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 garnered a lot of attention, as it should. There’s still some uncertainty around what the phosphine discovery means, though.
Now a team of researchers claims they’ve discovered the amino acid glycine in
Venus’ atmosphere.
The paper announcing the finding is titled “Detection of simplest amino acid
glycine in the atmosphere of the Venus.” The lead author is Arijit Manna, a
Ph.D. Research Scholar in the Dept. of Physics at Midnapore College in West
Bengal, India. The paper is at the pre-print site arxiv.org, which means it
hasn’t been peer-reviewed and published in a journal… yet.
There are about 500 known amino acids, but only 20 are present in the genetic
code. Glycine is the simplest of them.
Though glycine and other amino acids aren’t biosignatures, they are some of
the building blocks of life. In fact, they’re 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 detect glycine in Venus’ atmosphere with spectroscopy. They found it in the
mid-latitudes, near the equator. That’s where the signal was strongest, and
there was none detected at the poles.
In their paper, the authors write “Its detection in the atmosphere of Venus
might be one of the keys to understanding the formation mechanisms of
prebiotic molecules in the atmosphere of Venus. The upper atmosphere of
Venus may be going through nearly the same biological method as Earth
billions of years ago.”
Those two sentences pack a real punch. Could there be some kind of
biological process going on in the clouds of Venus? It “might” be one of the
keys, and it “may be going” through the same thing Earth did. What does it
mean?
First Phosphine, Then Glycine
In mid-September, a team of researchers reported finding phosphine in the
upper atmosphere of Venus (Greaves et al, 2020). Like glycine, it was also
detected more strongly at mid-latitudes. Phosphine can be a biosignature and
is on Earth. But it can also be created chemically, though that requires an
enormous amount of energy. It’s been detected at Jupiter and Saturn, where
there’s abundant energy for its production. But Venus doesn’t have the
required energy to create it.
That team of researchers that discovered phosphine was circumspect with
regards to their own findings. In their paper, they almost pleaded with
other researchers to account for phosphine’s presence without invoking life.
“Now, astronomers will think of all the ways to justify phosphine without
life, and I welcome that. Please do, because we are at the end of our
possibilities to show abiotic processes that can make phosphine.”
Then a couple of weeks later, another team of researchers did just that.
In their paper, called a hypothesis perspective, they said that volcanoes
could account for the phosphine. “We hypothesize that trace amounts of
phosphides formed in the mantle would be brought to the surface by
volcanism, and then subsequently ejected 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 larger questions around Venus: Is their
life or the potential for life at Venus? Or are these chemicals unrelated
to life?
Researchers have identified a region of Venus’ atmosphere that might be
able to host life. It would be a bizarre and unusual arrangement from our
perspective.
Venus is extremely inhospitable, for the most part. The atmosphere is
acidic, the temperature is hot enough to melt spacecraft, and the
atmospheric pressure is crushing. But high in the clouds, between about 48
and 60 km (30 and 37 miles) above the surface, the temperature isn’t so
lethal. At that altitude, the temperature ranges from -1 C to 93 C (30 to
200 degrees F). It’s very controversial, but some scientists think a type
of simple life could survive there, perpetually reproducing, without ever
touching the planet’s surface. Phosphine is easily degraded, so it must be
continuously produced for it to be detected. Life at that altitude could
be the source of the phosphine.
This new discovery of glycine only adds to the mystery and the uncertainty.
In their paper, the researchers propose that Hadley cells could be
responsible for providing a home for life. “The mid-latitude Hadley
circulation may give the most stable life-supporting condition with
circulation times of 70–90 days being sufficient for (Earth-like) microbial
life reproduction.”
Also, the detection of glycine matches up with the detection of phosphine.
“The latitude dependent distribution of glycine roughly matches (within
?10?) with the detection limit of recently detected phosphine and with the
proposed upper Hadley-cell boundary where gas circulates between upper and
lower altitudes.”
Don’t Launch the Spacecraft Yet
While an intriguing finding and worthy of more study, the presence of
glycine is nowhere close to a knockout blow in the quest to find life
elsewhere. The authors know this and are careful to point it out.
“It should be noted that detection of glycine in Venus’ atmosphere is a
hint of the existence of life but not robust evidence.”
Their paper points to some historic experiments designed to test the
chemical origin of life on Earth. In 1953, the now-famous Miller-Urey
experiment recreated the early conditions on Earth. The researchers created
a chemical mixture of water, methane, ammonia, and hydrogen and then applied
energy to mimic lightning. The result was a soup of more complex organic
compounds.
The experiment produced glycolic acid, a precursor to glycine, and the
results backed up the abiogenesis theory. The glycine detected in Venus’
atmosphere could have been produced via the same pathway as the Miller-Urey
experiment. There are also other chemical pathways to glycine that are
possible in Venus’ atmosphere.
“In astrophysics, chemical physics and biophysics, synthetic reaction
routes of the simplest amino acid glycine, from simple molecules have
great significance with chemical evolution and the origin of life,” the
authors write. “The detection of glycine in the atmosphere of Venus may
indicate
the existence of an early form of life in the atmosphere of the solar
planet because amino acid is a building block of protein. Venus may be
going through the primary stage of biological evolution.”
Or it may not.
“Though in Earth, glycine produces by biological procedures, it is
possible that in Venus glycine is produced by other photochemical or
geochemical means, not common on Earth.” Venus is very different from
Earth, and there are processes taking place there that are not present
here on Earth.
Here’s where all the cautions come in.
The paper itself hasn’t been peer-reviewed yet. And there are some
weaknesses in the results.
For example, the spectroscopic signal of glycine is very close to that of
sulfur oxide, so it’s possible there’s an error in the detection of
glycine. And this is only a single detection, not duplicated or verified.
Also, glycine is the simplest of the amino acids and has been found
elsewhere. It’s been detected on comets and meteorites, where there’s
really no hope of life.
It also hasn’t been seen on any other planets than Earth, which means it
would be surprising to see on a world as hostile as Venus.
To find out, we need more spacecraft visiting Venus. “A Venus mission with
direct sampling from Venusian surface and cloud may confirm the source of
glycine in the planet,” the authors state.
The detection of glycine, if confirmed, is another intriguing development in
the quest to understand the rise of life. Or it may be showing us that
chemistry that appears to be prebiotic is only prebiotic in rare cases, and
the rest of the time, it means next to nothing. There’s so much we don’t
know, and missions to Venus are the only way to find out more and to answer
some of our questions.
But for now, we can rest assured that life hasn’t been found on Venus.
Instead, we may have uncovered just one more piece of the jigsaw puzzle that
is Venus’ complicated atmosphere.
Reference:
Detection of simplest amino acid glycine in the atmosphere of the Venus
Arijit Manna, Sabyasachi Pal, Mangal Hazra
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