One of my favorite children’s books is called Cloudy With a Chance of Meatballs. In this fanciful story a town called Chewandswallow has bizarre weather where it rains soup and orange juice, it snows mashed potatoes, the wind blows in storms of hamburgers, and there are tomato tornados.
Some scientists find the idea of organic life raining down on Earth from space equally fanciful. The concept is called panspermia: the theory that life originated in space, spreading through the universe, and that evolution on Earth was driven by an influx of microbes.
Greek philosopher Anaxagoras first proposed that the seeds of life are ubiquitous throughout the cosmos. Even Louis Pasteur thought that spontaneous generation of life could not have occurred on Earth.
Chandra Wickramasinghe and Janaki Wickramasinghe from the Cardiff Center for Astrobiology in Cardiff, Wales say that microbial life from Venus could be swept into the Earth's atmosphere by the steady breeze of the solar wind – the constant flow of charged particles form the sun. Their theory is in a science letter published in the Astrophysics and Space Science journal.
Wickramasinghe and his mentor the late Sir Fred Hoyle developed the modern concept of panspermia over the past few decades. They popularized the unorthodox idea that some viruses can come from comets and infect life on the Earth. Wickramasinghe has gone so far as to suggest that the SARS virus came from outer space.
Even if alien bugs made it to Earth it’s extremely unlikely they could become infectious because they would not have evolved mechanisms to overcome native life’s the natural defenses.
The idea of migrating interplanetary microbes gained new life when a potato-shaped meteorite found in Antarctica, labeled ALH 84001, was suspected of containing fossilized Martian bacteria and other biotracers.
A science team from NASA’S Johnson Spaceflight Center reported in 1996 that "lines of evidence" pointed to the likelihood that a primitive form of microscopic life that flourished on the red planet 3 billion years ago had been found aboard a meteorite that fell to Earth 13,000 years ago. This theory remains highly controversial ever since the research was first presented 12 years ago. Evidence for life transported to Earth from Mars is at best a “definite maybe” say even more optomistic scientists.
It’s estimated that over time tons of rocks from Mars have been hurled into space by asteroid impacts and eventually landed on Earth as meteorites. If organisms existed on ancient Mars, they might have survived within the rocks and colonized Earth. Conversely, asteroid impacts on Earth and Venus could have spread life to Mars, though it much harder because more energy is needed to escape either planet’s stronger gravitational field.
Though Venus’ bone-dry surface is 800 degrees Fahrenheit, the upper atmosphere can be reasonably comfortable and downright earthlike, as I pointed out in an earlier blog.
The climates on Venus and Earth may have been very similar when the planets were born 4.5 billion years ago. Way back then Venus’ surface could have been habitable. However, if Venus had primeval oceans they dried up within the first half billion years.
Scientists have speculated that acid-loving bugs could have evolved to take refuge in the clouds as a runaway greenhouse effect engulfed Earth’s sister planet. This idea dates back to the popular astronomer Carl Sagan who in the 1960s suggested that Venusian microbes might dwell in the atmosphere. The idea was considered so flaky at the time by some astronomers (the term extremeophile didn’t even exist yet) that it didn’t help Sagan’s bid for tenure at Harvard University.
But now there is a claim, albeit highly speculative, of a biotracers in Venus’ atmosphere. Wickramasinghe argues that there should be a lot of Venusian carbon monoxide from continuous lighting activity tearing apart the carbon dioxide that comprises the bulk of Venus’ atmosphere. But The European Space Agency's Venus Express probe found comparatively little carbon monoxide.
Wickramasinghe hypothesizes that Venus has extremeophiles that use carbon monoxide as their only carbon diet. They would be cousins to certain Earth Archaea known as hydrogenogenes that feast on carbon monoxide. He proposes that Venusian extremeophiles live off water and other nutrients supplied by infalling meteors.
Wickramasinghe goes on to further speculate that the presence of hydrogen sulfide and sulfur oxide in Venus’ atmosphere could be biotracers from extremeophiles living in sulfuric acid raindrops.
Finally, he proposes that the aerosols in the upper Venusian atmosphere are consistent with the sizes of bacterial spores. Whew! This place has more action than my septic tank!
Venus has a negligible magnetic field to shield the planet so the solar wind eats into the cloud tops. This has been observed by Venus Express as a tail of outflowing atmospheric gases streaming off Venus like the wake of a comet.
In 1997 the SOHO solar observatory satellite detected a flux of oxygen and carbon ions from Venus reaching Earth. This happened when Venus was exactly between Earth and the sun at inferior conjunction.
Wickramasinghe says that under certain conditions microbes from high in Venus's atmosphere could be blown into the Earth's atmosphere like seeds off a dandelion. The microbes could surf their way to Earth in a few days or weeks, riding on electrostatically charged dust grains.
But the Sun, Earth and Venus must be exactly aligned. This last happened in 2004 and will happen again in 2012.
So If Wickramasinghe is right, what happens when the little buggers get here? He speculates the a fraction of the extremeophiles-laded particles make it through Earth’s magnetosphere down to the troposphere.
The particles may serve as condensation nuclei for raindrops. The Venusian extremeophiles would crash land on raindrops and then compete with terrestrial organisms for food. Without finding some surface niche they would in all likelihood perish, says Wickramasinghe
As farfetched as these ideas sound, the notion of terrestrial planets exchanging biological material is becoming accepted. Any future worries about contaminating Earth with a rock sample returned from a Mars mission may be moot. Earth has possibly been receiving extraterrestrial visitors over billions of years.
Photos, top to bottom: NOAO; NASA; NASA; ESA; ESA
Recent Comments