Context

As per the recently published study in the journal Icarus, an international team of scientists has discovered strong evidence indicating the presence of ozone on Jupiter’s moon Callisto.

Ozone Found On Jupiter’s Moon Callisto: Study

• Scientists are currently studying various celestial bodies in the Solar System that show signs of ozone, suggesting the existence of stable atmospheric conditions and, by extension, the possibility of their being able to host life.
• The detection of sulfur dioxide on Callisto’s surface has encouraged this team of scientists to conduct spectroscopic observations to gain a better understanding of the moon’s surface composition and formation.

Key Findings of Study 

• Formation of Ozone: The study outlines the researchers’ investigation into the chemical evolution of “SO2 astrochemical ice”, which is ice primarily composed of sulphur dioxide (SO2) in the presence of ultraviolet irradiation. 
  • This shed light on the chemical processes and composition on the surface of Callisto. 

• Confirmation: The researchers also compared their experimental data with data collected by the Hubble Space Telescope, which had also suggested the presence of sulfur dioxide and ozone on the surface of Callisto in 1997.

About the Conducted Experiment

• Conducted at: The experiments were conducted at the National Synchrotron Radiation Research Centre (NSRRC) in Taiwan, which provided access to high-energy radiation sources required to recreate the radiation coming from the Sun.
• Recreating Conditions on the Earth: Scientists of the Atomic, Molecular, and Optical Physics Division, Physical Research Laboratory, Ahmedabad, set out to investigate the chemical evolution of sulfur dioxide ice under irradiation, leading to the formation of ozone.
  • Scientists have previously demonstrated this process in laboratory experiments. 
• Use of Vacuum Ultraviolet Photons: To recreate the conditions, the researchers used vacuum ultraviolet photons, which mimic the solar radiation that reaches the moon’s surface.
• Experimentation: Recreation of Environment: Researchers placed a substrate of lithium fluoride in a chamber with very low pressure (an environment similar to those found in outer space). 
  • The samples were initially kept at a low temperature of around 9 K (-264.15 degrees C), in line with the conditions on Callisto’s surface. Then, they slowly warmed it up to 120 K to resemble different environmental scenarios.
  • In this process, they irradiated the ice with vacuum-ultraviolet photons (of wavelength 137.7 nanometres) and recorded its ultraviolet absorption spectrum during and after the irradiation using a photomultiplier tube detector. 
    • Photomultiplier Tube Detector measures low levels of electromagnetic radiation by converting photons into electrical signals.
• Deposition of Samples: The sulfur dioxide ice samples were deposited onto the substrate, setting the stage for the final step (observing the absorption spectrum).
• Observation: The absorption spectrum is the unique fingerprint of a substance. It shows the wavelengths of light it absorbs, providing insights into its composition and properties.

About Callisto

• A Moon of Jupiter: After Saturn, Jupiter has the most moons in the Solar System. Callisto is one of Jupiter’s largest moons and the third-largest moon in the Solar System after Ganymede and Titan.

• Composition: Callisto is primarily composed of water ice, rocky materials, sulphur dioxide, and some organic compounds. 
• Cratered Surface: Callisto’s surface is heavily cratered, indicating a long history of being struck by asteroids and comets. 
  • It also lacks the extensive seismic activity seen on some of Jupiter’s other moons, such as Io and Europa.
• Geologically Inactive: The presence of relatively few geological features suggests Callisto’s surface is geologically inactive. 
  • It means, its surface has likely been relatively stable for a long time. 
  • Significance: This stability could be vital to preserve any subsurface ocean or potential habitats beneath the icy crust.

About Ozone and its Importance

• Comprises: The ozone molecule is composed of three oxygen atoms bonded together. 
• Importance: The ozone layer, found in the lower part of the earth’s stratosphere, around 15-35 km above ground, serves as a shield. 
  • Without the ozone layer, ultraviolet radiation levels would be much higher on the planet’s surface, rendering it uninhabitable for many species and disrupting entire ecosystems.

Significance of the Discovery of Ozone on Callisto

• Presence of Oxygen: The discovery of ozone on Callisto suggests the presence of oxygen, a fundamental element for the formation of complex molecules required for life, such as amino acids, raising questions about the moon’s habitability. 
  • This extends to other icy moons in our Solar System, potentially informing our understanding of habitable conditions beyond Earth.
• Valuable Insights into Geological and Atmospheric Processes: This finding could provide valuable insights into geological and atmospheric processes on these moons. 
  • It could help us to understand the precise mechanisms that led to the formation of Jupiter and its moons.

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