There are probably many more ingredients for life on Saturn's Enceladus than those identified so far, says Dr. Frank Postberg from Heidelberg University in Germany, the author of a paper published on June 27, revealing the presence of complex carbon-based molecules in the core of the moon. He says that a new mission could reveal a "rich zoo" of such organic molecules and provide solid proof of life beyond the earth.
You analyzed data collected by the Nasas Cassini probe from the ice-cream plumes spurting out of Saturn's Moon Enceladus. What did you find?
We really discovered large, complex organic (carbon-based) molecules emitted from Enceladus. Previously, there were very simple organic substances known to be released into the plume. Something like methane, or methanol, or perhaps ethane, molecules consisting of maybe two or more three carbon atoms. It's pretty common. And sometimes you'll find comets or meteorites some more complex things like simple amino acids. But what we see here is very complicated. There are hundreds of carbon atoms, hydrogen, oxygen and nitrogen from which these large molecules are built.
does it mean life on Enceladus?
There is a wide range of possibilities. Of course, complex organic molecules do not necessarily mean that there is life. Actually they can be poisonous. But on the other hand, complex organic molecules are a necessary precursor to life.
Enceladus endorses this underground ocean, so the organics come from that sea. The moon also has hydrothermal activity at the bottom of this ocean. So astrobiologists rank this moon to (ha) the highest (probability) to host living lives today, potentially. And so, the foundation of organic molecules, with the complexity we have here, of course, reveals these speculations of sustainability or even the life of that moon.
What is so unusual about these molecules?
Molecules of such complexity are not often seen outside the world. It was also a surprise to us that Enceladus delivers these organic substances to Cassini spacecraft. We observe processes that probably happen 60 km below the surface of the moon. There is the 5 km thick ice crust and then, under the 50 km thick global ocean, and then the hydrothermal activity is at the core of the moon.
Hydrothermal fluids are heated inside the core of the moon, and probably that is what the organism is from which Enceladus lives in space so we can see it with a spacecraft flying forward.
Was there anything surprising about the results?
People said that if the organic must go through 50 km of sea, they would hydrolyze ̵
Can we draw conclusions from the fact that the molecules were not hydrolyzed?
It probably tells us that we only see the top of the iceberg when it comes to Enceladus Organic Chemistry. These are things that have not reacted with the water and are easily identifiable using the Cassini Spacecraft tools.
Cassini instruments were never designed to investigate Enceladus plume, because Cassini himself discovered this plume. We were pleased that Cassini had such a versatile instrumentation that we could immediately investigate the new discovery, but it is still not meant to do that.
That's why the data we have not allowed (us) to tell exactly what the molecules are. But we know the principle principle (there and) we can try this with a follow-up mission, with instruments designed for the task. We know that the organic and enriched grains are there, and with modern instruments we can tell if they are life or not.
Do you think they are life indicators?
We can not tell you. What we can tell it is very likely that these complex organic substances come from this hydrothermal system at the core of Enceladus. Whether biotic chemistry is in progress, or just abiotic organic synthesis, (where) are you organizing organic substances in this hot high pressure environment … both are possible.
But even the abiotic thought that you have this hydrothermal active moon that produces increasingly complex molecules-even if it's not life, it can develop into prebiotic chemistry. Whatever it is, it is very interesting.
Now we know where to look and what should we look for, will we see much more of these types of molecules?
Yes. These are the organic substances that are the highest concentrations of icecream. We can also identify them with the simple Cassini instruments, and they leave a fingerprint so obvious that we can detect it. If we go there with more sensitive instruments, we are sure that we will discover more organic substances, a rich zoo of organic molecules that will tell us how far organic chemistry has evolved and if it has evolved even to life .
There is no follow-up mission to Enceladus yet. But the results of the past year or so, now we know we have hydrothermal activity there, we know we can try it, we know how it works, I think it really happens for a follow-up mission.
You are also studying other odd moons in the solar system. Could we find the same molecules elsewhere?
There are five or six ocean monsters now, but only for Europe – it's a sea mound around Jupiter – we know that the ocean is in contact with the rocky kernel and it is also very likely that hydrothermal reactions are at work there . It is not proven, as in the case of Enceladus, but this is the other place where similar processes can happen. Therefore, there are two or three missions already in the books to go to Europe to do similar investigations made by Cassini to Enceladus.
And the fact that we only have two objects in our solar system alone, which are so good candidates to be habitable, are fascinating if you only extrapolate what it means to the universe's home in general.
This discovery was made through your work on the Habitat OASIS project, which is a five-year project and you are only 1.5 years old. Are there more results to get out of data?
We understand, of course, that we can refine the analysis of the type of organics we presented in the Nature Paper. So there will be refinements that might give us a clue if there is biotic chemistry or not, but on the other hand we also look for other organic species. And it is safe on the cards that we find other very different organic species in data.
And then the second aspect of the contribution is to prepare for the European mission. (So) that we use the knowledge we now get from Enceladus (to) knows which associations to look for, what are the masses, how we best analyze data, how to derive the composition of complex organic molecules. So that we learn from Cassini to the next mission to Europe.
And finally, do these findings tell of something about the origins of life on earth?
It's a long shot. Now it's a bit early, but it says in any case that these hydrothermal systems can produce complex organic substances at high concentrations. It's something new, it was not clear. Now we know that hydrothermal systems outside the earth, which might have similar early relationships to life on earth, produce at least one very complex organic chemistry. If we find life alive, Enceladus is on its way to life, or even has life, then this would favor similar scenarios for the origins of life on earth.
Macromolecular organic compounds from the depths of Enceladus by Frank Postberg, https://doi.org/10.1038/s41586-018-0246-4
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