Despite recent reports of possible fossils in Martian meteorites, Venus, not Mars, may hold the most promise for harboring life elsewhere in our solar system, according to a University of Colorado at Boulder professor.
Some four billion years ago when the sun was 40 percent cooler than today, Earth and Mars probably were frozen, said CU-Boulder Assistant Professor David Grinspoon of the astrophysical and planetary sciences department. But Venus, closer to the sun, may have had warm liquid oceans and a mild climate at the time. "There is some reason to believe Venus may have been the best haven for life in the early solar system," he said.
Humans on Earth "may have evolved from life forms provided by Venus," Grinspoon said. "Pieces of planets were blasting off of each other all the time early in the evolution of the solar system, and microbes from Venus could easily have wound up on Earth."
With 900 degree Fahrenheit surface temperatures and an atmosphere permeated by carbon dioxide, chlorine and sulfuric acid clouds today, Venus seems inhospitable to "our kind of life," he said. "But we really don't know much about life -- its requirements, it's differences and how to recognize it."
The standard scientific view is that life requires water and carbon-based molecules, he said. "We simply do not know if that is the only chemical system that can make life, because the only example of a biosphere we have is our own," said Grinspoon, who has been studying the surface, atmosphere and clouds of Venus for 10 years through NASA-sponsored programs.
Grinspoon is the author of "Venus Revealed," released this month by Addison-Wesley Publishing Co. of Reading, Mass. Written for non-scientists, the book contains a number of surprising new findings and speculations gleaned from recent space missions in addition to photos and illustrations.
In some ways, Venus may have a better environment for nurturing life than Mars, he said. Like Earth, Venus has a "chemically lively surface and atmosphere" that could provide organisms with energy and nutrients.
"In my view, what makes Earth special is its atmospheric cycles that renew themselves like a garden tilling itself," he said. "It could well be that kind of an environment on Venus is just as important for life as carbon."
Because the surface and atmosphere of Venus are constantly renewing themselves through volcanic activity, there is "more potential for interesting chemical and even biochemical processes on Venus than on Mars."
It's possible, he said, that Venus could have tiny microbes in its cloud particles, or that some form of Venusian life could have developed by using ultraviolet light much like Earth's plants use sunlight to make food. There could even be a non-carbon-based equivalent to lichens atop Venus' five-mile-high volcanoes, perhaps feeding on sulfur gases, he said.
The interactions of Earth's oceans, clouds, surface and biosphere has led some scientists to support the Gaia theory that Earth itself is a living system, he said. "By constantly exhaling sulfur gases that react with the clouds and surface minerals, Venus could be considered in that Gaia realm."
Although NASA's 1989 Magellan probe opened a new window on the planet using sophisticated radar mapping, there is still much to learn about Venus, said Grinspoon. One key is to keep an open mind about chemical and perhaps biological processes that may be occurring there and on other planets.
"Venus is the closest thing Earth has to a twin," he said. "Studying Venus is how we learned about the problem with our ozone layer, and it's a way for us to become wiser in taking care of our own planet."
Excerpts and images from "Venus Revealed" can be accessed on the World Wide Web at: http://sunra.colorado. edu/david/book.html