Planetary scientist, Dr. David Grinspoon, of the Southwest Research Institute, has studied Venus as a Principal Investigator for NASA's Planetary Atmospheres and Venus Data Analysis Program. As he describes this cloudy world: "Brighter than any star, never in the same place for long, Venus is a live-wire, sparkling and dancing through our evening and morning skies."
|Venus up-close, as photographed by the Soviet Venera 13 lander, which parachuted to the Venusian surface on March 1, 1982
While Venus shares with Earth a similar size (95%) and mass (80%), its thick greenhouse atmosphere has transformed a potential terrestrial twin into a hostile, burning acidic world. When the Soviet Venera landers (1975-1982) first touched down amidst solidified lava flows and acid rain, the bright planet's shroud was momentarily lifted: pictures revealed the 'morning-' and 'evening-star' up close, as if under one's feet. In total, more than 20 spacecraft have now tried to visit Venus, most recently highlighted by the US Magellan mission to plot detailed radar maps. Unlike earlier portrayals in mythology or in science-fiction, Venus offers life-as-we-know-it anything but a hospitable place. Underneath those luminous clouds that reflect back 80% of incoming sunlight, writes Grinspoon, "the most important single quality distinguishing Venus from Earth is the near total lack of water there."
"At a conference I attended recently," he reflects, "a colleague began his talk on exobiology by stating: 'We assume that life requires liquid water because otherwise the problem is completely unconstrained.' He went on to give a brilliant talk on the prospects for finding habitable planets."
As Dr. Grinspoon shares in the preface to his book, "Venus Revealed: A New Look Below the Clouds of our Mysterious Twin Planet," the world nearest to us offers opportunities for 'planetary self-knowledge': "Like most nerds, I was drawn into my field (planetary sciences) simply because it was the coolest thing I could imagine doing. ..Recently, we have learned that Venus seems to embody an active planetary system with many complex feedbacks among surface, atmosphere, climate and clouds. Thus Venus may serve as a valuable companion to Earth as we learn to live on, and with, our world."
"The portrait of Venus, as a verdant, rainy, overgrown swamp planet--perhaps complete with tree ferns and jungle animals--", writes Dr. Grinspoon, "became widespread in the popular and scientific literature through the nineteenth and most of the twentieth centuries." When one considers that as recently as 1955 -just a few years before the dawn of the space-age, the famous British astrophysicist, Fred Hoyle, considered Venus to be covered planetwide in oil, apparently our nearest neighbor still has many secrets left to reveal. [Hoyle speculated upon what became known as 'Hoyle Oil': "Venus is probably endowed beyond the dreams of the richest Texas oil-king".]
|Much of the surface of Venus is covered by lava flows (shown above).
The details are foreboding. At its surface, the Venusian atmosphere is 90 times denser than Earth's, or about the same as being 1 km (0.6 miles) beneath terrestrial oceans. The average surface temperature (470 degrees C, or 870 F) is hot enough to melt lead. At night, amidst distant lightning strikes high in the clouds, the ground would glow a faint red. Venus' surface is the hottest in our solar system, despite being twice the distance of Mercury from the Sun. Or as Dr. Grinspoon illustrates: "You could fry an egg on the sidewalk, but you'd have to do it quickly, before the sidewalk melted."
Venus has no tilted axis, and thus no winter, summer, nor any seasonal change. A relatively gentle breeze of a few miles per hour at the surface builds to a cloud-top gale that swirls like perpetual hurricanes: 350 km/hr, or 210 mph. While rather quiet geologically for the last few hundred million years, today's Venus is still volcanically active. Its terrain is marked by several large shield volcanoes, and is covered with solidified lava flows. Because of its slow rotation, the Venusian day and night each last 59 Earth days, or about two Earth months.
Journey with Dr. Grinspoon, as he takes a fly-by of mighty Aphrodite, Earth's environmentally-evil twin: the second rock from the Sun, sulfurous, suffering from a runaway greenhouse effect.
Excerpt from Venus Revealed: A New Look Below the Clouds of our Mysterious Twin Planet [Copyright Grinspoon]
|David Grinspoon, Principal Investigator for NASA's Exobiology Research Program, believes that the simultaneous existence of hydrogen sulfide and sulfur dioxide suggests the presence of life.
Is there life on Venus? Could there be life on Venus? The standard answers are "No and NO!". Venus is usually dismissed in a paragraph or two before an extensive discussion of the prospects for life on Mars, the icy moons Europa and Titan, and Earth-like planets elsewhere in the universe. Where life is concerned, Venus is consistently voted "least likely to succeed". In my opinion, this quick dismissal is not justified; It presupposes knowledge of the universal nature of life and the general characteristics of inhabited planets; knowledge that we do not yet possess. ...In our present state of ignorance we should avoid all dogma in exobiology (the study of possible life beyond Earth).
The current paradigm of exobiology has been around for about 30 years or so: life is carbon based, made by chemical evolution of organics in water. Earth-like environments are the only places where life can really be expected to flourish. You have to wonder, though, about any theory that concludes that our kind of life is the only kind, and that our planet is uniquely qualified to become alive.
Of course there is a serious objection to this. Neither organic (carbon) compounds nor liquid water can exist at the temperature of the Venusian surface. But how sure can we be that this rules out life?
