Chemical that should not be in Venus’s atmosphere


in great shape / Spectral signature of charged phosphine on an image of Venus.

Today, researchers are declaring that they have seen a chemical in the atmosphere of Venus that has no right. The chemical, phosphine (a phosphorus atom inclined to three hydrogens), will be unstable in the conditions found in Venus’s atmosphere, and there is no clear way to account for the chemistry of the planet.

This is why there is a lot of speculation about the possibility of Venus not having any possibility of life in the upper atmosphere. But many people about this work require input to not be included in the initial study, which signals today’s publication. However, there are certainly reasons to think that phosphine is present on Venus, requiring some very involved computer analysis to detect it. And of course there are some creative chemists who want to rethink the possible chemistry of our nearest neighbor.

What is Phosphine?

Phosphorus is a row under nitrogen on the periodic table. And just as nitrogen can combine with three hydrogen atoms to form the familiar ammonia, phosphorus can bind to three hydrogens to form phosphine. Under Earth-like conditions, phosphine is a gas, but not a pleasant one: it is highly toxic and has a tendency to spontaneously combust in the presence of oxygen. And the latter feature is why we don’t see it much today; It is simply unstable in the presence of any oxygen.

We make it for our own use. And some germs that live in an oxygen-free environment also produce it, although we have neither identified the biochemical process nor the enzymes involved. Nevertheless, any phosphine that manages to escape into the atmosphere quickly dissipates into oxygen and is destroyed.

This is not to say that it does not exist on other planets. Gas giants like Jupiter have. But there is an abundance of hydrogen in their atmosphere and no oxygen, allowing chemicals such as phosphine, methane, and ammonia to survive in the atmosphere. And intense heat and pressure close to the massive core of a gas provide a situation in which phosphine can spontaneously form.

So we have a clear division between gas giants, with hydrogen-rich atmospheres where phosphine can form, and rocky planets, where the oxidizing atmosphere must ensure that it is destroyed. For that reason, people have suggested that phosphine may be a biosignature that we can detect in the atmosphere of rocky planets: we know that it is produced by life on Earth and is unlikely to exist on these planets when Until it is replaced continuously. Which some researchers ended up pointing to a telescope in Venus’s atmosphere.

Looking for signs

Specifically, researchers turned to the 15-meter James Clerk Maxwell Telescope Telescope in Hawaii. JCMT is able to image in wavelengths around one millimeter, which is an interesting one for Venus’ atmosphere. In the warm lower atmosphere of Venus, there is an abundance of radiation in this region of the spectrum. And absorbs phosphine at a specific wavelength in the region. Therefore if phosphine is present in the upper atmosphere, its presence should create a gap at a specific location in the flood of radiation generated by the lower atmosphere of Venus.

In theory, this is an extremely simple observation. In fact, however, it is a nightmare, simply because the levels are so low. Here on Earth, where we know that phosphine is made, the steady-state level in the atmosphere is in the region of one part-per-trillion because it is destroyed so quickly. Venus is also moving relative to the Earth, meaning that the location of any signal needs to be adjusted for Doppler transfer. Finally, any indication would also be complicated by what researchers have called “ripples” or instances when parts of the spectrum appeared to reflect somewhere between Venus and the telescope.

These extensive computer processing of telescope data was required. But to the surprise of scientists, this analysis shows the presence of phosphine. (In their paper, the researchers write, “The objective was a benchmark for future development, but unexpectedly, our initial observations suggested an exploratory volume of Venusian PH”3 Was present “) So they had someone else repeating the analysis independently. The signal was still there. The researchers also confirmed that their approach was able to detect water with deuterium, an isotope of hydrogen, which we know Venus is present in the atmosphere. They also ruled out the possibility that they would misidentify the nearby sulfur dioxide absorption line.

Denying obvious problems, he got a hold of time on the second telescope. That second telescope was the Atacama Large Millimeter Array or ALMA. It has a better resolution power, allowing researchers to consider Venus more than a point source of light. This confirmed that the phosphine signal was still there and was most acute in degeneration, absent from the poles and equator. This means that it is present at sites where atmospheric circulation is high.

The researchers eventually concluded that phosphine is present at a level of 20 parts-per-billion.

How did that happen in the world?

Assuming that analysis continues, the big question is how phosphine was found. The researchers estimated how quickly it would be destroyed by the conditions of Venus’ atmosphere, and they used it to calculate how much phosphine would have to be produced to maintain 20 parts-per-billion levels. And then they search for some kind of chemical reaction that can produce so much.

And, well, there is not a plethora of good choices. Under conditions prevalent in the atmosphere, both phosphorus and hydrogen will usually be oxidized, and there is not much of either. While solar radiation can potentially release some of the hydrogen, it will do very slowly, and thermodynamics will indicate that it is more likely to react with anything other than phosphorus. Similarly, reaction routes based on a potential volcano of Venus would decrease the production of sufficient phosphine by factors of about one million.

All of which leads researchers to a somewhat disappointing conclusion: “If no known chemical process can explain PH3 within Venus’s upper atmosphere, then it must be formulated by a process that already precedes Venus’s Not considered praiseworthy for the position. ” Apparently, however, there is a presumption that one of the reasons that needs to be considered is that people looked for phosphine in the first place, namely that it could be produced by living things.

But Venus is unlikely to be involved with life. Nothing we would recognize as life would possibly survive a ferocious hot planet surface bathed in supercritical carbon dioxide. The temperature in the upper atmosphere, where the phosphine signature originates, is very moderate. But this would require some form of life that moves permanently in the upper atmosphere and somehow escapes exposure to the planet’s sulfuric acid clouds.

Disagree

So we are left in a strange place. One of the researchers who led the work said, “It took about 18 months to explain myself. There was a hint.” You can expect that the rest of the field will now spend some time trying to explain itself, perhaps by pointing to an entire flock of extra telescopes on Venus. Meanwhile, chemists are trying to think of additional reaction pathways that may work under conditions such as Venus.

There is a reasonable chance that we will report back on the results of these efforts long ago, indicating that nothing unusual is happening from the Sun to another planet. But if it does not, it will give a big push to the steady chorus of voices arguing that we need to do more to detect Venus. Some plans are made about the inclusion of airplanes that can spend extended periods moving about Venus’s upper atmosphere. Should these results hold up, airships would seem to be the right means to find out what is being produced of this chemical.

Nature Astronomy, 2020. DOI: 10.1038 / s41550-020-1174-4 (about DOI).