Xenobiologists at NASA's Jet Propulsion Laboratory are proposing to search for life beyond Earth in the wake of one simple reaction - the binding of amino acids to luminous substances, according to an article published in the journal Analytical Chemistry.
“Our technique allows us to understand which amino acids in the samples got into them from non-living sources, such as meteorites, and which molecules were produced by life. One of the main goals of NASA is to search for traces of life in the Universe. And the best chance to find it is to analyze water samples from water worlds, including Enceladus and Europa, the moons of Saturn and Jupiter,”said Peter Willis of NASA's Jet Propulsion Laboratory in Pasadena, USA.
What is life?
The discovery of dozens of Earth-like planets and thousands of planets in general in recent years has raised the question of scientists with renewed vigor - are we alone in the Universe? Moreover, the discovery of geysers on Enceladus, the moon of Saturn, and similar emissions of water on Europa, the moon of Jupiter, indicate the possibility of extraterrestrial life within the solar system.
Ever since the mid-60s, when the pioneers of space exploration at NASA and the USSR began to think about the search for extraterrestrial life, there has been a raging debate among scientists about what counts as life. Scientists argue about how it looks, how it can be seen, "tasted" or touched, and how its potential fossil footprints can be distinguished from the products of natural processes in inanimate nature.
According to Willis, the simplest and most convenient case for us would be the discovery of either the living organisms themselves, or their constituents - proteins, DNA molecules, complex sugars and fats - inside soil, water or the atmosphere of alien worlds. This is easier to do than distinguishing a real fossil from a bizarre cluster of multi-colored crystals, but it's still quite difficult to do.
According to scientists from NASA, there are two problems - the similarity of the "building blocks of life" from inanimate nature and their analogs in the organisms of primitive microbes, as well as their relative rarity. The primitive constituents of proteins, sugars and fats have recently been found in comets and asteroids, making their discovery in the waters of Europa or Enceladus no longer proof of life in their subglacial oceans.
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A drop of life in the sea
Willis and his colleagues solved both of these problems by creating a new method for analyzing water samples, which allows to simultaneously find all amino acids in the most microscopic concentrations, and to distinguish their "living" versions from the products of chemical evolution of substances in outer space or on the surface of planets.
For this, scientists have used a well-known pattern - the "left-handedness" of life. This is manifested in the fact that in the synthesis of protein molecules and enzymes, cells use exclusively those amino acids that are twisted to the left. With sugars, the situation is the opposite - life uses only "right" carbohydrates, twisted in the opposite direction.
Guided by this idea, Willis and his colleagues have created special glowing molecules that bind only to the "left" amino acids. When an amino acid is attached to such dyes, it changes its color and begins to move more slowly inside the solution, which makes it possible to determine the presence of real "building blocks of life" even in the smallest concentrations, and to count them literally down to a molecule, passing them through ultra-thin capillary vessels.
To test the efficiency of this idea, scientists went to the most "extraterrestrial" place on Earth - to the shores of Lake Mono, California, whose waters contain so much alkali that so far only a few bacteria have been found in it. Today Mono is considered the closest analogue of what the subglacial ocean of Enceladus looks like, which also contains a lot of alkalis and salts.
The capillary technique of Willis and his colleagues bore fruit - scientists were able to record the presence of 17 amino acids at once in Mono waters at concentrations that are almost 10 thousand times lower than those that the SAM laboratory on board the Curiosity rover can "smell" outside the Earth.
In the near future, Willis and his colleagues plan to create another set of such tests for the "right" amino acids in case life on other planets will use them. Such a device, scientists hope, will become one of the main instruments on board the descent module of the Europa-Clipper mission, which will go to Jupiter's moon in mid-2020.
