Presence of ozone Jupiter’s moon Callisto 

News Excerpt: 

Strong evidence of ozone's presence on Jupiter's moon Callisto has been found by a team of scientists.

Key Highlights of the study:

  • Study outlines the researchers’ investigation into the chemical evolution of “SO2 astrochemical ice”, which is ice primarily composed of sulfur dioxide (SO2) in the presence of ultraviolet irradiation. 
  • This shed light on the chemical processes and composition on the surface of Callisto. By analyzing the UV absorption spectra of the irradiated ice samples, Scientists identified a distinct signature indicating the formation of ozone.
  • They corroborated their findings by comparing them with data from the Hubble Space Telescope to understand Callisto’s environment and the potential habitability of icy moons in the Solar System.

The importance of ozone

  • The earth has life not just because it found a way to originate here: it also had the resources to thrive, evolve, and diversify. 
    • These resources include sunlight containing the ‘right’ frequencies of radiation, water, a stable atmosphere providing a stable supply of the requisite gases and at the right temperature, and various compounds required for the life-forms’ biochemical processes.
  • Not all emissions from the Sun are good for organisms on the earth like:
    • Ultraviolet radiation in particular is harmful to many species .
    • Two of its components, called ultraviolet-B and ultraviolet-C, of wavelengths 290-320 nanometres and 100-280 nanometres respectively, 
      • It can damage DNA, trigger mutations, and increase the risk of skin cancer and cataracts in humans.
      • Ultraviolet light has also been known to inhibit plant growth and have detrimental effects on various organisms
  • This is why the ozone layer is a crucial part of the earth’s atmosphere: 
    • It completely absorbs ultraviolet-B and ultraviolet-C radiation.
    • The ozone molecule is composed of three oxygen atoms bonded together. 
    • 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.
    • Scientists are studying celestial bodies in the Solar System showing ozone signs of ozone.
      • They hint at stable atmospheric conditions and potential for hosting life.

Callisto and its unique environment:

  • 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.
  • Despite being as big as the planet Mercury, It has less than half as much mass
    • Callisto is primarily composed of water ice, rocky materials, sulfur dioxide, and some organic compounds. 
  • These substances make the moon a potential candidate for supporting life in the Solar System beyond the earth.
  • Callisto’s surface is heavily cratered, indicating a long history of being struck by asteroids and comets. (It may have the oldest surface in the Solar System). 
    • It also lacks the extensive seismic activity seen on some of Jupiter’s other moons, such as Io and Europa.
  • The presence of relatively few geological features suggests Callisto’s surface is geologically inactive. 
    • its surface has likely been relatively stable for a long time. 
  • This stability could be vital to preserve any subsurface ocean or potential habitats beneath the icy crust.
  • The detection of sulfur dioxide on Callisto’s surface has encouraged the scientists to conduct spectroscopic observations to gain a better understanding of the moon’s surface composition and formation.

Recreating conditions on the earth: 

  • Scientists investigate the chemical evolution of sulfur dioxide ice under irradiation, leading to the formation of ozone. 
  • Scientists aim was to recreate the conditions required for this process on the surface of Callisto when sunlight hits its surface. 
  • The researchers used vacuum ultraviolet photons, which mimic the solar radiation that reaches the moon’s surface.
  • The experiments were conducted at the National Synchrotron Radiation Research Centre (NSRRC) in Taiwan,
    • Under which provided access to high-energy radiation sources required to recreate the radiation coming from the Sun.
  • To model the surface of Callisto, the researchers placed a substrate of lithium fluoride in a chamber with very low pressure. 
    • This environment recreated conditions similar to those found in outer space
    • The sulfur dioxide ice samples were deposited onto the substrate, setting the stage for the final step: observing the absorption spectrum.
      • 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.
  • Temperature of sulfur dioxide ice samples was carefully controlled during the experiment.

Significance of ozone:

  • Ozone, a marker of oxygen, has been detected on Callisto, one of Jupiter's moons, indicating the potential presence of oxygen.
  • Oxygen is a crucial element for the formation of complex molecules necessary for life
    • such as amino acids, raising questions about Callisto's habitability.
  • Comparison with Hubble Space Telescope data from 1997 further supports the presence of ozone and sulphur dioxide on Callisto's surface.
  • This discovery extends our curiosity about the habitability of other icy moons within our solar system.
  • The detection of an unidentified absorption band in the spectrum, similar to one observed on Ganymede in 1996, suggests common molecular sources or chemical processes on these moons.
  • Insights gained from these findings contribute to understanding the geological and atmospheric processes of Jupiter's moons and aid in our quest to understand habitable conditions beyond Earth.