April 21, 2024

Lukmaan IAS

A Blog for IAS Examination




THE CONTEXT: In a groundbreaking discovery, a team led by scientists from the Physical Research Laboratory (PRL) in Ahmedabad, India, alongside international collaborators, has uncovered compelling evidence pointing to the presence of ozone on Jupiter’s moon, Callisto.


  • This discovery, detailed in the March 2024 issue of the journal Icarus, not only sheds light on the intricate chemical processes occurring on icy celestial bodies within our Solar System but also holds profound implications for the potential habitability of these moons.

Chemical Evolution of SO2 Astrochemical Ice

  • The research delved into the chemical evolution of “SO2 astrochemical ice,” predominantly composed of sulphur dioxide (SO2) under the influence of ultraviolet (UV) irradiation.
  • By scrutinizing the UV absorption spectra of irradiated ice samples, the team identified a distinct signature indicating the formation of ozone.

Importance of Ozone

  • Ozone, a molecule comprising three oxygen atoms bonded together, plays a pivotal role in shielding Earth from harmful ultraviolet radiation.
  • The ozone layer, situated in the stratosphere, acts as a protective barrier against UV-B and UV-C radiation, which can cause DNA damage and various health hazards.
  • The presence of ozone on celestial bodies like Callisto hints at stable atmospheric conditions, raising tantalizing prospects for potential habitability.

Callisto: A Unique Celestial Body

  • Callisto, one of Jupiter’s largest moons and the third-largest in the Solar System, boasts a composition primarily consisting of water ice, rocky materials, sulphur dioxide, and organic compounds.
  • Despite its impressive size comparable to Mercury, Callisto harbors less than half the mass.
  • Its surface, heavily cratered and potentially the oldest in the Solar System, underscores its history of asteroid and comet impacts.
  • The team endeavored to simulate the conditions conducive to ozone formation on Callisto’s surface.
  • Using vacuum ultraviolet photons to mimic solar radiation, they conducted experiments at the National Synchrotron Radiation Research Centre (NSRRC) in Taiwan.
  • By depositing sulphur dioxide ice samples onto a lithium fluoride substrate under low-pressure conditions akin to outer space, they replicated the environment prevalent on Callisto.

Observations and Findings

  • Through meticulous experimentation, the team observed the formation of ozone in sulphur dioxide ice samples following irradiation with vacuum-ultraviolet photons.
  • This revelation, confirmed by comparing experimental data with observations from the Hubble Space Telescope, suggests the presence of oxygen—a crucial precursor to the formation of complex organic molecules essential for life as we understand it.
  • The detection of ozone on Callisto offers compelling evidence for the existence of stable atmospheric conditions, prompting speculation about the moon’s potential habitability.
  • This finding not only raises intriguing questions about the possibility of life beyond Earth but also underscores the importance of further exploration of icy moons in our Solar System.

Insights and Future Research

  • In addition to ozone, the researchers identified an unidentified band in the absorption spectrum, reminiscent of observations on Ganymede in 1996.
  • This discovery hints at commonalities in surface compositions or chemical processes among Jupiter’s moons, offering valuable insights into their geological and atmospheric dynamics.
  • Furthermore, it provides a foundation for elucidating the mechanisms underlying the formation of Jupiter and its moons, a subject of ongoing scientific inquiry.

Ozone Hole:

  • The ozone hole is not technically a “hole” where no ozone is present, but is actually a region of exceptionally depleted ozone in the stratosphere over the Antarctic that happens at the beginning of Southern Hemisphere spring (August–October).
  • Satellite instruments provide us with daily images of ozone over the Antarctic region.
  • The ozone hole image below shows the very low values (blue and purple colored area) centered over Antarctica on 4 October 2004.
  • From the historical record we know that total column ozone values of less than 220 Dobson Units were not observed prior to 1979.
  • From an aircraft field mission over Antarctica we also know that a total column ozone level of less than 220 Dobson Units is a result of catalyzed ozone loss from chlorine and bromine compounds.
  • For these reasons, we use 220 Dobson Units as the boundary of the region representing ozone loss.
  • Using the daily snapshots of total column ozone, we can calculate the area on the Earth that is enclosed by a line with values of 220 Dobson Units (the white line in the figure below).

The ozone hole is the region over Antarctica with total ozone of 220 Dobson Units or lower

SOURCE: https://www.thehindu.com/sci-tech/science/prl-ahmedabad-ozone-callisto-habitability/article68015568.ece/amp/

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