What if the only alien bacteria were there?

Speculation about life on Venus : A gas as an indication of extraterrestrial life forms?

Venus is considered a planet of hell: on its surface there are temperatures around 450 degrees Celsius and almost a hundred times the atmospheric pressure of the earth. But in the atmosphere, at an altitude of 50 to 60 kilometers, there are tolerable temperatures and pressures - conditions under which bacteria could feel comfortable.

Now an international team of researchers has found traces of the gas monophosphine in this well-tempered region of the Venusian atmosphere - which is not chemically stable there. A reference to life?

Despite an intensive search, the scientists have not yet been able to identify any chemical process that could produce monophosphane. Either a previously unknown process is producing the gas - or it is of biological origin, according to the researchers in the journal "Nature".

An ideal candidate for pointing to life?

The detection of trace gases that are not chemically stable in their environment is considered by astrobiologists to be a particularly suitable method for the detection of biological activity. "An ideal biosignature gas would be clear: living organisms would be the only conceivable source," write Jane Greaves of Cardiff University in Great Britain and her colleagues.

Unfortunately, in addition to the biological origin, there are often photochemical or geochemical processes that can be used for production - or the gas is difficult to detect using spectroscopy.

An ideal candidate is monophosphine, a molecule made up of one atom of phosphorus and three atoms of hydrogen. It occurs in traces in the terrestrial atmosphere - one molecule per one trillion atmospheric molecules - and is exclusively of biological or industrial origin.

This is why it is considered a biomarker, even though it is highly toxic in high concentrations. Because phosphorus is highly reactive, which is why monophosphine is extremely unstable in most atmospheres - including that of Venus - so it would have to be constantly replenished.

[Read more about the search for extraterrestrial life here - at Tagesspiegel Plus]

Greaves and her colleagues had set themselves the goal of setting an upper limit in a similar range as the terrestrial value for the trace gas in the Venusian atmosphere in order to test this detection method.

All that remains is the conclusion: Is there life on Venus?

But their observations with the James Clerk Maxwell Telescope in Hawaii and the ALMA telescope system in Chile came as a surprise: The researchers found clear absorption lines of monophosphane, which resulted in a frequency of 20 molecules per billion atmospheric molecules.

In meticulous detailed work, Greaves and her colleagues looked for ways to produce monophosphine under Venus conditions: through photochemical processes in the atmosphere, processes on the surface, outgassing from the interior of the planet, electrical discharges or the influx of meteorites from space. Without success.
"If no known chemical process can explain the monophosphane, then a process must generate the gas that has so far been considered implausible under the conditions on Venus," Greaves and her colleagues conclude cautiously. "It could be about unknown photochemical or geochemical processes - or about life."

Another indication speaks for the latter hypothesis: The observations show the trace gas only in low and middle latitudes, but not in the polar regions of the Venusian atmosphere. The monophosphane is thus in the region of special atmospheric circulations, the Hadley cells. And it is precisely there that, in the opinion of many astrobiologists, the conditions would be most favorable for bacteria.

But even this is only an indication and not yet clear evidence of life on Venus.

Now new: We give you 4 weeks of Tagesspiegel Plus! To home page