Evidence of Ozone on Callisto: Implications for Habitability and Beyond

Team led by PRL Ahmedabad discovers ozone on Callisto - Implications for Habitability and Beyond
Evidence of Ozone on Callisto: Implications for Habitability and Beyond [Source: The Hindu]

A team of international scientists, spearheaded by researchers from the Physical Research Laboratory (PRL) in Ahmedabad, has unearthed compelling evidence indicating the presence of ozone on Callisto, one of Jupiter’s most expansive moons.

Published in the March 2024 edition of the esteemed journal Icarus, their study delves into the intricate chemical processes unfolding on the icy terrain of Callisto, shedding light on its potential as a host for life.

Research Methodology:

Under the guidance of R. Ramachandran from PRL's Atomic, Molecular, and Optical Physics Division, the team embarked on an investigation into the chemical transformation of sulphur dioxide (SO2) ice under irradiation, mirroring the conditions prevalent on Callisto’s surface. This rigorous exploration was conducted at the National Synchrotron Radiation Research Center (NSRRC) in Taiwan, leveraging high-energy radiation sources to simulate solar radiation.

Experimental Techniques:

  • Vacuum Ultraviolet Irradiation: SO2 ice samples were meticulously deposited on a lithium fluoride substrate within a low-pressure chamber and subjected to irradiation by vacuum ultraviolet photons, closely mimicking solar radiation.
  • Temperature Regulation: Maintaining the ice samples at an icy 9 K (-264.15°C) to replicate Callisto’s frigid environment, the team gradually elevated the temperature to 120 K to observe varied environmental impacts.
  • Ultraviolet Absorption Spectroscopy: Employing a photomultiplier tube detector, the researchers captured the ultraviolet absorption spectrum of the irradiated ice samples, discerning the formation of distinct chemical species.

Discovery of Ozone:

Analysis of the ultraviolet absorption spectrum unveiled a conspicuous signature indicative of ozone (O3) formation within the irradiated SO2 ice samples. This revelatory finding hints at the presence of oxygen on Callisto, a fundamental constituent for the synthesis of intricate molecules crucial for life.

Comparisons with observations made by the Hubble Space Telescope in 1997, which hinted at the existence of sulphur dioxide and ozone on Callisto’s surface, further bolstered the researchers’ assertions.

Implications for Habitability:

The revelation of ozone on Callisto holds profound implications for its potential habitability and extends the frontiers of our quest for extraterrestrial life. Ozone, arising from the dissociation and subsequent recombination of oxygen molecules under ultraviolet radiation, underscores the existence of a stable, oxygen-rich atmosphere—pivotal for the genesis of complex organic compounds and, plausibly, life.

Furthermore, this discovery prompts inquiries into the habitability of other icy moons in the Solar System, such as Europa and Ganymede, which share analogous surface compositions with Callisto and may harbor subsurface oceans.

Unidentified Absorption Band:

Intriguingly, alongside the ozone signature, the researchers discerned an enigmatic absorption band in the spectrum, reminiscent of one detected on Ganymede in 1996. This uncovers a potential commonality in molecular sources or chemical processes across the surfaces of these Jovian moons, providing invaluable insights into their geological and atmospheric dynamics.

Collaboration and Future Endeavors:

This pioneering study epitomizes collaborative synergy, uniting scientists from diverse institutions including PRL, NSRRC, and the Space Physics Laboratory at the Vikram Sarabhai Space Centre in Thiruvananthapuram, India. The team is poised to embark on further research endeavors, aiming to deepen our comprehension of Callisto’s chemical composition and surface evolution, and its ramifications for the pursuit of life in the outer reaches of the Solar System.

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