Between 2004 and 2017, the American spacecraft Cassini studied for the first time the Saturnian system from orbit. This prolonged mission made it possible to place a lander on Titan, to measure the rotation of Saturn or to show the amazing features of a tiny moon, Enceladus. With its 500 km diameter and surface temperatures around -200° Celsius, Enceladus could be expected to be completely dead. On the contrary, it is one of the most astonishing surprises unveiled by the Cassini mission.
Huge geysers were photographed near the south pole of Enceladus. They rise up to 500 km altitude before feeding the ring E of Saturn. Subsequent gravity and libration measures have brought certainty to the planetologist community : the Enceladus geysers have their source in an immense underground ocean. These discoveries have made the small moon one of the priorities for the search for extraterrestrial life. Unfortunately, the next mission towards Saturn is not planned before a long time.
However, there are still many discoveries to be made in the data collected by the Cassini mission. This is the case of a study published on October 2, 2019 by a German team. The researchers conducted a very thorough analysis of the data collected by a scientific instrument of the space probe, the cosmic dust analyzer. They discovered new chemical signatures that had previously gone unnoticed. They found what they think are organic compounds with nitrogen and oxygen atoms. They think that these compounds are ethanal and ethylamine.
What makes this announcement very interesting is that on Earth these organic compounds are the source of the chemical reactions that produce amino acids and proteins, fundamental components for the appearance of life. The German team that announced these results is largely composed of the same researchers who reported the discovery of complex organic molecules in the Enceladus geysers in 2018.
Enceladus is thought to have geysers linked to a salty underground ocean that contains relatively complex organic compounds. This ocean is interacting with a rocky core. There may be hydrothermal vents, a source of energy that could be used to fuel the chemical reactions necessary for the formation of amino acids, proteins and perhaps more. On Earth, the oldest fossils of microorganisms have been discovered near hydrothermal vents. They could be more than 4 billion years old. Some researchers even think that it is in this environment that life appeared. If all the conditions are right, Enceladus could have known the same history.
Unfortunately, this hypothesis is difficult to verify. What interests us is at the bottom of an ocean, itself covered with a thick crust of ice. And Enceladus is located at a dozen years of travel from us, in good orbital conditions. Still, this discovery could push the development of a new space mission dedicated to Enceladus. The next spacecraft which will be sent towards Saturn is the Dragonfly mission, in 2026. The mission will drop a quadcopter drone on Titan, another fascinating moon of Saturn. Perhaps a small secondary payload could be grafted onto the robot to study the Enceladus geysers.
Like the Earth, Enceladus houses complex organic molecules
– News of July 3, 2018 –
Our system is rich in organic compounds. These molecules, whose composition comprises at least one carbon atom, are considered as the basic chemical elements of life. This is why they are called organic molecules. So far, the organic compounds found in the solar system are fairly simple : methane for example is composed of only 5 atoms. This simple organic chemistry seems very widespread. Some researchers even think that it could have formed in the interstellar medium before the birth of our solar system. But does our solar system also host complex organic chemistry outside the Earth ?
A team from the University of Heidelberg in Germany thinks this is possible on Enceladus. The data used as a basis for their study comes from the Cassini space probe that plunged into the atmosphere of Saturn last year. But before its spectacular epilogue, the Cassini space probe has conducted spectrum analyzes of the water geysers that form at the South Pole of Enceladus. These analyzes show the presence of complex organic molecules. This is the first time we detect it outside the Earth.
Until then, the different organic molecules detected in the solar system had a mass close to 50 units of unified atomic mass. This unit corresponds to one-twelfth of the mass of a carbon atom 12. A methane molecule, for example, has a mass of 16 units of unified atomic mass. Some of the fragments of organic molecules detected by Cassini in Enceladus geysers display masses greater than 200 units of unified atomic mass. They are very complex molecules composed of hundreds of carbon atoms, hydrogen, oxygen and nitrogen. These are molecules very different from those detected on the planet Mars or on comets.
Under the ice crust of Enceladus, complex chemistry allows these molecules to form. It is now almost certain that Enceladus has an ocean of salt water buried deep beneath its ice. Perhaps the ocean floor of Encelade hosts hydrothermal activity : black smokers, kinds of small underwater volcanoes, could provide the energy and heat necessary for these chemical reactions. The organic molecules would then be brought to the top of the ocean by bubbles before being ejected into space by the geysers. This ecosystem of black smokers, underground ocean and geysers could have existed for several billion years. This is insufficient for a protein to form spontaneously. The Enceladus geysers, however, offer a unique opportunity to know what is happening in the depths of Saturn’s little moon.
We will have to be patient : no space mission to the Saturnian system is planned, and even if such a mission is validated it will take between five and ten years of development, then five to ten years of travel before seeing the first results. It is therefore to be hoped that Cassini’s results analyzes will reveal new interesting data to exploit.
An organism of the terrestrian seabed could survive in the ocean of Enceladus
– News of March 13, 2018 –
In recent years, the places of the solar system where we hope to be able to be someday find traces of life are multiplying. There is Mars, of course, and also some frozen moons in orbit around the gas giants, or even other smaller celestial bodies, like Ceres. These environments could house at least some of the ingredients necessary for the appearance of life as we know it on Earth. In parallel, we discover on Earth more and more organisms capable of enduring extreme conditions that would kill almost all other forms of life. They are called extremophilic organisms. They are often very simple beings made up of a single cell, but that remains of life. With hard conditions and living beings able to resist hell, the equation of life may have found a favorable solution elsewhere in the solar system.
