Does it feel like all eyes are on Venus these days? The discovery of the potential biomarker phosphine in the planet's upper atmosphere last month got a lot of attention, as it should. However, there is still some uncertainty about what the phosphine discovery means.
Now a team of researchers claims they discovered the amino acid glycine in the atmosphere of Venus.
The paper in which the finding is announced is entitled "Detection of the simplest amino acid glycine in the atmosphere of Venus". The lead author is Arijit Manna, Ph.D. Research Associate in the Physics Department at Midnapore College in West Bengal, India. The paper is on the pre-print website arxiv.org, which means it has not yet been peer-reviewed and published in a journal.
About 500 amino acids are known, but only 20 are present in the genetic code. Glycine is the simplest of them.
The structure of the amino acid glycine. Photo credits: Von NEUROtiker – own work, public domain, https://commons.wikimedia.org/w/index.php?curid=1636637
Although glycine and other amino acids are not biosignatures, they are some of the building blocks of life. In fact, they are the building blocks of proteins. They were also some of the first organic molecules to appear on earth. Glycine is important for the development of proteins and other biological compounds.
The researchers used the Atacama Large Millimeter / Submillimeter Array (ALMA) to spectroscopically detect glycine in the Venusian atmosphere. They found it in the mid-latitudes near the equator. There the signal was strongest and none was recognized at the poles.
In their work, the authors write: “The evidence in the atmosphere of Venus could be one of the keys to understanding the mechanisms of formation of prebiotic molecules in the atmosphere of Venus. Venus' upper atmosphere may undergo much of the same biological process as Earth billions of years ago. "
These two sentences are a real blow. Could there be a biological process in the clouds of Venus? It "might" be one of the keys, and it "might" go through what the earth did. What does it mean?
First phosphine, then glycine
In mid-September, a research team reported that they had found phosphine in the upper atmosphere of Venus (Greaves et al., 2020). Like glycine, it was also more strongly detected in mid-latitudes. Phosphine can be a biosignature and is found on earth. But it can also be produced chemically, although this requires an enormous amount of energy. It was discovered at Jupiter and Saturn where there is ample energy for its production. But Venus does not have the energy to create it.
The team of researchers that discovered phosphine were careful about their own results. In their work, they almost asked other researchers to explain the presence of phosphine without consuming life. “Now astronomers are going to think about all the ways to justify lifeless phosphine, and I welcome that. Please do this, because we are at the end of our ability to identify abiotic processes that can produce phosphine. "
This illustration from an earlier study shows the atmospheric layer that contains phosphine. Photo credit: Truong et al., 2020.
A few weeks later, another team of researchers did just that. In what they called the hypothesized perspective, they said volcanoes could explain the phosphine. "We assume that traces of phosphides formed in the mantle are brought to the surface by volcanism and then expelled into the atmosphere, where they could react with water or sulfuric acid to form phosphine."
The detection of phosphine forms the background for this latest discovery. Both discoveries are part of the bigger questions surrounding Venus: Is her life or the life potential with Venus? Or do these chemicals have nothing to do with life?
Researchers have identified a region in Venus' atmosphere that may be where life can live. From our point of view, it would be a bizarre and unusual arrangement.
For the most part, Venus is extremely inhospitable. The atmosphere is acidic, the temperature hot enough to melt spacecraft, and atmospheric pressure is pushing. But high in the clouds, between 48 and 60 km (30 and 37 miles) above the surface, the temperature isn't that lethal. At this altitude, the temperature ranges from -1 ° C to 93 ° C (30 to 200 ° F). It is very controversial, but some scientists believe that some kind of simple life could survive there and reproduce constantly without ever touching the surface of the planet. Phosphine is easily broken down, so it must be produced continuously for it to be detected. Life at this altitude could be the source of the phosphine.