First let me say that I am a big fan of carbon-based life. Some of my best friends are carbon-based. Carbon and water are two substances that each have incredible properties on their own. In combination they do something completely different, something that neither could do on its own. Carbon, with some oxygen, nitrogen and a few other elements mixed in serves as the universal template, the flexible yet solid Lego blocks of life that can build up an endless variety of huge and complex molecules. Water is the universal solvent. Dissolved in water, carbon molecules are free to flop around, twist themselves into complex shapes and interact with one another in the intricate dance that we call life. Something magical and creative beyond belief happened here as a result of carbon and water. Once it started it never stopped and it completely re-made our world. Carbon in water crawls and flies, respirates and synthesizes, colonizes, adapts, seeks and hides, gives birth, invents, worries, wonders and sings. If that's not magic, then what is?
|The surface of Venus is scarred by a history of volcanism. The lack of liquid water probably prevents the planet’s tectonic plates from shifting around.
Image credit: NASA
An obvious objection to this line of argument is the following: we have not thought of any other ways to do it. If there are other possible biochemistries, then what are they? Make a counter-suggestion! I am not persuaded by this objection. It's true that no one has devised an alternative biochemistry, but this could be a measure of our ignorance. I think it is safe to say that we would not have thought of carbon-based life either, if we hadn't had the Earth's example to examine and dissect.
We are still trying to learn how biochemistry works here on Earth.
Admittedly, this is a long shot, but I consider life on Venus to still be an open question. In any case, thinking about it is a worthwhile exercise that may help us to better understand the real limits of life.
Reader's Advisory: This Box Contains Explict Speculation!
I have now crawled so far out on a limb that I see no reason to try climbing back. I may as well jump! So let me propose some possible signs of life on Venus. Let me state clearly that I regard each of these possibilities as extremely unlikely.
Here are four phenomena that could be signs of life on Venus:
1) The atmospheric 'superrotation' could be created by life.
This is one of the most obvious and large scale unexplained features of the planet. ..From the point of view of any Venusian bugs that want to use sunlight for energy, the superrotation would be a major plus because the night [59 days] is so long there. The planet may rotate too slowly for photosynthesis unless you have something like superrotation.
2) Maybe the 'unknown ultraviolet absorber' is a photosynthetic pigment.
|Ultraviolet image of Venus obtained by Pioneer-1.
Image Credit: BNSC
If Venusian life has evolved to take advantage of UV light, this might be done in the form of a pigment that absorbs ultraviolet. If this is some complex chemical unknown to us, that could explain why we have had such a tough time figuring out the identity of the 'unknown ultraviolet absorber'. [Venus viewed with an ultraviolet filter shows] a complex swirl of high contrast features, ranging from finely, detailed splotches to huge planetwide streaks. And the stuff moves around like crazy. The identity of this material, so dark in the ultraviolet that it is responsible for nearly half of the solar energy absorbed by Venus, is still not known, one of the great mysteries of Venus.
3) Maybe Mode 3 cloud particles are alive.
Mode 3 are the odd, large cloud particles. ...we do not have a good description of them or explanation for them. Some measurements suggest that they are made of sulfuric acid...but there is also evidence of more exotic chemicals, like chlorine or nitrogen compounds...In fact, conditions in the clouds of Venus are not too different from those at the surface of the Earth. There is a level in the clouds (about 33 miles up), where the atmospheric pressure is about 70% of the pressure at sea level on Earth, and the temperature is a balmy 107 degrees Fahrenheit. ..It's cool enough for liquid water, and small amounts of it exist there (in a strong sulfuric acid solution). Still, something in my gut tells me that the clouds of Venus are not a good biological habitat. That something is stomach acid, hydrochloric acid. Acid eats organic molecules.
4) The highly reflective mountain tops could be covered with life.
Some kind of transformation happens to the ground all around the planet above an altitude of 13,000 feet (which corresponds to a temperature of 820 degrees).
Now that I have gotten those flights of fantasy out of my system, it's time to come back down to Earth--or at least to Venus. Here is another reason why the possibilities of life on Venus may not be completely academic to students of exobiology: there are probably more Venus-like than Earth-like planets in the universe.
We know, for sure, that there are signs of life at a few places on Venus. We know because we left them there--the smashed, corroding remains of our inquisitive machines. The most recent addition to this smattering of Earth-junk is whatever is left of Magellan.
"How soon and in what style will we go back to Venus?..We could put a small craft with a few carefully chosen instruments in orbit around Venus, or land a very small package on the surface for a ballpark figure of $200 million...here are some questions for future missions:
- What drives the superrotation of the upper atmosphere?
- What is stabilizing the climate?
- What is the 'snow' at high altitudes?
- What is the present rate of volcanic eruptions?
- What does the surface look like up close?
The Soviet Vega mission of 1985 pioneered the use of balloon stations in the Venusian atmosphere. We could do alot more along these lines. By setting balloons adrift in the atmosphere, we could learn about circulation patterns...At lower altitudes, cameras on balloons could photograph the surface as they circled the planet, getting a free ride from the superrotation. ...[For instrumentation], the two that most excite me are cameras and seismometers...there are surely places of fantastic beauty and complexity..."