Enceladus, considered by many to be one of the most likely places in the solar system to host extraterrestrial life, has been attracting our attention. It has a liquid ocean hidden deep under the ice, full of possibilities for life, and its complex geological activity reveals the extraordinary nature of this satellite. Recently, a new study has revealed the chemical composition of Enceladus's plume, providing more clues to our exploration of the life potential of this icy world.
The study, published in the journal Nature Astronomy, is a reanalysis of data collected during the Cassini spacecraft's two flyby of Enceladus in 2011 and 2012. Cassini is a spacecraft developed by the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Italian Space Agency (ASI), launched in 1997 and ended its mission in 2017. It was the first spacecraft to orbit Saturn and its moons, and the first to detect the plume of Enceladus.
The Enceladus plume is a stream of material ejected from the South Pole region of a satellite, similar to a geyser or volcanic eruption on Earth. Cassini first discovered this phenomenon in 2005 and attracted a lot of attention from the scientific community. These plumes appear to come from the subsurface ocean beneath cracks in the satellite ice surface, meaning they can reflect the chemistry of the ocean, thus providing a window into the search for life.
Cassini carried an ion and neutral mass spectrometer (INMS) that could measure the type and number of molecules in the plume. Previous analyses have identified the presence in the plume of molecules such as water, carbon dioxide, methane, ammonia, and molecular hydrogen, all of which are essential building blocks of life, or metabolites of life. However, these analyses do not cover all possible molecules and do not take into account the interactions between molecules, so some important information may be missed.
To compensate for this shortcoming, the Harvard team used a new approach to re-examine the data processed by the INMS equipment team and compare it to a large known mass spectral library. They used a statistical analysis technique called Bayesian inference, which calculates the probability of billions of possible components of plume matter based on existing knowledge and observational data. With this approach, they discovered a number of previously unidentified molecules, including some organic molecules such as hydrogen cyanide, acetylene, propylene, and ethane, as well as alcohols (methanol) and molecular oxygen.
These newly discovered molecules increase the chemical complexity of the Enceladus plume and provide additional clues to the understanding of the nature and evolution of Enceladus' subsurface ocean. For example, hydrogen cyanide is an important organic molecule that can be involved in the synthesis of amino acids and nucleotides, which are the basic building blocks of proteins and nucleic acids. Acetylene and propylene are hydrocarbons that can undergo hydration reactions in water to produce more complex organic molecules. Alcohols are solvents that dissolve organic molecules and can also act as energy for life**. Molecular oxygen is an oxidant that can participate in redox reactions and can also act as a breathing gas for life.
The research team believes that these molecules suggest that there is a diverse "chemical storehouse" beneath the surface of Enceladus, which may be a habitable environment or can support some forms of microbiome. However, they also emphasize that whether these molecules can actually support life in Enceladus depends largely on how much they are diluted in the ocean below the surface, and how they react with other molecules. To answer these questions, more data and experiments, as well as more advanced detectors, are needed.
This study provides some valuable information and enlightenment for future Enceladus exploration missions. For example, the European Space Agency plans to launch a probe called the Enceladus Life Probe in 2026, which will carry a more advanced mass spectrometer that can measure molecules in the plume more precisely. In addition, NASA is also considering a concept called the Enceladus Seaworld Probe, which would carry a probe that could penetrate the ice and enter the ocean to directly probe the conditions and composition of the ocean. These missions are expected to be realized in the next decade, providing more opportunities and hope for mankind to unravel the mysteries of Enceladus and search for life outside the solar system. The Enceladus plume contains a variety of organic molecules