An artistic impression of the surface of Venus with its thunderstorms and a volcano in the distance. Credit and ©: European Space Agency / J. What more
This new discovery of glycine only adds to the mystery and uncertainty. In their work, the researchers suggest that Hadley cells may be responsible for creating a home for life. "Hadley's circulation in mid-latitudes can provide the most stable life-sustaining condition, with circulation times of 70 to 90 days being sufficient for the (earth-like) reproduction of microbial life."
The detection of glycine also corresponds to the detection of phosphine. "The latitude-dependent distribution of glycine roughly agrees (within? 10?) With the detection limit of recently detected phosphine and with the proposed upper Hadley cell limit where gas circulates between upper and lower altitudes."
This figure from the paper shows the mixing ratio of NH2CH2COOH (glycine) as a function of the atmospheric height (km) within the cloud
Layer (75-80 km) (red curve), compared to PH3 (phosphine) (black curve). Photo credit: Manna et al., 2020.
Don't start the spaceship yet
While the presence of glycine is a fascinating finding and deserves further investigation, it is nowhere near a knockout blow to finding another life. The authors know this and point it out.
"It should be noted that the evidence of glycine in Venus' atmosphere is an indication of the existence of life, but not solid evidence."
It is an ingredient used by life, but not an indication of life.
Her work points to some historical experiments aimed at investigating the chemical origin of life on earth. In 1953, the now famous Miller-Urey experiment restored early conditions on Earth. The researchers created a chemical mixture of water, methane, ammonia and hydrogen and then used energy to mimic lightning bolts. The result was a soup of more complex organic compounds.
A simple diagram of the Miller-Urey experiment. Photo credit: From the original uploader, Carny was at Hebrew Wikipedia. – Transferred from he.wikipedia to Commons., CC BY 2.5, https://commons.wikimedia.org/w/index.php?curid=2173230
The experiment found glycolic acid, a precursor to glycine, and the results supported the theory of abiogenesis. The glycine detected in the Venusian atmosphere could have been produced in the same way as the Miller-Urey experiment. There are other chemical routes to glycine that are possible in the Venusian atmosphere.
"In astrophysics, chemical physics and biophysics, synthetic reaction pathways of the simplest amino acid glycine from simple molecules are of great importance for chemical evolution and the origin of life," the authors write. “The evidence of glycine in the atmosphere of Venus could indicate this
the existence of an early life form in the atmosphere of the solar planet because amino acid is a building block of protein. Venus may be in the primary phase of biological evolution. "
Or maybe not.
"Although glycine is produced by biological processes on Earth, it is possible that glycine is produced on Venus by other photochemical or geochemical means that are not common on Earth." Venus is very different from Earth, and processes take place there that do not exist here on Earth.
This is where all the precautionary measures come into play.
The paper itself has not yet been reviewed by experts. And there are some weaknesses in the results.
For example, the spectroscopic signal of glycine is very close to that of sulfur oxide, so there may be an error in the detection of glycine. And this is just a single detection that has not been duplicated or verified. Glycine is also the simplest of the amino acids and has been found elsewhere. It was discovered on comets and meteorites where there is really no hope of life.
It has also not been seen on any planet other than Earth, which means it would be surprising to see on such a hostile world as Venus.
To find out, we need more spaceships visiting Venus. "A Venus mission with direct sampling from the surface and cloud of Venus could confirm the source of glycine on the planet," the authors say.
The DAVINCI (Deep Atmosphere Venus Investigation of Noble Gases, Chemistry and Imaging) mission proposed by NASA would study the chemical composition of the Venusian atmosphere as it descends to the surface. Photo credit: NASA.
The detection of glycine, if confirmed, is another fascinating development on the way to understanding the Ascension of Life. Or it shows us that chemistry that appears to be prebiotic is only rarely prebiotic, and for the rest of the time it means next to nothing. There is so much we don't know and missions to Venus are the only way we can find out more and answer some of our questions.
For now, however, we can be sure that no life has been found on Venus. Instead, we may have only discovered part of the puzzle that represents the intricate atmosphere of Venus.