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NASA researchers propose to look for signatures of life near the surface of Enceladus and Europa

NASA scientists conducted an experiment that simulated conditions on Jupiter's icy moons Europa and Saturn's EnceladusיAnd they came to the conclusion that if there is life on them, there is no need to dig deep to find at least their remains

This composite image shows suspicious jets of water vapor erupting at the 7 o'clock position outside the boundary of Jupiter's moon Europa. The streams, imaged by NASA's Hubble Space Telescope's Imaging Spectrometer camera, were seen in silhouette as the moon passed in front of Jupiter. The Hubble data were collected on January 26, 2014. The image of Europa superimposed on the Hubble data consists of data from the Galileo Voyager missions Credit: NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center
This composite image shows suspicious jets of water vapor erupting at seven o'clock outside the boundary of Jupiter's moon Europa. The streams, imaged by NASA's Hubble Space Telescope's Imaging Spectrometer camera, were silhouetted as the moon passed in front of Jupiter. The Hubble data was collected on January 26, 2014. The image of Europa, superimposed on the Hubble data, consists of data from the Galileo Voyager missions. Credit: NASA/ESA/W. Sparks (STScI)/USGS Astrogeology Science Center

Jupiter's moon Europa and Saturn's moon Enceladus show evidence of oceans beneath their icy crusts. A NASA experiment seeks to examine whether these oceans support life, by examining the signatures of life that appear in the form of organic molecules (eg amino acids, nucleic acids, etc.), and may survive just below the surface ice despite the harsh radiation on these worlds. If robots are sent to land on these moons to look for signs of life, they won't have to dig deep to find amino acids that have survived after being modified or destroyed by radiation.

"According to our experiments, the 'safe' sampling depth for amino acids on Europa is about 20 centimeters at high latitudes of the trailing hemisphere (the hemisphere that is in the opposite direction to Europa's motion around Jupiter) in an area where the surface has not been disturbed much by meteorite impacts," said Alexander Pavlov of NASA's Goddard Space Center in Greenbelt, Maryland, lead author of a paper on the study.

We will not be required to dig a sample deep below the surface to identify amino acids in Enceladus - these molecules will survive radiolysis (breakdown by radiation) anywhere under the surface of Enceladus and we can find the results of the exposure less than a few millimeters from the surface." Pavlov continued. The study was published in the journal Astrobiology.

The icy surfaces of these moons, which are almost devoid of atmosphere, are not considered suitable for life due to radiation from fast particles trapped in the magnetic fields of Jupiter and Saturn respectively, as well as those originating from powerful events in deep space. However, both moons have oceans beneath their icy crusts that are heated by tidal forces from the gravity of the host planet and nearby moons. These underground oceans may contain life if they also contain sources of energy, as well as elements and compounds used in biological molecules.

The research team conducted experiments with amino acids as possible representatives of biological molecules on icy moons. Amino acids can be formed by life or by non-biological chemistry. However, finding certain types of amino acids on Europa or Enceladus would be a possible sign of life, "because they are used by terrestrial life to build proteins."

Proteins are essential to life because they are used to create enzymes that speed up or regulate chemical reactions and to create structures. Amino acids and other compounds from subsurface oceans can be transported to the surface by geyser activity or ice sheet movement.

The study evaluated the survival of amino acids on these worlds. The team mixed samples of amino acids with ice cooled to a temperature of about minus 196 degrees Celsius) in sealed, airless bottles, and bombarded them with gamma rays, in different doses. Since the oceans may contain microscopic life, they also tested the survival of the amino acids in dead bacteria in the ice. Finally, they tested samples of amino acids in ice mixed with silicate dust to test the possibility of mixing material from meteorites or the interior with the surface ice.

The experiments provided crucial data to determine the decomposition rate of the amino acids - radiolysis constants. The team used this data, the ice age of the surface and the data of the radioactive environment of Europa and Enceladus, that about 10% of the amino acids will survive the radiolytic destruction.

Although experiments to test the survival of amino acids in ice have been done before, this is the first experiment to use low doses of radiation that do not completely break down the amino acids, because only a change or partial breakdown is enough to make it difficult to determine whether they are possible signs of life. This is also the first experiment to use Europa/Enceladus conditions to assess the survival of these compounds in microorganisms, and the first to test the survival of the amino acids mixed with dust.

The team found that amino acids break down faster when mixed with dust, but break down more slowly when they come from microorganisms.

"Slow decomposition rate of amino acids in biological samples under the surface conditions of Europa and Enceladus, strengthens the chance of discovering life on them during landing and inspection operations there," said Pavlov. "Our results show that the rate of decomposition of possible organic molecules in silica-rich regions on the surface of Europa and Enceladus is higher than in pure ice, so future missions to Europa and Enceladus should be careful in sampling silica-rich locations on the two icy moons."

A possible explanation for why amino acids survived longer in bacteria involves the ways in which ionizing radiation changes molecules—directly by breaking chemical bonds or indirectly by creating reactive compounds nearby that change or break down the molecule. Bacterial cell material may have protected amino acids from the reactive compounds produced by the radiation.

for the scientific article

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Comments

  1. Proofreading suggestions - continued:
    8) "About minus 196 degrees Celsius)" -> "About minus 196 degrees Celsius"
    9) "And bombarded them with gamma rays, in different doses." -> "And bombarded them with gamma rays in different doses."
    10) "Finally, they tested samples of amino acids in ice mixed with silicate dust to" -> "Finally they tested samples of amino acids mixed with silicate dust in ice, to"
    11) "With these, the team used the age of the ice surface and the radiative environment of Europa and Enceladus to" -> "The team used these data, the age of the surface ice and the radiative environment data of Europa and Enceladus, to"
    12) "When they are mixed with dust but decompose more slowly" -> "When they are mixed with dust, but decompose more slowly"
    13) "Slow disintegration rate... Europa and Enceladus strengthens the chance of future life detection tests during landing operations on Europa and Enceladus" ->* "Slow disintegration rate... Europa and Enceladus, strengthens the chance of discovering life on them during landing and test operations there"
    14) "Our results show that the dissolution rate of... Europa and Enceladus is higher than in pure ice," -> "Our results show that the dissolution rate of... Europa and Enceladus is higher than in pure ice."
    * Proofreading a quote, without seeing or hearing its source

  2. proofreading suggestions:
    1) "The moons of Enceladus and Europa" -> "The moons of Enceladus and Europa"
    2) "at the position of 7 o'clock" -> "at 7 o'clock"
    3) "Do these oceans support life by examining the signatures of life in the form of organic molecules (...) that may survive just below the surface ice" -> "Do these oceans support life, by examining the signatures of life that appear in the form of organic molecules (...), and may Survive in the ice just below the surface"
    4) "We will not be required to dig a sample below the surface... anywhere below the surface of Enceladus less than a few millimeters from the surface" -> "We will not be required to dig a sample deep below the surface... anywhere below the surface of Enceladus, less than a few millimeters from the surface "
    5) "Jupiter and Saturn respectively, also those originating from powerful events" -> "Jupiter and Saturn respectively, as well as those originating from powerful events"
    6) "Because they are used by earthly life as part of building proteins" -> "Because they are used by earthly life to build proteins"
    7) "The research evaluated the survival of the amino acids on these worlds, and the team mixed samples" -> "The research evaluated the survival of the amino acids on these worlds: the team mixed samples"

    Thanks, I got your suggestions, it's tiring.

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