Evidence for Life Elsewhere in the Solar System?

Environmental & Science Education, STEM, Cosmology, Astronomy, Solar System, Earth Science, Earth Systems, Nature of Science

Edward Hessler

There is not much to say about the discovery of the molecule phosphine (PH3) in the atmosphere of Venus other than that it was a great surprise. The original observations were made at the James Clerk Maxwell Telescope in Hawaii. In the study (link at end) authored by Cardiff University professor Jane Greaves and her colleagues, the discovery is more modest, couched in the language of science: "apparent presence of phosphine." On rocky planets it is produced only, as far as is known, by living critters so explaining its presence awaits further research, data and explanation. Phosphine is referred to as a biomarker/bioindicator.

Venus is inhospitable, to put it in the most kind terms. On the surface the temperature is ~860 degrees Fahrenheit (~460 Celsius). However at the upper limit of the Venusian atmosphere it is almost shirtsleeve weather: about  85 Fahrenheit (~29 C). The atmosphere is a choker, consisting mostly of only two gases:~ 96% carbon dioxide and ~3%+ nitrogen.

Phosphine seems an unlikely candidate as an indicator of life as Nell Greenfieldboyce (NPR) explains. Here are a few of the characteristics she describes. It stinks, is very toxic and is highly flammable. It is used as a fumigant and was also employed in chemical warfare during WWI. It also interferes with oxygen metabolism but as we know there is life on Earth that doesn't rely on oxygen, finding it toxic. They produce phosphine in large quantities. However, it  breaks down quickly so how could it possibly accumulate in detectable quantities in the clouds of Venus? Continual replacement  appears to be a possibility, for now a working hypothesis. Greenfieldboyce's report may be read in full.

I just jumped way, way ahead. You could infer that life as been found in the atmosphere of Venus. Far from it. What has been found is phosphine and the question is whether it is produced by living organisms OR by an unexpected/unknown chemistry independent of life.

It seems impossible that an opportunity currently exists to learn a little more almost immediately and without launching a satellite probe although in the end an orbiting satellite with detection equipment will add more clarity to these first observations. It would be very useful to know about the abundance of phosphine over time. In an essay for Forbes, Johnathan O'Callaghan describes this happy circumstance, one though without any guarantee of success..

"BepiColombo, launched in 2018, is on its way to enter orbit around Mercury, the innermost planet of the Solar System. But to achieve that it plans to use two flybys of Venus to slow itself down, one on October 15, 2020, and another on August 10, 2021. What is not known is whether the instrument on this probe is sensitive enough to detect phosphine."

The observations to be made on the first flyby--at 10,000 km (6000+ miles)--are quite literally chiseled in stone and can't be changed. Since the second flyby is about a year away this gives scientists and engineers time for planning as well as to profit from what they learned from the first flyby to revise their observation schedule and possibly measurement of observations for the second flyby at only 550 km (~340 miles). 

As Jorn Helbert of the German Aerospace Center puts it "On the first flyby we have to get very, very lucky. On the second one, we only have to get very lucky. But it’s really at the limit of what we can do.”

The original paper by Greaves et al., is technical! (my emphasis)