Before making such a discovery, we can already wonder if living beings of terrestrial origin could survive on another body of the solar system. A team of Austrian researchers think so. Their study published two weeks ago in the journal Nature is concerned with a particular form of life, called methanogenic archaea. The researchers were interested in the alleged conditions of the moon Enceladus which orbits around Saturn. It is strongly suspected of harboring an ocean of liquid water under a thick crust of ice. For the vast majority of Earth species, the ocean of Enceladus is not a paradise. There is no light, no oxygen and enormous pressure. But for archaeal methanogens, this is not a problem. They can not be classified in bacteria, even if they look a lot like them. They have a methanogenic metabolism, that is, they are able to produce methane and water from dihydrogen and carbon dioxide. This reaction provides it with the energy necessary for its metabolism, without having recourse to light or any form of oxygen. On Earth, it is found in the deep seabed near hydrothermal vents.
The Cassini probe allowed us to observe the chemistry of Enceladus geysers. There is carbon dioxide, dihydrogen and methane. Maybe methane is the product of the conversion of hydrogen and CO2. In appearance, nothing seems to oppose it. To make sure, the team of Austrian researchers has recreated the presumed conditions of the Enceladus ocean in a laboratory. Even under pressure not deemed very lenient with life, methane archaea continued to make methane and to reproduce. For them at least, Encelade seems livable.
Breakthrough Foundation studies an exploration mission of Enceladus
– News of November 21, 2017 –
NASA has developed an instrument to analyze the ocean chemistry of Enceladus, a moon of Saturn. But for the moment no mission is planned towards Saturn. It is not only the US space agency that is interested in Enceladus . The Breakthrough Foundation, funded by Russian billionaire Yuri Milner, has already invested heavily in extraterrestrial intelligence research with Breakthrough Listen, and interstellar travel with Breakthrough Starshot. The foundation of Yuri Milner is now examining the possibility of a private mission to the moon of Saturn. Enceladus attracts a lot of attention thanks to its geysers, discovered by the Cassini probe. The geysers testify to a high probability of the existence of an ocean of liquid water under its ice crust, and thus potentially of the existence of life.
A private interplanetary scientific mission would be a first. The engineers of the foundation imagined a first mission design that would amount to hundreds of millions of dollars. They are now entering a phase where they are looking to reduce costs by any means possible. Several tracks are mentioned, including the use of a solar sail. It seems that the Breakthrough Foundation likes to use photonic propulsion in its projects. During the first six months of 2018, the project will be in the study phase to try to create a mission design that can advance the knowledge of Enceladus and be quite economical to allow private financing.
This project could also be an opportunity for collaboration with NASA and ESA. The two space agencies have already been consulted on the concept. For its part, NASA is in the process to select the fourth mission of the New Frontiers program. Of the dozen or so candidate missions, at least two have Enceladus as the main focus. The choice of the mission will take place in 2019, for a launch scheduled for 2025. Even if NASA selects a mission to Enceladus, it will take at least fifteen years at best to have the results. The mission proposed by the Breakthrough Foundation could speed things up. Yuri Milner insists that he would like a fairly fast launch for his spacecraft. We can hope that a private actor could move quickly, free from the bureaucratic constraints that NASA meets for example. The links between NASA and the Breakthrough Foundation are quite close, as the president of the foundation is Pete Worden, the former director of the NASA research center.
SELFI will study the composition of Enceladus geysers
– News of November 14, 2017 –
Among the major discoveries of the Cassini mission, many clues suggest the existence of an ocean below the surface of Enceladus, a moon of Saturn, making it a prime target for the discovery of an extraterrestrial life in the solar system. But this ocean would be located under miles of ice. Luckily, Enceladus regularly emits geysers consisting mainly of water and that could allow us to study this ocean at a lower cost.
For this, a NASA team is developing an instrument specifically designed to analyze the Enceladus geysers. It’s called SELFI (Submillimeter Enceladus Life Fundamentals Instrument). The main mission of SELFI will be to understand the chemistry of the ocean of Enceladus. For this, the instrument will use a spectrometer that works in the field of radio waves. This should enable it to detect the presence or absence of 13 chemical compounds that are particularly important for the development of life as we know it. There is water of course, but also methanol, ammonia, ozone, hydrogen peroxide, sulfur dioxide and sodium chloride, which make the Earth’s oceans salty.
If SELFI is able to provide us with all this information, then we will have a much more accurate picture of what is happening beneath Enceladus’ surface, and especially if a life as we know it could have developed there. But SELFI has no mission to join, because NASA has not yet announced plans for future Saturnian exploration. The descendant of Cassini will focus on Enceladus, and there is a good chance that SELFI will be part of the mission.
In the meantime, the SELFI instrument or a similar concept could be integrated into the Europa Clipper mission which will be launched at the beginning of the next decade. The moon Europe of Jupiter indeed looks strongly like Enceladus. It is suspected that it also shelters an ocean under a thick layer of ice, and it also has geysers. Finally, NASA plans to use the James Webb space telescope to study these moons. The telescope will use its near-infrared spectrometer to try to determine the composition of Enceladus geysers and of Europe geysers. But it is not sure that these observations will be successful. James Webb must be able to make its observations at the precise moment when the geysers occur, and especially these geysers have to contain enough organic molecules to be detected from the Earth. In any case, an on-site mission will be necessary to have the details of the chemistry of these moons.
Enceladus has elements necessary for the presence of life
– News of April 18, 2017 –
The Cassini mission revealed that the ocean of Enceladus buried under kilometers of ice is supplied with hydrogen by the hydrothermal activity of the nucleus. Concretely this means that Enceladus has an additional brick favorable to the appearance of life. Thus, in addition to a liquid ocean, there is now evidence that potential life forms would have a viable source of energy through methanogenesis. As Thomas Zurbuchen, NASA Associate Administrator, points out, we have never been closer to discovering a potentially inhabited world.
