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According to Dr. Frank Postberg of the University of Heidelberg, Germany, the lead author of an article published on June 27 revealed the presence of many other ingredients on Saturn's moon Enceladus. complex carbon-based molecules in the nucleus of the moon. He says that a new mission could reveal a "rich zoo" of such organic molecules and provide solid evidence of life beyond the Earth.
You have analyzed the data collected by NASA's Cassini spacecraft of Enceladus moon ice grains plumes. What exactly did you find?
We discovered very complex and complex organic molecules (carbon-based) emitted by Enceladus. Previously, there were very simple organic compounds known to be emitted in the plume. Something like methane, or methanol, or maybe ethane, molecules that consist of maybe two or three carbon atoms at most. It's quite common. And sometimes you find in comets or meteorites more complex things like simple amino acids. But what we see here is much more complex. These are hundreds of carbon atoms, hydrogen, oxygen and nitrogen (from which) these large molecules are constructed.
Does this mean that there could be life on Encelade?
This is a wide range of possibilities. Of course, complex organic molecules do not necessarily mean that there is life. In fact, they can be toxic. But on the other hand, complex organic molecules are a necessary precursor to life.
Encelade houses this submarine ocean, so that organic matter comes from this ocean. The moon also has hydrothermal activity at the bottom of this ocean. Thus, astrobiologists classify this moon as having the highest probability of harboring current life, potentially. And so the discovery of organic molecules, with the complexity that we have here, of course feeds these speculations about livability or even life on this moon.
What is so unusual about these molecules?
Molecules of such complexity are not often observed outside the Earth. It was a kind of surprise for us too that Encelade delivers these organic materials to the Cassini spacecraft. Here we observe processes that probably occur 60 km below the surface of the moon. There is ice crust 5 km thick and then the global ocean 50 km thick, and then hydrothermal activity occurs in the heart of the moon.
Hydrothermal fluids are heated inside the heart of the moon and probably from where organic matter originates, which Enceladus kindly delivers in the space so we can see it with a flying spaceship.
People said that if organic matter had to travel 50 km from the ocean, they would hydrolyze – water would react with these organic matter and probably decompose it. But that really does not happen. We can not say for sure whether organic matter is biotic (related to living organisms) or abiotic, but that it is there, and that it obviously floats over the ocean, which is really surprising and amazing at the same time.
Can we draw conclusions from the fact that the molecules have not hydrolyzed?
It probably tells us that we only see the tip of the iceberg in terms of Enceladus' organic chemistry. These are things that have not reacted with water and are easily identifiable with the instruments of the Cassini spacecraft.
Cassini instruments were never designed to study Enceladus plume, as Cassini himself discovered this plume. We were happy that Cassini had such a diverse instrumentation that we could immediately investigate the new discovery, but still, it is not made for that.
That is why the data we have do not allow us to say exactly what are the molecules. But we know the proof of principle (there are some and we can) to probe this with a follow-up mission, with instruments designed for the task. We know that organic and fortified grains are there, and with modern instruments we can say whether they are alive or not.
Do you think they are indicators of life?
We can not say it. What we can say is very likely, these complex organic compounds come from this hydrothermal system in the nucleus of Enceladus. Whether it is biotic chemistry or abiotic organic synthesis (where) you are preparing organic foods in this hot and high pressure environment … both are possible.
But even the abiotic idea that you have this hydrothermally active moon producing increasingly complex molecules, even if it's not yet life, it could evolve into prebiotic chemistry. Whatever it is, it's really interesting.
Now we know where to look and what to look for, will we see many more of these types of molecules?
Yes. Organic matter is the highest concentration in ice grains. We can identify them even with Cassini's simple instruments, and they leave a fingerprint so obvious that we can see it. If we go there with more sensitive instruments, I'm sure we'll discover more organic matter, a zoo rich in organic molecules that will tell us how organic chemistry has evolved and if it has evolved even to life.
There is no follow-up mission for Enceladus yet. But last year's results, we now know that we have hydrothermal activity there, we know that we can sample it, we know how it works, I think it really requires a mission to followed.
You are also studying other icy moons in the solar system. Could we find the same molecules elsewhere?
There are now five or six oceanic moons, but only for Europa – this is an oceanic moon around Jupiter – do we know that the ocean is in contact with the rocky core, and there are also the reactions are at work there. This is not proven, as in the case of Enceladus, but it is the other place where similar processes could occur. That's why there are already two or three missions in the books to go to Europe to do surveys similar to those of Cassini for Enceladus.
And the fact that we have only two objects in our solar system that are such good candidates for being habitable is fascinating, if you simply extrapolate what it means for the habitability of the universe in general .
This discovery was made thanks to your work on the Habitat-OASIS project, which is a five year project and you only have one and a half year. Are there more results to draw from the data?
First of all, we know that we can refine the analysis of the type of organic compounds that we have presented in the journal Nature. So there will be refinements that may give us a clue if the biotic chemistry is involved or not, but on the other hand, we are looking for other biological species as well. And it is certainly on the cards, that we will find other really different organic species in the data.
And the other aspect of the grant is to prepare the Europa missions. (So) we use the knowledge we now get from Enceladus to know which compounds to look for, what are the masses, how to best analyze the data, how we can deduce the composition from complex organic molecules. As we take Cassini's lessons on the next mission in Europe.
And finally, do these discoveries tell us anything about the origins of life on Earth?
It's long. Now, it's a bit early, but at least that tells us that these hydrothermal systems can produce complex organic compounds at high concentrations. It's something totally new, it was not clear. We now know that hydrothermal systems outside the Earth, which may have conditions similar to life on Earth, produce at least a very complex organic chemistry. If we see life emerge, that Enceladus is on its way to life, or even to life, then it would promote similar scenarios for the origin of life on Earth.
More information:
Macromolecular organic compounds from the depths of Frank Postberg's Enceladus, https://doi.org/10.1038/s41586-018-0246-4[19659032] Proposed by Horizon: The European Magazine for Research and Innovation
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