[BRIEF NOTE] On Venus' lost oceans

[rfmcdonald]

I forget who posted a link to this CBC article, "Venus probe images hint at ancient ocean." Venus, it seems, now Earth's hellish twin, might once have been a lush water world. Thank the Venus Express space probe for this discovery.

Long before Venus became a hot, dry and barren planet with a choking mass of carbon dioxide for an atmosphere, it might have once been home to shifting continents and an ocean of water, according to the latest data from a European space probe.

Using infrared images of the planet's southern hemisphere taken in 2006 and 2007 from the Venus Express probe, German astronomers say they have produced a map that reveals the planet's highland plateaus were likely once ancient continents surrounded by water.

The researchers relied on infrared imagery because the planet's thick atmosphere of carbon dioxide and sulphuric acid makes visual imagery of the planet's surface difficult, and probes landing on the planet haven't lasted long on the surface, where temperatures can get up to 477 C.

The imagery showed that different areas of the planet had different surface temperatures, information that provided insight into the chemical composition of different areas of the planet.

A look at the highland plateaus suggests they are made of a substance similar to granite, which is formed on Earth when ancient rocks made of basalt are driven down into the planet by shifting continents, mix with water and then re-emerge through volcanic activity.

[. . .]

Past theories of the history of our sun suggest that about four billion years ago, it might have been just 70 per cent as bright, raising the possibility temperatures on Venus might have once been cool enough to have liquid water.

But as the sun's power grew, the thinking goes, conditions on Venus changed, and liquid water would have evaporated, leaving carbon dioxide in the atmosphere instead of dissolving in water. The increased carbon dioxide would in turn trap more heat on the planet.

This idea has been discussed for a long time, with mechanisms discussed in the early part of this century and mentions beforehand--Sagan and Druyan mentioned this possibility in their 1980s book Comet. The planet was doomed to be a hellhole, sadly; the idea ofterraforming the planet seems almost impossible given that Venus has good reasons to be a dead world.

Life could well have evolved on this world.

"If that's true, then the two warm and wet bodies in the early solar system would have been Earth and Venus, and as far as a place for the origin of life, Venus was equally favourable to Earth - Venus may be the closer analog to early Earth," [planetary scientist David Grimspoon] says.

If oceans on Venus lasted long enough, then more complex life forms might even have emerged, he says: "If we get into the 2 billion year range in timescale then you could imagine that more complex evolution happened - not just an origin of life, but time for interesting evolutionary development."

Life might even exist on Venus now, floating high in the clouds far from the rock-melting surface.

In September 2002, planetary scientists (Dirk Schulze-Makuch and Louis Irwin) made public their speculations that there may be microbial life in the high Venusian clouds (as those in Earth's clouds), based on their finding of atmospheric abnormalities uncovered in data from past Russian and U.S. space probes (Venera, Pioneer, and Magellan). Although Solar radiation and lightning (which has been detected by the ESA's Venus Express probe in 2007) should be producing large amounts of carbon monoxide (CO), the gas was found to be scarce, as if something was removing it (such as hydrogenogens, diverse bacteria and archaea that grow anaerobically utilizing CO as their sole carbon source and water as an electron acceptor to produce carbon dioxide and molecular hydrogen as waste products). The Venusian atmosphere also contains hydrogen sulphide and sulphur dioxide, although these two compounds react with each other and so are not usually found together unless they are being continually produced by anaerobic bacteria decomposing organic matter. In addition, carbonyl sulphide was also found, although it is most easily produced by organic processes

Hence, the scientists suspect that bacteria in Venusian clouds may be using energy from ultraviolet radiation to produce those unusual chemical compounds from carbon monoxide and sulphur dioxide. If they exist, these bacteria could be the evolved descendants of those that developed in oceanic waters on a cooler, early Venus, before those waters evaporated from a runaway greenhouse effect. If the planet's change of climate was slow enough for life to adapt, however, microbes like those on Earth (capable of aerobic and anaerobic biochemical processes involving sulfur compounds exhibited by diverse microorganisms that include autotrophic thiobacilli, methylotrophs, methanogens, and sulphate-reducing bacteria) could have survived, perhaps living today in acidic clouds at altitudes of about 31 miles (or 50 kilometers) where the temperature ranges only from about 50 to 70 °C. Venusian clouds at this altitude are very acidic, but this region of its atmosphere also has the highest concentration of water droplets.

Here's to hoping. I'd like some of Venus' biosphere--Earth's kindred biosphere, perhaps--to have survived that world's heat death.