Is it possible to find ‘living cells’ in the core of Saturn’s moon Enceladus? | sorae portal site to the universe

a satellite of SaturnEnceladus” has been attracting attention since it was observed by the Cassini spacecraft in 2005. There are geysers near the south pole of Enceladus that periodically release plumes of water into space.

Observational evidence provides strong evidence that the interior of Enceladus is heated and melted by tidal forces, and that there is a liquid ocean beneath the thick ice that covers the surface. In addition, the plume contains organic molecules that are rather complex, as well as chloride ions and sodium ions, so it is believed that this ocean is well equipped to support life.

If there is life in the oceans of Enceladus, it is thought to be similar to life on Earth’s deep ocean floor. In such an environment, chemosynthetic organisms such as methanogens that metabolize inorganic substances from hydrothermal vents resulting from geothermal activity live instead of sunlight, which cannot reach. If there is life in Enceladus, it should be life with such a metabolic pathway.

Enceladus is one of the leading candidates for extraterrestrial lifeBut finding that evidence is not easy. If there is an ocean beneath the ice of Enceladus, it is beneath an ice shell estimated to be 30-40 kilometers thick, and the ocean itself is believed to be 10 kilometers deep. Such a deep hole has never been dug even on Earth, and even if there is a biosphere, it is said to be very small in size, so even if underwater could be sent in, it would very difficult to search for. . Therefore, whether or not life can be found through direct exploration is likely to be a story for now.

[▲ Ffigur 2: Darlun graffigol o weithgareddau mewnol Enceladus. O dan y gramen rhewllyd mae cefnfor hylifol, y tybir bod ganddo fentiau hydrothermol ar y gwaelod o ganlyniad i weithgarwch geothermol. Yn ogystal, mae dŵr môr yn ffrwydro fel geiser o ran denau’r iâ. Mae’r plu a ddatgelwyd gan arsylwadau Cassini yn dystiolaeth gref o gefnforoedd hylifol a gweithgaredd geothermol. (Credyd delwedd: NASA / JPL-Caltech / Sefydliad Ymchwil De-orllewin)]

However, the plume ejected from Enceladus may contain living cells. Of course, the ejected organisms would be exposed to low temperatures and vacuum in an instant, so it would be impossible to see anything alive. However, there may be an opportunity to see frozen cells. However, it is not known whether they actually contain cells at technically detectable levels.

A research team led by Antonin Affholder at the University of Arizona tested whether future probes orbiting Enceladus and collecting plumes can detect biological cells. First, the research team estimated the number of cells in the upper part of the seawater based on the size of Enceladus’ presumed biosphere. Then, the number of cells that are ejected from the feather, how many cells can be collected by the spacecraft in one piece of the feather, the rate at which cells are destroyed by exposure to vacuum, and the performance limit of the measuring instrument We examined the probability of undetectable errors and calculated whether the cells could be detected realistically.

Consequently, we hypothesized that the number of cells in the plume would be up to 10 million cells per mL (milliliter), the amount that could be collected in one pass would be 0.00001 (1/100,000) mL, and that the rate of cell damage would is 94%.Cells can be detected after 100 fly passesI understand. 100 times may seem like a high barrier, but for example, in the case of the probe “Enceladus Orbilander,” which aims to reach the 2050s, the number of plumes is set at 1,000 times, so it is quite attainable. • a number of times.

In addition, even if direct detection of cells is not possible, alternative schemes to detect amino acids are also considered. Amino acids are substances that can be produced in natural environments other than life, but their abundance is thought to be limited in the absence of life. If the amount of complex organic molecules such as amino acids in the feathers is large, it is difficult to think of reasons other than life. Therefore, even if direct evidence of cells cannot be found, by measuring the amount of organic molecules instead, it is possible to consider whether the possibility that life does not exist is high or low.

It is probably quite a naive idea to expect to find life just by collecting feathers. However, the relatively simple method of narrowing down the possibility of the existence of life can be applied to observations of other celestial bodies where life is expected to exist, just like Enceladus.

Source

• Antonin Affholder, et.al. – “Putative Methanogenic Biosphere in the Deep Ocean of Enceladus: Biomass, Productivity, and Implications for Detection”. (The Planetary Science Journal)
• Kylianne Chadwick. – “What would it take to discover life on Saturn’s icy moon Enceladus”. (University of Arizona)

Text: Riri Ayae