Study group mulls life on Venus

By Leonard David

updated 5:51 p.m. ET Feb. 21, 2006

BOULDER, Colo. - A special study group has advised NASA that Venus is far too hellish of a world for life to exist on or below the planet’s surface. Furthermore, while the potential for life in the clouds of Venus can’t be ruled out, the expert panel gauged this possibility as extremely low.

The assessment concluded that “no significant risks” exist in contaminating Venus with Earth organisms on any future landers or atmospheric probes, including balloons. Likewise, any surface materials shot back from Venus or whiffs of its atmosphere returned to Earth pose no significant risk to our planet in terms of “back contamination.”

A Washington, D.C.-based arm of the National Academies, the National Research Council’s Space Studies Board, formed a Task Group on Planetary Protection Requirements for Venus Missions under its Committee on the Origin and Evolution of Life.

The six-person study group was chaired by Jack Szostak of the Howard Hughes Medical Institute, Massachusetts General Hospital, with their findings released today in a letter report to NASA that requested the advice.

“In its deliberations, the task group examined planetary protection considerations affecting Venus missions. The known aspects of the present-day environment of Venus offer compelling arguments against there being significant dangers of forward or reverse biological contamination, regardless of the unknowns,” Szostak explained to John Rummel, NASA’s Planetary Protection Officer, in a Feb. 8 cover letter to the task force findings.

Far from friendly
Since the early years of spacecraft exploration, Venus has been repeatedly targeted for up-close inspection—by orbiters, balloons, atmospheric probes, as well as landers.

Venus Express, launched by the European Space Agency (ESA) and now en route, will swing into orbit around the planet in April.

In its report, the task force noted that despite Venus being Earth’s near twin in terms of its mass, radius, and other bulk properties, the planet’s surface is far from friendly and perhaps represents “the most hostile planetary environment ever explored by robotic spacecraft.”

Surface temperatures are hot enough to melt lead. The surface pressure on Venus is the crushing equivalent of being nearly a mile deep in Earth’s ocean. The landscape, covered in volcanic rock, is desolate and waterless, but rich in sulfur. Venus’s atmosphere is more than 96 percent carbon dioxide, with 3 percent nitrogen and traces of other gases.

Enshrouding Venus are three distinct cloud layers. Water vapor there ranges from a few parts per million at the top of the cloud deck to a few tens of parts per million at the base. Cloud droplets, however, are formed of extremely concentrated sulfuric acid. Now toss in for good measure a high flux of solar ultraviolet radiation that floods the cloud deck.

Cloudy life
The task group said that there is general agreement that surface conditions on early Venus were much more Earth-like and far more conducive to life than what is present today. Many of the processes on Venus in its past are thought to be relevant to the origin of life here on Earth.

Plausible theories have been posed, the task force stated, about how life may have occurred on early Venus. As the planet’s environment was overtaken by a runaway greenhouse effect, some scientists suggest, perhaps microbial life that existed fled to more clement temperatures and pressures in the clouds.

In its report, the task force observed that any life remaining in the cloud deck would have had to adapt to conditions that do not overlap the range of conditions inhabited by life on Earth.

“Consequently, considerations of a possible origin of life on Venus are not relevant to considerations of the possibility that life currently exists on the surface of Venus or that living organisms of Earth origin could survive there,” the report states. “The origin of life within the Venus cloud deck must be considered to be highly improbable.”

Hostile chemistry
The task force questioned whether or not the surface of Venus has been volcanically active on a constant basis. It is not clear whether or not clouds have lingered throughout the history of the planet.

“There may well have been periods when Venus was entirely cloud free. If this has occurred, any cloud-based microbial ecology would have been permanently extinguished,” the report explained.

However, the task force added that while it is impossible to completely rule out the possibility that life might exist in the cloud decks of Venus, they consider this possibility to be “extremely low because of the hostile chemical nature of the cloud environment.”

Therefore, any hitchhiking terrestrial organisms having survived the trip from Earth to Venus on a spacecraft plowing through that planet’s atmosphere would be quickly destroyed.

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