, Venus today is generally considered too hot to sustain life. But, three billion years ago, according to Gilmore, when the sun was younger and cooler, Venus was one of three planets in our solar system’s habitable zone. Gilmore speculated that Mars, in its early history, should have been habitable due to early volcanic activity that has since ended. Earth, meanwhile, has been habitable for 3.8 billion years. And Venus, she estimated, was habitable for a couple of billion years. Venus, back then, possessed the three features necessary to sustain life.

First, Venus had volcanoes. Geologic activity is essential to supporting life on a planet. Researchers have found that at least 90% of Venus’ surface is covered by lava flows and broad shield volcanoes. As volcanoes erupt, water is released and emitted as vapor through a process called convection. “They’re our primary conduit for getting water out into the atmosphere,” Gilmore explained.

Second, Venus is big enough. Gravity is a function of size, and you can’t have an atmosphere without enough gravity. The Earth, Mars and the Moon all began with molten cores, but today, the Earth is the only body that remains hot. Due to their smaller size, Mars and the Moon cooled off much earlier. Gilmore explained that with this cooling, their volcanoes shut down, causing convection to stop. As a result, they can no longer maintain an atmosphere. “Planets must be large enough to stay geologically active long enough for life to develop,” said Gilmore, who pointed out that the Earth and Venus are almost identical in size. Gilmore contends that based on size alone, Venus was able to sustain an atmosphere.

So that leaves the third feature necessary to sustain life: water. In the early days of the solar system, when Earth, Mars and Venus were all in the habitable zone, all three planets had water.  “Mars lost its water early because its volcanoes turned off. Earth is still going strong,” said Gilmore. “And now we think that Venus had water on it for a couple billion years.”

For all these reasons, Gilmore declared with a smile, “Venus is better than Mars!”  So what does this mean for the rest of the planets? For the universe? For us?  For one, Gilmore said we should be spending a lot more time exploring Venus.  Here’s why. Gilmore presented graphs that depicted sulfur dioxide trends on Venus between 1980 and 2010. Sulfur dioxide is released by a volcano when its magma is approaching the surface. The sulfur dioxide levels were high in 1980, then dropped, then saw a bump in 1990, and then dropped again.

Then, in 2005, the European Space Agency launched the Venus Express spacecraft for its first mission to Venus. When the spacecraft arrived in April 2006, the level of sulfur dioxide measured was exceptionally high and unstable. Something was producing sulfur dioxide, said Gilmore, and releasing it into Venus’s atmosphere. She believes this evidence points to the fact that Venus is still geologically active today.

Gilmore concluded by imploring the audience to share the story of Venus and to even write to Congress to promote further exploration.  “Venus is important,” said Gilmore. “It’s a key to understanding earth-sized planets and exoplanets” throughout the universe.